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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlfunc - Perl builtin functions | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | The functions in this section can serve as terms in an expression. | |
8 | They fall into two major categories: list operators and named unary | |
9 | operators. These differ in their precedence relationship with a | |
10 | following comma. (See the precedence table in L<perlop>.) List | |
11 | operators take more than one argument, while unary operators can never | |
12 | take more than one argument. Thus, a comma terminates the argument of | |
13 | a unary operator, but merely separates the arguments of a list | |
14 | operator. A unary operator generally provides a scalar context to its | |
15 | argument, while a list operator may provide either scalar and list | |
16 | contexts for its arguments. If it does both, the scalar arguments will | |
5f05dabc | 17 | be first, and the list argument will follow. (Note that there can ever |
18 | be only one list argument.) For instance, splice() has three scalar | |
a0d0e21e LW |
19 | arguments followed by a list. |
20 | ||
21 | In the syntax descriptions that follow, list operators that expect a | |
22 | list (and provide list context for the elements of the list) are shown | |
23 | with LIST as an argument. Such a list may consist of any combination | |
24 | of scalar arguments or list values; the list values will be included | |
25 | in the list as if each individual element were interpolated at that | |
26 | point in the list, forming a longer single-dimensional list value. | |
27 | Elements of the LIST should be separated by commas. | |
28 | ||
29 | Any function in the list below may be used either with or without | |
30 | parentheses around its arguments. (The syntax descriptions omit the | |
5f05dabc | 31 | parentheses.) If you use the parentheses, the simple (but occasionally |
a0d0e21e LW |
32 | surprising) rule is this: It I<LOOKS> like a function, therefore it I<IS> a |
33 | function, and precedence doesn't matter. Otherwise it's a list | |
34 | operator or unary operator, and precedence does matter. And whitespace | |
35 | between the function and left parenthesis doesn't count--so you need to | |
36 | be careful sometimes: | |
37 | ||
68dc0745 | 38 | print 1+2+4; # Prints 7. |
39 | print(1+2) + 4; # Prints 3. | |
40 | print (1+2)+4; # Also prints 3! | |
41 | print +(1+2)+4; # Prints 7. | |
42 | print ((1+2)+4); # Prints 7. | |
a0d0e21e LW |
43 | |
44 | If you run Perl with the B<-w> switch it can warn you about this. For | |
45 | example, the third line above produces: | |
46 | ||
47 | print (...) interpreted as function at - line 1. | |
48 | Useless use of integer addition in void context at - line 1. | |
49 | ||
50 | For functions that can be used in either a scalar or list context, | |
54310121 | 51 | nonabortive failure is generally indicated in a scalar context by |
a0d0e21e LW |
52 | returning the undefined value, and in a list context by returning the |
53 | null list. | |
54 | ||
5a964f20 TC |
55 | Remember the following important rule: There is B<no rule> that relates |
56 | the behavior of an expression in list context to its behavior in scalar | |
57 | context, or vice versa. It might do two totally different things. | |
a0d0e21e LW |
58 | Each operator and function decides which sort of value it would be most |
59 | appropriate to return in a scalar context. Some operators return the | |
5a964f20 | 60 | length of the list that would have been returned in list context. Some |
a0d0e21e LW |
61 | operators return the first value in the list. Some operators return the |
62 | last value in the list. Some operators return a count of successful | |
63 | operations. In general, they do what you want, unless you want | |
64 | consistency. | |
65 | ||
5a964f20 TC |
66 | An named array in scalar context is quite different from what would at |
67 | first glance appear to be a list in scalar context. You can't get a list | |
68 | like C<(1,2,3)> into being in scalar context, because the compiler knows | |
69 | the context at compile time. It would generate the scalar comma operator | |
70 | there, not the list construction version of the comma. That means it | |
71 | was never a list to start with. | |
72 | ||
73 | In general, functions in Perl that serve as wrappers for system calls | |
f86cebdf | 74 | of the same name (like chown(2), fork(2), closedir(2), etc.) all return |
5a964f20 TC |
75 | true when they succeed and C<undef> otherwise, as is usually mentioned |
76 | in the descriptions below. This is different from the C interfaces, | |
7660c0ab A |
77 | which return C<-1> on failure. Exceptions to this rule are C<wait()>, |
78 | C<waitpid()>, and C<syscall()>. System calls also set the special C<$!> | |
5a964f20 TC |
79 | variable on failure. Other functions do not, except accidentally. |
80 | ||
cb1a09d0 AD |
81 | =head2 Perl Functions by Category |
82 | ||
83 | Here are Perl's functions (including things that look like | |
5a964f20 | 84 | functions, like some keywords and named operators) |
cb1a09d0 AD |
85 | arranged by category. Some functions appear in more |
86 | than one place. | |
87 | ||
88 | =over | |
89 | ||
90 | =item Functions for SCALARs or strings | |
91 | ||
22fae026 | 92 | C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>, |
ab4f32c2 A |
93 | C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<reverse>, |
94 | C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///> | |
cb1a09d0 AD |
95 | |
96 | =item Regular expressions and pattern matching | |
97 | ||
ab4f32c2 | 98 | C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//> |
cb1a09d0 AD |
99 | |
100 | =item Numeric functions | |
101 | ||
22fae026 TM |
102 | C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>, |
103 | C<sin>, C<sqrt>, C<srand> | |
cb1a09d0 AD |
104 | |
105 | =item Functions for real @ARRAYs | |
106 | ||
22fae026 | 107 | C<pop>, C<push>, C<shift>, C<splice>, C<unshift> |
cb1a09d0 AD |
108 | |
109 | =item Functions for list data | |
110 | ||
ab4f32c2 | 111 | C<grep>, C<join>, C<map>, C<qw/STRING/>, C<reverse>, C<sort>, C<unpack> |
cb1a09d0 AD |
112 | |
113 | =item Functions for real %HASHes | |
114 | ||
22fae026 | 115 | C<delete>, C<each>, C<exists>, C<keys>, C<values> |
cb1a09d0 AD |
116 | |
117 | =item Input and output functions | |
118 | ||
22fae026 TM |
119 | C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>, |
120 | C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>, | |
121 | C<readdir>, C<rewinddir>, C<seek>, C<seekdir>, C<select>, C<syscall>, | |
122 | C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>, | |
123 | C<warn>, C<write> | |
cb1a09d0 AD |
124 | |
125 | =item Functions for fixed length data or records | |
126 | ||
22fae026 | 127 | C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec> |
cb1a09d0 AD |
128 | |
129 | =item Functions for filehandles, files, or directories | |
130 | ||
22fae026 TM |
131 | C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>, |
132 | C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>, C<readlink>, | |
133 | C<rename>, C<rmdir>, C<stat>, C<symlink>, C<umask>, C<unlink>, C<utime> | |
cb1a09d0 AD |
134 | |
135 | =item Keywords related to the control flow of your perl program | |
136 | ||
22fae026 TM |
137 | C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>, |
138 | C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray> | |
cb1a09d0 | 139 | |
54310121 | 140 | =item Keywords related to scoping |
cb1a09d0 | 141 | |
22fae026 | 142 | C<caller>, C<import>, C<local>, C<my>, C<package>, C<use> |
cb1a09d0 AD |
143 | |
144 | =item Miscellaneous functions | |
145 | ||
22fae026 TM |
146 | C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<reset>, |
147 | C<scalar>, C<undef>, C<wantarray> | |
cb1a09d0 AD |
148 | |
149 | =item Functions for processes and process groups | |
150 | ||
22fae026 | 151 | C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>, |
ab4f32c2 | 152 | C<pipe>, C<qx/STRING/>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>, |
22fae026 | 153 | C<times>, C<wait>, C<waitpid> |
cb1a09d0 AD |
154 | |
155 | =item Keywords related to perl modules | |
156 | ||
22fae026 | 157 | C<do>, C<import>, C<no>, C<package>, C<require>, C<use> |
cb1a09d0 AD |
158 | |
159 | =item Keywords related to classes and object-orientedness | |
160 | ||
22fae026 TM |
161 | C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>, |
162 | C<untie>, C<use> | |
cb1a09d0 AD |
163 | |
164 | =item Low-level socket functions | |
165 | ||
22fae026 TM |
166 | C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>, |
167 | C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>, | |
168 | C<socket>, C<socketpair> | |
cb1a09d0 AD |
169 | |
170 | =item System V interprocess communication functions | |
171 | ||
22fae026 TM |
172 | C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>, |
173 | C<shmctl>, C<shmget>, C<shmread>, C<shmwrite> | |
cb1a09d0 AD |
174 | |
175 | =item Fetching user and group info | |
176 | ||
22fae026 TM |
177 | C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>, |
178 | C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>, | |
179 | C<getpwuid>, C<setgrent>, C<setpwent> | |
cb1a09d0 AD |
180 | |
181 | =item Fetching network info | |
182 | ||
22fae026 TM |
183 | C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>, |
184 | C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
185 | C<getprotobyname>, C<getprotobynumber>, C<getprotoent>, | |
186 | C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>, | |
187 | C<setnetent>, C<setprotoent>, C<setservent> | |
cb1a09d0 AD |
188 | |
189 | =item Time-related functions | |
190 | ||
22fae026 | 191 | C<gmtime>, C<localtime>, C<time>, C<times> |
cb1a09d0 | 192 | |
37798a01 | 193 | =item Functions new in perl5 |
194 | ||
22fae026 TM |
195 | C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>, |
196 | C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<prototype>, C<qx>, | |
197 | C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>, | |
198 | C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use> | |
37798a01 | 199 | |
200 | * - C<sub> was a keyword in perl4, but in perl5 it is an | |
5a964f20 | 201 | operator, which can be used in expressions. |
37798a01 | 202 | |
203 | =item Functions obsoleted in perl5 | |
204 | ||
22fae026 | 205 | C<dbmclose>, C<dbmopen> |
37798a01 | 206 | |
cb1a09d0 AD |
207 | =back |
208 | ||
209 | =head2 Alphabetical Listing of Perl Functions | |
210 | ||
a0d0e21e LW |
211 | =over 8 |
212 | ||
22fae026 | 213 | =item I<-X> FILEHANDLE |
a0d0e21e | 214 | |
22fae026 | 215 | =item I<-X> EXPR |
a0d0e21e | 216 | |
22fae026 | 217 | =item I<-X> |
a0d0e21e LW |
218 | |
219 | A file test, where X is one of the letters listed below. This unary | |
220 | operator takes one argument, either a filename or a filehandle, and | |
221 | tests the associated file to see if something is true about it. If the | |
7660c0ab | 222 | argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN. |
a0d0e21e LW |
223 | Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or |
224 | the undefined value if the file doesn't exist. Despite the funny | |
225 | names, precedence is the same as any other named unary operator, and | |
226 | the argument may be parenthesized like any other unary operator. The | |
227 | operator may be any of: | |
7e778d91 IZ |
228 | X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p> |
229 | X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C> | |
a0d0e21e LW |
230 | |
231 | -r File is readable by effective uid/gid. | |
232 | -w File is writable by effective uid/gid. | |
233 | -x File is executable by effective uid/gid. | |
234 | -o File is owned by effective uid. | |
235 | ||
236 | -R File is readable by real uid/gid. | |
237 | -W File is writable by real uid/gid. | |
238 | -X File is executable by real uid/gid. | |
239 | -O File is owned by real uid. | |
240 | ||
241 | -e File exists. | |
242 | -z File has zero size. | |
54310121 | 243 | -s File has nonzero size (returns size). |
a0d0e21e LW |
244 | |
245 | -f File is a plain file. | |
246 | -d File is a directory. | |
247 | -l File is a symbolic link. | |
9c4d0f16 | 248 | -p File is a named pipe (FIFO), or Filehandle is a pipe. |
a0d0e21e LW |
249 | -S File is a socket. |
250 | -b File is a block special file. | |
251 | -c File is a character special file. | |
252 | -t Filehandle is opened to a tty. | |
253 | ||
254 | -u File has setuid bit set. | |
255 | -g File has setgid bit set. | |
256 | -k File has sticky bit set. | |
257 | ||
258 | -T File is a text file. | |
259 | -B File is a binary file (opposite of -T). | |
260 | ||
261 | -M Age of file in days when script started. | |
262 | -A Same for access time. | |
263 | -C Same for inode change time. | |
264 | ||
265 | The interpretation of the file permission operators C<-r>, C<-R>, C<-w>, | |
5f05dabc | 266 | C<-W>, C<-x>, and C<-X> is based solely on the mode of the file and the |
a0d0e21e | 267 | uids and gids of the user. There may be other reasons you can't actually |
5a964f20 | 268 | read, write, or execute the file, such as AFS access control lists. Also note that, for the superuser, |
7660c0ab A |
269 | C<-r>, C<-R>, C<-w>, and C<-W> always return C<1>, and C<-x> and C<-X> return |
270 | C<1> if any execute bit is set in the mode. Scripts run by the superuser may | |
271 | thus need to do a C<stat()> to determine the actual mode of the | |
a0d0e21e LW |
272 | file, or temporarily set the uid to something else. |
273 | ||
274 | Example: | |
275 | ||
276 | while (<>) { | |
277 | chop; | |
278 | next unless -f $_; # ignore specials | |
5a964f20 | 279 | #... |
a0d0e21e LW |
280 | } |
281 | ||
282 | Note that C<-s/a/b/> does not do a negated substitution. Saying | |
283 | C<-exp($foo)> still works as expected, however--only single letters | |
284 | following a minus are interpreted as file tests. | |
285 | ||
286 | The C<-T> and C<-B> switches work as follows. The first block or so of the | |
287 | file is examined for odd characters such as strange control codes or | |
5a964f20 | 288 | characters with the high bit set. If too many strange characters (E<gt>30%) |
a0d0e21e LW |
289 | are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file |
290 | containing null in the first block is considered a binary file. If C<-T> | |
291 | or C<-B> is used on a filehandle, the current stdio buffer is examined | |
292 | rather than the first block. Both C<-T> and C<-B> return TRUE on a null | |
54310121 | 293 | file, or a file at EOF when testing a filehandle. Because you have to |
4633a7c4 LW |
294 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
295 | against the file first, as in C<next unless -f $file && -T $file>. | |
a0d0e21e | 296 | |
7660c0ab | 297 | If any of the file tests (or either the C<stat()> or C<lstat()> operators) are given |
28757baa | 298 | the special filehandle consisting of a solitary underline, then the stat |
a0d0e21e LW |
299 | structure of the previous file test (or stat operator) is used, saving |
300 | a system call. (This doesn't work with C<-t>, and you need to remember | |
301 | that lstat() and C<-l> will leave values in the stat structure for the | |
302 | symbolic link, not the real file.) Example: | |
303 | ||
304 | print "Can do.\n" if -r $a || -w _ || -x _; | |
305 | ||
306 | stat($filename); | |
307 | print "Readable\n" if -r _; | |
308 | print "Writable\n" if -w _; | |
309 | print "Executable\n" if -x _; | |
310 | print "Setuid\n" if -u _; | |
311 | print "Setgid\n" if -g _; | |
312 | print "Sticky\n" if -k _; | |
313 | print "Text\n" if -T _; | |
314 | print "Binary\n" if -B _; | |
315 | ||
316 | =item abs VALUE | |
317 | ||
54310121 | 318 | =item abs |
bbce6d69 | 319 | |
a0d0e21e | 320 | Returns the absolute value of its argument. |
7660c0ab | 321 | If VALUE is omitted, uses C<$_>. |
a0d0e21e LW |
322 | |
323 | =item accept NEWSOCKET,GENERICSOCKET | |
324 | ||
f86cebdf | 325 | Accepts an incoming socket connect, just as the accept(2) system call |
a0d0e21e | 326 | does. Returns the packed address if it succeeded, FALSE otherwise. |
4633a7c4 | 327 | See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
328 | |
329 | =item alarm SECONDS | |
330 | ||
54310121 | 331 | =item alarm |
bbce6d69 | 332 | |
a0d0e21e | 333 | Arranges to have a SIGALRM delivered to this process after the |
bbce6d69 | 334 | specified number of seconds have elapsed. If SECONDS is not specified, |
7660c0ab | 335 | the value stored in C<$_> is used. (On some machines, |
a0d0e21e LW |
336 | unfortunately, the elapsed time may be up to one second less than you |
337 | specified because of how seconds are counted.) Only one timer may be | |
338 | counting at once. Each call disables the previous timer, and an | |
7660c0ab | 339 | argument of C<0> may be supplied to cancel the previous timer without |
a0d0e21e LW |
340 | starting a new one. The returned value is the amount of time remaining |
341 | on the previous timer. | |
342 | ||
4633a7c4 | 343 | For delays of finer granularity than one second, you may use Perl's |
f86cebdf | 344 | C<syscall()> interface to access setitimer(2) if your system supports it, |
7660c0ab A |
345 | or else see L</select()>. It is usually a mistake to intermix C<alarm()> |
346 | and C<sleep()> calls. | |
a0d0e21e | 347 | |
7660c0ab | 348 | If you want to use C<alarm()> to time out a system call you need to use an |
ab4f32c2 | 349 | C<eval()>/C<die()> pair. You can't rely on the alarm causing the system call to |
f86cebdf | 350 | fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to |
ab4f32c2 | 351 | restart system calls on some systems. Using C<eval()>/C<die()> always works, |
5a964f20 | 352 | modulo the caveats given in L<perlipc/"Signals">. |
ff68c719 | 353 | |
354 | eval { | |
f86cebdf | 355 | local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required |
36477c24 | 356 | alarm $timeout; |
ff68c719 | 357 | $nread = sysread SOCKET, $buffer, $size; |
36477c24 | 358 | alarm 0; |
ff68c719 | 359 | }; |
ff68c719 | 360 | if ($@) { |
f86cebdf | 361 | die unless $@ eq "alarm\n"; # propagate unexpected errors |
ff68c719 | 362 | # timed out |
363 | } | |
364 | else { | |
365 | # didn't | |
366 | } | |
367 | ||
a0d0e21e LW |
368 | =item atan2 Y,X |
369 | ||
370 | Returns the arctangent of Y/X in the range -PI to PI. | |
371 | ||
7660c0ab | 372 | For the tangent operation, you may use the C<POSIX::tan()> |
28757baa | 373 | function, or use the familiar relation: |
374 | ||
375 | sub tan { sin($_[0]) / cos($_[0]) } | |
376 | ||
a0d0e21e LW |
377 | =item bind SOCKET,NAME |
378 | ||
379 | Binds a network address to a socket, just as the bind system call | |
380 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
381 | packed address of the appropriate type for the socket. See the examples in |
382 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e LW |
383 | |
384 | =item binmode FILEHANDLE | |
385 | ||
cb1a09d0 AD |
386 | Arranges for the file to be read or written in "binary" mode in operating |
387 | systems that distinguish between binary and text files. Files that are | |
388 | not in binary mode have CR LF sequences translated to LF on input and LF | |
54310121 | 389 | translated to CR LF on output. Binmode has no effect under Unix; in MS-DOS |
cb1a09d0 | 390 | and similarly archaic systems, it may be imperative--otherwise your |
54310121 | 391 | MS-DOS-damaged C library may mangle your file. The key distinction between |
ab4f32c2 | 392 | systems that need C<binmode()> and those that don't is their text file |
5a964f20 | 393 | formats. Systems like Unix, MacOS, and Plan9 that delimit lines with a single |
7660c0ab | 394 | character, and that encode that character in C as C<"\n">, do not need |
ab4f32c2 | 395 | C<binmode()>. The rest need it. If FILEHANDLE is an expression, the value |
cb1a09d0 | 396 | is taken as the name of the filehandle. |
a0d0e21e | 397 | |
4633a7c4 | 398 | =item bless REF,CLASSNAME |
a0d0e21e LW |
399 | |
400 | =item bless REF | |
401 | ||
28757baa | 402 | This function tells the thingy referenced by REF that it is now |
4633a7c4 LW |
403 | an object in the CLASSNAME package--or the current package if no CLASSNAME |
404 | is specified, which is often the case. It returns the reference for | |
7660c0ab | 405 | convenience, because a C<bless()> is often the last thing in a constructor. |
4633a7c4 | 406 | Always use the two-argument version if the function doing the blessing |
5a964f20 TC |
407 | might be inherited by a derived class. See L<perltoot> and L<perlobj> |
408 | for more about the blessing (and blessings) of objects. | |
a0d0e21e LW |
409 | |
410 | =item caller EXPR | |
411 | ||
412 | =item caller | |
413 | ||
5a964f20 | 414 | Returns the context of the current subroutine call. In scalar context, |
28757baa | 415 | returns the caller's package name if there is a caller, that is, if |
7660c0ab | 416 | we're in a subroutine or C<eval()> or C<require()>, and the undefined value |
5a964f20 | 417 | otherwise. In list context, returns |
a0d0e21e | 418 | |
748a9306 | 419 | ($package, $filename, $line) = caller; |
a0d0e21e LW |
420 | |
421 | With EXPR, it returns some extra information that the debugger uses to | |
422 | print a stack trace. The value of EXPR indicates how many call frames | |
423 | to go back before the current one. | |
424 | ||
54310121 | 425 | ($package, $filename, $line, $subroutine, |
e7ea3e70 IZ |
426 | $hasargs, $wantarray, $evaltext, $is_require) = caller($i); |
427 | ||
7660c0ab | 428 | Here C<$subroutine> may be C<"(eval)"> if the frame is not a subroutine |
ab4f32c2 | 429 | call, but an C<eval()>. In such a case additional elements C<$evaltext> and |
7660c0ab A |
430 | C<$is_require> are set: C<$is_require> is true if the frame is created by a |
431 | C<require> or C<use> statement, C<$evaltext> contains the text of the | |
dc848c6f | 432 | C<eval EXPR> statement. In particular, for a C<eval BLOCK> statement, |
7660c0ab | 433 | C<$filename> is C<"(eval)">, but C<$evaltext> is undefined. (Note also that |
dc848c6f | 434 | each C<use> statement creates a C<require> frame inside an C<eval EXPR>) |
435 | frame. | |
748a9306 LW |
436 | |
437 | Furthermore, when called from within the DB package, caller returns more | |
7660c0ab | 438 | detailed information: it sets the list variable C<@DB::args> to be the |
54310121 | 439 | arguments with which the subroutine was invoked. |
748a9306 | 440 | |
7660c0ab | 441 | Be aware that the optimizer might have optimized call frames away before |
ab4f32c2 | 442 | C<caller()> had a chance to get the information. That means that C<caller(N)> |
7660c0ab A |
443 | might not return information about the call frame you expect it do, for |
444 | C<N E<gt> 1>. In particular, C<@DB::args> might have information from the | |
445 | previous time C<caller()> was called. | |
446 | ||
a0d0e21e LW |
447 | =item chdir EXPR |
448 | ||
449 | Changes the working directory to EXPR, if possible. If EXPR is | |
450 | omitted, changes to home directory. Returns TRUE upon success, FALSE | |
7660c0ab | 451 | otherwise. See example under C<die()>. |
a0d0e21e LW |
452 | |
453 | =item chmod LIST | |
454 | ||
455 | Changes the permissions of a list of files. The first element of the | |
4633a7c4 | 456 | list must be the numerical mode, which should probably be an octal |
2f9daede TP |
457 | number, and which definitely should I<not> a string of octal digits: |
458 | C<0644> is okay, C<'0644'> is not. Returns the number of files | |
dc848c6f | 459 | successfully changed. See also L</oct>, if all you have is a string. |
a0d0e21e LW |
460 | |
461 | $cnt = chmod 0755, 'foo', 'bar'; | |
462 | chmod 0755, @executables; | |
f86cebdf GS |
463 | $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to |
464 | # --w----r-T | |
2f9daede TP |
465 | $mode = '0644'; chmod oct($mode), 'foo'; # this is better |
466 | $mode = 0644; chmod $mode, 'foo'; # this is best | |
a0d0e21e LW |
467 | |
468 | =item chomp VARIABLE | |
469 | ||
470 | =item chomp LIST | |
471 | ||
472 | =item chomp | |
473 | ||
3e3baf6d | 474 | This is a slightly safer version of L</chop>. It removes any |
a0d0e21e | 475 | line ending that corresponds to the current value of C<$/> (also known as |
28757baa | 476 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total |
477 | number of characters removed from all its arguments. It's often used to | |
478 | remove the newline from the end of an input record when you're worried | |
479 | that the final record may be missing its newline. When in paragraph mode | |
480 | (C<$/ = "">), it removes all trailing newlines from the string. If | |
7660c0ab | 481 | VARIABLE is omitted, it chomps C<$_>. Example: |
a0d0e21e LW |
482 | |
483 | while (<>) { | |
484 | chomp; # avoid \n on last field | |
485 | @array = split(/:/); | |
5a964f20 | 486 | # ... |
a0d0e21e LW |
487 | } |
488 | ||
489 | You can actually chomp anything that's an lvalue, including an assignment: | |
490 | ||
491 | chomp($cwd = `pwd`); | |
492 | chomp($answer = <STDIN>); | |
493 | ||
494 | If you chomp a list, each element is chomped, and the total number of | |
495 | characters removed is returned. | |
496 | ||
497 | =item chop VARIABLE | |
498 | ||
499 | =item chop LIST | |
500 | ||
501 | =item chop | |
502 | ||
503 | Chops off the last character of a string and returns the character | |
504 | chopped. It's used primarily to remove the newline from the end of an | |
505 | input record, but is much more efficient than C<s/\n//> because it neither | |
7660c0ab | 506 | scans nor copies the string. If VARIABLE is omitted, chops C<$_>. |
a0d0e21e LW |
507 | Example: |
508 | ||
509 | while (<>) { | |
510 | chop; # avoid \n on last field | |
511 | @array = split(/:/); | |
5a964f20 | 512 | #... |
a0d0e21e LW |
513 | } |
514 | ||
515 | You can actually chop anything that's an lvalue, including an assignment: | |
516 | ||
517 | chop($cwd = `pwd`); | |
518 | chop($answer = <STDIN>); | |
519 | ||
520 | If you chop a list, each element is chopped. Only the value of the | |
ab4f32c2 | 521 | last C<chop()> is returned. |
a0d0e21e | 522 | |
ab4f32c2 | 523 | Note that C<chop()> returns the last character. To return all but the last |
748a9306 LW |
524 | character, use C<substr($string, 0, -1)>. |
525 | ||
a0d0e21e LW |
526 | =item chown LIST |
527 | ||
528 | Changes the owner (and group) of a list of files. The first two | |
529 | elements of the list must be the I<NUMERICAL> uid and gid, in that order. | |
530 | Returns the number of files successfully changed. | |
531 | ||
532 | $cnt = chown $uid, $gid, 'foo', 'bar'; | |
533 | chown $uid, $gid, @filenames; | |
534 | ||
54310121 | 535 | Here's an example that looks up nonnumeric uids in the passwd file: |
a0d0e21e LW |
536 | |
537 | print "User: "; | |
538 | chop($user = <STDIN>); | |
5a964f20 | 539 | print "Files: "; |
a0d0e21e LW |
540 | chop($pattern = <STDIN>); |
541 | ||
542 | ($login,$pass,$uid,$gid) = getpwnam($user) | |
543 | or die "$user not in passwd file"; | |
544 | ||
5a964f20 | 545 | @ary = glob($pattern); # expand filenames |
a0d0e21e LW |
546 | chown $uid, $gid, @ary; |
547 | ||
54310121 | 548 | On most systems, you are not allowed to change the ownership of the |
4633a7c4 LW |
549 | file unless you're the superuser, although you should be able to change |
550 | the group to any of your secondary groups. On insecure systems, these | |
551 | restrictions may be relaxed, but this is not a portable assumption. | |
552 | ||
a0d0e21e LW |
553 | =item chr NUMBER |
554 | ||
54310121 | 555 | =item chr |
bbce6d69 | 556 | |
a0d0e21e | 557 | Returns the character represented by that NUMBER in the character set. |
a0ed51b3 LW |
558 | For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and |
559 | chr(0x263a) is a Unicode smiley face (but only within the scope of a | |
560 | C<use utf8>). For the reverse, use L</ord>. | |
a0d0e21e | 561 | |
7660c0ab | 562 | If NUMBER is omitted, uses C<$_>. |
bbce6d69 | 563 | |
a0d0e21e LW |
564 | =item chroot FILENAME |
565 | ||
54310121 | 566 | =item chroot |
bbce6d69 | 567 | |
5a964f20 | 568 | This function works like the system call by the same name: it makes the |
4633a7c4 | 569 | named directory the new root directory for all further pathnames that |
7660c0ab | 570 | begin with a C<"/"> by your process and all its children. (It doesn't |
28757baa | 571 | change your current working directory, which is unaffected.) For security |
4633a7c4 | 572 | reasons, this call is restricted to the superuser. If FILENAME is |
ab4f32c2 | 573 | omitted, does a C<chroot()> to C<$_>. |
a0d0e21e LW |
574 | |
575 | =item close FILEHANDLE | |
576 | ||
6a518fbc TP |
577 | =item close |
578 | ||
a0d0e21e LW |
579 | Closes the file or pipe associated with the file handle, returning TRUE |
580 | only if stdio successfully flushes buffers and closes the system file | |
6a518fbc TP |
581 | descriptor. Closes the currently selected filehandle if the argument |
582 | is omitted. | |
fb73857a | 583 | |
584 | You don't have to close FILEHANDLE if you are immediately going to do | |
7660c0ab | 585 | another C<open()> on it, because C<open()> will close it for you. (See |
ab4f32c2 | 586 | C<open()>.) However, an explicit C<close()> on an input file resets the line |
7660c0ab | 587 | counter (C<$.>), while the implicit close done by C<open()> does not. |
fb73857a | 588 | |
ab4f32c2 | 589 | If the file handle came from a piped open C<close()> will additionally |
fb73857a | 590 | return FALSE if one of the other system calls involved fails or if the |
591 | program exits with non-zero status. (If the only problem was that the | |
7660c0ab | 592 | program exited non-zero C<$!> will be set to C<0>.) Also, closing a pipe |
5a964f20 | 593 | waits for the process executing on the pipe to complete, in case you |
fb73857a | 594 | want to look at the output of the pipe afterwards. Closing a pipe |
595 | explicitly also puts the exit status value of the command into C<$?>. | |
5a964f20 | 596 | |
fb73857a | 597 | Example: |
a0d0e21e | 598 | |
fb73857a | 599 | open(OUTPUT, '|sort >foo') # pipe to sort |
600 | or die "Can't start sort: $!"; | |
5a964f20 | 601 | #... # print stuff to output |
fb73857a | 602 | close OUTPUT # wait for sort to finish |
603 | or warn $! ? "Error closing sort pipe: $!" | |
604 | : "Exit status $? from sort"; | |
605 | open(INPUT, 'foo') # get sort's results | |
606 | or die "Can't open 'foo' for input: $!"; | |
a0d0e21e | 607 | |
5a964f20 TC |
608 | FILEHANDLE may be an expression whose value can be used as an indirect |
609 | filehandle, usually the real filehandle name. | |
a0d0e21e LW |
610 | |
611 | =item closedir DIRHANDLE | |
612 | ||
7660c0ab | 613 | Closes a directory opened by C<opendir()> and returns the success of that |
5a964f20 TC |
614 | system call. |
615 | ||
616 | DIRHANDLE may be an expression whose value can be used as an indirect | |
617 | dirhandle, usually the real dirhandle name. | |
a0d0e21e LW |
618 | |
619 | =item connect SOCKET,NAME | |
620 | ||
621 | Attempts to connect to a remote socket, just as the connect system call | |
622 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
623 | packed address of the appropriate type for the socket. See the examples in |
624 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 625 | |
cb1a09d0 AD |
626 | =item continue BLOCK |
627 | ||
628 | Actually a flow control statement rather than a function. If there is a | |
629 | C<continue> BLOCK attached to a BLOCK (typically in a C<while> or | |
630 | C<foreach>), it is always executed just before the conditional is about to | |
631 | be evaluated again, just like the third part of a C<for> loop in C. Thus | |
632 | it can be used to increment a loop variable, even when the loop has been | |
633 | continued via the C<next> statement (which is similar to the C C<continue> | |
634 | statement). | |
635 | ||
1d2dff63 GS |
636 | C<last>, C<next>, or C<redo> may appear within a C<continue> |
637 | block. C<last> and C<redo> will behave as if they had been executed within | |
638 | the main block. So will C<next>, but since it will execute a C<continue> | |
639 | block, it may be more entertaining. | |
640 | ||
641 | while (EXPR) { | |
642 | ### redo always comes here | |
643 | do_something; | |
644 | } continue { | |
645 | ### next always comes here | |
646 | do_something_else; | |
647 | # then back the top to re-check EXPR | |
648 | } | |
649 | ### last always comes here | |
650 | ||
651 | Omitting the C<continue> section is semantically equivalent to using an | |
652 | empty one, logically enough. In that case, C<next> goes directly back | |
653 | to check the condition at the top of the loop. | |
654 | ||
a0d0e21e LW |
655 | =item cos EXPR |
656 | ||
5a964f20 | 657 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 658 | takes cosine of C<$_>. |
a0d0e21e | 659 | |
7660c0ab | 660 | For the inverse cosine operation, you may use the C<POSIX::acos()> |
28757baa | 661 | function, or use this relation: |
662 | ||
663 | sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } | |
664 | ||
a0d0e21e LW |
665 | =item crypt PLAINTEXT,SALT |
666 | ||
f86cebdf | 667 | Encrypts a string exactly like the crypt(3) function in the C library |
4633a7c4 LW |
668 | (assuming that you actually have a version there that has not been |
669 | extirpated as a potential munition). This can prove useful for checking | |
670 | the password file for lousy passwords, amongst other things. Only the | |
671 | guys wearing white hats should do this. | |
a0d0e21e | 672 | |
7660c0ab | 673 | Note that C<crypt()> is intended to be a one-way function, much like breaking |
11155c91 CS |
674 | eggs to make an omelette. There is no (known) corresponding decrypt |
675 | function. As a result, this function isn't all that useful for | |
676 | cryptography. (For that, see your nearby CPAN mirror.) | |
2f9daede | 677 | |
a0d0e21e LW |
678 | Here's an example that makes sure that whoever runs this program knows |
679 | their own password: | |
680 | ||
681 | $pwd = (getpwuid($<))[1]; | |
682 | $salt = substr($pwd, 0, 2); | |
683 | ||
684 | system "stty -echo"; | |
685 | print "Password: "; | |
686 | chop($word = <STDIN>); | |
687 | print "\n"; | |
688 | system "stty echo"; | |
689 | ||
690 | if (crypt($word, $salt) ne $pwd) { | |
691 | die "Sorry...\n"; | |
692 | } else { | |
693 | print "ok\n"; | |
54310121 | 694 | } |
a0d0e21e | 695 | |
9f8f0c9d | 696 | Of course, typing in your own password to whoever asks you |
748a9306 | 697 | for it is unwise. |
a0d0e21e | 698 | |
aa689395 | 699 | =item dbmclose HASH |
a0d0e21e | 700 | |
7660c0ab | 701 | [This function has been superseded by the C<untie()> function.] |
a0d0e21e | 702 | |
aa689395 | 703 | Breaks the binding between a DBM file and a hash. |
a0d0e21e | 704 | |
aa689395 | 705 | =item dbmopen HASH,DBNAME,MODE |
a0d0e21e | 706 | |
7660c0ab | 707 | [This function has been superseded by the C<tie()> function.] |
a0d0e21e | 708 | |
7b8d334a | 709 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a |
ab4f32c2 | 710 | hash. HASH is the name of the hash. (Unlike normal C<open()>, the first |
aa689395 | 711 | argument is I<NOT> a filehandle, even though it looks like one). DBNAME |
712 | is the name of the database (without the F<.dir> or F<.pag> extension if | |
713 | any). If the database does not exist, it is created with protection | |
7660c0ab A |
714 | specified by MODE (as modified by the C<umask()>). If your system supports |
715 | only the older DBM functions, you may perform only one C<dbmopen()> in your | |
aa689395 | 716 | program. In older versions of Perl, if your system had neither DBM nor |
7660c0ab | 717 | ndbm, calling C<dbmopen()> produced a fatal error; it now falls back to |
aa689395 | 718 | sdbm(3). |
719 | ||
720 | If you don't have write access to the DBM file, you can only read hash | |
721 | variables, not set them. If you want to test whether you can write, | |
7660c0ab | 722 | either use file tests or try setting a dummy hash entry inside an C<eval()>, |
aa689395 | 723 | which will trap the error. |
a0d0e21e | 724 | |
7660c0ab A |
725 | Note that functions such as C<keys()> and C<values()> may return huge lists |
726 | when used on large DBM files. You may prefer to use the C<each()> | |
a0d0e21e LW |
727 | function to iterate over large DBM files. Example: |
728 | ||
729 | # print out history file offsets | |
730 | dbmopen(%HIST,'/usr/lib/news/history',0666); | |
731 | while (($key,$val) = each %HIST) { | |
732 | print $key, ' = ', unpack('L',$val), "\n"; | |
733 | } | |
734 | dbmclose(%HIST); | |
735 | ||
cb1a09d0 | 736 | See also L<AnyDBM_File> for a more general description of the pros and |
184e9718 | 737 | cons of the various dbm approaches, as well as L<DB_File> for a particularly |
cb1a09d0 | 738 | rich implementation. |
4633a7c4 | 739 | |
a0d0e21e LW |
740 | =item defined EXPR |
741 | ||
54310121 | 742 | =item defined |
bbce6d69 | 743 | |
2f9daede TP |
744 | Returns a Boolean value telling whether EXPR has a value other than |
745 | the undefined value C<undef>. If EXPR is not present, C<$_> will be | |
746 | checked. | |
747 | ||
748 | Many operations return C<undef> to indicate failure, end of file, | |
749 | system error, uninitialized variable, and other exceptional | |
750 | conditions. This function allows you to distinguish C<undef> from | |
751 | other values. (A simple Boolean test will not distinguish among | |
7660c0ab | 752 | C<undef>, zero, the empty string, and C<"0">, which are all equally |
2f9daede | 753 | false.) Note that since C<undef> is a valid scalar, its presence |
7660c0ab | 754 | doesn't I<necessarily> indicate an exceptional condition: C<pop()> |
2f9daede TP |
755 | returns C<undef> when its argument is an empty array, I<or> when the |
756 | element to return happens to be C<undef>. | |
757 | ||
7660c0ab | 758 | You may also use C<defined()> to check whether a subroutine exists, by |
5a964f20 | 759 | saying C<defined &func> without parentheses. On the other hand, use |
7660c0ab | 760 | of C<defined()> upon aggregates (hashes and arrays) is not guaranteed to |
5a964f20 | 761 | produce intuitive results, and should probably be avoided. |
2f9daede TP |
762 | |
763 | When used on a hash element, it tells you whether the value is defined, | |
dc848c6f | 764 | not whether the key exists in the hash. Use L</exists> for the latter |
2f9daede | 765 | purpose. |
a0d0e21e LW |
766 | |
767 | Examples: | |
768 | ||
769 | print if defined $switch{'D'}; | |
770 | print "$val\n" while defined($val = pop(@ary)); | |
771 | die "Can't readlink $sym: $!" | |
772 | unless defined($value = readlink $sym); | |
a0d0e21e | 773 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
2f9daede | 774 | $debugging = 0 unless defined $debugging; |
a0d0e21e | 775 | |
7660c0ab A |
776 | Note: Many folks tend to overuse C<defined()>, and then are surprised to |
777 | discover that the number C<0> and C<""> (the zero-length string) are, in fact, | |
2f9daede | 778 | defined values. For example, if you say |
a5f75d66 AD |
779 | |
780 | "ab" =~ /a(.*)b/; | |
781 | ||
7660c0ab | 782 | The pattern match succeeds, and C<$1> is defined, despite the fact that it |
a5f75d66 | 783 | matched "nothing". But it didn't really match nothing--rather, it |
7660c0ab | 784 | matched something that happened to be C<0> characters long. This is all |
a5f75d66 | 785 | very above-board and honest. When a function returns an undefined value, |
2f9daede | 786 | it's an admission that it couldn't give you an honest answer. So you |
7660c0ab A |
787 | should use C<defined()> only when you're questioning the integrity of what |
788 | you're trying to do. At other times, a simple comparison to C<0> or C<""> is | |
2f9daede TP |
789 | what you want. |
790 | ||
7660c0ab | 791 | Currently, using C<defined()> on an entire array or hash reports whether |
2f9daede TP |
792 | memory for that aggregate has ever been allocated. So an array you set |
793 | to the empty list appears undefined initially, and one that once was full | |
794 | and that you then set to the empty list still appears defined. You | |
795 | should instead use a simple test for size: | |
28757baa | 796 | |
797 | if (@an_array) { print "has array elements\n" } | |
798 | if (%a_hash) { print "has hash members\n" } | |
799 | ||
7660c0ab | 800 | Using C<undef()> on these, however, does clear their memory and then report |
5a964f20 | 801 | them as not defined anymore, but you shouldn't do that unless you don't |
28757baa | 802 | plan to use them again, because it saves time when you load them up |
5a964f20 TC |
803 | again to have memory already ready to be filled. The normal way to |
804 | free up space used by an aggregate is to assign the empty list. | |
28757baa | 805 | |
7660c0ab | 806 | This counterintuitive behavior of C<defined()> on aggregates may be |
28757baa | 807 | changed, fixed, or broken in a future release of Perl. |
808 | ||
dc848c6f | 809 | See also L</undef>, L</exists>, L</ref>. |
2f9daede | 810 | |
a0d0e21e LW |
811 | =item delete EXPR |
812 | ||
aa689395 | 813 | Deletes the specified key(s) and their associated values from a hash. |
814 | For each key, returns the deleted value associated with that key, or | |
815 | the undefined value if there was no such key. Deleting from C<$ENV{}> | |
816 | modifies the environment. Deleting from a hash tied to a DBM file | |
7660c0ab | 817 | deletes the entry from the DBM file. (But deleting from a C<tie()>d hash |
5f05dabc | 818 | doesn't necessarily return anything.) |
a0d0e21e | 819 | |
aa689395 | 820 | The following deletes all the values of a hash: |
a0d0e21e | 821 | |
5f05dabc | 822 | foreach $key (keys %HASH) { |
823 | delete $HASH{$key}; | |
a0d0e21e LW |
824 | } |
825 | ||
5f05dabc | 826 | And so does this: |
827 | ||
828 | delete @HASH{keys %HASH} | |
829 | ||
5a964f20 | 830 | (But both of these are slower than just assigning the empty list, or |
7660c0ab | 831 | using C<undef()>.) Note that the EXPR can be arbitrarily complicated as |
5a964f20 | 832 | long as the final operation is a hash element lookup or hash slice: |
a0d0e21e LW |
833 | |
834 | delete $ref->[$x][$y]{$key}; | |
5f05dabc | 835 | delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; |
a0d0e21e LW |
836 | |
837 | =item die LIST | |
838 | ||
7660c0ab A |
839 | Outside an C<eval()>, prints the value of LIST to C<STDERR> and exits with |
840 | the current value of C<$!> (errno). If C<$!> is C<0>, exits with the value of | |
54310121 | 841 | C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)> |
7660c0ab A |
842 | is C<0>, exits with C<255>. Inside an C<eval(),> the error message is stuffed into |
843 | C<$@> and the C<eval()> is terminated with the undefined value. This makes | |
844 | C<die()> the way to raise an exception. | |
a0d0e21e LW |
845 | |
846 | Equivalent examples: | |
847 | ||
848 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; | |
54310121 | 849 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
a0d0e21e LW |
850 | |
851 | If the value of EXPR does not end in a newline, the current script line | |
852 | number and input line number (if any) are also printed, and a newline | |
7660c0ab A |
853 | is supplied. Hint: sometimes appending C<", stopped"> to your message |
854 | will cause it to make better sense when the string C<"at foo line 123"> is | |
a0d0e21e LW |
855 | appended. Suppose you are running script "canasta". |
856 | ||
857 | die "/etc/games is no good"; | |
858 | die "/etc/games is no good, stopped"; | |
859 | ||
860 | produce, respectively | |
861 | ||
862 | /etc/games is no good at canasta line 123. | |
863 | /etc/games is no good, stopped at canasta line 123. | |
864 | ||
7660c0ab | 865 | See also C<exit()> and C<warn()>. |
a0d0e21e | 866 | |
7660c0ab A |
867 | If LIST is empty and C<$@> already contains a value (typically from a |
868 | previous eval) that value is reused after appending C<"\t...propagated">. | |
fb73857a | 869 | This is useful for propagating exceptions: |
870 | ||
871 | eval { ... }; | |
872 | die unless $@ =~ /Expected exception/; | |
873 | ||
7660c0ab | 874 | If C<$@> is empty then the string C<"Died"> is used. |
fb73857a | 875 | |
7660c0ab | 876 | You can arrange for a callback to be run just before the C<die()> does |
774d564b | 877 | its deed, by setting the C<$SIG{__DIE__}> hook. The associated handler |
878 | will be called with the error text and can change the error message, if | |
7660c0ab | 879 | it sees fit, by calling C<die()> again. See L<perlvar/$SIG{expr}> for details on |
fb73857a | 880 | setting C<%SIG> entries, and L<"eval BLOCK"> for some examples. |
881 | ||
882 | Note that the C<$SIG{__DIE__}> hook is called even inside eval()ed | |
883 | blocks/strings. If one wants the hook to do nothing in such | |
884 | situations, put | |
885 | ||
886 | die @_ if $^S; | |
887 | ||
888 | as the first line of the handler (see L<perlvar/$^S>). | |
774d564b | 889 | |
a0d0e21e LW |
890 | =item do BLOCK |
891 | ||
892 | Not really a function. Returns the value of the last command in the | |
893 | sequence of commands indicated by BLOCK. When modified by a loop | |
894 | modifier, executes the BLOCK once before testing the loop condition. | |
895 | (On other statements the loop modifiers test the conditional first.) | |
896 | ||
897 | =item do SUBROUTINE(LIST) | |
898 | ||
899 | A deprecated form of subroutine call. See L<perlsub>. | |
900 | ||
901 | =item do EXPR | |
902 | ||
903 | Uses the value of EXPR as a filename and executes the contents of the | |
904 | file as a Perl script. Its primary use is to include subroutines | |
905 | from a Perl subroutine library. | |
906 | ||
907 | do 'stat.pl'; | |
908 | ||
909 | is just like | |
910 | ||
fb73857a | 911 | scalar eval `cat stat.pl`; |
a0d0e21e | 912 | |
5a964f20 | 913 | except that it's more efficient and concise, keeps track of the |
a0d0e21e LW |
914 | current filename for error messages, and searches all the B<-I> |
915 | libraries if the file isn't in the current directory (see also the @INC | |
dc1be6b5 GS |
916 | array in L<perlvar/Predefined Names>). It is also different in how |
917 | code evaluated with C<do FILENAME> doesn't see lexicals in the enclosing | |
918 | scope like C<eval STRING> does. It's the same, however, in that it does | |
54310121 | 919 | reparse the file every time you call it, so you probably don't want to |
a0d0e21e LW |
920 | do this inside a loop. |
921 | ||
8e30cc93 MG |
922 | If C<do> cannot read the file, it returns undef and sets C<$!> to the |
923 | error. If C<do> can read the file but cannot compile it, it | |
924 | returns undef and sets an error message in C<$@>. If the file is | |
925 | successfully compiled, C<do> returns the value of the last expression | |
926 | evaluated. | |
927 | ||
a0d0e21e | 928 | Note that inclusion of library modules is better done with the |
7660c0ab | 929 | C<use()> and C<require()> operators, which also do automatic error checking |
4633a7c4 | 930 | and raise an exception if there's a problem. |
a0d0e21e | 931 | |
5a964f20 TC |
932 | You might like to use C<do> to read in a program configuration |
933 | file. Manual error checking can be done this way: | |
934 | ||
935 | # read in config files: system first, then user | |
f86cebdf GS |
936 | for $file ("/share/prog/defaults.rc", |
937 | "$ENV{HOME}/.someprogrc") { | |
5a964f20 | 938 | unless ($return = do $file) { |
f86cebdf GS |
939 | warn "couldn't parse $file: $@" if $@; |
940 | warn "couldn't do $file: $!" unless defined $return; | |
941 | warn "couldn't run $file" unless $return; | |
5a964f20 TC |
942 | } |
943 | } | |
944 | ||
a0d0e21e LW |
945 | =item dump LABEL |
946 | ||
947 | This causes an immediate core dump. Primarily this is so that you can | |
948 | use the B<undump> program to turn your core dump into an executable binary | |
949 | after having initialized all your variables at the beginning of the | |
950 | program. When the new binary is executed it will begin by executing a | |
951 | C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of | |
f86cebdf | 952 | it as a goto with an intervening core dump and reincarnation. If C<LABEL> |
5a964f20 | 953 | is omitted, restarts the program from the top. WARNING: Any files |
a0d0e21e LW |
954 | opened at the time of the dump will NOT be open any more when the |
955 | program is reincarnated, with possible resulting confusion on the part | |
956 | of Perl. See also B<-u> option in L<perlrun>. | |
957 | ||
958 | Example: | |
959 | ||
960 | #!/usr/bin/perl | |
961 | require 'getopt.pl'; | |
962 | require 'stat.pl'; | |
963 | %days = ( | |
964 | 'Sun' => 1, | |
965 | 'Mon' => 2, | |
966 | 'Tue' => 3, | |
967 | 'Wed' => 4, | |
968 | 'Thu' => 5, | |
969 | 'Fri' => 6, | |
970 | 'Sat' => 7, | |
971 | ); | |
972 | ||
973 | dump QUICKSTART if $ARGV[0] eq '-d'; | |
974 | ||
975 | QUICKSTART: | |
976 | Getopt('f'); | |
977 | ||
5a964f20 TC |
978 | This operator is largely obsolete, partly because it's very hard to |
979 | convert a core file into an executable, and because the real perl-to-C | |
980 | compiler has superseded it. | |
981 | ||
aa689395 | 982 | =item each HASH |
983 | ||
5a964f20 | 984 | When called in list context, returns a 2-element list consisting of the |
aa689395 | 985 | key and value for the next element of a hash, so that you can iterate over |
5a964f20 | 986 | it. When called in scalar context, returns the key for only the "next" |
7660c0ab | 987 | element in the hash. (Note: Keys may be C<"0"> or C<"">, which are logically |
2f9daede TP |
988 | false; you may wish to avoid constructs like C<while ($k = each %foo) {}> |
989 | for this reason.) | |
990 | ||
991 | Entries are returned in an apparently random order. When the hash is | |
992 | entirely read, a null array is returned in list context (which when | |
7660c0ab A |
993 | assigned produces a FALSE (C<0>) value), and C<undef> in |
994 | scalar context. The next call to C<each()> after that will start iterating | |
995 | again. There is a single iterator for each hash, shared by all C<each()>, | |
996 | C<keys()>, and C<values()> function calls in the program; it can be reset by | |
2f9daede TP |
997 | reading all the elements from the hash, or by evaluating C<keys HASH> or |
998 | C<values HASH>. If you add or delete elements of a hash while you're | |
999 | iterating over it, you may get entries skipped or duplicated, so don't. | |
aa689395 | 1000 | |
f86cebdf | 1001 | The following prints out your environment like the printenv(1) program, |
aa689395 | 1002 | only in a different order: |
a0d0e21e LW |
1003 | |
1004 | while (($key,$value) = each %ENV) { | |
1005 | print "$key=$value\n"; | |
1006 | } | |
1007 | ||
7660c0ab | 1008 | See also C<keys()> and C<values()>. |
a0d0e21e LW |
1009 | |
1010 | =item eof FILEHANDLE | |
1011 | ||
4633a7c4 LW |
1012 | =item eof () |
1013 | ||
a0d0e21e LW |
1014 | =item eof |
1015 | ||
1016 | Returns 1 if the next read on FILEHANDLE will return end of file, or if | |
1017 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value | |
5a964f20 | 1018 | gives the real filehandle. (Note that this function actually |
7660c0ab | 1019 | reads a character and then C<ungetc()>s it, so isn't very useful in an |
748a9306 LW |
1020 | interactive context.) Do not read from a terminal file (or call |
1021 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such | |
1022 | as terminals may lose the end-of-file condition if you do. | |
1023 | ||
1024 | An C<eof> without an argument uses the last file read as argument. | |
5a964f20 | 1025 | Using C<eof()> with empty parentheses is very different. It indicates the pseudo file formed of |
2f9daede TP |
1026 | the files listed on the command line, i.e., C<eof()> is reasonable to |
1027 | use inside a C<while (E<lt>E<gt>)> loop to detect the end of only the | |
1028 | last file. Use C<eof(ARGV)> or eof without the parentheses to test | |
1029 | I<EACH> file in a while (E<lt>E<gt>) loop. Examples: | |
a0d0e21e | 1030 | |
748a9306 LW |
1031 | # reset line numbering on each input file |
1032 | while (<>) { | |
5a964f20 | 1033 | next if /^\s*#/; # skip comments |
748a9306 | 1034 | print "$.\t$_"; |
5a964f20 TC |
1035 | } continue { |
1036 | close ARGV if eof; # Not eof()! | |
748a9306 LW |
1037 | } |
1038 | ||
a0d0e21e LW |
1039 | # insert dashes just before last line of last file |
1040 | while (<>) { | |
5a964f20 | 1041 | if (eof()) { # check for end of current file |
a0d0e21e | 1042 | print "--------------\n"; |
748a9306 LW |
1043 | close(ARGV); # close or break; is needed if we |
1044 | # are reading from the terminal | |
a0d0e21e LW |
1045 | } |
1046 | print; | |
1047 | } | |
1048 | ||
a0d0e21e | 1049 | Practical hint: you almost never need to use C<eof> in Perl, because the |
3b02c43c GS |
1050 | input operators return false values when they run out of data, or if there |
1051 | was an error. | |
a0d0e21e LW |
1052 | |
1053 | =item eval EXPR | |
1054 | ||
1055 | =item eval BLOCK | |
1056 | ||
c7cc6f1c GS |
1057 | In the first form, the return value of EXPR is parsed and executed as if it |
1058 | were a little Perl program. The value of the expression (which is itself | |
5a964f20 | 1059 | determined within scalar context) is first parsed, and if there weren't any |
c7cc6f1c | 1060 | errors, executed in the context of the current Perl program, so that any |
5f05dabc | 1061 | variable settings or subroutine and format definitions remain afterwards. |
c7cc6f1c GS |
1062 | Note that the value is parsed every time the eval executes. If EXPR is |
1063 | omitted, evaluates C<$_>. This form is typically used to delay parsing | |
1064 | and subsequent execution of the text of EXPR until run time. | |
1065 | ||
1066 | In the second form, the code within the BLOCK is parsed only once--at the | |
1067 | same time the code surrounding the eval itself was parsed--and executed | |
1068 | within the context of the current Perl program. This form is typically | |
1069 | used to trap exceptions more efficiently than the first (see below), while | |
1070 | also providing the benefit of checking the code within BLOCK at compile | |
1071 | time. | |
1072 | ||
1073 | The final semicolon, if any, may be omitted from the value of EXPR or within | |
1074 | the BLOCK. | |
1075 | ||
1076 | In both forms, the value returned is the value of the last expression | |
5a964f20 | 1077 | evaluated inside the mini-program; a return statement may be also used, just |
c7cc6f1c | 1078 | as with subroutines. The expression providing the return value is evaluated |
5a964f20 | 1079 | in void, scalar, or list context, depending on the context of the eval itself. |
c7cc6f1c | 1080 | See L</wantarray> for more on how the evaluation context can be determined. |
a0d0e21e | 1081 | |
7660c0ab A |
1082 | If there is a syntax error or runtime error, or a C<die()> statement is |
1083 | executed, an undefined value is returned by C<eval()>, and C<$@> is set to the | |
a0d0e21e | 1084 | error message. If there was no error, C<$@> is guaranteed to be a null |
7660c0ab | 1085 | string. Beware that using C<eval()> neither silences perl from printing |
c7cc6f1c GS |
1086 | warnings to STDERR, nor does it stuff the text of warning messages into C<$@>. |
1087 | To do either of those, you have to use the C<$SIG{__WARN__}> facility. See | |
1088 | L</warn> and L<perlvar>. | |
a0d0e21e | 1089 | |
7660c0ab A |
1090 | Note that, because C<eval()> traps otherwise-fatal errors, it is useful for |
1091 | determining whether a particular feature (such as C<socket()> or C<symlink()>) | |
a0d0e21e LW |
1092 | is implemented. It is also Perl's exception trapping mechanism, where |
1093 | the die operator is used to raise exceptions. | |
1094 | ||
1095 | If the code to be executed doesn't vary, you may use the eval-BLOCK | |
1096 | form to trap run-time errors without incurring the penalty of | |
1097 | recompiling each time. The error, if any, is still returned in C<$@>. | |
1098 | Examples: | |
1099 | ||
54310121 | 1100 | # make divide-by-zero nonfatal |
a0d0e21e LW |
1101 | eval { $answer = $a / $b; }; warn $@ if $@; |
1102 | ||
1103 | # same thing, but less efficient | |
1104 | eval '$answer = $a / $b'; warn $@ if $@; | |
1105 | ||
1106 | # a compile-time error | |
5a964f20 | 1107 | eval { $answer = }; # WRONG |
a0d0e21e LW |
1108 | |
1109 | # a run-time error | |
1110 | eval '$answer ='; # sets $@ | |
1111 | ||
7660c0ab | 1112 | When using the C<eval{}> form as an exception trap in libraries, you may |
774d564b | 1113 | wish not to trigger any C<__DIE__> hooks that user code may have |
1114 | installed. You can use the C<local $SIG{__DIE__}> construct for this | |
1115 | purpose, as shown in this example: | |
1116 | ||
1117 | # a very private exception trap for divide-by-zero | |
f86cebdf GS |
1118 | eval { local $SIG{'__DIE__'}; $answer = $a / $b; }; |
1119 | warn $@ if $@; | |
774d564b | 1120 | |
1121 | This is especially significant, given that C<__DIE__> hooks can call | |
7660c0ab | 1122 | C<die()> again, which has the effect of changing their error messages: |
774d564b | 1123 | |
1124 | # __DIE__ hooks may modify error messages | |
1125 | { | |
f86cebdf GS |
1126 | local $SIG{'__DIE__'} = |
1127 | sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x }; | |
c7cc6f1c GS |
1128 | eval { die "foo lives here" }; |
1129 | print $@ if $@; # prints "bar lives here" | |
774d564b | 1130 | } |
1131 | ||
7660c0ab | 1132 | With an C<eval()>, you should be especially careful to remember what's |
a0d0e21e LW |
1133 | being looked at when: |
1134 | ||
1135 | eval $x; # CASE 1 | |
1136 | eval "$x"; # CASE 2 | |
1137 | ||
1138 | eval '$x'; # CASE 3 | |
1139 | eval { $x }; # CASE 4 | |
1140 | ||
5a964f20 | 1141 | eval "\$$x++"; # CASE 5 |
a0d0e21e LW |
1142 | $$x++; # CASE 6 |
1143 | ||
2f9daede | 1144 | Cases 1 and 2 above behave identically: they run the code contained in |
7660c0ab | 1145 | the variable C<$x>. (Although case 2 has misleading double quotes making |
2f9daede | 1146 | the reader wonder what else might be happening (nothing is).) Cases 3 |
7660c0ab | 1147 | and 4 likewise behave in the same way: they run the code C<'$x'>, which |
2f9daede TP |
1148 | does nothing but return the value of C<$x>. (Case 4 is preferred for |
1149 | purely visual reasons, but it also has the advantage of compiling at | |
1150 | compile-time instead of at run-time.) Case 5 is a place where | |
54310121 | 1151 | normally you I<WOULD> like to use double quotes, except that in this |
2f9daede TP |
1152 | particular situation, you can just use symbolic references instead, as |
1153 | in case 6. | |
a0d0e21e LW |
1154 | |
1155 | =item exec LIST | |
1156 | ||
8bf3b016 GS |
1157 | =item exec PROGRAM LIST |
1158 | ||
7660c0ab A |
1159 | The C<exec()> function executes a system command I<AND NEVER RETURNS> - |
1160 | use C<system()> instead of C<exec()> if you want it to return. It fails and | |
fb73857a | 1161 | returns FALSE only if the command does not exist I<and> it is executed |
1162 | directly instead of via your system's command shell (see below). | |
a0d0e21e | 1163 | |
7660c0ab A |
1164 | Since it's a common mistake to use C<exec()> instead of C<system()>, Perl |
1165 | warns you if there is a following statement which isn't C<die()>, C<warn()>, | |
1166 | or C<exit()> (if C<-w> is set - but you always do that). If you | |
1167 | I<really> want to follow an C<exec()> with some other statement, you | |
55d729e4 GS |
1168 | can use one of these styles to avoid the warning: |
1169 | ||
5a964f20 TC |
1170 | exec ('foo') or print STDERR "couldn't exec foo: $!"; |
1171 | { exec ('foo') }; print STDERR "couldn't exec foo: $!"; | |
55d729e4 | 1172 | |
5a964f20 | 1173 | If there is more than one argument in LIST, or if LIST is an array |
f86cebdf | 1174 | with more than one value, calls execvp(3) with the arguments in LIST. |
5a964f20 TC |
1175 | If there is only one scalar argument or an array with one element in it, |
1176 | the argument is checked for shell metacharacters, and if there are any, | |
1177 | the entire argument is passed to the system's command shell for parsing | |
1178 | (this is C</bin/sh -c> on Unix platforms, but varies on other platforms). | |
1179 | If there are no shell metacharacters in the argument, it is split into | |
7660c0ab A |
1180 | words and passed directly to C<execvp()>, which is more efficient. Note: |
1181 | C<exec()> and C<system()> do not flush your output buffer, so you may need to | |
5a964f20 | 1182 | set C<$|> to avoid lost output. Examples: |
a0d0e21e LW |
1183 | |
1184 | exec '/bin/echo', 'Your arguments are: ', @ARGV; | |
1185 | exec "sort $outfile | uniq"; | |
1186 | ||
1187 | If you don't really want to execute the first argument, but want to lie | |
1188 | to the program you are executing about its own name, you can specify | |
1189 | the program you actually want to run as an "indirect object" (without a | |
1190 | comma) in front of the LIST. (This always forces interpretation of the | |
54310121 | 1191 | LIST as a multivalued list, even if there is only a single scalar in |
a0d0e21e LW |
1192 | the list.) Example: |
1193 | ||
1194 | $shell = '/bin/csh'; | |
1195 | exec $shell '-sh'; # pretend it's a login shell | |
1196 | ||
1197 | or, more directly, | |
1198 | ||
1199 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell | |
1200 | ||
bb32b41a GS |
1201 | When the arguments get executed via the system shell, results will |
1202 | be subject to its quirks and capabilities. See L<perlop/"`STRING`"> | |
1203 | for details. | |
1204 | ||
ab4f32c2 | 1205 | Using an indirect object with C<exec()> or C<system()> is also more secure. |
5a964f20 TC |
1206 | This usage forces interpretation of the arguments as a multivalued list, |
1207 | even if the list had just one argument. That way you're safe from the | |
1208 | shell expanding wildcards or splitting up words with whitespace in them. | |
1209 | ||
1210 | @args = ( "echo surprise" ); | |
1211 | ||
f86cebdf GS |
1212 | system @args; # subject to shell escapes |
1213 | # if @args == 1 | |
5a964f20 TC |
1214 | system { $args[0] } @args; # safe even with one-arg list |
1215 | ||
1216 | The first version, the one without the indirect object, ran the I<echo> | |
1217 | program, passing it C<"surprise"> an argument. The second version | |
1218 | didn't--it tried to run a program literally called I<"echo surprise">, | |
1219 | didn't find it, and set C<$?> to a non-zero value indicating failure. | |
1220 | ||
ab4f32c2 | 1221 | Note that C<exec()> will not call your C<END> blocks, nor will it call |
7660c0ab A |
1222 | any C<DESTROY> methods in your objects. |
1223 | ||
a0d0e21e LW |
1224 | =item exists EXPR |
1225 | ||
1226 | Returns TRUE if the specified hash key exists in its hash array, even | |
1227 | if the corresponding value is undefined. | |
1228 | ||
1229 | print "Exists\n" if exists $array{$key}; | |
1230 | print "Defined\n" if defined $array{$key}; | |
1231 | print "True\n" if $array{$key}; | |
1232 | ||
5f05dabc | 1233 | A hash element can be TRUE only if it's defined, and defined if |
a0d0e21e LW |
1234 | it exists, but the reverse doesn't necessarily hold true. |
1235 | ||
1236 | Note that the EXPR can be arbitrarily complicated as long as the final | |
1237 | operation is a hash key lookup: | |
1238 | ||
5a964f20 TC |
1239 | if (exists $ref->{"A"}{"B"}{$key}) { ... } |
1240 | ||
1241 | Although the last element will not spring into existence just because its | |
1242 | existence was tested, intervening ones will. Thus C<$ref-E<gt>{"A"}> | |
1243 | C<$ref-E<gt>{"B"}> will spring into existence due to the existence | |
1244 | test for a $key element. This autovivification may be fixed in a later | |
1245 | release. | |
a0d0e21e LW |
1246 | |
1247 | =item exit EXPR | |
1248 | ||
1249 | Evaluates EXPR and exits immediately with that value. (Actually, it | |
1250 | calls any defined C<END> routines first, but the C<END> routines may not | |
1251 | abort the exit. Likewise any object destructors that need to be called | |
1252 | are called before exit.) Example: | |
1253 | ||
1254 | $ans = <STDIN>; | |
1255 | exit 0 if $ans =~ /^[Xx]/; | |
1256 | ||
7660c0ab A |
1257 | See also C<die()>. If EXPR is omitted, exits with C<0> status. The only |
1258 | universally portable values for EXPR are C<0> for success and C<1> for error; | |
f86702cc | 1259 | all other values are subject to unpredictable interpretation depending |
1260 | on the environment in which the Perl program is running. | |
a0d0e21e | 1261 | |
7660c0ab A |
1262 | You shouldn't use C<exit()> to abort a subroutine if there's any chance that |
1263 | someone might want to trap whatever error happened. Use C<die()> instead, | |
1264 | which can be trapped by an C<eval()>. | |
28757baa | 1265 | |
5a964f20 TC |
1266 | All C<END{}> blocks are run at exit time. See L<perlsub> for details. |
1267 | ||
a0d0e21e LW |
1268 | =item exp EXPR |
1269 | ||
54310121 | 1270 | =item exp |
bbce6d69 | 1271 | |
54310121 | 1272 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
a0d0e21e LW |
1273 | If EXPR is omitted, gives C<exp($_)>. |
1274 | ||
1275 | =item fcntl FILEHANDLE,FUNCTION,SCALAR | |
1276 | ||
f86cebdf | 1277 | Implements the fcntl(2) function. You'll probably have to say |
a0d0e21e LW |
1278 | |
1279 | use Fcntl; | |
1280 | ||
0ade1984 | 1281 | first to get the correct constant definitions. Argument processing and |
7660c0ab | 1282 | value return works just like C<ioctl()> below. |
a0d0e21e LW |
1283 | For example: |
1284 | ||
1285 | use Fcntl; | |
5a964f20 TC |
1286 | fcntl($filehandle, F_GETFL, $packed_return_buffer) |
1287 | or die "can't fcntl F_GETFL: $!"; | |
1288 | ||
ab4f32c2 A |
1289 | You don't have to check for C<defined()> on the return from |
1290 | C<fnctl()>. Like C<ioctl()>, it maps a C<0> return from the system | |
7660c0ab A |
1291 | call into "C<0> but true" in Perl. This string is true in |
1292 | boolean context and C<0> in numeric context. It is also | |
5a964f20 TC |
1293 | exempt from the normal B<-w> warnings on improper numeric |
1294 | conversions. | |
1295 | ||
7660c0ab | 1296 | Note that C<fcntl()> will produce a fatal error if used on a machine that |
f86cebdf | 1297 | doesn't implement fcntl(2). |
a0d0e21e LW |
1298 | |
1299 | =item fileno FILEHANDLE | |
1300 | ||
1301 | Returns the file descriptor for a filehandle. This is useful for | |
7660c0ab | 1302 | constructing bitmaps for C<select()> and low-level POSIX tty-handling |
5a964f20 TC |
1303 | operations. If FILEHANDLE is an expression, the value is taken as |
1304 | an indirect filehandle, generally its name. | |
1305 | ||
1306 | You can use this to find out whether two handles refer to the | |
1307 | same underlying descriptor: | |
1308 | ||
1309 | if (fileno(THIS) == fileno(THAT)) { | |
1310 | print "THIS and THAT are dups\n"; | |
1311 | } | |
a0d0e21e LW |
1312 | |
1313 | =item flock FILEHANDLE,OPERATION | |
1314 | ||
f86cebdf | 1315 | Calls flock(2), or an emulation of it, on FILEHANDLE. Returns TRUE for |
68dc0745 | 1316 | success, FALSE on failure. Produces a fatal error if used on a machine |
f86cebdf | 1317 | that doesn't implement flock(2), fcntl(2) locking, or lockf(3). C<flock()> |
68dc0745 | 1318 | is Perl's portable file locking interface, although it locks only entire |
1319 | files, not records. | |
8ebc5c01 | 1320 | |
a3cb178b | 1321 | On many platforms (including most versions or clones of Unix), locks |
7660c0ab | 1322 | established by C<flock()> are B<merely advisory>. Such discretionary locks |
5a964f20 | 1323 | are more flexible, but offer fewer guarantees. This means that files |
7660c0ab A |
1324 | locked with C<flock()> may be modified by programs that do not also use |
1325 | C<flock()>. Windows NT and OS/2 are among the platforms which | |
5a964f20 | 1326 | enforce mandatory locking. See your local documentation for details. |
a3cb178b | 1327 | |
8ebc5c01 | 1328 | OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with |
1329 | LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but | |
68dc0745 | 1330 | you can use the symbolic names if import them from the Fcntl module, |
1331 | either individually, or as a group using the ':flock' tag. LOCK_SH | |
1332 | requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN | |
1333 | releases a previously requested lock. If LOCK_NB is added to LOCK_SH or | |
7660c0ab | 1334 | LOCK_EX then C<flock()> will return immediately rather than blocking |
68dc0745 | 1335 | waiting for the lock (check the return status to see if you got it). |
1336 | ||
1337 | To avoid the possibility of mis-coordination, Perl flushes FILEHANDLE | |
1338 | before (un)locking it. | |
8ebc5c01 | 1339 | |
f86cebdf | 1340 | Note that the emulation built with lockf(3) doesn't provide shared |
8ebc5c01 | 1341 | locks, and it requires that FILEHANDLE be open with write intent. These |
f86cebdf GS |
1342 | are the semantics that lockf(3) implements. Most (all?) systems |
1343 | implement lockf(3) in terms of fcntl(2) locking, though, so the | |
8ebc5c01 | 1344 | differing semantics shouldn't bite too many people. |
1345 | ||
7660c0ab A |
1346 | Note also that some versions of C<flock()> cannot lock things over the |
1347 | network; you would need to use the more system-specific C<fcntl()> for | |
f86cebdf GS |
1348 | that. If you like you can force Perl to ignore your system's flock(2) |
1349 | function, and so provide its own fcntl(2)-based emulation, by passing | |
8ebc5c01 | 1350 | the switch C<-Ud_flock> to the F<Configure> program when you configure |
1351 | perl. | |
4633a7c4 LW |
1352 | |
1353 | Here's a mailbox appender for BSD systems. | |
a0d0e21e | 1354 | |
7e1af8bc | 1355 | use Fcntl ':flock'; # import LOCK_* constants |
a0d0e21e LW |
1356 | |
1357 | sub lock { | |
7e1af8bc | 1358 | flock(MBOX,LOCK_EX); |
a0d0e21e LW |
1359 | # and, in case someone appended |
1360 | # while we were waiting... | |
1361 | seek(MBOX, 0, 2); | |
1362 | } | |
1363 | ||
1364 | sub unlock { | |
7e1af8bc | 1365 | flock(MBOX,LOCK_UN); |
a0d0e21e LW |
1366 | } |
1367 | ||
1368 | open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}") | |
1369 | or die "Can't open mailbox: $!"; | |
1370 | ||
1371 | lock(); | |
1372 | print MBOX $msg,"\n\n"; | |
1373 | unlock(); | |
1374 | ||
cb1a09d0 | 1375 | See also L<DB_File> for other flock() examples. |
a0d0e21e LW |
1376 | |
1377 | =item fork | |
1378 | ||
f86cebdf | 1379 | Does a fork(2) system call. Returns the child pid to the parent process, |
7660c0ab | 1380 | C<0> to the child process, or C<undef> if the fork is unsuccessful. |
5a964f20 | 1381 | |
a0d0e21e | 1382 | Note: unflushed buffers remain unflushed in both processes, which means |
7660c0ab A |
1383 | you may need to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> |
1384 | method of C<IO::Handle> to avoid duplicate output. | |
a0d0e21e | 1385 | |
7660c0ab | 1386 | If you C<fork()> without ever waiting on your children, you will accumulate |
a0d0e21e LW |
1387 | zombies: |
1388 | ||
4633a7c4 | 1389 | $SIG{CHLD} = sub { wait }; |
a0d0e21e | 1390 | |
54310121 | 1391 | There's also the double-fork trick (error checking on |
7660c0ab | 1392 | C<fork()> returns omitted); |
a0d0e21e LW |
1393 | |
1394 | unless ($pid = fork) { | |
1395 | unless (fork) { | |
1396 | exec "what you really wanna do"; | |
1397 | die "no exec"; | |
1398 | # ... or ... | |
4633a7c4 | 1399 | ## (some_perl_code_here) |
a0d0e21e LW |
1400 | exit 0; |
1401 | } | |
1402 | exit 0; | |
1403 | } | |
1404 | waitpid($pid,0); | |
1405 | ||
cb1a09d0 AD |
1406 | See also L<perlipc> for more examples of forking and reaping |
1407 | moribund children. | |
1408 | ||
28757baa | 1409 | Note that if your forked child inherits system file descriptors like |
1410 | STDIN and STDOUT that are actually connected by a pipe or socket, even | |
5a964f20 | 1411 | if you exit, then the remote server (such as, say, httpd or rsh) won't think |
7660c0ab | 1412 | you're done. You should reopen those to F</dev/null> if it's any issue. |
28757baa | 1413 | |
cb1a09d0 AD |
1414 | =item format |
1415 | ||
7660c0ab | 1416 | Declare a picture format for use by the C<write()> function. For |
cb1a09d0 AD |
1417 | example: |
1418 | ||
54310121 | 1419 | format Something = |
cb1a09d0 AD |
1420 | Test: @<<<<<<<< @||||| @>>>>> |
1421 | $str, $%, '$' . int($num) | |
1422 | . | |
1423 | ||
1424 | $str = "widget"; | |
184e9718 | 1425 | $num = $cost/$quantity; |
cb1a09d0 AD |
1426 | $~ = 'Something'; |
1427 | write; | |
1428 | ||
1429 | See L<perlform> for many details and examples. | |
1430 | ||
8903cb82 | 1431 | =item formline PICTURE,LIST |
a0d0e21e | 1432 | |
5a964f20 | 1433 | This is an internal function used by C<format>s, though you may call it, |
a0d0e21e LW |
1434 | too. It formats (see L<perlform>) a list of values according to the |
1435 | contents of PICTURE, placing the output into the format output | |
7660c0ab A |
1436 | accumulator, C<$^A> (or C<$ACCUMULATOR> in English). |
1437 | Eventually, when a C<write()> is done, the contents of | |
a0d0e21e | 1438 | C<$^A> are written to some filehandle, but you could also read C<$^A> |
7660c0ab A |
1439 | yourself and then set C<$^A> back to C<"">. Note that a format typically |
1440 | does one C<formline()> per line of form, but the C<formline()> function itself | |
748a9306 | 1441 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 | 1442 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 LW |
1443 | You may therefore need to use multiple formlines to implement a single |
1444 | record format, just like the format compiler. | |
1445 | ||
5f05dabc | 1446 | Be careful if you put double quotes around the picture, because an "C<@>" |
748a9306 | 1447 | character may be taken to mean the beginning of an array name. |
7660c0ab | 1448 | C<formline()> always returns TRUE. See L<perlform> for other examples. |
a0d0e21e LW |
1449 | |
1450 | =item getc FILEHANDLE | |
1451 | ||
1452 | =item getc | |
1453 | ||
1454 | Returns the next character from the input file attached to FILEHANDLE, | |
9bc64814 | 1455 | or the undefined value at end of file, or if there was an error. If |
3b02c43c GS |
1456 | FILEHANDLE is omitted, reads from STDIN. This is not particularly |
1457 | efficient. It cannot be used to get unbuffered single-characters, | |
1458 | however. For that, try something more like: | |
4633a7c4 LW |
1459 | |
1460 | if ($BSD_STYLE) { | |
1461 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; | |
1462 | } | |
1463 | else { | |
54310121 | 1464 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 LW |
1465 | } |
1466 | ||
1467 | $key = getc(STDIN); | |
1468 | ||
1469 | if ($BSD_STYLE) { | |
1470 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; | |
1471 | } | |
1472 | else { | |
5f05dabc | 1473 | system "stty", 'icanon', 'eol', '^@'; # ASCII null |
4633a7c4 LW |
1474 | } |
1475 | print "\n"; | |
1476 | ||
54310121 | 1477 | Determination of whether $BSD_STYLE should be set |
1478 | is left as an exercise to the reader. | |
cb1a09d0 | 1479 | |
7660c0ab | 1480 | The C<POSIX::getattr()> function can do this more portably on systems |
5a964f20 | 1481 | purporting POSIX compliance. |
cb1a09d0 | 1482 | See also the C<Term::ReadKey> module from your nearest CPAN site; |
54310121 | 1483 | details on CPAN can be found on L<perlmod/CPAN>. |
a0d0e21e LW |
1484 | |
1485 | =item getlogin | |
1486 | ||
5a964f20 TC |
1487 | Implements the C library function of the same name, which on most |
1488 | systems returns the current login from F</etc/utmp>, if any. If null, | |
7660c0ab | 1489 | use C<getpwuid()>. |
a0d0e21e | 1490 | |
f86702cc | 1491 | $login = getlogin || getpwuid($<) || "Kilroy"; |
a0d0e21e | 1492 | |
7660c0ab A |
1493 | Do not consider C<getlogin()> for authentication: it is not as |
1494 | secure as C<getpwuid()>. | |
4633a7c4 | 1495 | |
a0d0e21e LW |
1496 | =item getpeername SOCKET |
1497 | ||
1498 | Returns the packed sockaddr address of other end of the SOCKET connection. | |
1499 | ||
4633a7c4 LW |
1500 | use Socket; |
1501 | $hersockaddr = getpeername(SOCK); | |
1502 | ($port, $iaddr) = unpack_sockaddr_in($hersockaddr); | |
1503 | $herhostname = gethostbyaddr($iaddr, AF_INET); | |
1504 | $herstraddr = inet_ntoa($iaddr); | |
a0d0e21e LW |
1505 | |
1506 | =item getpgrp PID | |
1507 | ||
47e29363 | 1508 | Returns the current process group for the specified PID. Use |
7660c0ab | 1509 | a PID of C<0> to get the current process group for the |
4633a7c4 | 1510 | current process. Will raise an exception if used on a machine that |
f86cebdf | 1511 | doesn't implement getpgrp(2). If PID is omitted, returns process |
7660c0ab A |
1512 | group of current process. Note that the POSIX version of C<getpgrp()> |
1513 | does not accept a PID argument, so only C<PID==0> is truly portable. | |
a0d0e21e LW |
1514 | |
1515 | =item getppid | |
1516 | ||
1517 | Returns the process id of the parent process. | |
1518 | ||
1519 | =item getpriority WHICH,WHO | |
1520 | ||
4633a7c4 LW |
1521 | Returns the current priority for a process, a process group, or a user. |
1522 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a | |
f86cebdf | 1523 | machine that doesn't implement getpriority(2). |
a0d0e21e LW |
1524 | |
1525 | =item getpwnam NAME | |
1526 | ||
1527 | =item getgrnam NAME | |
1528 | ||
1529 | =item gethostbyname NAME | |
1530 | ||
1531 | =item getnetbyname NAME | |
1532 | ||
1533 | =item getprotobyname NAME | |
1534 | ||
1535 | =item getpwuid UID | |
1536 | ||
1537 | =item getgrgid GID | |
1538 | ||
1539 | =item getservbyname NAME,PROTO | |
1540 | ||
1541 | =item gethostbyaddr ADDR,ADDRTYPE | |
1542 | ||
1543 | =item getnetbyaddr ADDR,ADDRTYPE | |
1544 | ||
1545 | =item getprotobynumber NUMBER | |
1546 | ||
1547 | =item getservbyport PORT,PROTO | |
1548 | ||
1549 | =item getpwent | |
1550 | ||
1551 | =item getgrent | |
1552 | ||
1553 | =item gethostent | |
1554 | ||
1555 | =item getnetent | |
1556 | ||
1557 | =item getprotoent | |
1558 | ||
1559 | =item getservent | |
1560 | ||
1561 | =item setpwent | |
1562 | ||
1563 | =item setgrent | |
1564 | ||
1565 | =item sethostent STAYOPEN | |
1566 | ||
1567 | =item setnetent STAYOPEN | |
1568 | ||
1569 | =item setprotoent STAYOPEN | |
1570 | ||
1571 | =item setservent STAYOPEN | |
1572 | ||
1573 | =item endpwent | |
1574 | ||
1575 | =item endgrent | |
1576 | ||
1577 | =item endhostent | |
1578 | ||
1579 | =item endnetent | |
1580 | ||
1581 | =item endprotoent | |
1582 | ||
1583 | =item endservent | |
1584 | ||
1585 | These routines perform the same functions as their counterparts in the | |
5a964f20 | 1586 | system library. In list context, the return values from the |
a0d0e21e LW |
1587 | various get routines are as follows: |
1588 | ||
1589 | ($name,$passwd,$uid,$gid, | |
6ee623d5 | 1590 | $quota,$comment,$gcos,$dir,$shell,$expire) = getpw* |
a0d0e21e LW |
1591 | ($name,$passwd,$gid,$members) = getgr* |
1592 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* | |
1593 | ($name,$aliases,$addrtype,$net) = getnet* | |
1594 | ($name,$aliases,$proto) = getproto* | |
1595 | ($name,$aliases,$port,$proto) = getserv* | |
1596 | ||
1597 | (If the entry doesn't exist you get a null list.) | |
1598 | ||
5a964f20 | 1599 | In scalar context, you get the name, unless the function was a |
a0d0e21e LW |
1600 | lookup by name, in which case you get the other thing, whatever it is. |
1601 | (If the entry doesn't exist you get the undefined value.) For example: | |
1602 | ||
5a964f20 TC |
1603 | $uid = getpwnam($name); |
1604 | $name = getpwuid($num); | |
1605 | $name = getpwent(); | |
1606 | $gid = getgrnam($name); | |
1607 | $name = getgrgid($num; | |
1608 | $name = getgrent(); | |
1609 | #etc. | |
a0d0e21e | 1610 | |
7660c0ab | 1611 | In I<getpw*()> the fields C<$quota>, C<$comment>, and C<$expire> are special |
6ee623d5 | 1612 | cases in the sense that in many systems they are unsupported. If the |
7660c0ab A |
1613 | C<$quota> is unsupported, it is an empty scalar. If it is supported, it |
1614 | usually encodes the disk quota. If the C<$comment> field is unsupported, | |
6ee623d5 GS |
1615 | it is an empty scalar. If it is supported it usually encodes some |
1616 | administrative comment about the user. In some systems the $quota | |
7660c0ab A |
1617 | field may be C<$change> or C<$age>, fields that have to do with password |
1618 | aging. In some systems the C<$comment> field may be C<$class>. The C<$expire> | |
6ee623d5 GS |
1619 | field, if present, encodes the expiration period of the account or the |
1620 | password. For the availability and the exact meaning of these fields | |
f86cebdf | 1621 | in your system, please consult your getpwnam(3) documentation and your |
7660c0ab A |
1622 | F<pwd.h> file. You can also find out from within Perl which meaning |
1623 | your C<$quota> and C<$comment> fields have and whether you have the C<$expire> | |
1624 | field by using the C<Config> module and the values C<d_pwquota>, C<d_pwage>, | |
1625 | C<d_pwchange>, C<d_pwcomment>, and C<d_pwexpire>. | |
6ee623d5 | 1626 | |
7660c0ab | 1627 | The C<$members> value returned by I<getgr*()> is a space separated list of |
a0d0e21e LW |
1628 | the login names of the members of the group. |
1629 | ||
1630 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in | |
1631 | C, it will be returned to you via C<$?> if the function call fails. The | |
7660c0ab | 1632 | C<@addrs> value returned by a successful call is a list of the raw |
a0d0e21e LW |
1633 | addresses returned by the corresponding system library call. In the |
1634 | Internet domain, each address is four bytes long and you can unpack it | |
1635 | by saying something like: | |
1636 | ||
1637 | ($a,$b,$c,$d) = unpack('C4',$addr[0]); | |
1638 | ||
5a964f20 TC |
1639 | If you get tired of remembering which element of the return list contains |
1640 | which return value, by-name interfaces are also provided in modules: | |
7660c0ab A |
1641 | C<File::stat>, C<Net::hostent>, C<Net::netent>, C<Net::protoent>, C<Net::servent>, |
1642 | C<Time::gmtime>, C<Time::localtime>, and C<User::grent>. These override the | |
5a964f20 TC |
1643 | normal built-in, replacing them with versions that return objects with |
1644 | the appropriate names for each field. For example: | |
1645 | ||
1646 | use File::stat; | |
1647 | use User::pwent; | |
1648 | $is_his = (stat($filename)->uid == pwent($whoever)->uid); | |
1649 | ||
1650 | Even though it looks like they're the same method calls (uid), | |
7660c0ab | 1651 | they aren't, because a C<File::stat> object is different from a C<User::pwent> object. |
5a964f20 | 1652 | |
a0d0e21e LW |
1653 | =item getsockname SOCKET |
1654 | ||
1655 | Returns the packed sockaddr address of this end of the SOCKET connection. | |
1656 | ||
4633a7c4 LW |
1657 | use Socket; |
1658 | $mysockaddr = getsockname(SOCK); | |
1659 | ($port, $myaddr) = unpack_sockaddr_in($mysockaddr); | |
a0d0e21e LW |
1660 | |
1661 | =item getsockopt SOCKET,LEVEL,OPTNAME | |
1662 | ||
5a964f20 | 1663 | Returns the socket option requested, or undef if there is an error. |
a0d0e21e LW |
1664 | |
1665 | =item glob EXPR | |
1666 | ||
0a753a76 | 1667 | =item glob |
1668 | ||
7660c0ab | 1669 | Returns the value of EXPR with filename expansions such as the standard Unix shell F</bin/sh> would |
68dc0745 | 1670 | do. This is the internal function implementing the C<E<lt>*.cE<gt>> |
7660c0ab | 1671 | operator, but you can use it directly. If EXPR is omitted, C<$_> is used. |
68dc0745 | 1672 | The C<E<lt>*.cE<gt>> operator is discussed in more detail in |
1673 | L<perlop/"I/O Operators">. | |
a0d0e21e LW |
1674 | |
1675 | =item gmtime EXPR | |
1676 | ||
1677 | Converts a time as returned by the time function to a 9-element array | |
54310121 | 1678 | with the time localized for the standard Greenwich time zone. |
4633a7c4 | 1679 | Typically used as follows: |
a0d0e21e | 1680 | |
54310121 | 1681 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e LW |
1682 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1683 | gmtime(time); | |
1684 | ||
1685 | All array elements are numeric, and come straight out of a struct tm. | |
7660c0ab A |
1686 | In particular this means that C<$mon> has the range C<0..11> and C<$wday> has |
1687 | the range C<0..6> with sunday as day C<0>. Also, C<$year> is the number of | |
1688 | years since 1900, that is, C<$year> is C<123> in year 2023, I<not> simply the last two digits of the year. | |
2f9daede TP |
1689 | |
1690 | If EXPR is omitted, does C<gmtime(time())>. | |
a0d0e21e | 1691 | |
f86cebdf | 1692 | In scalar context, returns the ctime(3) value: |
0a753a76 | 1693 | |
1694 | $now_string = gmtime; # e.g., "Thu Oct 13 04:54:34 1994" | |
1695 | ||
7660c0ab | 1696 | Also see the C<timegm()> function provided by the C<Time::Local> module, |
f86cebdf | 1697 | and the strftime(3) function available via the POSIX module. |
7660c0ab A |
1698 | |
1699 | This scalar value is B<not> locale dependent, see L<perllocale>, but | |
1700 | instead a Perl builtin. Also see the C<Time::Local> module, and the | |
f86cebdf | 1701 | strftime(3) and mktime(3) function available via the POSIX module. To |
7660c0ab A |
1702 | get somewhat similar but locale dependent date strings, set up your |
1703 | locale environment variables appropriately (please see L<perllocale>) | |
1704 | and try for example: | |
1705 | ||
1706 | use POSIX qw(strftime); | |
1707 | $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime; | |
1708 | ||
1709 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
1710 | and the month of the year, may not necessarily be three characters wide. | |
0a753a76 | 1711 | |
a0d0e21e LW |
1712 | =item goto LABEL |
1713 | ||
748a9306 LW |
1714 | =item goto EXPR |
1715 | ||
a0d0e21e LW |
1716 | =item goto &NAME |
1717 | ||
7660c0ab | 1718 | The C<goto-LABEL> form finds the statement labeled with LABEL and resumes |
a0d0e21e | 1719 | execution there. It may not be used to go into any construct that |
7660c0ab | 1720 | requires initialization, such as a subroutine or a C<foreach> loop. It |
0a753a76 | 1721 | also can't be used to go into a construct that is optimized away, |
7660c0ab | 1722 | or to get out of a block or subroutine given to C<sort()>. |
0a753a76 | 1723 | It can be used to go almost anywhere else within the dynamic scope, |
a0d0e21e | 1724 | including out of subroutines, but it's usually better to use some other |
ab4f32c2 | 1725 | construct such as C<last> or C<die()>. The author of Perl has never felt the |
7660c0ab | 1726 | need to use this form of C<goto> (in Perl, that is--C is another matter). |
a0d0e21e | 1727 | |
7660c0ab A |
1728 | The C<goto-EXPR> form expects a label name, whose scope will be resolved |
1729 | dynamically. This allows for computed C<goto>s per FORTRAN, but isn't | |
748a9306 LW |
1730 | necessarily recommended if you're optimizing for maintainability: |
1731 | ||
1732 | goto ("FOO", "BAR", "GLARCH")[$i]; | |
1733 | ||
7660c0ab | 1734 | The C<goto-&NAME> form is highly magical, and substitutes a call to the |
a0d0e21e | 1735 | named subroutine for the currently running subroutine. This is used by |
7660c0ab | 1736 | C<AUTOLOAD> subroutines that wish to load another subroutine and then |
a0d0e21e | 1737 | pretend that the other subroutine had been called in the first place |
7660c0ab A |
1738 | (except that any modifications to C<@_> in the current subroutine are |
1739 | propagated to the other subroutine.) After the C<goto>, not even C<caller()> | |
a0d0e21e LW |
1740 | will be able to tell that this routine was called first. |
1741 | ||
1742 | =item grep BLOCK LIST | |
1743 | ||
1744 | =item grep EXPR,LIST | |
1745 | ||
f86cebdf | 1746 | This is similar in spirit to, but not the same as, grep(1) |
2f9daede TP |
1747 | and its relatives. In particular, it is not limited to using |
1748 | regular expressions. | |
1749 | ||
a0d0e21e | 1750 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
7660c0ab | 1751 | C<$_> to each element) and returns the list value consisting of those |
a0d0e21e LW |
1752 | elements for which the expression evaluated to TRUE. In a scalar |
1753 | context, returns the number of times the expression was TRUE. | |
1754 | ||
1755 | @foo = grep(!/^#/, @bar); # weed out comments | |
1756 | ||
1757 | or equivalently, | |
1758 | ||
1759 | @foo = grep {!/^#/} @bar; # weed out comments | |
1760 | ||
7660c0ab | 1761 | Note that, because C<$_> is a reference into the list value, it can be used |
a0d0e21e LW |
1762 | to modify the elements of the array. While this is useful and |
1763 | supported, it can cause bizarre results if the LIST is not a named | |
2f9daede | 1764 | array. Similarly, grep returns aliases into the original list, |
f86cebdf | 1765 | much like the way that a for loop's index variable aliases the list |
2f9daede | 1766 | elements. That is, modifying an element of a list returned by grep |
ab4f32c2 | 1767 | (for example, in a C<foreach>, C<map()> or another C<grep()>) |
2f9daede | 1768 | actually modifies the element in the original list. |
a0d0e21e | 1769 | |
fb73857a | 1770 | See also L</map> for an array composed of the results of the BLOCK or EXPR. |
38325410 | 1771 | |
a0d0e21e LW |
1772 | =item hex EXPR |
1773 | ||
54310121 | 1774 | =item hex |
bbce6d69 | 1775 | |
54310121 | 1776 | Interprets EXPR as a hex string and returns the corresponding |
2f9daede | 1777 | value. (To convert strings that might start with either 0 or 0x |
7660c0ab | 1778 | see L</oct>.) If EXPR is omitted, uses C<$_>. |
2f9daede TP |
1779 | |
1780 | print hex '0xAf'; # prints '175' | |
1781 | print hex 'aF'; # same | |
a0d0e21e LW |
1782 | |
1783 | =item import | |
1784 | ||
7660c0ab | 1785 | There is no builtin C<import()> function. It is just an ordinary |
4633a7c4 | 1786 | method (subroutine) defined (or inherited) by modules that wish to export |
7660c0ab | 1787 | names to another module. The C<use()> function calls the C<import()> method |
54310121 | 1788 | for the package used. See also L</use()>, L<perlmod>, and L<Exporter>. |
a0d0e21e LW |
1789 | |
1790 | =item index STR,SUBSTR,POSITION | |
1791 | ||
1792 | =item index STR,SUBSTR | |
1793 | ||
4633a7c4 LW |
1794 | Returns the position of the first occurrence of SUBSTR in STR at or after |
1795 | POSITION. If POSITION is omitted, starts searching from the beginning of | |
7660c0ab | 1796 | the string. The return value is based at C<0> (or whatever you've set the C<$[> |
4633a7c4 | 1797 | variable to--but don't do that). If the substring is not found, returns |
7660c0ab | 1798 | one less than the base, ordinarily C<-1>. |
a0d0e21e LW |
1799 | |
1800 | =item int EXPR | |
1801 | ||
54310121 | 1802 | =item int |
bbce6d69 | 1803 | |
7660c0ab | 1804 | Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>. |
5a964f20 | 1805 | You should not use this for rounding, because it truncates |
7660c0ab A |
1806 | towards C<0>, and because machine representations of floating point |
1807 | numbers can sometimes produce counterintuitive results. Usually C<sprintf()> or C<printf()>, | |
1808 | or the C<POSIX::floor> or C<POSIX::ceil> functions, would serve you better. | |
a0d0e21e LW |
1809 | |
1810 | =item ioctl FILEHANDLE,FUNCTION,SCALAR | |
1811 | ||
f86cebdf | 1812 | Implements the ioctl(2) function. You'll probably have to say |
a0d0e21e | 1813 | |
4633a7c4 | 1814 | require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph |
a0d0e21e | 1815 | |
4633a7c4 | 1816 | first to get the correct function definitions. If F<ioctl.ph> doesn't |
a0d0e21e | 1817 | exist or doesn't have the correct definitions you'll have to roll your |
4633a7c4 | 1818 | own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>. |
5a964f20 | 1819 | (There is a Perl script called B<h2ph> that comes with the Perl kit that |
54310121 | 1820 | may help you in this, but it's nontrivial.) SCALAR will be read and/or |
4633a7c4 | 1821 | written depending on the FUNCTION--a pointer to the string value of SCALAR |
ab4f32c2 | 1822 | will be passed as the third argument of the actual C<ioctl()> call. (If SCALAR |
4633a7c4 LW |
1823 | has no string value but does have a numeric value, that value will be |
1824 | passed rather than a pointer to the string value. To guarantee this to be | |
7660c0ab | 1825 | TRUE, add a C<0> to the scalar before using it.) The C<pack()> and C<unpack()> |
4633a7c4 | 1826 | functions are useful for manipulating the values of structures used by |
7660c0ab | 1827 | C<ioctl()>. The following example sets the erase character to DEL. |
a0d0e21e LW |
1828 | |
1829 | require 'ioctl.ph'; | |
4633a7c4 LW |
1830 | $getp = &TIOCGETP; |
1831 | die "NO TIOCGETP" if $@ || !$getp; | |
a0d0e21e | 1832 | $sgttyb_t = "ccccs"; # 4 chars and a short |
4633a7c4 | 1833 | if (ioctl(STDIN,$getp,$sgttyb)) { |
a0d0e21e LW |
1834 | @ary = unpack($sgttyb_t,$sgttyb); |
1835 | $ary[2] = 127; | |
1836 | $sgttyb = pack($sgttyb_t,@ary); | |
4633a7c4 | 1837 | ioctl(STDIN,&TIOCSETP,$sgttyb) |
a0d0e21e LW |
1838 | || die "Can't ioctl: $!"; |
1839 | } | |
1840 | ||
ab4f32c2 | 1841 | The return value of C<ioctl()> (and C<fcntl()>) is as follows: |
a0d0e21e LW |
1842 | |
1843 | if OS returns: then Perl returns: | |
1844 | -1 undefined value | |
1845 | 0 string "0 but true" | |
1846 | anything else that number | |
1847 | ||
1848 | Thus Perl returns TRUE on success and FALSE on failure, yet you can | |
1849 | still easily determine the actual value returned by the operating | |
1850 | system: | |
1851 | ||
1852 | ($retval = ioctl(...)) || ($retval = -1); | |
1853 | printf "System returned %d\n", $retval; | |
1854 | ||
7660c0ab | 1855 | The special string "C<0> but true" is excempt from B<-w> complaints |
5a964f20 TC |
1856 | about improper numeric conversions. |
1857 | ||
a0d0e21e LW |
1858 | =item join EXPR,LIST |
1859 | ||
54310121 | 1860 | Joins the separate strings of LIST into a single string with |
a0d0e21e LW |
1861 | fields separated by the value of EXPR, and returns the string. |
1862 | Example: | |
1863 | ||
1864 | $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); | |
1865 | ||
7660c0ab | 1866 | See L</split>. |
a0d0e21e | 1867 | |
aa689395 | 1868 | =item keys HASH |
1869 | ||
1d2dff63 GS |
1870 | Returns a list consisting of all the keys of the named hash. (In a |
1871 | scalar context, returns the number of keys.) The keys are returned in | |
aa689395 | 1872 | an apparently random order, but it is the same order as either the |
7660c0ab | 1873 | C<values()> or C<each()> function produces (given that the hash has not been |
aa689395 | 1874 | modified). As a side effect, it resets HASH's iterator. |
a0d0e21e | 1875 | |
aa689395 | 1876 | Here is yet another way to print your environment: |
a0d0e21e LW |
1877 | |
1878 | @keys = keys %ENV; | |
1879 | @values = values %ENV; | |
1880 | while ($#keys >= 0) { | |
1881 | print pop(@keys), '=', pop(@values), "\n"; | |
1882 | } | |
1883 | ||
1884 | or how about sorted by key: | |
1885 | ||
1886 | foreach $key (sort(keys %ENV)) { | |
1887 | print $key, '=', $ENV{$key}, "\n"; | |
1888 | } | |
1889 | ||
aca803df | 1890 | To sort a hash by value, you'll need to use a C<sort()> function. |
aa689395 | 1891 | Here's a descending numeric sort of a hash by its values: |
4633a7c4 | 1892 | |
5a964f20 | 1893 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) { |
4633a7c4 LW |
1894 | printf "%4d %s\n", $hash{$key}, $key; |
1895 | } | |
1896 | ||
ab4f32c2 | 1897 | As an lvalue C<keys()> allows you to increase the number of hash buckets |
aa689395 | 1898 | allocated for the given hash. This can gain you a measure of efficiency if |
1899 | you know the hash is going to get big. (This is similar to pre-extending | |
1900 | an array by assigning a larger number to $#array.) If you say | |
55497cff | 1901 | |
1902 | keys %hash = 200; | |
1903 | ||
5a964f20 TC |
1904 | then C<%hash> will have at least 200 buckets allocated for it--256 of them, in fact, since |
1905 | it rounds up to the next power of two. These | |
55497cff | 1906 | buckets will be retained even if you do C<%hash = ()>, use C<undef |
1907 | %hash> if you want to free the storage while C<%hash> is still in scope. | |
1908 | You can't shrink the number of buckets allocated for the hash using | |
ab4f32c2 | 1909 | C<keys()> in this way (but you needn't worry about doing this by accident, |
55497cff | 1910 | as trying has no effect). |
1911 | ||
a0d0e21e LW |
1912 | =item kill LIST |
1913 | ||
54310121 | 1914 | Sends a signal to a list of processes. The first element of |
1915 | the list must be the signal to send. Returns the number of | |
4633a7c4 | 1916 | processes successfully signaled. |
a0d0e21e LW |
1917 | |
1918 | $cnt = kill 1, $child1, $child2; | |
1919 | kill 9, @goners; | |
1920 | ||
4633a7c4 LW |
1921 | Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills |
1922 | process groups instead of processes. (On System V, a negative I<PROCESS> | |
1923 | number will also kill process groups, but that's not portable.) That | |
1924 | means you usually want to use positive not negative signals. You may also | |
da0045b7 | 1925 | use a signal name in quotes. See L<perlipc/"Signals"> for details. |
a0d0e21e LW |
1926 | |
1927 | =item last LABEL | |
1928 | ||
1929 | =item last | |
1930 | ||
1931 | The C<last> command is like the C<break> statement in C (as used in | |
1932 | loops); it immediately exits the loop in question. If the LABEL is | |
1933 | omitted, the command refers to the innermost enclosing loop. The | |
1934 | C<continue> block, if any, is not executed: | |
1935 | ||
4633a7c4 LW |
1936 | LINE: while (<STDIN>) { |
1937 | last LINE if /^$/; # exit when done with header | |
5a964f20 | 1938 | #... |
a0d0e21e LW |
1939 | } |
1940 | ||
1d2dff63 GS |
1941 | See also L</continue> for an illustration of how C<last>, C<next>, and |
1942 | C<redo> work. | |
1943 | ||
a0d0e21e LW |
1944 | =item lc EXPR |
1945 | ||
54310121 | 1946 | =item lc |
bbce6d69 | 1947 | |
a0d0e21e | 1948 | Returns an lowercased version of EXPR. This is the internal function |
7660c0ab | 1949 | implementing the C<\L> escape in double-quoted strings. |
a0ed51b3 | 1950 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e | 1951 | |
7660c0ab | 1952 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 1953 | |
a0d0e21e LW |
1954 | =item lcfirst EXPR |
1955 | ||
54310121 | 1956 | =item lcfirst |
bbce6d69 | 1957 | |
a0d0e21e | 1958 | Returns the value of EXPR with the first character lowercased. This is |
7660c0ab | 1959 | the internal function implementing the C<\l> escape in double-quoted strings. |
a0ed51b3 | 1960 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e | 1961 | |
7660c0ab | 1962 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 1963 | |
a0d0e21e LW |
1964 | =item length EXPR |
1965 | ||
54310121 | 1966 | =item length |
bbce6d69 | 1967 | |
a0ed51b3 | 1968 | Returns the length in characters of the value of EXPR. If EXPR is |
7660c0ab | 1969 | omitted, returns length of C<$_>. |
a0d0e21e LW |
1970 | |
1971 | =item link OLDFILE,NEWFILE | |
1972 | ||
5a964f20 TC |
1973 | Creates a new filename linked to the old filename. Returns TRUE for |
1974 | success, FALSE otherwise. | |
a0d0e21e LW |
1975 | |
1976 | =item listen SOCKET,QUEUESIZE | |
1977 | ||
1978 | Does the same thing that the listen system call does. Returns TRUE if | |
4633a7c4 | 1979 | it succeeded, FALSE otherwise. See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
1980 | |
1981 | =item local EXPR | |
1982 | ||
5a964f20 TC |
1983 | A local modifies the listed variables to be local to the enclosing |
1984 | block, file, or eval. If more than one value is listed, the list must | |
1985 | be placed in parentheses. See L<perlsub/"Temporary Values via local()"> | |
1986 | for details, including issues with tied arrays and hashes. | |
a0d0e21e | 1987 | |
7660c0ab | 1988 | You really probably want to be using C<my()> instead, because C<local()> isn't |
7b8d334a | 1989 | what most people think of as "local". See L<perlsub/"Private Variables |
cb1a09d0 | 1990 | via my()"> for details. |
a0d0e21e LW |
1991 | |
1992 | =item localtime EXPR | |
1993 | ||
1994 | Converts a time as returned by the time function to a 9-element array | |
5f05dabc | 1995 | with the time analyzed for the local time zone. Typically used as |
a0d0e21e LW |
1996 | follows: |
1997 | ||
54310121 | 1998 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e LW |
1999 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
2000 | localtime(time); | |
2001 | ||
2002 | All array elements are numeric, and come straight out of a struct tm. | |
7660c0ab A |
2003 | In particular this means that C<$mon> has the range C<0..11> and C<$wday> has |
2004 | the range C<0..6> with sunday as day C<0>. Also, C<$year> is the number of | |
2005 | years since 1900, that is, C<$year> is C<123> in year 2023, and I<not> simply the last two digits of the year. | |
54310121 | 2006 | |
2007 | If EXPR is omitted, uses the current time (C<localtime(time)>). | |
a0d0e21e | 2008 | |
f86cebdf | 2009 | In scalar context, returns the ctime(3) value: |
a0d0e21e | 2010 | |
5f05dabc | 2011 | $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" |
a0d0e21e | 2012 | |
a3cb178b | 2013 | This scalar value is B<not> locale dependent, see L<perllocale>, but |
7660c0ab | 2014 | instead a Perl builtin. Also see the C<Time::Local> module, and the |
f86cebdf | 2015 | strftime(3) and mktime(3) function available via the POSIX module. To |
a3cb178b GS |
2016 | get somewhat similar but locale dependent date strings, set up your |
2017 | locale environment variables appropriately (please see L<perllocale>) | |
5a964f20 | 2018 | and try for example: |
a3cb178b | 2019 | |
5a964f20 | 2020 | use POSIX qw(strftime); |
a3cb178b GS |
2021 | $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime; |
2022 | ||
2023 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
2024 | and the month of the year, may not necessarily be three characters wide. | |
a0d0e21e LW |
2025 | |
2026 | =item log EXPR | |
2027 | ||
54310121 | 2028 | =item log |
bbce6d69 | 2029 | |
5a964f20 | 2030 | Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log |
7660c0ab | 2031 | of C<$_>. |
a0d0e21e LW |
2032 | |
2033 | =item lstat FILEHANDLE | |
2034 | ||
2035 | =item lstat EXPR | |
2036 | ||
54310121 | 2037 | =item lstat |
bbce6d69 | 2038 | |
7660c0ab | 2039 | Does the same thing as the C<stat()> function (including setting the |
5a964f20 TC |
2040 | special C<_> filehandle) but stats a symbolic link instead of the file |
2041 | the symbolic link points to. If symbolic links are unimplemented on | |
7660c0ab | 2042 | your system, a normal C<stat()> is done. |
a0d0e21e | 2043 | |
7660c0ab | 2044 | If EXPR is omitted, stats C<$_>. |
bbce6d69 | 2045 | |
a0d0e21e LW |
2046 | =item m// |
2047 | ||
2048 | The match operator. See L<perlop>. | |
2049 | ||
2050 | =item map BLOCK LIST | |
2051 | ||
2052 | =item map EXPR,LIST | |
2053 | ||
7660c0ab | 2054 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting C<$_> to each |
a0d0e21e LW |
2055 | element) and returns the list value composed of the results of each such |
2056 | evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST | |
2057 | may produce zero, one, or more elements in the returned value. | |
2058 | ||
2059 | @chars = map(chr, @nums); | |
2060 | ||
2061 | translates a list of numbers to the corresponding characters. And | |
2062 | ||
4633a7c4 | 2063 | %hash = map { getkey($_) => $_ } @array; |
a0d0e21e LW |
2064 | |
2065 | is just a funny way to write | |
2066 | ||
2067 | %hash = (); | |
2068 | foreach $_ (@array) { | |
4633a7c4 | 2069 | $hash{getkey($_)} = $_; |
a0d0e21e LW |
2070 | } |
2071 | ||
7660c0ab | 2072 | Note that, because C<$_> is a reference into the list value, it can be used |
fb73857a | 2073 | to modify the elements of the array. While this is useful and |
2074 | supported, it can cause bizarre results if the LIST is not a named | |
2075 | array. See also L</grep> for an array composed of those items of the | |
2076 | original list for which the BLOCK or EXPR evaluates to true. | |
2077 | ||
a0d0e21e LW |
2078 | =item mkdir FILENAME,MODE |
2079 | ||
2080 | Creates the directory specified by FILENAME, with permissions specified | |
5a964f20 TC |
2081 | by MODE (as modified by umask). If it succeeds it returns TRUE, otherwise |
2082 | it returns FALSE and sets C<$!> (errno). | |
a0d0e21e LW |
2083 | |
2084 | =item msgctl ID,CMD,ARG | |
2085 | ||
f86cebdf | 2086 | Calls the System V IPC function msgctl(2). You'll probably have to say |
0ade1984 JH |
2087 | |
2088 | use IPC::SysV; | |
2089 | ||
7660c0ab A |
2090 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
2091 | then ARG must be a variable which will hold the returned C<msqid_ds> | |
ab4f32c2 | 2092 | structure. Returns like C<ioctl()>: the undefined value for error, "C<0> but |
0ade1984 | 2093 | true" for zero, or the actual return value otherwise. See also |
7660c0ab | 2094 | C<IPC::SysV> and C<IPC::Semaphore::Msg> documentation. |
a0d0e21e LW |
2095 | |
2096 | =item msgget KEY,FLAGS | |
2097 | ||
f86cebdf | 2098 | Calls the System V IPC function msgget(2). Returns the message queue |
7660c0ab A |
2099 | id, or the undefined value if there is an error. See also C<IPC::SysV> |
2100 | and C<IPC::SysV::Msg> documentation. | |
a0d0e21e LW |
2101 | |
2102 | =item msgsnd ID,MSG,FLAGS | |
2103 | ||
2104 | Calls the System V IPC function msgsnd to send the message MSG to the | |
2105 | message queue ID. MSG must begin with the long integer message type, | |
c07a80fd | 2106 | which may be created with C<pack("l", $type)>. Returns TRUE if |
7660c0ab A |
2107 | successful, or FALSE if there is an error. See also C<IPC::SysV> |
2108 | and C<IPC::SysV::Msg> documentation. | |
a0d0e21e LW |
2109 | |
2110 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS | |
2111 | ||
2112 | Calls the System V IPC function msgrcv to receive a message from | |
2113 | message queue ID into variable VAR with a maximum message size of | |
0ade1984 JH |
2114 | SIZE. Note that if a message is received, the message type will be |
2115 | the first thing in VAR, and the maximum length of VAR is SIZE plus the | |
2116 | size of the message type. Returns TRUE if successful, or FALSE if | |
7660c0ab | 2117 | there is an error. See also C<IPC::SysV> and C<IPC::SysV::Msg> documentation. |
a0d0e21e LW |
2118 | |
2119 | =item my EXPR | |
2120 | ||
ab4f32c2 A |
2121 | A C<my()> declares the listed variables to be local (lexically) to the |
2122 | enclosing block, file, or C<eval()>. If | |
5f05dabc | 2123 | more than one value is listed, the list must be placed in parentheses. See |
cb1a09d0 | 2124 | L<perlsub/"Private Variables via my()"> for details. |
4633a7c4 | 2125 | |
a0d0e21e LW |
2126 | =item next LABEL |
2127 | ||
2128 | =item next | |
2129 | ||
2130 | The C<next> command is like the C<continue> statement in C; it starts | |
2131 | the next iteration of the loop: | |
2132 | ||
4633a7c4 LW |
2133 | LINE: while (<STDIN>) { |
2134 | next LINE if /^#/; # discard comments | |
5a964f20 | 2135 | #... |
a0d0e21e LW |
2136 | } |
2137 | ||
2138 | Note that if there were a C<continue> block on the above, it would get | |
2139 | executed even on discarded lines. If the LABEL is omitted, the command | |
2140 | refers to the innermost enclosing loop. | |
2141 | ||
1d2dff63 GS |
2142 | See also L</continue> for an illustration of how C<last>, C<next>, and |
2143 | C<redo> work. | |
2144 | ||
a0d0e21e LW |
2145 | =item no Module LIST |
2146 | ||
7660c0ab | 2147 | See the L</use> function, which C<no> is the opposite of. |
a0d0e21e LW |
2148 | |
2149 | =item oct EXPR | |
2150 | ||
54310121 | 2151 | =item oct |
bbce6d69 | 2152 | |
4633a7c4 | 2153 | Interprets EXPR as an octal string and returns the corresponding |
7660c0ab | 2154 | value. (If EXPR happens to start off with C<0x>, interprets it as |
4633a7c4 LW |
2155 | a hex string instead.) The following will handle decimal, octal, and |
2156 | hex in the standard Perl or C notation: | |
a0d0e21e LW |
2157 | |
2158 | $val = oct($val) if $val =~ /^0/; | |
2159 | ||
7660c0ab A |
2160 | If EXPR is omitted, uses C<$_>. This function is commonly used when |
2161 | a string such as C<644> needs to be converted into a file mode, for | |
2f9daede TP |
2162 | example. (Although perl will automatically convert strings into |
2163 | numbers as needed, this automatic conversion assumes base 10.) | |
a0d0e21e LW |
2164 | |
2165 | =item open FILEHANDLE,EXPR | |
2166 | ||
2167 | =item open FILEHANDLE | |
2168 | ||
2169 | Opens the file whose filename is given by EXPR, and associates it with | |
5f05dabc | 2170 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the |
2171 | name of the real filehandle wanted. If EXPR is omitted, the scalar | |
2172 | variable of the same name as the FILEHANDLE contains the filename. | |
ab4f32c2 A |
2173 | (Note that lexical variables--those declared with C<my()>--will not work |
2174 | for this purpose; so if you're using C<my()>, specify EXPR in your call | |
5f05dabc | 2175 | to open.) |
2176 | ||
7660c0ab A |
2177 | If the filename begins with C<'E<lt>'> or nothing, the file is opened for input. |
2178 | If the filename begins with C<'E<gt>'>, the file is truncated and opened for | |
2179 | output, being created if necessary. If the filename begins with C<'E<gt>E<gt>'>, | |
fbb426e4 | 2180 | the file is opened for appending, again being created if necessary. |
7660c0ab A |
2181 | You can put a C<'+'> in front of the C<'E<gt>'> or C<'E<lt>'> to indicate that |
2182 | you want both read and write access to the file; thus C<'+E<lt>'> is almost | |
2183 | always preferred for read/write updates--the C<'+E<gt>'> mode would clobber the | |
5a964f20 TC |
2184 | file first. You can't usually use either read-write mode for updating |
2185 | textfiles, since they have variable length records. See the B<-i> | |
2186 | switch in L<perlrun> for a better approach. | |
2187 | ||
2188 | The prefix and the filename may be separated with spaces. | |
f86cebdf | 2189 | These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>, C<'w'>, |
7660c0ab | 2190 | C<'w+'>, C<'a'>, and C<'a+'>. |
5f05dabc | 2191 | |
7660c0ab | 2192 | If the filename begins with C<'|'>, the filename is interpreted as a |
5a964f20 | 2193 | command to which output is to be piped, and if the filename ends with a |
7660c0ab A |
2194 | C<'|'>, the filename is interpreted See L<perlipc/"Using open() for IPC"> |
2195 | for more examples of this. (You are not allowed to C<open()> to a command | |
5a964f20 TC |
2196 | that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>, |
2197 | and L<perlipc/"Bidirectional Communication"> for alternatives.) | |
cb1a09d0 | 2198 | |
7660c0ab | 2199 | Opening C<'-'> opens STDIN and opening C<'E<gt>-'> opens STDOUT. Open returns |
ab4f32c2 | 2200 | nonzero upon success, the undefined value otherwise. If the C<open()> |
4633a7c4 | 2201 | involved a pipe, the return value happens to be the pid of the |
54310121 | 2202 | subprocess. |
cb1a09d0 AD |
2203 | |
2204 | If you're unfortunate enough to be running Perl on a system that | |
2205 | distinguishes between text files and binary files (modern operating | |
2206 | systems don't care), then you should check out L</binmode> for tips for | |
ab4f32c2 | 2207 | dealing with this. The key distinction between systems that need C<binmode()> |
5a964f20 TC |
2208 | and those that don't is their text file formats. Systems like Unix, MacOS, and |
2209 | Plan9, which delimit lines with a single character, and which encode that | |
ab4f32c2 | 2210 | character in C as C<"\n">, do not need C<binmode()>. The rest need it. |
cb1a09d0 | 2211 | |
fb73857a | 2212 | When opening a file, it's usually a bad idea to continue normal execution |
ab4f32c2 A |
2213 | if the request failed, so C<open()> is frequently used in connection with |
2214 | C<die()>. Even if C<die()> won't do what you want (say, in a CGI script, | |
fb73857a | 2215 | where you want to make a nicely formatted error message (but there are |
5a964f20 | 2216 | modules that can help with that problem)) you should always check |
fb73857a | 2217 | the return value from opening a file. The infrequent exception is when |
2218 | working with an unopened filehandle is actually what you want to do. | |
2219 | ||
cb1a09d0 | 2220 | Examples: |
a0d0e21e LW |
2221 | |
2222 | $ARTICLE = 100; | |
2223 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; | |
2224 | while (<ARTICLE>) {... | |
2225 | ||
2226 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) | |
fb73857a | 2227 | # if the open fails, output is discarded |
a0d0e21e | 2228 | |
fb73857a | 2229 | open(DBASE, '+<dbase.mine') # open for update |
2230 | or die "Can't open 'dbase.mine' for update: $!"; | |
cb1a09d0 | 2231 | |
fb73857a | 2232 | open(ARTICLE, "caesar <$article |") # decrypt article |
2233 | or die "Can't start caesar: $!"; | |
a0d0e21e | 2234 | |
fb73857a | 2235 | open(EXTRACT, "|sort >/tmp/Tmp$$") # $$ is our process id |
2236 | or die "Can't start sort: $!"; | |
a0d0e21e LW |
2237 | |
2238 | # process argument list of files along with any includes | |
2239 | ||
2240 | foreach $file (@ARGV) { | |
2241 | process($file, 'fh00'); | |
2242 | } | |
2243 | ||
2244 | sub process { | |
5a964f20 | 2245 | my($filename, $input) = @_; |
a0d0e21e LW |
2246 | $input++; # this is a string increment |
2247 | unless (open($input, $filename)) { | |
2248 | print STDERR "Can't open $filename: $!\n"; | |
2249 | return; | |
2250 | } | |
2251 | ||
5a964f20 | 2252 | local $_; |
a0d0e21e LW |
2253 | while (<$input>) { # note use of indirection |
2254 | if (/^#include "(.*)"/) { | |
2255 | process($1, $input); | |
2256 | next; | |
2257 | } | |
5a964f20 | 2258 | #... # whatever |
a0d0e21e LW |
2259 | } |
2260 | } | |
2261 | ||
2262 | You may also, in the Bourne shell tradition, specify an EXPR beginning | |
7660c0ab | 2263 | with C<'E<gt>&'>, in which case the rest of the string is interpreted as the |
5a964f20 | 2264 | name of a filehandle (or file descriptor, if numeric) to be |
7660c0ab A |
2265 | duped and opened. You may use C<&> after C<E<gt>>, C<E<gt>E<gt>>, C<E<lt>>, C<+E<gt>>, |
2266 | C<+E<gt>E<gt>>, and C<+E<lt>>. The | |
a0d0e21e | 2267 | mode you specify should match the mode of the original filehandle. |
184e9718 | 2268 | (Duping a filehandle does not take into account any existing contents of |
cb1a09d0 | 2269 | stdio buffers.) |
a0d0e21e LW |
2270 | Here is a script that saves, redirects, and restores STDOUT and |
2271 | STDERR: | |
2272 | ||
2273 | #!/usr/bin/perl | |
5a964f20 TC |
2274 | open(OLDOUT, ">&STDOUT"); |
2275 | open(OLDERR, ">&STDERR"); | |
a0d0e21e LW |
2276 | |
2277 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; | |
2278 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; | |
2279 | ||
2280 | select(STDERR); $| = 1; # make unbuffered | |
2281 | select(STDOUT); $| = 1; # make unbuffered | |
2282 | ||
2283 | print STDOUT "stdout 1\n"; # this works for | |
2284 | print STDERR "stderr 1\n"; # subprocesses too | |
2285 | ||
2286 | close(STDOUT); | |
2287 | close(STDERR); | |
2288 | ||
5a964f20 TC |
2289 | open(STDOUT, ">&OLDOUT"); |
2290 | open(STDERR, ">&OLDERR"); | |
a0d0e21e LW |
2291 | |
2292 | print STDOUT "stdout 2\n"; | |
2293 | print STDERR "stderr 2\n"; | |
2294 | ||
2295 | ||
7660c0ab A |
2296 | If you specify C<'E<lt>&=N'>, where C<N> is a number, then Perl will do an |
2297 | equivalent of C's C<fdopen()> of that file descriptor; this is more | |
4633a7c4 | 2298 | parsimonious of file descriptors. For example: |
a0d0e21e LW |
2299 | |
2300 | open(FILEHANDLE, "<&=$fd") | |
2301 | ||
7660c0ab | 2302 | If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>, then |
a0d0e21e | 2303 | there is an implicit fork done, and the return value of open is the pid |
7660c0ab | 2304 | of the child within the parent process, and C<0> within the child |
184e9718 | 2305 | process. (Use C<defined($pid)> to determine whether the open was successful.) |
a0d0e21e LW |
2306 | The filehandle behaves normally for the parent, but i/o to that |
2307 | filehandle is piped from/to the STDOUT/STDIN of the child process. | |
2308 | In the child process the filehandle isn't opened--i/o happens from/to | |
2309 | the new STDOUT or STDIN. Typically this is used like the normal | |
2310 | piped open when you want to exercise more control over just how the | |
2311 | pipe command gets executed, such as when you are running setuid, and | |
54310121 | 2312 | don't want to have to scan shell commands for metacharacters. |
4633a7c4 | 2313 | The following pairs are more or less equivalent: |
a0d0e21e LW |
2314 | |
2315 | open(FOO, "|tr '[a-z]' '[A-Z]'"); | |
2316 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; | |
2317 | ||
2318 | open(FOO, "cat -n '$file'|"); | |
2319 | open(FOO, "-|") || exec 'cat', '-n', $file; | |
2320 | ||
4633a7c4 LW |
2321 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
2322 | ||
5a964f20 | 2323 | NOTE: On any operation that may do a fork, any unflushed buffers remain |
184e9718 | 2324 | unflushed in both processes, which means you may need to set C<$|> to |
a0d0e21e LW |
2325 | avoid duplicate output. |
2326 | ||
0dccf244 CS |
2327 | Closing any piped filehandle causes the parent process to wait for the |
2328 | child to finish, and returns the status value in C<$?>. | |
2329 | ||
5a964f20 | 2330 | The filename passed to open will have leading and trailing |
f86cebdf | 2331 | whitespace deleted, and the normal redirection characters |
5a964f20 TC |
2332 | honored. This property, known as "magic open", |
2333 | can often be used to good effect. A user could specify a filename of | |
7660c0ab | 2334 | F<"rsh cat file |">, or you could change certain filenames as needed: |
5a964f20 TC |
2335 | |
2336 | $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/; | |
2337 | open(FH, $filename) or die "Can't open $filename: $!"; | |
2338 | ||
2339 | However, to open a file with arbitrary weird characters in it, it's | |
2340 | necessary to protect any leading and trailing whitespace: | |
2341 | ||
2342 | $file =~ s#^(\s)#./$1#; | |
2343 | open(FOO, "< $file\0"); | |
2344 | ||
7660c0ab A |
2345 | If you want a "real" C C<open()> (see L<open(2)> on your system), then you |
2346 | should use the C<sysopen()> function, which involves no such magic. This is | |
5a964f20 TC |
2347 | another way to protect your filenames from interpretation. For example: |
2348 | ||
2349 | use IO::Handle; | |
2350 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL) | |
2351 | or die "sysopen $path: $!"; | |
2352 | $oldfh = select(HANDLE); $| = 1; select($oldfh); | |
2353 | print HANDLE "stuff $$\n"); | |
2354 | seek(HANDLE, 0, 0); | |
2355 | print "File contains: ", <HANDLE>; | |
2356 | ||
7660c0ab A |
2357 | Using the constructor from the C<IO::Handle> package (or one of its |
2358 | subclasses, such as C<IO::File> or C<IO::Socket>), you can generate anonymous | |
5a964f20 TC |
2359 | filehandles that have the scope of whatever variables hold references to |
2360 | them, and automatically close whenever and however you leave that scope: | |
c07a80fd | 2361 | |
5f05dabc | 2362 | use IO::File; |
5a964f20 | 2363 | #... |
c07a80fd | 2364 | sub read_myfile_munged { |
2365 | my $ALL = shift; | |
5f05dabc | 2366 | my $handle = new IO::File; |
c07a80fd | 2367 | open($handle, "myfile") or die "myfile: $!"; |
2368 | $first = <$handle> | |
2369 | or return (); # Automatically closed here. | |
2370 | mung $first or die "mung failed"; # Or here. | |
2371 | return $first, <$handle> if $ALL; # Or here. | |
2372 | $first; # Or here. | |
2373 | } | |
2374 | ||
cb1a09d0 | 2375 | See L</seek()> for some details about mixing reading and writing. |
a0d0e21e LW |
2376 | |
2377 | =item opendir DIRHANDLE,EXPR | |
2378 | ||
7660c0ab A |
2379 | Opens a directory named EXPR for processing by C<readdir()>, C<telldir()>, |
2380 | C<seekdir()>, C<rewinddir()>, and C<closedir()>. Returns TRUE if successful. | |
a0d0e21e LW |
2381 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
2382 | ||
2383 | =item ord EXPR | |
2384 | ||
54310121 | 2385 | =item ord |
bbce6d69 | 2386 | |
a0ed51b3 | 2387 | Returns the numeric (ASCII or Unicode) value of the first character of EXPR. If |
7660c0ab | 2388 | EXPR is omitted, uses C<$_>. For the reverse, see L</chr>. |
a0d0e21e LW |
2389 | |
2390 | =item pack TEMPLATE,LIST | |
2391 | ||
2392 | Takes an array or list of values and packs it into a binary structure, | |
2393 | returning the string containing the structure. The TEMPLATE is a | |
2394 | sequence of characters that give the order and type of values, as | |
2395 | follows: | |
2396 | ||
2397 | A An ascii string, will be space padded. | |
2398 | a An ascii string, will be null padded. | |
2399 | b A bit string (ascending bit order, like vec()). | |
2400 | B A bit string (descending bit order). | |
2401 | h A hex string (low nybble first). | |
2402 | H A hex string (high nybble first). | |
2403 | ||
2404 | c A signed char value. | |
a0ed51b3 | 2405 | C An unsigned char value. Only does bytes. See U for Unicode. |
96e4d5b1 | 2406 | |
a0d0e21e LW |
2407 | s A signed short value. |
2408 | S An unsigned short value. | |
96e4d5b1 | 2409 | (This 'short' is _exactly_ 16 bits, which may differ from |
2410 | what a local C compiler calls 'short'.) | |
2411 | ||
a0d0e21e LW |
2412 | i A signed integer value. |
2413 | I An unsigned integer value. | |
f86cebdf GS |
2414 | (This 'integer' is _at_least_ 32 bits wide. Its exact |
2415 | size depends on what a local C compiler calls 'int', | |
2416 | and may even be larger than the 'long' described in | |
2417 | the next item.) | |
96e4d5b1 | 2418 | |
a0d0e21e LW |
2419 | l A signed long value. |
2420 | L An unsigned long value. | |
96e4d5b1 | 2421 | (This 'long' is _exactly_ 32 bits, which may differ from |
2422 | what a local C compiler calls 'long'.) | |
a0d0e21e | 2423 | |
96e4d5b1 | 2424 | n A short in "network" (big-endian) order. |
2425 | N A long in "network" (big-endian) order. | |
a0d0e21e LW |
2426 | v A short in "VAX" (little-endian) order. |
2427 | V A long in "VAX" (little-endian) order. | |
96e4d5b1 | 2428 | (These 'shorts' and 'longs' are _exactly_ 16 bits and |
2429 | _exactly_ 32 bits, respectively.) | |
a0d0e21e LW |
2430 | |
2431 | f A single-precision float in the native format. | |
2432 | d A double-precision float in the native format. | |
2433 | ||
2434 | p A pointer to a null-terminated string. | |
2435 | P A pointer to a structure (fixed-length string). | |
2436 | ||
2437 | u A uuencoded string. | |
a0ed51b3 LW |
2438 | U A Unicode character number. Encodes to UTF-8 internally. |
2439 | Works even if C<use utf8> is not in effect. | |
a0d0e21e | 2440 | |
96e4d5b1 | 2441 | w A BER compressed integer. Its bytes represent an unsigned |
f86cebdf GS |
2442 | integer in base 128, most significant digit first, with as |
2443 | few digits as possible. Bit eight (the high bit) is set | |
2444 | on each byte except the last. | |
def98dd4 | 2445 | |
a0d0e21e LW |
2446 | x A null byte. |
2447 | X Back up a byte. | |
2448 | @ Null fill to absolute position. | |
2449 | ||
5a964f20 | 2450 | Each letter may optionally be followed by a number giving a repeat |
7660c0ab A |
2451 | count. With all types except C<"a">, C<"A">, C<"b">, C<"B">, C<"h">, C<"H">, and C<"P"> the |
2452 | pack function will gobble up that many values from the LIST. A C<*> for the | |
2453 | repeat count means to use however many items are left. The C<"a"> and C<"A"> | |
a0d0e21e | 2454 | types gobble just one value, but pack it as a string of length count, |
7660c0ab A |
2455 | padding with nulls or spaces as necessary. (When unpacking, C<"A"> strips |
2456 | trailing spaces and nulls, but C<"a"> does not.) Likewise, the C<"b"> and C<"B"> | |
2457 | fields pack a string that many bits long. The C<"h"> and C<"H"> fields pack a | |
2458 | string that many nybbles long. The C<"p"> type packs a pointer to a null- | |
84902520 TB |
2459 | terminated string. You are responsible for ensuring the string is not a |
2460 | temporary value (which can potentially get deallocated before you get | |
7660c0ab | 2461 | around to using the packed result). The C<"P"> packs a pointer to a structure |
61167c6f | 2462 | of the size indicated by the length. A NULL pointer is created if the |
7660c0ab | 2463 | corresponding value for C<"p"> or C<"P"> is C<undef>. |
61167c6f | 2464 | Real numbers (floats and doubles) are |
a0d0e21e LW |
2465 | in the native machine format only; due to the multiplicity of floating |
2466 | formats around, and the lack of a standard "network" representation, no | |
2467 | facility for interchange has been made. This means that packed floating | |
2468 | point data written on one machine may not be readable on another - even if | |
2469 | both use IEEE floating point arithmetic (as the endian-ness of the memory | |
2470 | representation is not part of the IEEE spec). Note that Perl uses doubles | |
2471 | internally for all numeric calculation, and converting from double into | |
5f05dabc | 2472 | float and thence back to double again will lose precision (i.e., |
7660c0ab | 2473 | C<unpack("f", pack("f", $foo)>) will not in general equal C<$foo>). |
a0d0e21e LW |
2474 | |
2475 | Examples: | |
2476 | ||
a0ed51b3 | 2477 | $foo = pack("CCCC",65,66,67,68); |
a0d0e21e | 2478 | # foo eq "ABCD" |
a0ed51b3 | 2479 | $foo = pack("C4",65,66,67,68); |
a0d0e21e | 2480 | # same thing |
a0ed51b3 LW |
2481 | $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9); |
2482 | # same thing with Unicode circled letters | |
a0d0e21e LW |
2483 | |
2484 | $foo = pack("ccxxcc",65,66,67,68); | |
2485 | # foo eq "AB\0\0CD" | |
2486 | ||
2487 | $foo = pack("s2",1,2); | |
2488 | # "\1\0\2\0" on little-endian | |
2489 | # "\0\1\0\2" on big-endian | |
2490 | ||
2491 | $foo = pack("a4","abcd","x","y","z"); | |
2492 | # "abcd" | |
2493 | ||
2494 | $foo = pack("aaaa","abcd","x","y","z"); | |
2495 | # "axyz" | |
2496 | ||
2497 | $foo = pack("a14","abcdefg"); | |
2498 | # "abcdefg\0\0\0\0\0\0\0" | |
2499 | ||
2500 | $foo = pack("i9pl", gmtime); | |
2501 | # a real struct tm (on my system anyway) | |
2502 | ||
2503 | sub bintodec { | |
2504 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); | |
2505 | } | |
2506 | ||
2507 | The same template may generally also be used in the unpack function. | |
2508 | ||
5a964f20 TC |
2509 | =item package |
2510 | ||
cb1a09d0 AD |
2511 | =item package NAMESPACE |
2512 | ||
2513 | Declares the compilation unit as being in the given namespace. The scope | |
2514 | of the package declaration is from the declaration itself through the end of | |
7660c0ab | 2515 | the enclosing block (the same scope as the C<local()> operator). All further |
cb1a09d0 | 2516 | unqualified dynamic identifiers will be in this namespace. A package |
5f05dabc | 2517 | statement affects only dynamic variables--including those you've used |
7660c0ab | 2518 | C<local()> on--but I<not> lexical variables created with C<my()>. Typically it |
cb1a09d0 AD |
2519 | would be the first declaration in a file to be included by the C<require> |
2520 | or C<use> operator. You can switch into a package in more than one place; | |
5a964f20 | 2521 | it merely influences which symbol table is used by the compiler for the |
cb1a09d0 AD |
2522 | rest of that block. You can refer to variables and filehandles in other |
2523 | packages by prefixing the identifier with the package name and a double | |
2524 | colon: C<$Package::Variable>. If the package name is null, the C<main> | |
2525 | package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. | |
2526 | ||
5a964f20 TC |
2527 | If NAMESPACE is omitted, then there is no current package, and all |
2528 | identifiers must be fully qualified or lexicals. This is stricter | |
2529 | than C<use strict>, since it also extends to function names. | |
2530 | ||
cb1a09d0 AD |
2531 | See L<perlmod/"Packages"> for more information about packages, modules, |
2532 | and classes. See L<perlsub> for other scoping issues. | |
2533 | ||
a0d0e21e LW |
2534 | =item pipe READHANDLE,WRITEHANDLE |
2535 | ||
2536 | Opens a pair of connected pipes like the corresponding system call. | |
2537 | Note that if you set up a loop of piped processes, deadlock can occur | |
2538 | unless you are very careful. In addition, note that Perl's pipes use | |
184e9718 | 2539 | stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE |
a0d0e21e LW |
2540 | after each command, depending on the application. |
2541 | ||
7e1af8bc | 2542 | See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication"> |
4633a7c4 LW |
2543 | for examples of such things. |
2544 | ||
a0d0e21e LW |
2545 | =item pop ARRAY |
2546 | ||
54310121 | 2547 | =item pop |
28757baa | 2548 | |
a0d0e21e LW |
2549 | Pops and returns the last value of the array, shortening the array by |
2550 | 1. Has a similar effect to | |
2551 | ||
2552 | $tmp = $ARRAY[$#ARRAY--]; | |
2553 | ||
2554 | If there are no elements in the array, returns the undefined value. | |
cb1a09d0 | 2555 | If ARRAY is omitted, pops the |
7660c0ab A |
2556 | C<@ARGV> array in the main program, and the C<@_> array in subroutines, just |
2557 | like C<shift()>. | |
a0d0e21e LW |
2558 | |
2559 | =item pos SCALAR | |
2560 | ||
54310121 | 2561 | =item pos |
bbce6d69 | 2562 | |
4633a7c4 | 2563 | Returns the offset of where the last C<m//g> search left off for the variable |
7660c0ab | 2564 | is in question (C<$_> is used when the variable is not specified). May be |
44a8e56a | 2565 | modified to change that offset. Such modification will also influence |
2566 | the C<\G> zero-width assertion in regular expressions. See L<perlre> and | |
2567 | L<perlop>. | |
a0d0e21e LW |
2568 | |
2569 | =item print FILEHANDLE LIST | |
2570 | ||
2571 | =item print LIST | |
2572 | ||
2573 | =item print | |
2574 | ||
cb1a09d0 | 2575 | Prints a string or a comma-separated list of strings. Returns TRUE |
a0d0e21e | 2576 | if successful. FILEHANDLE may be a scalar variable name, in which case |
cb1a09d0 | 2577 | the variable contains the name of or a reference to the filehandle, thus introducing one |
a0d0e21e LW |
2578 | level of indirection. (NOTE: If FILEHANDLE is a variable and the next |
2579 | token is a term, it may be misinterpreted as an operator unless you | |
7660c0ab | 2580 | interpose a C<+> or put parentheses around the arguments.) If FILEHANDLE is |
a0d0e21e | 2581 | omitted, prints by default to standard output (or to the last selected |
7660c0ab | 2582 | output channel--see L</select>). If LIST is also omitted, prints C<$_> to |
5a964f20 | 2583 | the currently selected output channel. To set the default output channel to something other than |
a0d0e21e | 2584 | STDOUT use the select operation. Note that, because print takes a |
5a964f20 | 2585 | LIST, anything in the LIST is evaluated in list context, and any |
a0d0e21e | 2586 | subroutine that you call will have one or more of its expressions |
5a964f20 | 2587 | evaluated in list context. Also be careful not to follow the print |
a0d0e21e | 2588 | keyword with a left parenthesis unless you want the corresponding right |
7660c0ab | 2589 | parenthesis to terminate the arguments to the print--interpose a C<+> or |
5f05dabc | 2590 | put parentheses around all the arguments. |
a0d0e21e | 2591 | |
4633a7c4 | 2592 | Note that if you're storing FILEHANDLES in an array or other expression, |
da0045b7 | 2593 | you will have to use a block returning its value instead: |
4633a7c4 LW |
2594 | |
2595 | print { $files[$i] } "stuff\n"; | |
2596 | print { $OK ? STDOUT : STDERR } "stuff\n"; | |
2597 | ||
5f05dabc | 2598 | =item printf FILEHANDLE FORMAT, LIST |
a0d0e21e | 2599 | |
5f05dabc | 2600 | =item printf FORMAT, LIST |
a0d0e21e | 2601 | |
7660c0ab | 2602 | Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\> |
a3cb178b | 2603 | (the output record separator) is not appended. The first argument |
ab4f32c2 | 2604 | of the list will be interpreted as the C<printf()> format. If C<use locale> is |
a034a98d DD |
2605 | in effect, the character used for the decimal point in formatted real numbers |
2606 | is affected by the LC_NUMERIC locale. See L<perllocale>. | |
a0d0e21e | 2607 | |
7660c0ab A |
2608 | Don't fall into the trap of using a C<printf()> when a simple |
2609 | C<print()> would do. The C<print()> is more efficient and less | |
28757baa | 2610 | error prone. |
2611 | ||
da0045b7 | 2612 | =item prototype FUNCTION |
2613 | ||
2614 | Returns the prototype of a function as a string (or C<undef> if the | |
5f05dabc | 2615 | function has no prototype). FUNCTION is a reference to, or the name of, |
2616 | the function whose prototype you want to retrieve. | |
da0045b7 | 2617 | |
b6c543e3 IZ |
2618 | If FUNCTION is a string starting with C<CORE::>, the rest is taken as |
2619 | a name for Perl builtin. If builtin is not I<overridable> (such as | |
ab4f32c2 A |
2620 | C<qw//>) or its arguments cannot be expressed by a prototype (such as |
2621 | C<system()>) - in other words, the builtin does not behave like a Perl | |
b6c543e3 IZ |
2622 | function - returns C<undef>. Otherwise, the string describing the |
2623 | equivalent prototype is returned. | |
2624 | ||
a0d0e21e LW |
2625 | =item push ARRAY,LIST |
2626 | ||
2627 | Treats ARRAY as a stack, and pushes the values of LIST | |
2628 | onto the end of ARRAY. The length of ARRAY increases by the length of | |
2629 | LIST. Has the same effect as | |
2630 | ||
2631 | for $value (LIST) { | |
2632 | $ARRAY[++$#ARRAY] = $value; | |
2633 | } | |
2634 | ||
2635 | but is more efficient. Returns the new number of elements in the array. | |
2636 | ||
2637 | =item q/STRING/ | |
2638 | ||
2639 | =item qq/STRING/ | |
2640 | ||
8782bef2 GB |
2641 | =item qr/STRING/ |
2642 | ||
a0d0e21e LW |
2643 | =item qx/STRING/ |
2644 | ||
2645 | =item qw/STRING/ | |
2646 | ||
2647 | Generalized quotes. See L<perlop>. | |
2648 | ||
2649 | =item quotemeta EXPR | |
2650 | ||
54310121 | 2651 | =item quotemeta |
bbce6d69 | 2652 | |
68dc0745 | 2653 | Returns the value of EXPR with all non-alphanumeric |
a034a98d DD |
2654 | characters backslashed. (That is, all characters not matching |
2655 | C</[A-Za-z_0-9]/> will be preceded by a backslash in the | |
2656 | returned string, regardless of any locale settings.) | |
2657 | This is the internal function implementing | |
7660c0ab | 2658 | the C<\Q> escape in double-quoted strings. |
a0d0e21e | 2659 | |
7660c0ab | 2660 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2661 | |
a0d0e21e LW |
2662 | =item rand EXPR |
2663 | ||
2664 | =item rand | |
2665 | ||
7660c0ab | 2666 | Returns a random fractional number greater than or equal to C<0> and less |
3e3baf6d | 2667 | than the value of EXPR. (EXPR should be positive.) If EXPR is |
7660c0ab A |
2668 | omitted, the value C<1> is used. Automatically calls C<srand()> unless |
2669 | C<srand()> has already been called. See also C<srand()>. | |
a0d0e21e | 2670 | |
2f9daede | 2671 | (Note: If your rand function consistently returns numbers that are too |
a0d0e21e | 2672 | large or too small, then your version of Perl was probably compiled |
2f9daede | 2673 | with the wrong number of RANDBITS.) |
a0d0e21e LW |
2674 | |
2675 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET | |
2676 | ||
2677 | =item read FILEHANDLE,SCALAR,LENGTH | |
2678 | ||
2679 | Attempts to read LENGTH bytes of data into variable SCALAR from the | |
3b02c43c GS |
2680 | specified FILEHANDLE. Returns the number of bytes actually read, |
2681 | C<0> at end of file, or undef if there was an error. SCALAR will be grown | |
2682 | or shrunk to the length actually read. An OFFSET may be specified to | |
2683 | place the read data at some other place than the beginning of the | |
f86cebdf GS |
2684 | string. This call is actually implemented in terms of stdio's fread(3) |
2685 | call. To get a true read(2) system call, see C<sysread()>. | |
a0d0e21e LW |
2686 | |
2687 | =item readdir DIRHANDLE | |
2688 | ||
7660c0ab | 2689 | Returns the next directory entry for a directory opened by C<opendir()>. |
5a964f20 | 2690 | If used in list context, returns all the rest of the entries in the |
a0d0e21e | 2691 | directory. If there are no more entries, returns an undefined value in |
5a964f20 | 2692 | scalar context or a null list in list context. |
a0d0e21e | 2693 | |
7660c0ab | 2694 | If you're planning to filetest the return values out of a C<readdir()>, you'd |
5f05dabc | 2695 | better prepend the directory in question. Otherwise, because we didn't |
7660c0ab | 2696 | C<chdir()> there, it would have been testing the wrong file. |
cb1a09d0 AD |
2697 | |
2698 | opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!"; | |
2699 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); | |
2700 | closedir DIR; | |
2701 | ||
84902520 TB |
2702 | =item readline EXPR |
2703 | ||
5a964f20 | 2704 | Reads from the filehandle whose typeglob is contained in EXPR. In scalar context, a single line |
84902520 TB |
2705 | is read and returned. In list context, reads until end-of-file is |
2706 | reached and returns a list of lines (however you've defined lines | |
7660c0ab | 2707 | with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
2708 | This is the internal function implementing the C<E<lt>EXPRE<gt>> |
2709 | operator, but you can use it directly. The C<E<lt>EXPRE<gt>> | |
2710 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
2711 | ||
5a964f20 TC |
2712 | $line = <STDIN>; |
2713 | $line = readline(*STDIN); # same thing | |
2714 | ||
a0d0e21e LW |
2715 | =item readlink EXPR |
2716 | ||
54310121 | 2717 | =item readlink |
bbce6d69 | 2718 | |
a0d0e21e LW |
2719 | Returns the value of a symbolic link, if symbolic links are |
2720 | implemented. If not, gives a fatal error. If there is some system | |
184e9718 | 2721 | error, returns the undefined value and sets C<$!> (errno). If EXPR is |
7660c0ab | 2722 | omitted, uses C<$_>. |
a0d0e21e | 2723 | |
84902520 TB |
2724 | =item readpipe EXPR |
2725 | ||
5a964f20 | 2726 | EXPR is executed as a system command. |
84902520 TB |
2727 | The collected standard output of the command is returned. |
2728 | In scalar context, it comes back as a single (potentially | |
2729 | multi-line) string. In list context, returns a list of lines | |
7660c0ab | 2730 | (however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
2731 | This is the internal function implementing the C<qx/EXPR/> |
2732 | operator, but you can use it directly. The C<qx/EXPR/> | |
2733 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
2734 | ||
a0d0e21e LW |
2735 | =item recv SOCKET,SCALAR,LEN,FLAGS |
2736 | ||
2737 | Receives a message on a socket. Attempts to receive LENGTH bytes of | |
2738 | data into variable SCALAR from the specified SOCKET filehandle. | |
7660c0ab | 2739 | Actually does a C C<recvfrom()>, so that it can return the address of the |
a0d0e21e LW |
2740 | sender. Returns the undefined value if there's an error. SCALAR will |
2741 | be grown or shrunk to the length actually read. Takes the same flags | |
54310121 | 2742 | as the system call of the same name. |
4633a7c4 | 2743 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e LW |
2744 | |
2745 | =item redo LABEL | |
2746 | ||
2747 | =item redo | |
2748 | ||
2749 | The C<redo> command restarts the loop block without evaluating the | |
2750 | conditional again. The C<continue> block, if any, is not executed. If | |
2751 | the LABEL is omitted, the command refers to the innermost enclosing | |
2752 | loop. This command is normally used by programs that want to lie to | |
2753 | themselves about what was just input: | |
2754 | ||
2755 | # a simpleminded Pascal comment stripper | |
2756 | # (warning: assumes no { or } in strings) | |
4633a7c4 | 2757 | LINE: while (<STDIN>) { |
a0d0e21e LW |
2758 | while (s|({.*}.*){.*}|$1 |) {} |
2759 | s|{.*}| |; | |
2760 | if (s|{.*| |) { | |
2761 | $front = $_; | |
2762 | while (<STDIN>) { | |
2763 | if (/}/) { # end of comment? | |
5a964f20 | 2764 | s|^|$front\{|; |
4633a7c4 | 2765 | redo LINE; |
a0d0e21e LW |
2766 | } |
2767 | } | |
2768 | } | |
2769 | print; | |
2770 | } | |
2771 | ||
1d2dff63 GS |
2772 | See also L</continue> for an illustration of how C<last>, C<next>, and |
2773 | C<redo> work. | |
2774 | ||
a0d0e21e LW |
2775 | =item ref EXPR |
2776 | ||
54310121 | 2777 | =item ref |
bbce6d69 | 2778 | |
2f9daede | 2779 | Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR |
7660c0ab | 2780 | is not specified, C<$_> will be used. The value returned depends on the |
bbce6d69 | 2781 | type of thing the reference is a reference to. |
a0d0e21e LW |
2782 | Builtin types include: |
2783 | ||
2784 | REF | |
2785 | SCALAR | |
2786 | ARRAY | |
2787 | HASH | |
2788 | CODE | |
2789 | GLOB | |
2790 | ||
54310121 | 2791 | If the referenced object has been blessed into a package, then that package |
7660c0ab | 2792 | name is returned instead. You can think of C<ref()> as a C<typeof()> operator. |
a0d0e21e LW |
2793 | |
2794 | if (ref($r) eq "HASH") { | |
aa689395 | 2795 | print "r is a reference to a hash.\n"; |
54310121 | 2796 | } |
5a964f20 | 2797 | if (!ref($r)) { |
a0d0e21e | 2798 | print "r is not a reference at all.\n"; |
54310121 | 2799 | } |
a0d0e21e LW |
2800 | |
2801 | See also L<perlref>. | |
2802 | ||
2803 | =item rename OLDNAME,NEWNAME | |
2804 | ||
7660c0ab | 2805 | Changes the name of a file. Returns C<1> for success, C<0> otherwise. Will |
5f05dabc | 2806 | not work across file system boundaries. |
a0d0e21e LW |
2807 | |
2808 | =item require EXPR | |
2809 | ||
2810 | =item require | |
2811 | ||
7660c0ab | 2812 | Demands some semantics specified by EXPR, or by C<$_> if EXPR is not |
a0d0e21e | 2813 | supplied. If EXPR is numeric, demands that the current version of Perl |
184e9718 | 2814 | (C<$]> or $PERL_VERSION) be equal or greater than EXPR. |
a0d0e21e LW |
2815 | |
2816 | Otherwise, demands that a library file be included if it hasn't already | |
2817 | been included. The file is included via the do-FILE mechanism, which is | |
7660c0ab | 2818 | essentially just a variety of C<eval()>. Has semantics similar to the following |
a0d0e21e LW |
2819 | subroutine: |
2820 | ||
2821 | sub require { | |
5a964f20 | 2822 | my($filename) = @_; |
a0d0e21e | 2823 | return 1 if $INC{$filename}; |
5a964f20 | 2824 | my($realfilename,$result); |
a0d0e21e LW |
2825 | ITER: { |
2826 | foreach $prefix (@INC) { | |
2827 | $realfilename = "$prefix/$filename"; | |
2828 | if (-f $realfilename) { | |
2829 | $result = do $realfilename; | |
2830 | last ITER; | |
2831 | } | |
2832 | } | |
2833 | die "Can't find $filename in \@INC"; | |
2834 | } | |
2835 | die $@ if $@; | |
2836 | die "$filename did not return true value" unless $result; | |
2837 | $INC{$filename} = $realfilename; | |
5a964f20 | 2838 | return $result; |
a0d0e21e LW |
2839 | } |
2840 | ||
2841 | Note that the file will not be included twice under the same specified | |
2842 | name. The file must return TRUE as the last statement to indicate | |
2843 | successful execution of any initialization code, so it's customary to | |
7660c0ab | 2844 | end such a file with "C<1;>" unless you're sure it'll return TRUE |
a0d0e21e LW |
2845 | otherwise. But it's better just to put the "C<1;>", in case you add more |
2846 | statements. | |
2847 | ||
54310121 | 2848 | If EXPR is a bareword, the require assumes a "F<.pm>" extension and |
da0045b7 | 2849 | replaces "F<::>" with "F</>" in the filename for you, |
54310121 | 2850 | to make it easy to load standard modules. This form of loading of |
a0d0e21e LW |
2851 | modules does not risk altering your namespace. |
2852 | ||
ee580363 GS |
2853 | In other words, if you try this: |
2854 | ||
f86cebdf | 2855 | require Foo::Bar; # a splendid bareword |
ee580363 | 2856 | |
7660c0ab A |
2857 | The require function will actually look for the "F<Foo/Bar.pm>" file in the |
2858 | directories specified in the C<@INC> array. | |
ee580363 | 2859 | |
5a964f20 | 2860 | But if you try this: |
ee580363 GS |
2861 | |
2862 | $class = 'Foo::Bar'; | |
f86cebdf | 2863 | require $class; # $class is not a bareword |
5a964f20 | 2864 | #or |
f86cebdf | 2865 | require "Foo::Bar"; # not a bareword because of the "" |
ee580363 | 2866 | |
7660c0ab A |
2867 | The require function will look for the "F<Foo::Bar>" file in the @INC array and |
2868 | will complain about not finding "F<Foo::Bar>" there. In this case you can do: | |
ee580363 GS |
2869 | |
2870 | eval "require $class"; | |
2871 | ||
2872 | For a yet-more-powerful import facility, see L</use> and L<perlmod>. | |
a0d0e21e LW |
2873 | |
2874 | =item reset EXPR | |
2875 | ||
2876 | =item reset | |
2877 | ||
2878 | Generally used in a C<continue> block at the end of a loop to clear | |
7660c0ab | 2879 | variables and reset C<??> searches so that they work again. The |
a0d0e21e LW |
2880 | expression is interpreted as a list of single characters (hyphens |
2881 | allowed for ranges). All variables and arrays beginning with one of | |
2882 | those letters are reset to their pristine state. If the expression is | |
7660c0ab | 2883 | omitted, one-match searches (C<?pattern?>) are reset to match again. Resets |
5f05dabc | 2884 | only variables or searches in the current package. Always returns |
a0d0e21e LW |
2885 | 1. Examples: |
2886 | ||
2887 | reset 'X'; # reset all X variables | |
2888 | reset 'a-z'; # reset lower case variables | |
2889 | reset; # just reset ?? searches | |
2890 | ||
7660c0ab A |
2891 | Resetting C<"A-Z"> is not recommended because you'll wipe out your |
2892 | C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package variables--lexical variables | |
a0d0e21e | 2893 | are unaffected, but they clean themselves up on scope exit anyway, |
da0045b7 | 2894 | so you'll probably want to use them instead. See L</my>. |
a0d0e21e | 2895 | |
54310121 | 2896 | =item return EXPR |
2897 | ||
2898 | =item return | |
2899 | ||
7660c0ab | 2900 | Returns from a subroutine, C<eval()>, or C<do FILE> with the value |
5a964f20 | 2901 | given in EXPR. Evaluation of EXPR may be in list, scalar, or void |
54310121 | 2902 | context, depending on how the return value will be used, and the context |
7660c0ab | 2903 | may vary from one execution to the next (see C<wantarray()>). If no EXPR |
5a964f20 TC |
2904 | is given, returns an empty list in list context, an undefined value in |
2905 | scalar context, or nothing in a void context. | |
a0d0e21e | 2906 | |
68dc0745 | 2907 | (Note that in the absence of a return, a subroutine, eval, or do FILE |
2908 | will automatically return the value of the last expression evaluated.) | |
a0d0e21e LW |
2909 | |
2910 | =item reverse LIST | |
2911 | ||
5a964f20 TC |
2912 | In list context, returns a list value consisting of the elements |
2913 | of LIST in the opposite order. In scalar context, concatenates the | |
a0ed51b3 LW |
2914 | elements of LIST, and returns a string value with all the characters |
2915 | in the opposite order. | |
4633a7c4 | 2916 | |
2f9daede | 2917 | print reverse <>; # line tac, last line first |
4633a7c4 | 2918 | |
2f9daede | 2919 | undef $/; # for efficiency of <> |
a0ed51b3 | 2920 | print scalar reverse <>; # character tac, last line tsrif |
2f9daede TP |
2921 | |
2922 | This operator is also handy for inverting a hash, although there are some | |
2923 | caveats. If a value is duplicated in the original hash, only one of those | |
2924 | can be represented as a key in the inverted hash. Also, this has to | |
2925 | unwind one hash and build a whole new one, which may take some time | |
2926 | on a large hash. | |
2927 | ||
2928 | %by_name = reverse %by_address; # Invert the hash | |
a0d0e21e LW |
2929 | |
2930 | =item rewinddir DIRHANDLE | |
2931 | ||
2932 | Sets the current position to the beginning of the directory for the | |
7660c0ab | 2933 | C<readdir()> routine on DIRHANDLE. |
a0d0e21e LW |
2934 | |
2935 | =item rindex STR,SUBSTR,POSITION | |
2936 | ||
2937 | =item rindex STR,SUBSTR | |
2938 | ||
2939 | Works just like index except that it returns the position of the LAST | |
2940 | occurrence of SUBSTR in STR. If POSITION is specified, returns the | |
2941 | last occurrence at or before that position. | |
2942 | ||
2943 | =item rmdir FILENAME | |
2944 | ||
54310121 | 2945 | =item rmdir |
bbce6d69 | 2946 | |
5a964f20 TC |
2947 | Deletes the directory specified by FILENAME if that directory is empty. If it |
2948 | succeeds it returns TRUE, otherwise it returns FALSE and sets C<$!> (errno). If | |
7660c0ab | 2949 | FILENAME is omitted, uses C<$_>. |
a0d0e21e LW |
2950 | |
2951 | =item s/// | |
2952 | ||
2953 | The substitution operator. See L<perlop>. | |
2954 | ||
2955 | =item scalar EXPR | |
2956 | ||
5a964f20 | 2957 | Forces EXPR to be interpreted in scalar context and returns the value |
54310121 | 2958 | of EXPR. |
cb1a09d0 AD |
2959 | |
2960 | @counts = ( scalar @a, scalar @b, scalar @c ); | |
2961 | ||
54310121 | 2962 | There is no equivalent operator to force an expression to |
5a964f20 | 2963 | be interpolated in list context because it's in practice never |
cb1a09d0 AD |
2964 | needed. If you really wanted to do so, however, you could use |
2965 | the construction C<@{[ (some expression) ]}>, but usually a simple | |
2966 | C<(some expression)> suffices. | |
a0d0e21e LW |
2967 | |
2968 | =item seek FILEHANDLE,POSITION,WHENCE | |
2969 | ||
ab4f32c2 | 2970 | Sets FILEHANDLE's position, just like the C<fseek()> call of C<stdio()>. |
8903cb82 | 2971 | FILEHANDLE may be an expression whose value gives the name of the |
7660c0ab A |
2972 | filehandle. The values for WHENCE are C<0> to set the new position to |
2973 | POSITION, C<1> to set it to the current position plus POSITION, and C<2> to | |
8903cb82 | 2974 | set it to EOF plus POSITION (typically negative). For WHENCE you may |
7660c0ab A |
2975 | use the constants C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END> from either the |
2976 | C<IO::Seekable> or the POSIX module. Returns C<1> upon success, C<0> otherwise. | |
8903cb82 | 2977 | |
7660c0ab A |
2978 | If you want to position file for C<sysread()> or C<syswrite()>, don't use |
2979 | C<seek()> -- buffering makes its effect on the file's system position | |
2980 | unpredictable and non-portable. Use C<sysseek()> instead. | |
a0d0e21e | 2981 | |
cb1a09d0 AD |
2982 | On some systems you have to do a seek whenever you switch between reading |
2983 | and writing. Amongst other things, this may have the effect of calling | |
f86cebdf | 2984 | stdio's clearerr(3). A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving |
8903cb82 | 2985 | the file position: |
cb1a09d0 AD |
2986 | |
2987 | seek(TEST,0,1); | |
2988 | ||
2989 | This is also useful for applications emulating C<tail -f>. Once you hit | |
2990 | EOF on your read, and then sleep for a while, you might have to stick in a | |
7660c0ab | 2991 | seek() to reset things. The C<seek()> doesn't change the current position, |
8903cb82 | 2992 | but it I<does> clear the end-of-file condition on the handle, so that the |
2993 | next C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope. | |
cb1a09d0 AD |
2994 | |
2995 | If that doesn't work (some stdios are particularly cantankerous), then | |
2996 | you may need something more like this: | |
2997 | ||
2998 | for (;;) { | |
f86cebdf GS |
2999 | for ($curpos = tell(FILE); $_ = <FILE>; |
3000 | $curpos = tell(FILE)) { | |
cb1a09d0 AD |
3001 | # search for some stuff and put it into files |
3002 | } | |
3003 | sleep($for_a_while); | |
3004 | seek(FILE, $curpos, 0); | |
3005 | } | |
3006 | ||
a0d0e21e LW |
3007 | =item seekdir DIRHANDLE,POS |
3008 | ||
7660c0ab A |
3009 | Sets the current position for the C<readdir()> routine on DIRHANDLE. POS |
3010 | must be a value returned by C<telldir()>. Has the same caveats about | |
a0d0e21e LW |
3011 | possible directory compaction as the corresponding system library |
3012 | routine. | |
3013 | ||
3014 | =item select FILEHANDLE | |
3015 | ||
3016 | =item select | |
3017 | ||
3018 | Returns the currently selected filehandle. Sets the current default | |
3019 | filehandle for output, if FILEHANDLE is supplied. This has two | |
ab4f32c2 | 3020 | effects: first, a C<write()> or a C<print()> without a filehandle will |
a0d0e21e LW |
3021 | default to this FILEHANDLE. Second, references to variables related to |
3022 | output will refer to this output channel. For example, if you have to | |
3023 | set the top of form format for more than one output channel, you might | |
3024 | do the following: | |
3025 | ||
3026 | select(REPORT1); | |
3027 | $^ = 'report1_top'; | |
3028 | select(REPORT2); | |
3029 | $^ = 'report2_top'; | |
3030 | ||
3031 | FILEHANDLE may be an expression whose value gives the name of the | |
3032 | actual filehandle. Thus: | |
3033 | ||
3034 | $oldfh = select(STDERR); $| = 1; select($oldfh); | |
3035 | ||
4633a7c4 LW |
3036 | Some programmers may prefer to think of filehandles as objects with |
3037 | methods, preferring to write the last example as: | |
a0d0e21e | 3038 | |
28757baa | 3039 | use IO::Handle; |
a0d0e21e LW |
3040 | STDERR->autoflush(1); |
3041 | ||
3042 | =item select RBITS,WBITS,EBITS,TIMEOUT | |
3043 | ||
f86cebdf | 3044 | This calls the select(2) system call with the bit masks specified, which |
7660c0ab | 3045 | can be constructed using C<fileno()> and C<vec()>, along these lines: |
a0d0e21e LW |
3046 | |
3047 | $rin = $win = $ein = ''; | |
3048 | vec($rin,fileno(STDIN),1) = 1; | |
3049 | vec($win,fileno(STDOUT),1) = 1; | |
3050 | $ein = $rin | $win; | |
3051 | ||
3052 | If you want to select on many filehandles you might wish to write a | |
3053 | subroutine: | |
3054 | ||
3055 | sub fhbits { | |
5a964f20 TC |
3056 | my(@fhlist) = split(' ',$_[0]); |
3057 | my($bits); | |
a0d0e21e LW |
3058 | for (@fhlist) { |
3059 | vec($bits,fileno($_),1) = 1; | |
3060 | } | |
3061 | $bits; | |
3062 | } | |
4633a7c4 | 3063 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e LW |
3064 | |
3065 | The usual idiom is: | |
3066 | ||
3067 | ($nfound,$timeleft) = | |
3068 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); | |
3069 | ||
54310121 | 3070 | or to block until something becomes ready just do this |
a0d0e21e LW |
3071 | |
3072 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); | |
3073 | ||
7660c0ab A |
3074 | Most systems do not bother to return anything useful in C<$timeleft>, so |
3075 | calling select() in scalar context just returns C<$nfound>. | |
c07a80fd | 3076 | |
5f05dabc | 3077 | Any of the bit masks can also be undef. The timeout, if specified, is |
a0d0e21e | 3078 | in seconds, which may be fractional. Note: not all implementations are |
7660c0ab A |
3079 | capable of returning theC<$timeleft>. If not, they always return |
3080 | C<$timeleft> equal to the supplied C<$timeout>. | |
a0d0e21e | 3081 | |
ff68c719 | 3082 | You can effect a sleep of 250 milliseconds this way: |
a0d0e21e LW |
3083 | |
3084 | select(undef, undef, undef, 0.25); | |
3085 | ||
7660c0ab A |
3086 | B<WARNING>: One should not attempt to mix buffered I/O (like C<read()> |
3087 | or E<lt>FHE<gt>) with C<select()>, except as permitted by POSIX, and even | |
3088 | then only on POSIX systems. You have to use C<sysread()> instead. | |
a0d0e21e LW |
3089 | |
3090 | =item semctl ID,SEMNUM,CMD,ARG | |
3091 | ||
ab4f32c2 | 3092 | Calls the System V IPC function C<semctl()>. You'll probably have to say |
0ade1984 JH |
3093 | |
3094 | use IPC::SysV; | |
3095 | ||
3096 | first to get the correct constant definitions. If CMD is IPC_STAT or | |
3097 | GETALL, then ARG must be a variable which will hold the returned | |
ab4f32c2 | 3098 | semid_ds structure or semaphore value array. Returns like C<ioctl()>: the |
7660c0ab A |
3099 | undefined value for error, "C<0> but true" for zero, or the actual return |
3100 | value otherwise. See also C<IPC::SysV> and C<IPC::Semaphore> documentation. | |
a0d0e21e LW |
3101 | |
3102 | =item semget KEY,NSEMS,FLAGS | |
3103 | ||
3104 | Calls the System V IPC function semget. Returns the semaphore id, or | |
7660c0ab A |
3105 | the undefined value if there is an error. See also C<IPC::SysV> and |
3106 | C<IPC::SysV::Semaphore> documentation. | |
a0d0e21e LW |
3107 | |
3108 | =item semop KEY,OPSTRING | |
3109 | ||
3110 | Calls the System V IPC function semop to perform semaphore operations | |
3111 | such as signaling and waiting. OPSTRING must be a packed array of | |
3112 | semop structures. Each semop structure can be generated with | |
3113 | C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore | |
3114 | operations is implied by the length of OPSTRING. Returns TRUE if | |
3115 | successful, or FALSE if there is an error. As an example, the | |
7660c0ab | 3116 | following code waits on semaphore C<$semnum> of semaphore id C<$semid>: |
a0d0e21e LW |
3117 | |
3118 | $semop = pack("sss", $semnum, -1, 0); | |
3119 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); | |
3120 | ||
7660c0ab A |
3121 | To signal the semaphore, replace C<-1> with C<1>. See also C<IPC::SysV> |
3122 | and C<IPC::SysV::Semaphore> documentation. | |
a0d0e21e LW |
3123 | |
3124 | =item send SOCKET,MSG,FLAGS,TO | |
3125 | ||
3126 | =item send SOCKET,MSG,FLAGS | |
3127 | ||
3128 | Sends a message on a socket. Takes the same flags as the system call | |
3129 | of the same name. On unconnected sockets you must specify a | |
7660c0ab | 3130 | destination to send TO, in which case it does a C C<sendto()>. Returns |
a0d0e21e LW |
3131 | the number of characters sent, or the undefined value if there is an |
3132 | error. | |
4633a7c4 | 3133 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e LW |
3134 | |
3135 | =item setpgrp PID,PGRP | |
3136 | ||
7660c0ab | 3137 | Sets the current process group for the specified PID, C<0> for the current |
a0d0e21e | 3138 | process. Will produce a fatal error if used on a machine that doesn't |
f86cebdf | 3139 | implement setpgrp(2). If the arguments are omitted, it defaults to |
7660c0ab A |
3140 | C<0,0>. Note that the POSIX version of C<setpgrp()> does not accept any |
3141 | arguments, so only setpgrp C<0,0> is portable. | |
a0d0e21e LW |
3142 | |
3143 | =item setpriority WHICH,WHO,PRIORITY | |
3144 | ||
3145 | Sets the current priority for a process, a process group, or a user. | |
f86cebdf GS |
3146 | (See setpriority(2).) Will produce a fatal error if used on a machine |
3147 | that doesn't implement setpriority(2). | |
a0d0e21e LW |
3148 | |
3149 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL | |
3150 | ||
3151 | Sets the socket option requested. Returns undefined if there is an | |
7660c0ab | 3152 | error. OPTVAL may be specified as C<undef> if you don't want to pass an |
a0d0e21e LW |
3153 | argument. |
3154 | ||
3155 | =item shift ARRAY | |
3156 | ||
3157 | =item shift | |
3158 | ||
3159 | Shifts the first value of the array off and returns it, shortening the | |
3160 | array by 1 and moving everything down. If there are no elements in the | |
3161 | array, returns the undefined value. If ARRAY is omitted, shifts the | |
7660c0ab A |
3162 | C<@_> array within the lexical scope of subroutines and formats, and the |
3163 | C<@ARGV> array at file scopes or within the lexical scopes established by | |
977336f5 | 3164 | the C<eval ''>, C<BEGIN {}>, C<END {}>, and C<INIT {}> constructs. |
7660c0ab A |
3165 | See also C<unshift()>, C<push()>, and C<pop()>. C<Shift()> and C<unshift()> do the |
3166 | same thing to the left end of an array that C<pop()> and C<push()> do to the | |
977336f5 | 3167 | right end. |
a0d0e21e LW |
3168 | |
3169 | =item shmctl ID,CMD,ARG | |
3170 | ||
0ade1984 JH |
3171 | Calls the System V IPC function shmctl. You'll probably have to say |
3172 | ||
3173 | use IPC::SysV; | |
3174 | ||
7660c0ab A |
3175 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
3176 | then ARG must be a variable which will hold the returned C<shmid_ds> | |
3177 | structure. Returns like ioctl: the undefined value for error, "C<0> but | |
0ade1984 | 3178 | true" for zero, or the actual return value otherwise. |
7660c0ab | 3179 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3180 | |
3181 | =item shmget KEY,SIZE,FLAGS | |
3182 | ||
3183 | Calls the System V IPC function shmget. Returns the shared memory | |
3184 | segment id, or the undefined value if there is an error. | |
7660c0ab | 3185 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3186 | |
3187 | =item shmread ID,VAR,POS,SIZE | |
3188 | ||
3189 | =item shmwrite ID,STRING,POS,SIZE | |
3190 | ||
3191 | Reads or writes the System V shared memory segment ID starting at | |
3192 | position POS for size SIZE by attaching to it, copying in/out, and | |
5a964f20 | 3193 | detaching from it. When reading, VAR must be a variable that will |
a0d0e21e LW |
3194 | hold the data read. When writing, if STRING is too long, only SIZE |
3195 | bytes are used; if STRING is too short, nulls are written to fill out | |
3196 | SIZE bytes. Return TRUE if successful, or FALSE if there is an error. | |
7660c0ab | 3197 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3198 | |
3199 | =item shutdown SOCKET,HOW | |
3200 | ||
3201 | Shuts down a socket connection in the manner indicated by HOW, which | |
3202 | has the same interpretation as in the system call of the same name. | |
3203 | ||
f86cebdf GS |
3204 | shutdown(SOCKET, 0); # I/we have stopped reading data |
3205 | shutdown(SOCKET, 1); # I/we have stopped writing data | |
3206 | shutdown(SOCKET, 2); # I/we have stopped using this socket | |
5a964f20 TC |
3207 | |
3208 | This is useful with sockets when you want to tell the other | |
3209 | side you're done writing but not done reading, or vice versa. | |
3210 | It's also a more insistent form of close because it also | |
3211 | disables the filedescriptor in any forked copies in other | |
3212 | processes. | |
3213 | ||
a0d0e21e LW |
3214 | =item sin EXPR |
3215 | ||
54310121 | 3216 | =item sin |
bbce6d69 | 3217 | |
a0d0e21e | 3218 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 3219 | returns sine of C<$_>. |
a0d0e21e | 3220 | |
7660c0ab | 3221 | For the inverse sine operation, you may use the C<POSIX::asin()> |
28757baa | 3222 | function, or use this relation: |
3223 | ||
3224 | sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } | |
3225 | ||
a0d0e21e LW |
3226 | =item sleep EXPR |
3227 | ||
3228 | =item sleep | |
3229 | ||
3230 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. | |
7660c0ab | 3231 | May be interrupted if the process receives a signal such as C<SIGALRM>. |
1d3434b8 | 3232 | Returns the number of seconds actually slept. You probably cannot |
7660c0ab A |
3233 | mix C<alarm()> and C<sleep()> calls, because C<sleep()> is often implemented |
3234 | using C<alarm()>. | |
a0d0e21e LW |
3235 | |
3236 | On some older systems, it may sleep up to a full second less than what | |
3237 | you requested, depending on how it counts seconds. Most modern systems | |
5a964f20 TC |
3238 | always sleep the full amount. They may appear to sleep longer than that, |
3239 | however, because your process might not be scheduled right away in a | |
3240 | busy multitasking system. | |
a0d0e21e | 3241 | |
cb1a09d0 | 3242 | For delays of finer granularity than one second, you may use Perl's |
f86cebdf | 3243 | C<syscall()> interface to access setitimer(2) if your system supports it, |
7b8d334a | 3244 | or else see L</select()> above. |
cb1a09d0 | 3245 | |
7660c0ab | 3246 | See also the POSIX module's C<sigpause()> function. |
5f05dabc | 3247 | |
a0d0e21e LW |
3248 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
3249 | ||
3250 | Opens a socket of the specified kind and attaches it to filehandle | |
5f05dabc | 3251 | SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for the |
7660c0ab | 3252 | system call of the same name. You should "C<use Socket;>" first to get |
4633a7c4 | 3253 | the proper definitions imported. See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
3254 | |
3255 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL | |
3256 | ||
3257 | Creates an unnamed pair of sockets in the specified domain, of the | |
5f05dabc | 3258 | specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as |
a0d0e21e LW |
3259 | for the system call of the same name. If unimplemented, yields a fatal |
3260 | error. Returns TRUE if successful. | |
3261 | ||
ab4f32c2 | 3262 | Some systems defined C<pipe()> in terms of C<socketpair()>, in which a call |
5a964f20 TC |
3263 | to C<pipe(Rdr, Wtr)> is essentially: |
3264 | ||
3265 | use Socket; | |
3266 | socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC); | |
3267 | shutdown(Rdr, 1); # no more writing for reader | |
3268 | shutdown(Wtr, 0); # no more reading for writer | |
3269 | ||
3270 | See L<perlipc> for an example of socketpair use. | |
3271 | ||
a0d0e21e LW |
3272 | =item sort SUBNAME LIST |
3273 | ||
3274 | =item sort BLOCK LIST | |
3275 | ||
3276 | =item sort LIST | |
3277 | ||
2f9daede | 3278 | Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK |
ab4f32c2 | 3279 | is omitted, C<sort()>s in standard string comparison order. If SUBNAME is |
2f9daede | 3280 | specified, it gives the name of a subroutine that returns an integer |
7660c0ab | 3281 | less than, equal to, or greater than C<0>, depending on how the elements |
2f9daede TP |
3282 | of the array are to be ordered. (The C<E<lt>=E<gt>> and C<cmp> |
3283 | operators are extremely useful in such routines.) SUBNAME may be a | |
1d3434b8 GS |
3284 | scalar variable name (unsubscripted), in which case the value provides |
3285 | the name of (or a reference to) the actual subroutine to use. In place | |
3286 | of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort | |
3287 | subroutine. | |
a0d0e21e | 3288 | |
cb1a09d0 AD |
3289 | In the interests of efficiency the normal calling code for subroutines is |
3290 | bypassed, with the following effects: the subroutine may not be a | |
3291 | recursive subroutine, and the two elements to be compared are passed into | |
7660c0ab A |
3292 | the subroutine not via C<@_> but as the package global variables C<$a> and |
3293 | C<$b> (see example below). They are passed by reference, so don't | |
3294 | modify C<$a> and C<$b>. And don't try to declare them as lexicals either. | |
a0d0e21e | 3295 | |
0a753a76 | 3296 | You also cannot exit out of the sort block or subroutine using any of the |
7660c0ab |