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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlvar - Perl predefined variables | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
b0c22438 | 7 | =head2 The Syntax of Variable Names |
8 | ||
241a59d9 | 9 | Variable names in Perl can have several formats. Usually, they |
b0c22438 | 10 | must begin with a letter or underscore, in which case they can be |
11 | arbitrarily long (up to an internal limit of 251 characters) and | |
12 | may contain letters, digits, underscores, or the special sequence | |
241a59d9 | 13 | C<::> or C<'>. In this case, the part before the last C<::> or |
b0c22438 | 14 | C<'> is taken to be a I<package qualifier>; see L<perlmod>. |
15 | ||
16 | Perl variable names may also be a sequence of digits or a single | |
b44599e0 KW |
17 | punctuation or control character (with the literal control character |
18 | form deprecated). These names are all reserved for | |
b0c22438 | 19 | special uses by Perl; for example, the all-digits names are used |
20 | to hold data captured by backreferences after a regular expression | |
241a59d9 | 21 | match. Perl has a special syntax for the single-control-character |
b0c22438 | 22 | names: It understands C<^X> (caret C<X>) to mean the control-C<X> |
241a59d9 | 23 | character. For example, the notation C<$^W> (dollar-sign caret |
b0c22438 | 24 | C<W>) is the scalar variable whose name is the single character |
241a59d9 | 25 | control-C<W>. This is better than typing a literal control-C<W> |
b0c22438 | 26 | into your program. |
27 | ||
60cf4914 | 28 | Since Perl v5.6.0, Perl variable names may be alphanumeric |
b0c22438 | 29 | strings that begin with control characters (or better yet, a caret). |
30 | These variables must be written in the form C<${^Foo}>; the braces | |
241a59d9 FC |
31 | are not optional. C<${^Foo}> denotes the scalar variable whose |
32 | name is a control-C<F> followed by two C<o>'s. These variables are | |
b0c22438 | 33 | reserved for future special uses by Perl, except for the ones that |
241a59d9 | 34 | begin with C<^_> (control-underscore or caret-underscore). No |
b0c22438 | 35 | control-character name that begins with C<^_> will acquire a special |
36 | meaning in any future version of Perl; such names may therefore be | |
241a59d9 | 37 | used safely in programs. C<$^_> itself, however, I<is> reserved. |
b0c22438 | 38 | |
39 | Perl identifiers that begin with digits, control characters, or | |
40 | punctuation characters are exempt from the effects of the C<package> | |
41 | declaration and are always forced to be in package C<main>; they are | |
241a59d9 | 42 | also exempt from C<strict 'vars'> errors. A few other names are also |
b0c22438 | 43 | exempt in these ways: |
44 | ||
9548c15c FC |
45 | ENV STDIN |
46 | INC STDOUT | |
47 | ARGV STDERR | |
48 | ARGVOUT | |
49 | SIG | |
b0c22438 | 50 | |
69520822 | 51 | In particular, the special C<${^_XYZ}> variables are always taken |
b0c22438 | 52 | to be in package C<main>, regardless of any C<package> declarations |
53 | presently in scope. | |
54 | ||
55 | =head1 SPECIAL VARIABLES | |
a0d0e21e | 56 | |
241a59d9 | 57 | The following names have special meaning to Perl. Most punctuation |
0b9346e6 | 58 | names have reasonable mnemonics, or analogs in the shells. |
59 | Nevertheless, if you wish to use long variable names, you need only say: | |
a0d0e21e | 60 | |
9548c15c | 61 | use English; |
a0d0e21e | 62 | |
241a59d9 FC |
63 | at the top of your program. This aliases all the short names to the long |
64 | names in the current package. Some even have medium names, generally | |
1e7d0944 | 65 | borrowed from B<awk>. For more info, please see L<English>. |
a1ce9542 | 66 | |
241a59d9 | 67 | Before you continue, note the sort order for variables. In general, we |
0b9346e6 | 68 | first list the variables in case-insensitive, almost-lexigraphical |
69 | order (ignoring the C<{> or C<^> preceding words, as in C<${^UNICODE}> | |
70 | or C<$^T>), although C<$_> and C<@_> move up to the top of the pile. | |
71 | For variables with the same identifier, we list it in order of scalar, | |
72 | array, hash, and bareword. | |
a1ce9542 | 73 | |
b0c22438 | 74 | =head2 General Variables |
a0d0e21e | 75 | |
84dabc03 | 76 | =over 8 |
77 | ||
a0d0e21e LW |
78 | =item $ARG |
79 | ||
80 | =item $_ | |
a054c801 | 81 | X<$_> X<$ARG> |
a0d0e21e | 82 | |
241a59d9 | 83 | The default input and pattern-searching space. The following pairs are |
a0d0e21e LW |
84 | equivalent: |
85 | ||
9548c15c FC |
86 | while (<>) {...} # equivalent only in while! |
87 | while (defined($_ = <>)) {...} | |
a0d0e21e | 88 | |
9548c15c FC |
89 | /^Subject:/ |
90 | $_ =~ /^Subject:/ | |
a0d0e21e | 91 | |
9548c15c FC |
92 | tr/a-z/A-Z/ |
93 | $_ =~ tr/a-z/A-Z/ | |
a0d0e21e | 94 | |
9548c15c FC |
95 | chomp |
96 | chomp($_) | |
a0d0e21e | 97 | |
0b9346e6 | 98 | Here are the places where Perl will assume C<$_> even if you don't use it: |
cb1a09d0 AD |
99 | |
100 | =over 3 | |
101 | ||
102 | =item * | |
103 | ||
84dabc03 | 104 | The following functions use C<$_> as a default argument: |
db1511c8 | 105 | |
f61f53cc | 106 | abs, alarm, chomp, chop, chr, chroot, |
ae815a4d FC |
107 | cos, defined, eval, evalbytes, exp, fc, glob, hex, int, lc, |
108 | lcfirst, length, log, lstat, mkdir, oct, ord, pos, print, printf, | |
b0169937 | 109 | quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only), |
ae815a4d FC |
110 | rmdir, say, sin, split (for its second |
111 | argument), sqrt, stat, study, uc, ucfirst, | |
b0169937 | 112 | unlink, unpack. |
cb1a09d0 AD |
113 | |
114 | =item * | |
115 | ||
db1511c8 GS |
116 | All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN. |
117 | See L<perlfunc/-X> | |
118 | ||
cb1a09d0 AD |
119 | =item * |
120 | ||
b0169937 GS |
121 | The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>) |
122 | when used without an C<=~> operator. | |
cb1a09d0 | 123 | |
54310121 | 124 | =item * |
cb1a09d0 AD |
125 | |
126 | The default iterator variable in a C<foreach> loop if no other | |
127 | variable is supplied. | |
128 | ||
54310121 | 129 | =item * |
cb1a09d0 | 130 | |
b0c22438 | 131 | The implicit iterator variable in the C<grep()> and C<map()> functions. |
cb1a09d0 | 132 | |
54310121 | 133 | =item * |
cb1a09d0 | 134 | |
b0c22438 | 135 | The implicit variable of C<given()>. |
db1511c8 GS |
136 | |
137 | =item * | |
138 | ||
ae815a4d FC |
139 | The default place to put the next value or input record |
140 | when a C<< <FH> >>, C<readline>, C<readdir> or C<each> | |
cb1a09d0 | 141 | operation's result is tested by itself as the sole criterion of a C<while> |
241a59d9 | 142 | test. Outside a C<while> test, this will not happen. |
cb1a09d0 AD |
143 | |
144 | =back | |
145 | ||
fc33dad2 FC |
146 | C<$_> is by default a global variable. However, as |
147 | of perl v5.10.0, you can use a lexical version of | |
241a59d9 | 148 | C<$_> by declaring it in a file or in a block with C<my>. Moreover, |
fc33dad2 FC |
149 | declaring C<our $_> restores the global C<$_> in the current scope. Though |
150 | this seemed like a good idea at the time it was introduced, lexical C<$_> | |
151 | actually causes more problems than it solves. If you call a function that | |
152 | expects to be passed information via C<$_>, it may or may not work, | |
153 | depending on how the function is written, there not being any easy way to | |
154 | solve this. Just avoid lexical C<$_>, unless you are feeling particularly | |
dd73cf18 RS |
155 | masochistic. For this reason lexical C<$_> is still experimental and will |
156 | produce a warning unless warnings have been disabled. As with other | |
157 | experimental features, the behavior of lexical C<$_> is subject to change | |
158 | without notice, including change into a fatal error. | |
59f00321 | 159 | |
b0c22438 | 160 | Mnemonic: underline is understood in certain operations. |
a0d0e21e | 161 | |
0b9346e6 | 162 | =item @ARG |
cde0cee5 | 163 | |
0b9346e6 | 164 | =item @_ |
165 | X<@_> X<@ARG> | |
a0d0e21e | 166 | |
0b9346e6 | 167 | Within a subroutine the array C<@_> contains the parameters passed to |
241a59d9 | 168 | that subroutine. Inside a subroutine, C<@_> is the default array for |
0b9346e6 | 169 | the array operators C<push>, C<pop>, C<shift>, and C<unshift>. |
a0d0e21e | 170 | |
0b9346e6 | 171 | See L<perlsub>. |
a0d0e21e | 172 | |
1311257d | 173 | =item $LIST_SEPARATOR |
174 | ||
175 | =item $" | |
176 | X<$"> X<$LIST_SEPARATOR> | |
177 | ||
69520822 | 178 | When an array or an array slice is interpolated into a double-quoted |
179 | string or a similar context such as C</.../>, its elements are | |
241a59d9 | 180 | separated by this value. Default is a space. For example, this: |
69520822 | 181 | |
9548c15c | 182 | print "The array is: @array\n"; |
69520822 | 183 | |
184 | is equivalent to this: | |
185 | ||
9548c15c | 186 | print "The array is: " . join($", @array) . "\n"; |
69520822 | 187 | |
188 | Mnemonic: works in double-quoted context. | |
1311257d | 189 | |
b0c22438 | 190 | =item $PROCESS_ID |
cde0cee5 | 191 | |
b0c22438 | 192 | =item $PID |
a0d0e21e | 193 | |
b0c22438 | 194 | =item $$ |
195 | X<$$> X<$PID> X<$PROCESS_ID> | |
a0d0e21e | 196 | |
241a59d9 | 197 | The process number of the Perl running this script. Though you I<can> set |
4a904372 | 198 | this variable, doing so is generally discouraged, although it can be |
241a59d9 | 199 | invaluable for some testing purposes. It will be reset automatically |
b0c22438 | 200 | across C<fork()> calls. |
a0d0e21e | 201 | |
d7c042c9 AB |
202 | Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl |
203 | would emulate POSIX semantics on Linux systems using LinuxThreads, a | |
204 | partial implementation of POSIX Threads that has since been superseded | |
205 | by the Native POSIX Thread Library (NPTL). | |
206 | ||
e3f68f70 | 207 | LinuxThreads is now obsolete on Linux, and caching C<getpid()> |
d7c042c9 AB |
208 | like this made embedding perl unnecessarily complex (since you'd have |
209 | to manually update the value of $$), so now C<$$> and C<getppid()> | |
210 | will always return the same values as the underlying C library. | |
211 | ||
212 | Debian GNU/kFreeBSD systems also used LinuxThreads up until and | |
213 | including the 6.0 release, but after that moved to FreeBSD thread | |
214 | semantics, which are POSIX-like. | |
215 | ||
216 | To see if your system is affected by this discrepancy check if | |
217 | C<getconf GNU_LIBPTHREAD_VERSION | grep -q NPTL> returns a false | |
1e7d0944 | 218 | value. NTPL threads preserve the POSIX semantics. |
a0d0e21e | 219 | |
b0c22438 | 220 | Mnemonic: same as shells. |
ad83b128 | 221 | |
66d7055b DR |
222 | =item $PROGRAM_NAME |
223 | ||
224 | =item $0 | |
225 | X<$0> X<$PROGRAM_NAME> | |
226 | ||
227 | Contains the name of the program being executed. | |
228 | ||
229 | On some (but not all) operating systems assigning to C<$0> modifies | |
241a59d9 | 230 | the argument area that the C<ps> program sees. On some platforms you |
66d7055b | 231 | may have to use special C<ps> options or a different C<ps> to see the |
241a59d9 | 232 | changes. Modifying the C<$0> is more useful as a way of indicating the |
66d7055b DR |
233 | current program state than it is for hiding the program you're |
234 | running. | |
235 | ||
236 | Note that there are platform-specific limitations on the maximum | |
241a59d9 | 237 | length of C<$0>. In the most extreme case it may be limited to the |
66d7055b DR |
238 | space occupied by the original C<$0>. |
239 | ||
240 | In some platforms there may be arbitrary amount of padding, for | |
241 | example space characters, after the modified name as shown by C<ps>. | |
242 | In some platforms this padding may extend all the way to the original | |
243 | length of the argument area, no matter what you do (this is the case | |
244 | for example with Linux 2.2). | |
245 | ||
246 | Note for BSD users: setting C<$0> does not completely remove "perl" | |
241a59d9 | 247 | from the ps(1) output. For example, setting C<$0> to C<"foobar"> may |
66d7055b DR |
248 | result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix |
249 | and the " (perl)" suffix are shown depends on your exact BSD variant | |
241a59d9 | 250 | and version). This is an operating system feature, Perl cannot help it. |
66d7055b DR |
251 | |
252 | In multithreaded scripts Perl coordinates the threads so that any | |
253 | thread may modify its copy of the C<$0> and the change becomes visible | |
241a59d9 | 254 | to ps(1) (assuming the operating system plays along). Note that |
66d7055b DR |
255 | the view of C<$0> the other threads have will not change since they |
256 | have their own copies of it. | |
257 | ||
258 | If the program has been given to perl via the switches C<-e> or C<-E>, | |
259 | C<$0> will contain the string C<"-e">. | |
260 | ||
60cf4914 | 261 | On Linux as of perl v5.14.0 the legacy process name will be set with |
66d7055b | 262 | C<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as |
241a59d9 | 263 | perl has done since version 4.000. Now system utilities that read the |
66d7055b | 264 | legacy process name such as ps, top and killall will recognize the |
241a59d9 | 265 | name you set when assigning to C<$0>. The string you supply will be |
66d7055b DR |
266 | cut off at 16 bytes, this is a limitation imposed by Linux. |
267 | ||
268 | Mnemonic: same as B<sh> and B<ksh>. | |
269 | ||
b0c22438 | 270 | =item $REAL_GROUP_ID |
a01268b5 | 271 | |
b0c22438 | 272 | =item $GID |
a01268b5 | 273 | |
b0c22438 | 274 | =item $( |
275 | X<$(> X<$GID> X<$REAL_GROUP_ID> | |
a01268b5 | 276 | |
241a59d9 | 277 | The real gid of this process. If you are on a machine that supports |
b0c22438 | 278 | membership in multiple groups simultaneously, gives a space separated |
241a59d9 | 279 | list of groups you are in. The first number is the one returned by |
b0c22438 | 280 | C<getgid()>, and the subsequent ones by C<getgroups()>, one of which may be |
281 | the same as the first number. | |
a01268b5 | 282 | |
b0c22438 | 283 | However, a value assigned to C<$(> must be a single number used to |
241a59d9 FC |
284 | set the real gid. So the value given by C<$(> should I<not> be assigned |
285 | back to C<$(> without being forced numeric, such as by adding zero. Note | |
b0c22438 | 286 | that this is different to the effective gid (C<$)>) which does take a |
287 | list. | |
fe307981 | 288 | |
b0c22438 | 289 | You can change both the real gid and the effective gid at the same |
241a59d9 FC |
290 | time by using C<POSIX::setgid()>. Changes |
291 | to C<$(> require a check to C<$!> | |
b0c22438 | 292 | to detect any possible errors after an attempted change. |
6cef1e77 | 293 | |
241a59d9 | 294 | Mnemonic: parentheses are used to I<group> things. The real gid is the |
b0c22438 | 295 | group you I<left>, if you're running setgid. |
6cef1e77 | 296 | |
b0c22438 | 297 | =item $EFFECTIVE_GROUP_ID |
8e08999f | 298 | |
b0c22438 | 299 | =item $EGID |
81714fb9 | 300 | |
b0c22438 | 301 | =item $) |
302 | X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID> | |
81714fb9 | 303 | |
241a59d9 | 304 | The effective gid of this process. If you are on a machine that |
b0c22438 | 305 | supports membership in multiple groups simultaneously, gives a space |
241a59d9 | 306 | separated list of groups you are in. The first number is the one |
b0c22438 | 307 | returned by C<getegid()>, and the subsequent ones by C<getgroups()>, |
308 | one of which may be the same as the first number. | |
81714fb9 | 309 | |
b0c22438 | 310 | Similarly, a value assigned to C<$)> must also be a space-separated |
241a59d9 FC |
311 | list of numbers. The first number sets the effective gid, and |
312 | the rest (if any) are passed to C<setgroups()>. To get the effect of an | |
b0c22438 | 313 | empty list for C<setgroups()>, just repeat the new effective gid; that is, |
314 | to force an effective gid of 5 and an effectively empty C<setgroups()> | |
315 | list, say C< $) = "5 5" >. | |
81714fb9 | 316 | |
b0c22438 | 317 | You can change both the effective gid and the real gid at the same |
318 | time by using C<POSIX::setgid()> (use only a single numeric argument). | |
319 | Changes to C<$)> require a check to C<$!> to detect any possible errors | |
320 | after an attempted change. | |
44a2ac75 | 321 | |
b0c22438 | 322 | C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on |
241a59d9 | 323 | machines that support the corresponding I<set[re][ug]id()> routine. C<$(> |
b0c22438 | 324 | and C<$)> can be swapped only on machines supporting C<setregid()>. |
3195cf34 | 325 | |
241a59d9 | 326 | Mnemonic: parentheses are used to I<group> things. The effective gid |
b0c22438 | 327 | is the group that's I<right> for you, if you're running setgid. |
44a2ac75 | 328 | |
c82f2f4e DR |
329 | =item $REAL_USER_ID |
330 | ||
331 | =item $UID | |
332 | ||
333 | =item $< | |
334 | X<< $< >> X<$UID> X<$REAL_USER_ID> | |
335 | ||
241a59d9 FC |
336 | The real uid of this process. You can change both the real uid and the |
337 | effective uid at the same time by using C<POSIX::setuid()>. Since | |
c82f2f4e DR |
338 | changes to C<< $< >> require a system call, check C<$!> after a change |
339 | attempt to detect any possible errors. | |
340 | ||
341 | Mnemonic: it's the uid you came I<from>, if you're running setuid. | |
342 | ||
343 | =item $EFFECTIVE_USER_ID | |
344 | ||
345 | =item $EUID | |
346 | ||
347 | =item $> | |
348 | X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID> | |
349 | ||
241a59d9 | 350 | The effective uid of this process. For example: |
c82f2f4e | 351 | |
9548c15c FC |
352 | $< = $>; # set real to effective uid |
353 | ($<,$>) = ($>,$<); # swap real and effective uids | |
c82f2f4e DR |
354 | |
355 | You can change both the effective uid and the real uid at the same | |
241a59d9 | 356 | time by using C<POSIX::setuid()>. Changes to C<< $> >> require a check |
c82f2f4e DR |
357 | to C<$!> to detect any possible errors after an attempted change. |
358 | ||
359 | C<< $< >> and C<< $> >> can be swapped only on machines | |
360 | supporting C<setreuid()>. | |
361 | ||
362 | Mnemonic: it's the uid you went I<to>, if you're running setuid. | |
363 | ||
0b9346e6 | 364 | =item $SUBSCRIPT_SEPARATOR |
365 | ||
366 | =item $SUBSEP | |
367 | ||
368 | =item $; | |
369 | X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR> | |
370 | ||
241a59d9 | 371 | The subscript separator for multidimensional array emulation. If you |
0b9346e6 | 372 | refer to a hash element as |
373 | ||
592708b4 | 374 | $foo{$x,$y,$z} |
0b9346e6 | 375 | |
376 | it really means | |
377 | ||
592708b4 | 378 | $foo{join($;, $x, $y, $z)} |
0b9346e6 | 379 | |
380 | But don't put | |
381 | ||
592708b4 | 382 | @foo{$x,$y,$z} # a slice--note the @ |
0b9346e6 | 383 | |
384 | which means | |
385 | ||
592708b4 | 386 | ($foo{$x},$foo{$y},$foo{$z}) |
0b9346e6 | 387 | |
241a59d9 | 388 | Default is "\034", the same as SUBSEP in B<awk>. If your keys contain |
0b9346e6 | 389 | binary data there might not be any safe value for C<$;>. |
390 | ||
391 | Consider using "real" multidimensional arrays as described | |
392 | in L<perllol>. | |
393 | ||
394 | Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon. | |
395 | ||
0b9346e6 | 396 | =item $a |
397 | ||
398 | =item $b | |
399 | X<$a> X<$b> | |
400 | ||
401 | Special package variables when using C<sort()>, see L<perlfunc/sort>. | |
402 | Because of this specialness C<$a> and C<$b> don't need to be declared | |
403 | (using C<use vars>, or C<our()>) even when using the C<strict 'vars'> | |
241a59d9 | 404 | pragma. Don't lexicalize them with C<my $a> or C<my $b> if you want to |
0b9346e6 | 405 | be able to use them in the C<sort()> comparison block or function. |
406 | ||
0b9346e6 | 407 | =item %ENV |
408 | X<%ENV> | |
409 | ||
241a59d9 | 410 | The hash C<%ENV> contains your current environment. Setting a |
0b9346e6 | 411 | value in C<ENV> changes the environment for any child processes |
412 | you subsequently C<fork()> off. | |
413 | ||
32e006ac | 414 | As of v5.18.0, both keys and values stored in C<%ENV> are stringified. |
a5effbbc KF |
415 | |
416 | my $foo = 1; | |
417 | $ENV{'bar'} = \$foo; | |
418 | if( ref $ENV{'bar'} ) { | |
32e006ac | 419 | say "Pre 5.18.0 Behaviour"; |
a5effbbc | 420 | } else { |
32e006ac | 421 | say "Post 5.18.0 Behaviour"; |
a5effbbc KF |
422 | } |
423 | ||
424 | Previously, only child processes received stringified values: | |
425 | ||
426 | my $foo = 1; | |
427 | $ENV{'bar'} = \$foo; | |
428 | ||
429 | # Always printed 'non ref' | |
6d3f582d FC |
430 | system($^X, '-e', |
431 | q/print ( ref $ENV{'bar'} ? 'ref' : 'non ref' ) /); | |
a5effbbc KF |
432 | |
433 | This happens because you can't really share arbitrary data structures with | |
434 | foreign processes. | |
435 | ||
b0c22438 | 436 | =item $SYSTEM_FD_MAX |
5b2b9c68 | 437 | |
b0c22438 | 438 | =item $^F |
439 | X<$^F> X<$SYSTEM_FD_MAX> | |
5b2b9c68 | 440 | |
241a59d9 | 441 | The maximum system file descriptor, ordinarily 2. System file |
b0c22438 | 442 | descriptors are passed to C<exec()>ed processes, while higher file |
241a59d9 FC |
443 | descriptors are not. Also, during an |
444 | C<open()>, system file descriptors are | |
b0c22438 | 445 | preserved even if the C<open()> fails (ordinary file descriptors are |
241a59d9 | 446 | closed before the C<open()> is attempted). The close-on-exec |
b0c22438 | 447 | status of a file descriptor will be decided according to the value of |
448 | C<$^F> when the corresponding file, pipe, or socket was opened, not the | |
449 | time of the C<exec()>. | |
5b2b9c68 | 450 | |
0b9346e6 | 451 | =item @F |
452 | X<@F> | |
453 | ||
454 | The array C<@F> contains the fields of each line read in when autosplit | |
241a59d9 | 455 | mode is turned on. See L<perlrun> for the B<-a> switch. This array |
0b9346e6 | 456 | is package-specific, and must be declared or given a full package name |
457 | if not in package main when running under C<strict 'vars'>. | |
458 | ||
0b9346e6 | 459 | =item @INC |
460 | X<@INC> | |
461 | ||
462 | The array C<@INC> contains the list of places that the C<do EXPR>, | |
241a59d9 | 463 | C<require>, or C<use> constructs look for their library files. It |
0b9346e6 | 464 | initially consists of the arguments to any B<-I> command-line |
465 | switches, followed by the default Perl library, probably | |
466 | F</usr/local/lib/perl>, followed by ".", to represent the current | |
241a59d9 | 467 | directory. ("." will not be appended if taint checks are enabled, |
0b9346e6 | 468 | either by C<-T> or by C<-t>.) If you need to modify this at runtime, |
469 | you should use the C<use lib> pragma to get the machine-dependent | |
470 | library properly loaded also: | |
471 | ||
9548c15c FC |
472 | use lib '/mypath/libdir/'; |
473 | use SomeMod; | |
0b9346e6 | 474 | |
475 | You can also insert hooks into the file inclusion system by putting Perl | |
241a59d9 FC |
476 | code directly into C<@INC>. Those hooks may be subroutine references, |
477 | array references or blessed objects. See L<perlfunc/require> for details. | |
0b9346e6 | 478 | |
479 | =item %INC | |
480 | X<%INC> | |
481 | ||
482 | The hash C<%INC> contains entries for each filename included via the | |
241a59d9 | 483 | C<do>, C<require>, or C<use> operators. The key is the filename |
0b9346e6 | 484 | you specified (with module names converted to pathnames), and the |
241a59d9 | 485 | value is the location of the file found. The C<require> |
0b9346e6 | 486 | operator uses this hash to determine whether a particular file has |
487 | already been included. | |
488 | ||
489 | If the file was loaded via a hook (e.g. a subroutine reference, see | |
490 | L<perlfunc/require> for a description of these hooks), this hook is | |
241a59d9 | 491 | by default inserted into C<%INC> in place of a filename. Note, however, |
0b9346e6 | 492 | that the hook may have set the C<%INC> entry by itself to provide some more |
493 | specific info. | |
494 | ||
b0c22438 | 495 | =item $INPLACE_EDIT |
a0d0e21e | 496 | |
b0c22438 | 497 | =item $^I |
498 | X<$^I> X<$INPLACE_EDIT> | |
a0d0e21e | 499 | |
241a59d9 | 500 | The current value of the inplace-edit extension. Use C<undef> to disable |
b0c22438 | 501 | inplace editing. |
a0d0e21e | 502 | |
b0c22438 | 503 | Mnemonic: value of B<-i> switch. |
a0d0e21e | 504 | |
b0c22438 | 505 | =item $^M |
506 | X<$^M> | |
a0d0e21e | 507 | |
b0c22438 | 508 | By default, running out of memory is an untrappable, fatal error. |
509 | However, if suitably built, Perl can use the contents of C<$^M> | |
241a59d9 | 510 | as an emergency memory pool after C<die()>ing. Suppose that your Perl |
b0c22438 | 511 | were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc. |
512 | Then | |
a0d0e21e | 513 | |
9548c15c | 514 | $^M = 'a' x (1 << 16); |
a0d0e21e | 515 | |
241a59d9 | 516 | would allocate a 64K buffer for use in an emergency. See the |
b0c22438 | 517 | F<INSTALL> file in the Perl distribution for information on how to |
241a59d9 | 518 | add custom C compilation flags when compiling perl. To discourage casual |
b0c22438 | 519 | use of this advanced feature, there is no L<English|English> long name for |
520 | this variable. | |
a0d0e21e | 521 | |
b0c22438 | 522 | This variable was added in Perl 5.004. |
a0d0e21e | 523 | |
b0c22438 | 524 | =item $OSNAME |
a0d0e21e | 525 | |
b0c22438 | 526 | =item $^O |
527 | X<$^O> X<$OSNAME> | |
a0d0e21e | 528 | |
b0c22438 | 529 | The name of the operating system under which this copy of Perl was |
241a59d9 | 530 | built, as determined during the configuration process. For examples |
b0c22438 | 531 | see L<perlport/PLATFORMS>. |
a0d0e21e | 532 | |
241a59d9 | 533 | The value is identical to C<$Config{'osname'}>. See also L<Config> |
b0c22438 | 534 | and the B<-V> command-line switch documented in L<perlrun>. |
a0d0e21e | 535 | |
b0c22438 | 536 | In Windows platforms, C<$^O> is not very helpful: since it is always |
537 | C<MSWin32>, it doesn't tell the difference between | |
241a59d9 | 538 | 95/98/ME/NT/2000/XP/CE/.NET. Use C<Win32::GetOSName()> or |
b0c22438 | 539 | Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish |
540 | between the variants. | |
a0d0e21e | 541 | |
b0c22438 | 542 | This variable was added in Perl 5.003. |
a0d0e21e | 543 | |
1fa81471 DR |
544 | =item %SIG |
545 | X<%SIG> | |
a0d0e21e | 546 | |
241a59d9 | 547 | The hash C<%SIG> contains signal handlers for signals. For example: |
a0d0e21e | 548 | |
9548c15c FC |
549 | sub handler { # 1st argument is signal name |
550 | my($sig) = @_; | |
551 | print "Caught a SIG$sig--shutting down\n"; | |
552 | close(LOG); | |
553 | exit(0); | |
554 | } | |
a0d0e21e | 555 | |
9548c15c FC |
556 | $SIG{'INT'} = \&handler; |
557 | $SIG{'QUIT'} = \&handler; | |
558 | ... | |
559 | $SIG{'INT'} = 'DEFAULT'; # restore default action | |
560 | $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT | |
a0d0e21e | 561 | |
1fa81471 | 562 | Using a value of C<'IGNORE'> usually has the effect of ignoring the |
241a59d9 | 563 | signal, except for the C<CHLD> signal. See L<perlipc> for more about |
1fa81471 | 564 | this special case. |
a0d0e21e | 565 | |
1fa81471 | 566 | Here are some other examples: |
a0d0e21e | 567 | |
9548c15c FC |
568 | $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not |
569 | # recommended) | |
570 | $SIG{"PIPE"} = \&Plumber; # just fine; assume current | |
571 | # Plumber | |
572 | $SIG{"PIPE"} = *Plumber; # somewhat esoteric | |
573 | $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() | |
574 | # return?? | |
a0d0e21e | 575 | |
1fa81471 DR |
576 | Be sure not to use a bareword as the name of a signal handler, |
577 | lest you inadvertently call it. | |
a0d0e21e | 578 | |
1fa81471 | 579 | If your system has the C<sigaction()> function then signal handlers |
241a59d9 | 580 | are installed using it. This means you get reliable signal handling. |
a0d0e21e | 581 | |
60cf4914 | 582 | The default delivery policy of signals changed in Perl v5.8.0 from |
1fa81471 | 583 | immediate (also known as "unsafe") to deferred, also known as "safe |
241a59d9 | 584 | signals". See L<perlipc> for more information. |
a0d0e21e | 585 | |
241a59d9 | 586 | Certain internal hooks can be also set using the C<%SIG> hash. The |
1fa81471 | 587 | routine indicated by C<$SIG{__WARN__}> is called when a warning |
241a59d9 FC |
588 | message is about to be printed. The warning message is passed as the |
589 | first argument. The presence of a C<__WARN__> hook causes the | |
590 | ordinary printing of warnings to C<STDERR> to be suppressed. You can | |
1fa81471 DR |
591 | use this to save warnings in a variable, or turn warnings into fatal |
592 | errors, like this: | |
a0d0e21e | 593 | |
9548c15c FC |
594 | local $SIG{__WARN__} = sub { die $_[0] }; |
595 | eval $proggie; | |
a8f8344d | 596 | |
b0c22438 | 597 | As the C<'IGNORE'> hook is not supported by C<__WARN__>, you can |
598 | disable warnings using the empty subroutine: | |
f86702cc | 599 | |
9548c15c | 600 | local $SIG{__WARN__} = sub {}; |
55602bd2 | 601 | |
b0c22438 | 602 | The routine indicated by C<$SIG{__DIE__}> is called when a fatal |
241a59d9 FC |
603 | exception is about to be thrown. The error message is passed as the |
604 | first argument. When a C<__DIE__> hook routine returns, the exception | |
b0c22438 | 605 | processing continues as it would have in the absence of the hook, |
c94b42ea DM |
606 | unless the hook routine itself exits via a C<goto &sub>, a loop exit, |
607 | or a C<die()>. The C<__DIE__> handler is explicitly disabled during | |
608 | the call, so that you can die from a C<__DIE__> handler. Similarly | |
609 | for C<__WARN__>. | |
e5218da5 | 610 | |
b0c22438 | 611 | Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called |
241a59d9 | 612 | even inside an C<eval()>. Do not use this to rewrite a pending |
b0c22438 | 613 | exception in C<$@>, or as a bizarre substitute for overriding |
241a59d9 | 614 | C<CORE::GLOBAL::die()>. This strange action at a distance may be fixed |
b0c22438 | 615 | in a future release so that C<$SIG{__DIE__}> is only called if your |
241a59d9 | 616 | program is about to exit, as was the original intent. Any other use is |
b0c22438 | 617 | deprecated. |
618 | ||
619 | C<__DIE__>/C<__WARN__> handlers are very special in one respect: they | |
241a59d9 | 620 | may be called to report (probable) errors found by the parser. In such |
b0c22438 | 621 | a case the parser may be in inconsistent state, so any attempt to |
622 | evaluate Perl code from such a handler will probably result in a | |
241a59d9 | 623 | segfault. This means that warnings or errors that result from parsing |
b0c22438 | 624 | Perl should be used with extreme caution, like this: |
e5218da5 | 625 | |
9548c15c FC |
626 | require Carp if defined $^S; |
627 | Carp::confess("Something wrong") if defined &Carp::confess; | |
628 | die "Something wrong, but could not load Carp to give " | |
629 | . "backtrace...\n\t" | |
630 | . "To see backtrace try starting Perl with -MCarp switch"; | |
e5218da5 | 631 | |
b0c22438 | 632 | Here the first line will load C<Carp> I<unless> it is the parser who |
241a59d9 FC |
633 | called the handler. The second line will print backtrace and die if |
634 | C<Carp> was available. The third line will be executed only if C<Carp> was | |
b0c22438 | 635 | not available. |
0a378802 | 636 | |
0b9346e6 | 637 | Having to even think about the C<$^S> variable in your exception |
241a59d9 FC |
638 | handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented |
639 | invites grievous and difficult to track down errors. Avoid it | |
0b9346e6 | 640 | and use an C<END{}> or CORE::GLOBAL::die override instead. |
641 | ||
b0c22438 | 642 | See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and |
643 | L<warnings> for additional information. | |
0a378802 | 644 | |
b0c22438 | 645 | =item $BASETIME |
6ab308ee | 646 | |
b0c22438 | 647 | =item $^T |
648 | X<$^T> X<$BASETIME> | |
6ab308ee | 649 | |
b0c22438 | 650 | The time at which the program began running, in seconds since the |
241a59d9 | 651 | epoch (beginning of 1970). The values returned by the B<-M>, B<-A>, |
b0c22438 | 652 | and B<-C> filetests are based on this value. |
a0d0e21e | 653 | |
b0c22438 | 654 | =item $PERL_VERSION |
a0d0e21e | 655 | |
b0c22438 | 656 | =item $^V |
657 | X<$^V> X<$PERL_VERSION> | |
a0d0e21e | 658 | |
b0c22438 | 659 | The revision, version, and subversion of the Perl interpreter, |
660 | represented as a C<version> object. | |
748a9306 | 661 | |
60cf4914 BF |
662 | This variable first appeared in perl v5.6.0; earlier versions of perl |
663 | will see an undefined value. Before perl v5.10.0 C<$^V> was represented | |
b0c22438 | 664 | as a v-string. |
55602bd2 | 665 | |
b0c22438 | 666 | C<$^V> can be used to determine whether the Perl interpreter executing |
241a59d9 | 667 | a script is in the right range of versions. For example: |
a0d0e21e | 668 | |
9548c15c | 669 | warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1 |
a0d0e21e | 670 | |
b0c22438 | 671 | To convert C<$^V> into its string representation use C<sprintf()>'s |
672 | C<"%vd"> conversion: | |
a0d0e21e | 673 | |
9548c15c | 674 | printf "version is v%vd\n", $^V; # Perl's version |
a0d0e21e | 675 | |
b0c22438 | 676 | See the documentation of C<use VERSION> and C<require VERSION> |
677 | for a convenient way to fail if the running Perl interpreter is too old. | |
4d76a344 | 678 | |
b0c22438 | 679 | See also C<$]> for an older representation of the Perl version. |
a0d0e21e | 680 | |
60cf4914 | 681 | This variable was added in Perl v5.6.0. |
a0d0e21e | 682 | |
b0c22438 | 683 | Mnemonic: use ^V for Version Control. |
a0d0e21e | 684 | |
b0c22438 | 685 | =item ${^WIN32_SLOPPY_STAT} |
5b442a2a | 686 | X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl> |
a0d0e21e | 687 | |
b0c22438 | 688 | If this variable is set to a true value, then C<stat()> on Windows will |
241a59d9 | 689 | not try to open the file. This means that the link count cannot be |
b0c22438 | 690 | determined and file attributes may be out of date if additional |
241a59d9 | 691 | hardlinks to the file exist. On the other hand, not opening the file |
b0c22438 | 692 | is considerably faster, especially for files on network drives. |
a0d0e21e | 693 | |
b0c22438 | 694 | This variable could be set in the F<sitecustomize.pl> file to |
695 | configure the local Perl installation to use "sloppy" C<stat()> by | |
241a59d9 | 696 | default. See the documentation for B<-f> in |
b0c22438 | 697 | L<perlrun|perlrun/"Command Switches"> for more information about site |
698 | customization. | |
a0d0e21e | 699 | |
60cf4914 | 700 | This variable was added in Perl v5.10.0. |
a0d0e21e | 701 | |
b0c22438 | 702 | =item $EXECUTABLE_NAME |
a0d0e21e | 703 | |
b0c22438 | 704 | =item $^X |
705 | X<$^X> X<$EXECUTABLE_NAME> | |
a0d0e21e | 706 | |
b0c22438 | 707 | The name used to execute the current copy of Perl, from C's |
708 | C<argv[0]> or (where supported) F</proc/self/exe>. | |
a043a685 | 709 | |
b0c22438 | 710 | Depending on the host operating system, the value of C<$^X> may be |
711 | a relative or absolute pathname of the perl program file, or may | |
712 | be the string used to invoke perl but not the pathname of the | |
241a59d9 | 713 | perl program file. Also, most operating systems permit invoking |
b0c22438 | 714 | programs that are not in the PATH environment variable, so there |
241a59d9 | 715 | is no guarantee that the value of C<$^X> is in PATH. For VMS, the |
b0c22438 | 716 | value may or may not include a version number. |
a0d0e21e | 717 | |
b0c22438 | 718 | You usually can use the value of C<$^X> to re-invoke an independent |
719 | copy of the same perl that is currently running, e.g., | |
a0d0e21e | 720 | |
9548c15c | 721 | @first_run = `$^X -le "print int rand 100 for 1..100"`; |
a0d0e21e | 722 | |
b0c22438 | 723 | But recall that not all operating systems support forking or |
724 | capturing of the output of commands, so this complex statement | |
725 | may not be portable. | |
a0d0e21e | 726 | |
b0c22438 | 727 | It is not safe to use the value of C<$^X> as a path name of a file, |
728 | as some operating systems that have a mandatory suffix on | |
729 | executable files do not require use of the suffix when invoking | |
241a59d9 | 730 | a command. To convert the value of C<$^X> to a path name, use the |
b0c22438 | 731 | following statements: |
8cc95fdb | 732 | |
9548c15c FC |
733 | # Build up a set of file names (not command names). |
734 | use Config; | |
735 | my $this_perl = $^X; | |
736 | if ($^O ne 'VMS') { | |
737 | $this_perl .= $Config{_exe} | |
738 | unless $this_perl =~ m/$Config{_exe}$/i; | |
739 | } | |
8cc95fdb | 740 | |
b0c22438 | 741 | Because many operating systems permit anyone with read access to |
742 | the Perl program file to make a copy of it, patch the copy, and | |
743 | then execute the copy, the security-conscious Perl programmer | |
744 | should take care to invoke the installed copy of perl, not the | |
241a59d9 | 745 | copy referenced by C<$^X>. The following statements accomplish |
b0c22438 | 746 | this goal, and produce a pathname that can be invoked as a |
747 | command or referenced as a file. | |
a043a685 | 748 | |
9548c15c FC |
749 | use Config; |
750 | my $secure_perl_path = $Config{perlpath}; | |
751 | if ($^O ne 'VMS') { | |
752 | $secure_perl_path .= $Config{_exe} | |
753 | unless $secure_perl_path =~ m/$Config{_exe}$/i; | |
754 | } | |
a0d0e21e | 755 | |
b0c22438 | 756 | =back |
a0d0e21e | 757 | |
b0c22438 | 758 | =head2 Variables related to regular expressions |
759 | ||
760 | Most of the special variables related to regular expressions are side | |
241a59d9 FC |
761 | effects. Perl sets these variables when it has a successful match, so |
762 | you should check the match result before using them. For instance: | |
b0c22438 | 763 | |
9548c15c FC |
764 | if( /P(A)TT(ER)N/ ) { |
765 | print "I found $1 and $2\n"; | |
766 | } | |
b0c22438 | 767 | |
0b9346e6 | 768 | These variables are read-only and dynamically-scoped, unless we note |
b0c22438 | 769 | otherwise. |
770 | ||
0b9346e6 | 771 | The dynamic nature of the regular expression variables means that |
772 | their value is limited to the block that they are in, as demonstrated | |
773 | by this bit of code: | |
b0c22438 | 774 | |
9548c15c FC |
775 | my $outer = 'Wallace and Grommit'; |
776 | my $inner = 'Mutt and Jeff'; | |
0b9346e6 | 777 | |
9548c15c | 778 | my $pattern = qr/(\S+) and (\S+)/; |
0b9346e6 | 779 | |
9548c15c | 780 | sub show_n { print "\$1 is $1; \$2 is $2\n" } |
0b9346e6 | 781 | |
9548c15c FC |
782 | { |
783 | OUTER: | |
784 | show_n() if $outer =~ m/$pattern/; | |
0b9346e6 | 785 | |
9548c15c FC |
786 | INNER: { |
787 | show_n() if $inner =~ m/$pattern/; | |
788 | } | |
0b9346e6 | 789 | |
9548c15c FC |
790 | show_n(); |
791 | } | |
b0c22438 | 792 | |
0b9346e6 | 793 | The output shows that while in the C<OUTER> block, the values of C<$1> |
241a59d9 | 794 | and C<$2> are from the match against C<$outer>. Inside the C<INNER> |
0b9346e6 | 795 | block, the values of C<$1> and C<$2> are from the match against |
796 | C<$inner>, but only until the end of the block (i.e. the dynamic | |
241a59d9 | 797 | scope). After the C<INNER> block completes, the values of C<$1> and |
0b9346e6 | 798 | C<$2> return to the values for the match against C<$outer> even though |
b0c22438 | 799 | we have not made another match: |
800 | ||
9548c15c FC |
801 | $1 is Wallace; $2 is Grommit |
802 | $1 is Mutt; $2 is Jeff | |
803 | $1 is Wallace; $2 is Grommit | |
a0d0e21e | 804 | |
40445027 | 805 | =head3 Performance issues |
0b9346e6 | 806 | |
40445027 DM |
807 | Traditionally in Perl, any use of any of the three variables C<$`>, C<$&> |
808 | or C<$'> (or their C<use English> equivalents) anywhere in the code, caused | |
809 | all subsequent successful pattern matches to make a copy of the matched | |
810 | string, in case the code might subsequently access one of those variables. | |
811 | This imposed a considerable performance penalty across the whole program, | |
812 | so generally the use of these variables has been discouraged. | |
0b9346e6 | 813 | |
40445027 DM |
814 | In Perl 5.6.0 the C<@-> and C<@+> dynamic arrays were introduced that |
815 | supply the indices of successful matches. So you could for example do | |
816 | this: | |
817 | ||
818 | $str =~ /pattern/; | |
819 | ||
820 | print $`, $&, $'; # bad: perfomance hit | |
821 | ||
822 | print # good: no perfomance hit | |
823 | substr($str, 0, $-[0]), | |
824 | substr($str, $-[0], $+[0]-$-[0]), | |
825 | substr($str, $+[0]); | |
826 | ||
827 | In Perl 5.10.0 the C</p> match operator flag and the C<${^PREMATCH}>, | |
828 | C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed | |
829 | you to suffer the penalties only on patterns marked with C</p>. | |
830 | ||
831 | In Perl 5.18.0 onwards, perl started noting the presence of each of the | |
832 | three variables separately, and only copied that part of the string | |
833 | required; so in | |
834 | ||
835 | $`; $&; "abcdefgh" =~ /d/ | |
836 | ||
837 | perl would only copy the "abcd" part of the string. That could make a big | |
838 | difference in something like | |
839 | ||
840 | $str = 'x' x 1_000_000; | |
841 | $&; # whoops | |
842 | $str =~ /x/g # one char copied a million times, not a million chars | |
843 | ||
844 | In Perl 5.20.0 a new copy-on-write system was enabled by default, which | |
845 | finally fixes all performance issues with these three variables, and makes | |
846 | them safe to use anywhere. | |
847 | ||
848 | The C<Devel::NYTProf> and C<Devel::FindAmpersand> modules can help you | |
849 | find uses of these problematic match variables in your code. | |
13b0f67d | 850 | |
b0c22438 | 851 | =over 8 |
a0d0e21e | 852 | |
b0c22438 | 853 | =item $<I<digits>> ($1, $2, ...) |
854 | X<$1> X<$2> X<$3> | |
8cc95fdb | 855 | |
b0c22438 | 856 | Contains the subpattern from the corresponding set of capturing |
857 | parentheses from the last successful pattern match, not counting patterns | |
858 | matched in nested blocks that have been exited already. | |
8cc95fdb | 859 | |
b0c22438 | 860 | These variables are read-only and dynamically-scoped. |
a043a685 | 861 | |
b0c22438 | 862 | Mnemonic: like \digits. |
a0d0e21e | 863 | |
b0c22438 | 864 | =item $MATCH |
a0d0e21e | 865 | |
b0c22438 | 866 | =item $& |
867 | X<$&> X<$MATCH> | |
a0d0e21e | 868 | |
b0c22438 | 869 | The string matched by the last successful pattern match (not counting |
870 | any matches hidden within a BLOCK or C<eval()> enclosed by the current | |
871 | BLOCK). | |
a0d0e21e | 872 | |
40445027 DM |
873 | See L</Performance issues> above for the serious performance implications |
874 | of using this variable (even once) in your code. | |
80bca1b4 | 875 | |
b0c22438 | 876 | This variable is read-only and dynamically-scoped. |
f9cbb277 | 877 | |
b0c22438 | 878 | Mnemonic: like C<&> in some editors. |
0b9346e6 | 879 | |
b0c22438 | 880 | =item ${^MATCH} |
881 | X<${^MATCH}> | |
a0d0e21e | 882 | |
b0c22438 | 883 | This is similar to C<$&> (C<$MATCH>) except that it does not incur the |
13b0f67d | 884 | performance penalty associated with that variable. |
40445027 DM |
885 | |
886 | See L</Performance issues> above. | |
887 | ||
13b0f67d | 888 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 889 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
890 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
891 | C<${^MATCH}> does the same thing as C<$MATCH>. | |
80bca1b4 | 892 | |
60cf4914 | 893 | This variable was added in Perl v5.10.0. |
4bc88a62 | 894 | |
b0c22438 | 895 | This variable is read-only and dynamically-scoped. |
e2975953 | 896 | |
b0c22438 | 897 | =item $PREMATCH |
52c447a8 | 898 | |
b0c22438 | 899 | =item $` |
5b442a2a | 900 | X<$`> X<$PREMATCH> X<${^PREMATCH}> |
7636ea95 | 901 | |
b0c22438 | 902 | The string preceding whatever was matched by the last successful |
903 | pattern match, not counting any matches hidden within a BLOCK or C<eval> | |
0b9346e6 | 904 | enclosed by the current BLOCK. |
a0d0e21e | 905 | |
40445027 DM |
906 | See L</Performance issues> above for the serious performance implications |
907 | of using this variable (even once) in your code. | |
a0d0e21e | 908 | |
b0c22438 | 909 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 910 | |
b0c22438 | 911 | Mnemonic: C<`> often precedes a quoted string. |
f83ed198 | 912 | |
b0c22438 | 913 | =item ${^PREMATCH} |
5b442a2a | 914 | X<$`> X<${^PREMATCH}> |
a0d0e21e | 915 | |
b0c22438 | 916 | This is similar to C<$`> ($PREMATCH) except that it does not incur the |
13b0f67d | 917 | performance penalty associated with that variable. |
40445027 DM |
918 | |
919 | See L</Performance issues> above. | |
920 | ||
13b0f67d | 921 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 922 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
923 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
924 | C<${^PREMATCH}> does the same thing as C<$PREMATCH>. | |
a0d0e21e | 925 | |
4a70680a | 926 | This variable was added in Perl v5.10.0. |
a0d0e21e | 927 | |
b0c22438 | 928 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 929 | |
b0c22438 | 930 | =item $POSTMATCH |
16070b82 | 931 | |
b0c22438 | 932 | =item $' |
5b442a2a | 933 | X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@-> |
305aace0 | 934 | |
b0c22438 | 935 | The string following whatever was matched by the last successful |
936 | pattern match (not counting any matches hidden within a BLOCK or C<eval()> | |
241a59d9 | 937 | enclosed by the current BLOCK). Example: |
305aace0 | 938 | |
9548c15c FC |
939 | local $_ = 'abcdefghi'; |
940 | /def/; | |
941 | print "$`:$&:$'\n"; # prints abc:def:ghi | |
305aace0 | 942 | |
40445027 DM |
943 | See L</Performance issues> above for the serious performance implications |
944 | of using this variable (even once) in your code. | |
a0d0e21e | 945 | |
b0c22438 | 946 | This variable is read-only and dynamically-scoped. |
947 | ||
948 | Mnemonic: C<'> often follows a quoted string. | |
949 | ||
950 | =item ${^POSTMATCH} | |
5b442a2a | 951 | X<${^POSTMATCH}> X<$'> X<$POSTMATCH> |
b0c22438 | 952 | |
953 | This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the | |
13b0f67d | 954 | performance penalty associated with that variable. |
40445027 DM |
955 | |
956 | See L</Performance issues> above. | |
957 | ||
13b0f67d | 958 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 959 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
960 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
961 | C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>. | |
b0c22438 | 962 | |
60cf4914 | 963 | This variable was added in Perl v5.10.0. |
b0c22438 | 964 | |
965 | This variable is read-only and dynamically-scoped. | |
966 | ||
967 | =item $LAST_PAREN_MATCH | |
968 | ||
969 | =item $+ | |
970 | X<$+> X<$LAST_PAREN_MATCH> | |
971 | ||
972 | The text matched by the last bracket of the last successful search pattern. | |
973 | This is useful if you don't know which one of a set of alternative patterns | |
241a59d9 | 974 | matched. For example: |
b0c22438 | 975 | |
9548c15c | 976 | /Version: (.*)|Revision: (.*)/ && ($rev = $+); |
b0c22438 | 977 | |
978 | This variable is read-only and dynamically-scoped. | |
979 | ||
980 | Mnemonic: be positive and forward looking. | |
981 | ||
982 | =item $LAST_SUBMATCH_RESULT | |
983 | ||
984 | =item $^N | |
5b442a2a | 985 | X<$^N> X<$LAST_SUBMATCH_RESULT> |
b0c22438 | 986 | |
987 | The text matched by the used group most-recently closed (i.e. the group | |
988 | with the rightmost closing parenthesis) of the last successful search | |
989 | pattern. | |
990 | ||
991 | This is primarily used inside C<(?{...})> blocks for examining text | |
241a59d9 | 992 | recently matched. For example, to effectively capture text to a variable |
b0c22438 | 993 | (in addition to C<$1>, C<$2>, etc.), replace C<(...)> with |
994 | ||
9548c15c | 995 | (?:(...)(?{ $var = $^N })) |
b0c22438 | 996 | |
997 | By setting and then using C<$var> in this way relieves you from having to | |
998 | worry about exactly which numbered set of parentheses they are. | |
999 | ||
60cf4914 | 1000 | This variable was added in Perl v5.8.0. |
b0c22438 | 1001 | |
1002 | Mnemonic: the (possibly) Nested parenthesis that most recently closed. | |
1003 | ||
1004 | =item @LAST_MATCH_END | |
1005 | ||
1006 | =item @+ | |
1007 | X<@+> X<@LAST_MATCH_END> | |
1008 | ||
1009 | This array holds the offsets of the ends of the last successful | |
241a59d9 FC |
1010 | submatches in the currently active dynamic scope. C<$+[0]> is |
1011 | the offset into the string of the end of the entire match. This | |
b0c22438 | 1012 | is the same value as what the C<pos> function returns when called |
241a59d9 | 1013 | on the variable that was matched against. The I<n>th element |
b0c22438 | 1014 | of this array holds the offset of the I<n>th submatch, so |
1015 | C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset | |
241a59d9 FC |
1016 | past where C<$2> ends, and so on. You can use C<$#+> to determine |
1017 | how many subgroups were in the last successful match. See the | |
b0c22438 | 1018 | examples given for the C<@-> variable. |
1019 | ||
60cf4914 | 1020 | This variable was added in Perl v5.6.0. |
b0c22438 | 1021 | |
1022 | =item %LAST_PAREN_MATCH | |
1023 | ||
1024 | =item %+ | |
5b442a2a | 1025 | X<%+> X<%LAST_PAREN_MATCH> |
b0c22438 | 1026 | |
1027 | Similar to C<@+>, the C<%+> hash allows access to the named capture | |
1028 | buffers, should they exist, in the last successful match in the | |
1029 | currently active dynamic scope. | |
1030 | ||
1031 | For example, C<$+{foo}> is equivalent to C<$1> after the following match: | |
1032 | ||
9548c15c | 1033 | 'foo' =~ /(?<foo>foo)/; |
b0c22438 | 1034 | |
1035 | The keys of the C<%+> hash list only the names of buffers that have | |
1036 | captured (and that are thus associated to defined values). | |
1037 | ||
1038 | The underlying behaviour of C<%+> is provided by the | |
1039 | L<Tie::Hash::NamedCapture> module. | |
1040 | ||
1041 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1042 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1043 | iterative access to them via C<each> may have unpredictable results. |
1044 | Likewise, if the last successful match changes, then the results may be | |
1045 | surprising. | |
1046 | ||
60cf4914 | 1047 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1048 | |
b0c22438 | 1049 | This variable is read-only and dynamically-scoped. |
1050 | ||
1051 | =item @LAST_MATCH_START | |
1052 | ||
1053 | =item @- | |
1054 | X<@-> X<@LAST_MATCH_START> | |
1055 | ||
1056 | C<$-[0]> is the offset of the start of the last successful match. | |
1057 | C<$-[>I<n>C<]> is the offset of the start of the substring matched by | |
1058 | I<n>-th subpattern, or undef if the subpattern did not match. | |
1059 | ||
1060 | Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0], | |
241a59d9 | 1061 | $+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n], |
b0c22438 | 1062 | $+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with |
241a59d9 FC |
1063 | C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the |
1064 | last matched subgroup in the last successful match. Contrast with | |
1065 | C<$#+>, the number of subgroups in the regular expression. Compare | |
b0c22438 | 1066 | with C<@+>. |
1067 | ||
1068 | This array holds the offsets of the beginnings of the last | |
1069 | successful submatches in the currently active dynamic scope. | |
1070 | C<$-[0]> is the offset into the string of the beginning of the | |
241a59d9 | 1071 | entire match. The I<n>th element of this array holds the offset |
b0c22438 | 1072 | of the I<n>th submatch, so C<$-[1]> is the offset where C<$1> |
1073 | begins, C<$-[2]> the offset where C<$2> begins, and so on. | |
1074 | ||
1075 | After a match against some variable C<$var>: | |
1076 | ||
1077 | =over 5 | |
1078 | ||
1079 | =item C<$`> is the same as C<substr($var, 0, $-[0])> | |
1080 | ||
1081 | =item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])> | |
1082 | ||
1083 | =item C<$'> is the same as C<substr($var, $+[0])> | |
1084 | ||
1085 | =item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])> | |
1086 | ||
1087 | =item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])> | |
1088 | ||
1089 | =item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])> | |
1090 | ||
1091 | =back | |
1092 | ||
60cf4914 | 1093 | This variable was added in Perl v5.6.0. |
b0c22438 | 1094 | |
5b442a2a | 1095 | =item %LAST_MATCH_START |
1096 | ||
b0c22438 | 1097 | =item %- |
5b442a2a | 1098 | X<%-> X<%LAST_MATCH_START> |
b0c22438 | 1099 | |
1100 | Similar to C<%+>, this variable allows access to the named capture groups | |
241a59d9 | 1101 | in the last successful match in the currently active dynamic scope. To |
b0c22438 | 1102 | each capture group name found in the regular expression, it associates a |
1103 | reference to an array containing the list of values captured by all | |
1104 | buffers with that name (should there be several of them), in the order | |
1105 | where they appear. | |
1106 | ||
1107 | Here's an example: | |
1108 | ||
1109 | if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) { | |
1110 | foreach my $bufname (sort keys %-) { | |
1111 | my $ary = $-{$bufname}; | |
1112 | foreach my $idx (0..$#$ary) { | |
1113 | print "\$-{$bufname}[$idx] : ", | |
9548c15c FC |
1114 | (defined($ary->[$idx]) |
1115 | ? "'$ary->[$idx]'" | |
1116 | : "undef"), | |
b0c22438 | 1117 | "\n"; |
1118 | } | |
1119 | } | |
1120 | } | |
1121 | ||
1122 | would print out: | |
1123 | ||
9548c15c FC |
1124 | $-{A}[0] : '1' |
1125 | $-{A}[1] : '3' | |
1126 | $-{B}[0] : '2' | |
1127 | $-{B}[1] : '4' | |
b0c22438 | 1128 | |
1129 | The keys of the C<%-> hash correspond to all buffer names found in | |
1130 | the regular expression. | |
1131 | ||
1132 | The behaviour of C<%-> is implemented via the | |
1133 | L<Tie::Hash::NamedCapture> module. | |
1134 | ||
1135 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1136 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1137 | iterative access to them via C<each> may have unpredictable results. |
1138 | Likewise, if the last successful match changes, then the results may be | |
1139 | surprising. | |
1140 | ||
60cf4914 | 1141 | This variable was added in Perl v5.10.0. |
b0c22438 | 1142 | |
1143 | This variable is read-only and dynamically-scoped. | |
1144 | ||
1145 | =item $LAST_REGEXP_CODE_RESULT | |
1146 | ||
1147 | =item $^R | |
1148 | X<$^R> X<$LAST_REGEXP_CODE_RESULT> | |
1149 | ||
1150 | The result of evaluation of the last successful C<(?{ code })> | |
241a59d9 | 1151 | regular expression assertion (see L<perlre>). May be written to. |
b0c22438 | 1152 | |
1153 | This variable was added in Perl 5.005. | |
a0d0e21e | 1154 | |
a3621e74 | 1155 | =item ${^RE_DEBUG_FLAGS} |
ca1b95ae | 1156 | X<${^RE_DEBUG_FLAGS}> |
a3621e74 | 1157 | |
241a59d9 FC |
1158 | The current value of the regex debugging flags. Set to 0 for no debug output |
1159 | even when the C<re 'debug'> module is loaded. See L<re> for details. | |
b0c22438 | 1160 | |
60cf4914 | 1161 | This variable was added in Perl v5.10.0. |
a3621e74 | 1162 | |
0111c4fd | 1163 | =item ${^RE_TRIE_MAXBUF} |
ca1b95ae | 1164 | X<${^RE_TRIE_MAXBUF}> |
a3621e74 YO |
1165 | |
1166 | Controls how certain regex optimisations are applied and how much memory they | |
241a59d9 FC |
1167 | utilize. This value by default is 65536 which corresponds to a 512kB |
1168 | temporary cache. Set this to a higher value to trade | |
1169 | memory for speed when matching large alternations. Set | |
1170 | it to a lower value if you want the optimisations to | |
a3621e74 YO |
1171 | be as conservative of memory as possible but still occur, and set it to a |
1172 | negative value to prevent the optimisation and conserve the most memory. | |
1173 | Under normal situations this variable should be of no interest to you. | |
1174 | ||
60cf4914 | 1175 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1176 | |
b0c22438 | 1177 | =back |
a0d0e21e | 1178 | |
b0c22438 | 1179 | =head2 Variables related to filehandles |
a0d0e21e | 1180 | |
b0c22438 | 1181 | Variables that depend on the currently selected filehandle may be set |
1182 | by calling an appropriate object method on the C<IO::Handle> object, | |
1183 | although this is less efficient than using the regular built-in | |
241a59d9 | 1184 | variables. (Summary lines below for this contain the word HANDLE.) |
b0c22438 | 1185 | First you must say |
6e2995f4 | 1186 | |
9548c15c | 1187 | use IO::Handle; |
0462a1ab | 1188 | |
b0c22438 | 1189 | after which you may use either |
0462a1ab | 1190 | |
9548c15c | 1191 | method HANDLE EXPR |
0462a1ab | 1192 | |
b0c22438 | 1193 | or more safely, |
0462a1ab | 1194 | |
9548c15c | 1195 | HANDLE->method(EXPR) |
0462a1ab | 1196 | |
241a59d9 | 1197 | Each method returns the old value of the C<IO::Handle> attribute. The |
b0c22438 | 1198 | methods each take an optional EXPR, which, if supplied, specifies the |
241a59d9 | 1199 | new value for the C<IO::Handle> attribute in question. If not |
b0c22438 | 1200 | supplied, most methods do nothing to the current value--except for |
1201 | C<autoflush()>, which will assume a 1 for you, just to be different. | |
0462a1ab | 1202 | |
b0c22438 | 1203 | Because loading in the C<IO::Handle> class is an expensive operation, |
1204 | you should learn how to use the regular built-in variables. | |
1205 | ||
241a59d9 | 1206 | A few of these variables are considered "read-only". This means that |
b0c22438 | 1207 | if you try to assign to this variable, either directly or indirectly |
1208 | through a reference, you'll raise a run-time exception. | |
1209 | ||
1210 | You should be very careful when modifying the default values of most | |
241a59d9 | 1211 | special variables described in this document. In most cases you want |
b0c22438 | 1212 | to localize these variables before changing them, since if you don't, |
1213 | the change may affect other modules which rely on the default values | |
241a59d9 | 1214 | of the special variables that you have changed. This is one of the |
b0c22438 | 1215 | correct ways to read the whole file at once: |
1216 | ||
9548c15c FC |
1217 | open my $fh, "<", "foo" or die $!; |
1218 | local $/; # enable localized slurp mode | |
1219 | my $content = <$fh>; | |
1220 | close $fh; | |
b0c22438 | 1221 | |
1222 | But the following code is quite bad: | |
1223 | ||
9548c15c FC |
1224 | open my $fh, "<", "foo" or die $!; |
1225 | undef $/; # enable slurp mode | |
1226 | my $content = <$fh>; | |
1227 | close $fh; | |
b0c22438 | 1228 | |
1229 | since some other module, may want to read data from some file in the | |
1230 | default "line mode", so if the code we have just presented has been | |
1231 | executed, the global value of C<$/> is now changed for any other code | |
1232 | running inside the same Perl interpreter. | |
1233 | ||
1234 | Usually when a variable is localized you want to make sure that this | |
241a59d9 FC |
1235 | change affects the shortest scope possible. So unless you are already |
1236 | inside some short C<{}> block, you should create one yourself. For | |
b0c22438 | 1237 | example: |
1238 | ||
9548c15c FC |
1239 | my $content = ''; |
1240 | open my $fh, "<", "foo" or die $!; | |
1241 | { | |
1242 | local $/; | |
1243 | $content = <$fh>; | |
1244 | } | |
1245 | close $fh; | |
0462a1ab | 1246 | |
b0c22438 | 1247 | Here is an example of how your own code can go broken: |
0462a1ab | 1248 | |
9548c15c FC |
1249 | for ( 1..3 ){ |
1250 | $\ = "\r\n"; | |
1251 | nasty_break(); | |
1252 | print "$_"; | |
1253 | } | |
0b9346e6 | 1254 | |
9548c15c | 1255 | sub nasty_break { |
0b9346e6 | 1256 | $\ = "\f"; |
1257 | # do something with $_ | |
9548c15c | 1258 | } |
0462a1ab | 1259 | |
0b9346e6 | 1260 | You probably expect this code to print the equivalent of |
0462a1ab | 1261 | |
0b9346e6 | 1262 | "1\r\n2\r\n3\r\n" |
0462a1ab | 1263 | |
b0c22438 | 1264 | but instead you get: |
0462a1ab | 1265 | |
0b9346e6 | 1266 | "1\f2\f3\f" |
0462a1ab | 1267 | |
0b9346e6 | 1268 | Why? Because C<nasty_break()> modifies C<$\> without localizing it |
241a59d9 FC |
1269 | first. The value you set in C<nasty_break()> is still there when you |
1270 | return. The fix is to add C<local()> so the value doesn't leak out of | |
0b9346e6 | 1271 | C<nasty_break()>: |
6e2995f4 | 1272 | |
9548c15c | 1273 | local $\ = "\f"; |
a0d0e21e | 1274 | |
b0c22438 | 1275 | It's easy to notice the problem in such a short example, but in more |
1276 | complicated code you are looking for trouble if you don't localize | |
1277 | changes to the special variables. | |
a0d0e21e | 1278 | |
b0c22438 | 1279 | =over 8 |
a0d0e21e | 1280 | |
b0c22438 | 1281 | =item $ARGV |
1282 | X<$ARGV> | |
fb73857a | 1283 | |
ca1b95ae | 1284 | Contains the name of the current file when reading from C<< <> >>. |
b0c22438 | 1285 | |
1286 | =item @ARGV | |
1287 | X<@ARGV> | |
1288 | ||
ca1b95ae | 1289 | The array C<@ARGV> contains the command-line arguments intended for |
241a59d9 | 1290 | the script. C<$#ARGV> is generally the number of arguments minus |
b0c22438 | 1291 | one, because C<$ARGV[0]> is the first argument, I<not> the program's |
241a59d9 | 1292 | command name itself. See L</$0> for the command name. |
b0c22438 | 1293 | |
84dabc03 | 1294 | =item ARGV |
1295 | X<ARGV> | |
1296 | ||
1297 | The special filehandle that iterates over command-line filenames in | |
241a59d9 FC |
1298 | C<@ARGV>. Usually written as the null filehandle in the angle operator |
1299 | C<< <> >>. Note that currently C<ARGV> only has its magical effect | |
84dabc03 | 1300 | within the C<< <> >> operator; elsewhere it is just a plain filehandle |
241a59d9 | 1301 | corresponding to the last file opened by C<< <> >>. In particular, |
84dabc03 | 1302 | passing C<\*ARGV> as a parameter to a function that expects a filehandle |
1303 | may not cause your function to automatically read the contents of all the | |
1304 | files in C<@ARGV>. | |
1305 | ||
b0c22438 | 1306 | =item ARGVOUT |
1307 | X<ARGVOUT> | |
1308 | ||
1309 | The special filehandle that points to the currently open output file | |
241a59d9 FC |
1310 | when doing edit-in-place processing with B<-i>. Useful when you have |
1311 | to do a lot of inserting and don't want to keep modifying C<$_>. See | |
b0c22438 | 1312 | L<perlrun> for the B<-i> switch. |
1313 | ||
96948506 | 1314 | =item IO::Handle->output_field_separator( EXPR ) |
84dabc03 | 1315 | |
1316 | =item $OUTPUT_FIELD_SEPARATOR | |
1317 | ||
1318 | =item $OFS | |
1319 | ||
1320 | =item $, | |
1321 | X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR> | |
1322 | ||
241a59d9 FC |
1323 | The output field separator for the print operator. If defined, this |
1324 | value is printed between each of print's arguments. Default is C<undef>. | |
84dabc03 | 1325 | |
96948506 | 1326 | You cannot call C<output_field_separator()> on a handle, only as a |
008f9687 | 1327 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1328 | |
84dabc03 | 1329 | Mnemonic: what is printed when there is a "," in your print statement. |
1330 | ||
5b442a2a | 1331 | =item HANDLE->input_line_number( EXPR ) |
b0c22438 | 1332 | |
1333 | =item $INPUT_LINE_NUMBER | |
1334 | ||
1335 | =item $NR | |
1336 | ||
1337 | =item $. | |
1338 | X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number> | |
1339 | ||
1340 | Current line number for the last filehandle accessed. | |
1341 | ||
1342 | Each filehandle in Perl counts the number of lines that have been read | |
241a59d9 | 1343 | from it. (Depending on the value of C<$/>, Perl's idea of what |
b0c22438 | 1344 | constitutes a line may not match yours.) When a line is read from a |
1345 | filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or | |
1346 | C<seek()> is called on it, C<$.> becomes an alias to the line counter | |
1347 | for that filehandle. | |
1348 | ||
1349 | You can adjust the counter by assigning to C<$.>, but this will not | |
241a59d9 FC |
1350 | actually move the seek pointer. I<Localizing C<$.> will not localize |
1351 | the filehandle's line count>. Instead, it will localize perl's notion | |
b0c22438 | 1352 | of which filehandle C<$.> is currently aliased to. |
1353 | ||
1354 | C<$.> is reset when the filehandle is closed, but B<not> when an open | |
241a59d9 FC |
1355 | filehandle is reopened without an intervening C<close()>. For more |
1356 | details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does | |
b0c22438 | 1357 | an explicit close, line numbers increase across C<ARGV> files (but see |
1358 | examples in L<perlfunc/eof>). | |
1359 | ||
1360 | You can also use C<< HANDLE->input_line_number(EXPR) >> to access the | |
1361 | line counter for a given filehandle without having to worry about | |
1362 | which handle you last accessed. | |
1363 | ||
1364 | Mnemonic: many programs use "." to mean the current line number. | |
1365 | ||
96948506 | 1366 | =item IO::Handle->input_record_separator( EXPR ) |
b0c22438 | 1367 | |
1368 | =item $INPUT_RECORD_SEPARATOR | |
1369 | ||
1370 | =item $RS | |
1371 | ||
1372 | =item $/ | |
1373 | X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR> | |
1374 | ||
241a59d9 FC |
1375 | The input record separator, newline by default. This influences Perl's |
1376 | idea of what a "line" is. Works like B<awk>'s RS variable, including | |
84dabc03 | 1377 | treating empty lines as a terminator if set to the null string (an |
241a59d9 | 1378 | empty line cannot contain any spaces or tabs). You may set it to a |
84dabc03 | 1379 | multi-character string to match a multi-character terminator, or to |
241a59d9 | 1380 | C<undef> to read through the end of file. Setting it to C<"\n\n"> |
84dabc03 | 1381 | means something slightly different than setting to C<"">, if the file |
241a59d9 FC |
1382 | contains consecutive empty lines. Setting to C<""> will treat two or |
1383 | more consecutive empty lines as a single empty line. Setting to | |
84dabc03 | 1384 | C<"\n\n"> will blindly assume that the next input character belongs to |
1385 | the next paragraph, even if it's a newline. | |
b0c22438 | 1386 | |
1387 | local $/; # enable "slurp" mode | |
1388 | local $_ = <FH>; # whole file now here | |
1389 | s/\n[ \t]+/ /g; | |
1390 | ||
241a59d9 | 1391 | Remember: the value of C<$/> is a string, not a regex. B<awk> has to |
b0c22438 | 1392 | be better for something. :-) |
1393 | ||
1394 | Setting C<$/> to a reference to an integer, scalar containing an | |
1395 | integer, or scalar that's convertible to an integer will attempt to | |
1396 | read records instead of lines, with the maximum record size being the | |
3d249121 | 1397 | referenced integer number of characters. So this: |
b0c22438 | 1398 | |
1399 | local $/ = \32768; # or \"32768", or \$var_containing_32768 | |
1400 | open my $fh, "<", $myfile or die $!; | |
1401 | local $_ = <$fh>; | |
fb73857a | 1402 | |
f1ee460b | 1403 | will read a record of no more than 32768 characters from $fh. If you're |
b0c22438 | 1404 | not reading from a record-oriented file (or your OS doesn't have |
1405 | record-oriented files), then you'll likely get a full chunk of data | |
241a59d9 FC |
1406 | with every read. If a record is larger than the record size you've |
1407 | set, you'll get the record back in pieces. Trying to set the record | |
b3a2acfa YO |
1408 | size to zero or less is deprecated and will cause $/ to have the value |
1409 | of "undef", which will cause reading in the (rest of the) whole file. | |
1410 | ||
1411 | As of 5.19.9 setting C<$/> to any other form of reference will throw a | |
1412 | fatal exception. This is in preparation for supporting new ways to set | |
1413 | C<$/> in the future. | |
6e2995f4 | 1414 | |
78c28381 | 1415 | On VMS only, record reads bypass PerlIO layers and any associated |
3d249121 | 1416 | buffering, so you must not mix record and non-record reads on the |
78c28381 CB |
1417 | same filehandle. Record mode mixes with line mode only when the |
1418 | same buffering layer is in use for both modes. | |
5c055ba3 | 1419 | |
96948506 | 1420 | You cannot call C<input_record_separator()> on a handle, only as a |
008f9687 | 1421 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1422 | |
008f9687 | 1423 | See also L<perlport/"Newlines">. Also see L</$.>. |
9bf22702 | 1424 | |
b0c22438 | 1425 | Mnemonic: / delimits line boundaries when quoting poetry. |
5c055ba3 | 1426 | |
96948506 | 1427 | =item IO::Handle->output_record_separator( EXPR ) |
84902520 | 1428 | |
b0c22438 | 1429 | =item $OUTPUT_RECORD_SEPARATOR |
84902520 | 1430 | |
b0c22438 | 1431 | =item $ORS |
84902520 | 1432 | |
b0c22438 | 1433 | =item $\ |
1434 | X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR> | |
84902520 | 1435 | |
241a59d9 FC |
1436 | The output record separator for the print operator. If defined, this |
1437 | value is printed after the last of print's arguments. Default is C<undef>. | |
84902520 | 1438 | |
96948506 | 1439 | You cannot call C<output_record_separator()> on a handle, only as a |
008f9687 | 1440 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1441 | |
b0c22438 | 1442 | Mnemonic: you set C<$\> instead of adding "\n" at the end of the print. |
1443 | Also, it's just like C<$/>, but it's what you get "back" from Perl. | |
84902520 | 1444 | |
5b442a2a | 1445 | =item HANDLE->autoflush( EXPR ) |
1446 | ||
1447 | =item $OUTPUT_AUTOFLUSH | |
1448 | ||
84dabc03 | 1449 | =item $| |
1450 | X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH> | |
84902520 | 1451 | |
84dabc03 | 1452 | If set to nonzero, forces a flush right away and after every write or |
241a59d9 | 1453 | print on the currently selected output channel. Default is 0 |
84dabc03 | 1454 | (regardless of whether the channel is really buffered by the system or |
1455 | not; C<$|> tells you only whether you've asked Perl explicitly to | |
241a59d9 FC |
1456 | flush after each write). STDOUT will typically be line buffered if |
1457 | output is to the terminal and block buffered otherwise. Setting this | |
84dabc03 | 1458 | variable is useful primarily when you are outputting to a pipe or |
1459 | socket, such as when you are running a Perl program under B<rsh> and | |
241a59d9 FC |
1460 | want to see the output as it's happening. This has no effect on input |
1461 | buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on | |
1462 | how to select the output channel. See also L<IO::Handle>. | |
84dabc03 | 1463 | |
1464 | Mnemonic: when you want your pipes to be piping hot. | |
1465 | ||
8561ea1d FC |
1466 | =item ${^LAST_FH} |
1467 | X<${^LAST_FH}> | |
1468 | ||
1469 | This read-only variable contains a reference to the last-read filehandle. | |
1470 | This is set by C<< <HANDLE> >>, C<readline>, C<tell>, C<eof> and C<seek>. | |
1471 | This is the same handle that C<$.> and C<tell> and C<eof> without arguments | |
1472 | use. It is also the handle used when Perl appends ", <STDIN> line 1" to | |
1473 | an error or warning message. | |
1474 | ||
1475 | This variable was added in Perl v5.18.0. | |
1476 | ||
84dabc03 | 1477 | =back |
84902520 | 1478 | |
b0c22438 | 1479 | =head3 Variables related to formats |
83ee9e09 | 1480 | |
b0c22438 | 1481 | The special variables for formats are a subset of those for |
241a59d9 | 1482 | filehandles. See L<perlform> for more information about Perl's |
69b55ccc | 1483 | formats. |
83ee9e09 | 1484 | |
b0c22438 | 1485 | =over 8 |
83ee9e09 | 1486 | |
84dabc03 | 1487 | =item $ACCUMULATOR |
1488 | ||
1489 | =item $^A | |
1490 | X<$^A> X<$ACCUMULATOR> | |
1491 | ||
1492 | The current value of the C<write()> accumulator for C<format()> lines. | |
1493 | A format contains C<formline()> calls that put their result into | |
241a59d9 FC |
1494 | C<$^A>. After calling its format, C<write()> prints out the contents |
1495 | of C<$^A> and empties. So you never really see the contents of C<$^A> | |
1496 | unless you call C<formline()> yourself and then look at it. See | |
96090e4f | 1497 | L<perlform> and L<perlfunc/"formline PICTURE,LIST">. |
84dabc03 | 1498 | |
96948506 | 1499 | =item IO::Handle->format_formfeed(EXPR) |
5b442a2a | 1500 | |
1501 | =item $FORMAT_FORMFEED | |
1502 | ||
84dabc03 | 1503 | =item $^L |
1504 | X<$^L> X<$FORMAT_FORMFEED> | |
1505 | ||
241a59d9 | 1506 | What formats output as a form feed. The default is C<\f>. |
84dabc03 | 1507 | |
96948506 | 1508 | You cannot call C<format_formfeed()> on a handle, only as a static |
008f9687 | 1509 | method. See L<IO::Handle|IO::Handle>. |
96948506 | 1510 | |
b0c22438 | 1511 | =item HANDLE->format_page_number(EXPR) |
83ee9e09 | 1512 | |
b0c22438 | 1513 | =item $FORMAT_PAGE_NUMBER |
83ee9e09 | 1514 | |
b0c22438 | 1515 | =item $% |
1516 | X<$%> X<$FORMAT_PAGE_NUMBER> | |
83ee9e09 | 1517 | |
b0c22438 | 1518 | The current page number of the currently selected output channel. |
83ee9e09 | 1519 | |
b0c22438 | 1520 | Mnemonic: C<%> is page number in B<nroff>. |
7619c85e | 1521 | |
b0c22438 | 1522 | =item HANDLE->format_lines_left(EXPR) |
b9ac3b5b | 1523 | |
b0c22438 | 1524 | =item $FORMAT_LINES_LEFT |
66558a10 | 1525 | |
b0c22438 | 1526 | =item $- |
1527 | X<$-> X<$FORMAT_LINES_LEFT> | |
fb73857a | 1528 | |
b0c22438 | 1529 | The number of lines left on the page of the currently selected output |
1530 | channel. | |
fa05a9fd | 1531 | |
b0c22438 | 1532 | Mnemonic: lines_on_page - lines_printed. |
fa05a9fd | 1533 | |
96948506 | 1534 | =item IO::Handle->format_line_break_characters EXPR |
fb73857a | 1535 | |
84dabc03 | 1536 | =item $FORMAT_LINE_BREAK_CHARACTERS |
a0d0e21e | 1537 | |
84dabc03 | 1538 | =item $: |
1539 | X<$:> X<FORMAT_LINE_BREAK_CHARACTERS> | |
a0d0e21e | 1540 | |
84dabc03 | 1541 | The current set of characters after which a string may be broken to |
241a59d9 | 1542 | fill continuation fields (starting with C<^>) in a format. The default is |
84dabc03 | 1543 | S<" \n-">, to break on a space, newline, or a hyphen. |
a0d0e21e | 1544 | |
96948506 | 1545 | You cannot call C<format_line_break_characters()> on a handle, only as |
008f9687 | 1546 | a static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1547 | |
84dabc03 | 1548 | Mnemonic: a "colon" in poetry is a part of a line. |
1549 | ||
1550 | =item HANDLE->format_lines_per_page(EXPR) | |
1551 | ||
1552 | =item $FORMAT_LINES_PER_PAGE | |
1553 | ||
1554 | =item $= | |
1555 | X<$=> X<$FORMAT_LINES_PER_PAGE> | |
1556 | ||
1557 | The current page length (printable lines) of the currently selected | |
241a59d9 | 1558 | output channel. The default is 60. |
84dabc03 | 1559 | |
1560 | Mnemonic: = has horizontal lines. | |
7c36658b | 1561 | |
b0c22438 | 1562 | =item HANDLE->format_top_name(EXPR) |
7c36658b | 1563 | |
b0c22438 | 1564 | =item $FORMAT_TOP_NAME |
a05d7ebb | 1565 | |
b0c22438 | 1566 | =item $^ |
1567 | X<$^> X<$FORMAT_TOP_NAME> | |
fde18df1 | 1568 | |
b0c22438 | 1569 | The name of the current top-of-page format for the currently selected |
241a59d9 FC |
1570 | output channel. The default is the name of the filehandle with C<_TOP> |
1571 | appended. For example, the default format top name for the C<STDOUT> | |
12abbafd | 1572 | filehandle is C<STDOUT_TOP>. |
e07ea26a | 1573 | |
b0c22438 | 1574 | Mnemonic: points to top of page. |
e07ea26a | 1575 | |
84dabc03 | 1576 | =item HANDLE->format_name(EXPR) |
16070b82 | 1577 | |
84dabc03 | 1578 | =item $FORMAT_NAME |
aa2f2a36 | 1579 | |
84dabc03 | 1580 | =item $~ |
1581 | X<$~> X<$FORMAT_NAME> | |
aa2f2a36 | 1582 | |
84dabc03 | 1583 | The name of the current report format for the currently selected |
241a59d9 FC |
1584 | output channel. The default format name is the same as the filehandle |
1585 | name. For example, the default format name for the C<STDOUT> | |
84dabc03 | 1586 | filehandle is just C<STDOUT>. |
16070b82 | 1587 | |
84dabc03 | 1588 | Mnemonic: brother to C<$^>. |
16070b82 | 1589 | |
b0c22438 | 1590 | =back |
a0d0e21e | 1591 | |
84dabc03 | 1592 | =head2 Error Variables |
b0c22438 | 1593 | X<error> X<exception> |
a0d0e21e | 1594 | |
b0c22438 | 1595 | The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information |
1596 | about different types of error conditions that may appear during | |
241a59d9 | 1597 | execution of a Perl program. The variables are shown ordered by |
b0c22438 | 1598 | the "distance" between the subsystem which reported the error and |
241a59d9 | 1599 | the Perl process. They correspond to errors detected by the Perl |
b0c22438 | 1600 | interpreter, C library, operating system, or an external program, |
1601 | respectively. | |
4438c4b7 | 1602 | |
b0c22438 | 1603 | To illustrate the differences between these variables, consider the |
241a59d9 | 1604 | following Perl expression, which uses a single-quoted string. After |
7fd683ff | 1605 | execution of this statement, perl may have set all four special error |
7333b1c4 | 1606 | variables: |
4438c4b7 | 1607 | |
9548c15c FC |
1608 | eval q{ |
1609 | open my $pipe, "/cdrom/install |" or die $!; | |
1610 | my @res = <$pipe>; | |
1611 | close $pipe or die "bad pipe: $?, $!"; | |
1612 | }; | |
a0d0e21e | 1613 | |
7333b1c4 | 1614 | When perl executes the C<eval()> expression, it translates the |
1615 | C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library | |
241a59d9 | 1616 | and thence to the operating system kernel. perl sets C<$!> to |
7333b1c4 | 1617 | the C library's C<errno> if one of these calls fails. |
2a8c8378 | 1618 | |
84dabc03 | 1619 | C<$@> is set if the string to be C<eval>-ed did not compile (this may |
1620 | happen if C<open> or C<close> were imported with bad prototypes), or | |
241a59d9 | 1621 | if Perl code executed during evaluation C<die()>d. In these cases the |
0b9346e6 | 1622 | value of C<$@> is the compile error, or the argument to C<die> (which |
241a59d9 | 1623 | will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.) |
2a8c8378 | 1624 | |
84dabc03 | 1625 | Under a few operating systems, C<$^E> may contain a more verbose error |
241a59d9 | 1626 | indicator, such as in this case, "CDROM tray not closed." Systems that |
84dabc03 | 1627 | do not support extended error messages leave C<$^E> the same as C<$!>. |
a0d0e21e | 1628 | |
b0c22438 | 1629 | Finally, C<$?> may be set to non-0 value if the external program |
241a59d9 | 1630 | F</cdrom/install> fails. The upper eight bits reflect specific error |
84dabc03 | 1631 | conditions encountered by the program (the program's C<exit()> value). |
1632 | The lower eight bits reflect mode of failure, like signal death and | |
241a59d9 | 1633 | core dump information. See L<wait(2)> for details. In contrast to |
84dabc03 | 1634 | C<$!> and C<$^E>, which are set only if error condition is detected, |
1635 | the variable C<$?> is set on each C<wait> or pipe C<close>, | |
241a59d9 | 1636 | overwriting the old value. This is more like C<$@>, which on every |
84dabc03 | 1637 | C<eval()> is always set on failure and cleared on success. |
a0d0e21e | 1638 | |
b0c22438 | 1639 | For more details, see the individual descriptions at C<$@>, C<$!>, |
1640 | C<$^E>, and C<$?>. | |
38e4f4ae | 1641 | |
0b9346e6 | 1642 | =over 8 |
1643 | ||
b0c22438 | 1644 | =item ${^CHILD_ERROR_NATIVE} |
1645 | X<$^CHILD_ERROR_NATIVE> | |
a0d0e21e | 1646 | |
b0c22438 | 1647 | The native status returned by the last pipe close, backtick (C<``>) |
1648 | command, successful call to C<wait()> or C<waitpid()>, or from the | |
241a59d9 | 1649 | C<system()> operator. On POSIX-like systems this value can be decoded |
b0c22438 | 1650 | with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, |
1651 | WSTOPSIG and WIFCONTINUED functions provided by the L<POSIX> module. | |
a0d0e21e | 1652 | |
b0c22438 | 1653 | Under VMS this reflects the actual VMS exit status; i.e. it is the |
1654 | same as C<$?> when the pragma C<use vmsish 'status'> is in effect. | |
a0d0e21e | 1655 | |
60cf4914 | 1656 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1657 | |
5b442a2a | 1658 | =item $EXTENDED_OS_ERROR |
1659 | ||
84dabc03 | 1660 | =item $^E |
1661 | X<$^E> X<$EXTENDED_OS_ERROR> | |
1662 | ||
241a59d9 | 1663 | Error information specific to the current operating system. At the |
84dabc03 | 1664 | moment, this differs from C<$!> under only VMS, OS/2, and Win32 (and |
241a59d9 | 1665 | for MacPerl). On all other platforms, C<$^E> is always just the same |
84dabc03 | 1666 | as C<$!>. |
1667 | ||
1668 | Under VMS, C<$^E> provides the VMS status value from the last system | |
241a59d9 FC |
1669 | error. This is more specific information about the last system error |
1670 | than that provided by C<$!>. This is particularly important when C<$!> | |
84dabc03 | 1671 | is set to B<EVMSERR>. |
1672 | ||
1673 | Under OS/2, C<$^E> is set to the error code of the last call to OS/2 | |
1674 | API either via CRT, or directly from perl. | |
1675 | ||
1676 | Under Win32, C<$^E> always returns the last error information reported | |
1677 | by the Win32 call C<GetLastError()> which describes the last error | |
241a59d9 FC |
1678 | from within the Win32 API. Most Win32-specific code will report errors |
1679 | via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most | |
84dabc03 | 1680 | portable Perl code will report errors via C<$!>. |
1681 | ||
1682 | Caveats mentioned in the description of C<$!> generally apply to | |
1683 | C<$^E>, also. | |
1684 | ||
1685 | This variable was added in Perl 5.003. | |
1686 | ||
1687 | Mnemonic: Extra error explanation. | |
0b9346e6 | 1688 | |
84dabc03 | 1689 | =item $EXCEPTIONS_BEING_CAUGHT |
1690 | ||
1691 | =item $^S | |
1692 | X<$^S> X<$EXCEPTIONS_BEING_CAUGHT> | |
1693 | ||
1694 | Current state of the interpreter. | |
1695 | ||
ca1b95ae | 1696 | $^S State |
aa959a20 FC |
1697 | --------- ------------------------------------- |
1698 | undef Parsing module, eval, or main program | |
ca1b95ae | 1699 | true (1) Executing an eval |
1700 | false (0) Otherwise | |
84dabc03 | 1701 | |
1702 | The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}> | |
1703 | handlers. | |
1704 | ||
aa959a20 FC |
1705 | The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because |
1706 | the C<undef> value does not indicate whether exceptions are being caught, | |
1707 | since compilation of the main program does not catch exceptions. | |
1708 | ||
84dabc03 | 1709 | This variable was added in Perl 5.004. |
1710 | ||
1711 | =item $WARNING | |
1712 | ||
1713 | =item $^W | |
1714 | X<$^W> X<$WARNING> | |
1715 | ||
1716 | The current value of the warning switch, initially true if B<-w> was | |
1717 | used, false otherwise, but directly modifiable. | |
1718 | ||
1719 | See also L<warnings>. | |
1720 | ||
0b9346e6 | 1721 | Mnemonic: related to the B<-w> switch. |
84dabc03 | 1722 | |
1723 | =item ${^WARNING_BITS} | |
ca1b95ae | 1724 | X<${^WARNING_BITS}> |
84dabc03 | 1725 | |
1726 | The current set of warning checks enabled by the C<use warnings> pragma. | |
44567c86 FC |
1727 | It has the same scoping as the C<$^H> and C<%^H> variables. The exact |
1728 | values are considered internal to the L<warnings> pragma and may change | |
1729 | between versions of Perl. | |
84dabc03 | 1730 | |
60cf4914 | 1731 | This variable was added in Perl v5.6.0. |
84dabc03 | 1732 | |
b0c22438 | 1733 | =item $OS_ERROR |
5ccee41e | 1734 | |
b0c22438 | 1735 | =item $ERRNO |
5ccee41e | 1736 | |
b0c22438 | 1737 | =item $! |
1738 | X<$!> X<$ERRNO> X<$OS_ERROR> | |
9b0e6e7a | 1739 | |
a73bef78 JL |
1740 | When referenced, C<$!> retrieves the current value |
1741 | of the C C<errno> integer variable. | |
1742 | If C<$!> is assigned a numerical value, that value is stored in C<errno>. | |
1743 | When referenced as a string, C<$!> yields the system error string | |
1744 | corresponding to C<errno>. | |
1745 | ||
1746 | Many system or library calls set C<errno> if they fail, | |
1747 | to indicate the cause of failure. They usually do B<not> | |
1748 | set C<errno> to zero if they succeed. This means C<errno>, | |
1749 | hence C<$!>, is meaningful only I<immediately> after a B<failure>: | |
1750 | ||
1751 | if (open my $fh, "<", $filename) { | |
ca1b95ae | 1752 | # Here $! is meaningless. |
1753 | ... | |
7fd683ff | 1754 | } |
ca1b95ae | 1755 | else { |
1756 | # ONLY here is $! meaningful. | |
1757 | ... | |
1758 | # Already here $! might be meaningless. | |
b0c22438 | 1759 | } |
1760 | # Since here we might have either success or failure, | |
a73bef78 | 1761 | # $! is meaningless. |
a0d0e21e | 1762 | |
a73bef78 JL |
1763 | Here, I<meaningless> means that C<$!> may be unrelated to the outcome |
1764 | of the C<open()> operator. Assignment to C<$!> is similarly ephemeral. | |
1765 | It can be used immediately before invoking the C<die()> operator, | |
1766 | to set the exit value, or to inspect the system error string | |
1767 | corresponding to error I<n>, or to restore C<$!> to a meaningful state. | |
d54b56d5 | 1768 | |
b0c22438 | 1769 | Mnemonic: What just went bang? |
314d39ce | 1770 | |
b0c22438 | 1771 | =item %OS_ERROR |
fb73857a | 1772 | |
b0c22438 | 1773 | =item %ERRNO |
fb73857a | 1774 | |
b0c22438 | 1775 | =item %! |
5b442a2a | 1776 | X<%!> X<%OS_ERROR> X<%ERRNO> |
a0d0e21e | 1777 | |
b0c22438 | 1778 | Each element of C<%!> has a true value only if C<$!> is set to that |
241a59d9 | 1779 | value. For example, C<$!{ENOENT}> is true if and only if the current |
84dabc03 | 1780 | value of C<$!> is C<ENOENT>; that is, if the most recent error was "No |
1781 | such file or directory" (or its moral equivalent: not all operating | |
241a59d9 | 1782 | systems give that exact error, and certainly not all languages). To |
84dabc03 | 1783 | check if a particular key is meaningful on your system, use C<exists |
241a59d9 | 1784 | $!{the_key}>; for a list of legal keys, use C<keys %!>. See L<Errno> |
7333b1c4 | 1785 | for more information, and also see L</$!>. |
a0d0e21e | 1786 | |
b0c22438 | 1787 | This variable was added in Perl 5.005. |
44f0be63 | 1788 | |
84dabc03 | 1789 | =item $CHILD_ERROR |
b687b08b | 1790 | |
84dabc03 | 1791 | =item $? |
1792 | X<$?> X<$CHILD_ERROR> | |
a0d0e21e | 1793 | |
84dabc03 | 1794 | The status returned by the last pipe close, backtick (C<``>) command, |
1795 | successful call to C<wait()> or C<waitpid()>, or from the C<system()> | |
241a59d9 | 1796 | operator. This is just the 16-bit status word returned by the |
84dabc03 | 1797 | traditional Unix C<wait()> system call (or else is made up to look |
241a59d9 | 1798 | like it). Thus, the exit value of the subprocess is really (C<<< $? >> |
84dabc03 | 1799 | 8 >>>), and C<$? & 127> gives which signal, if any, the process died |
1800 | from, and C<$? & 128> reports whether there was a core dump. | |
a0d0e21e | 1801 | |
84dabc03 | 1802 | Additionally, if the C<h_errno> variable is supported in C, its value |
1803 | is returned via C<$?> if any C<gethost*()> function fails. | |
b687b08b | 1804 | |
84dabc03 | 1805 | If you have installed a signal handler for C<SIGCHLD>, the |
1806 | value of C<$?> will usually be wrong outside that handler. | |
a0d0e21e | 1807 | |
84dabc03 | 1808 | Inside an C<END> subroutine C<$?> contains the value that is going to be |
241a59d9 FC |
1809 | given to C<exit()>. You can modify C<$?> in an C<END> subroutine to |
1810 | change the exit status of your program. For example: | |
a0d0e21e | 1811 | |
84dabc03 | 1812 | END { |
1813 | $? = 1 if $? == 255; # die would make it 255 | |
1814 | } | |
a0d0e21e | 1815 | |
84dabc03 | 1816 | Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the |
1817 | actual VMS exit status, instead of the default emulation of POSIX | |
1818 | status; see L<perlvms/$?> for details. | |
1819 | ||
1820 | Mnemonic: similar to B<sh> and B<ksh>. | |
a0d0e21e | 1821 | |
b0c22438 | 1822 | =item $EVAL_ERROR |
f648820c | 1823 | |
b0c22438 | 1824 | =item $@ |
1825 | X<$@> X<$EVAL_ERROR> | |
a0d0e21e | 1826 | |
241a59d9 FC |
1827 | The Perl syntax error message from the |
1828 | last C<eval()> operator. If C<$@> is | |
0b9346e6 | 1829 | the null string, the last C<eval()> parsed and executed correctly |
b0c22438 | 1830 | (although the operations you invoked may have failed in the normal |
1831 | fashion). | |
a0d0e21e | 1832 | |
241a59d9 | 1833 | Warning messages are not collected in this variable. You can, however, |
b0c22438 | 1834 | set up a routine to process warnings by setting C<$SIG{__WARN__}> as |
7333b1c4 | 1835 | described in L</%SIG>. |
748a9306 | 1836 | |
b0c22438 | 1837 | Mnemonic: Where was the syntax error "at"? |
7f315d2e | 1838 | |
b0c22438 | 1839 | =back |
7f315d2e | 1840 | |
1fa81471 DR |
1841 | =head2 Variables related to the interpreter state |
1842 | ||
1843 | These variables provide information about the current interpreter state. | |
1844 | ||
1845 | =over 8 | |
1846 | ||
1847 | =item $COMPILING | |
1848 | ||
1849 | =item $^C | |
1850 | X<$^C> X<$COMPILING> | |
1851 | ||
1852 | The current value of the flag associated with the B<-c> switch. | |
1853 | Mainly of use with B<-MO=...> to allow code to alter its behavior | |
1854 | when being compiled, such as for example to C<AUTOLOAD> at compile | |
241a59d9 | 1855 | time rather than normal, deferred loading. Setting |
1fa81471 DR |
1856 | C<$^C = 1> is similar to calling C<B::minus_c>. |
1857 | ||
60cf4914 | 1858 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
1859 | |
1860 | =item $DEBUGGING | |
1861 | ||
1862 | =item $^D | |
1863 | X<$^D> X<$DEBUGGING> | |
1864 | ||
241a59d9 | 1865 | The current value of the debugging flags. May be read or set. Like its |
1fa81471 DR |
1866 | command-line equivalent, you can use numeric or symbolic values, eg |
1867 | C<$^D = 10> or C<$^D = "st">. | |
1868 | ||
1869 | Mnemonic: value of B<-D> switch. | |
1870 | ||
1871 | =item ${^ENCODING} | |
1872 | X<${^ENCODING}> | |
1873 | ||
a3ee04ba KW |
1874 | DEPRECATED!!! |
1875 | ||
1fa81471 | 1876 | The I<object reference> to the C<Encode> object that is used to convert |
241a59d9 | 1877 | the source code to Unicode. Thanks to this variable your Perl script |
a3ee04ba KW |
1878 | does not have to be written in UTF-8. Default is C<undef>. |
1879 | ||
1880 | Setting this variable to any other value than C<undef> is deprecated due | |
1881 | to fundamental defects in its design and implementation. It is planned | |
1882 | to remove it from a future Perl version. Its purpose was to allow your | |
1883 | non-ASCII Perl scripts to not have to be written in UTF-8; this was | |
1884 | useful before editors that worked on UTF-8 encoded text were common, but | |
1885 | that was long ago. It causes problems, such as affecting the operation | |
1886 | of other modules that aren't expecting it, causing general mayhem. Its | |
1887 | use can lead to segfaults. | |
1888 | ||
1889 | If you need something like this functionality, you should use the | |
1890 | L<encoding> pragma, which is also deprecated, but has fewer nasty side | |
1891 | effects. | |
1892 | ||
1893 | If you are coming here because code of yours is being adversely affected | |
1894 | by someone's use of this variable, you can usually work around it by | |
1895 | doing this: | |
1896 | ||
1897 | local ${^ENCODING}; | |
1898 | ||
1899 | near the beginning of the functions that are getting broken. This | |
1900 | undefines the variable during the scope of execution of the including | |
1901 | function. | |
1fa81471 DR |
1902 | |
1903 | This variable was added in Perl 5.8.2. | |
1904 | ||
1905 | =item ${^GLOBAL_PHASE} | |
1906 | X<${^GLOBAL_PHASE}> | |
1907 | ||
1908 | The current phase of the perl interpreter. | |
1909 | ||
1910 | Possible values are: | |
1911 | ||
1912 | =over 8 | |
1913 | ||
1914 | =item CONSTRUCT | |
1915 | ||
241a59d9 | 1916 | The C<PerlInterpreter*> is being constructed via C<perl_construct>. This |
1fa81471 | 1917 | value is mostly there for completeness and for use via the |
241a59d9 | 1918 | underlying C variable C<PL_phase>. It's not really possible for Perl |
1fa81471 DR |
1919 | code to be executed unless construction of the interpreter is |
1920 | finished. | |
1921 | ||
1922 | =item START | |
1923 | ||
241a59d9 | 1924 | This is the global compile-time. That includes, basically, every |
1fa81471 DR |
1925 | C<BEGIN> block executed directly or indirectly from during the |
1926 | compile-time of the top-level program. | |
1927 | ||
1928 | This phase is not called "BEGIN" to avoid confusion with | |
1929 | C<BEGIN>-blocks, as those are executed during compile-time of any | |
241a59d9 | 1930 | compilation unit, not just the top-level program. A new, localised |
1fa81471 DR |
1931 | compile-time entered at run-time, for example by constructs as |
1932 | C<eval "use SomeModule"> are not global interpreter phases, and | |
1933 | therefore aren't reflected by C<${^GLOBAL_PHASE}>. | |
1934 | ||
1935 | =item CHECK | |
1936 | ||
1937 | Execution of any C<CHECK> blocks. | |
1938 | ||
1939 | =item INIT | |
1940 | ||
1941 | Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks. | |
1942 | ||
1943 | =item RUN | |
1944 | ||
1945 | The main run-time, i.e. the execution of C<PL_main_root>. | |
1946 | ||
1947 | =item END | |
1948 | ||
1949 | Execution of any C<END> blocks. | |
1950 | ||
1951 | =item DESTRUCT | |
1952 | ||
1953 | Global destruction. | |
1954 | ||
1955 | =back | |
1956 | ||
241a59d9 | 1957 | Also note that there's no value for UNITCHECK-blocks. That's because |
1fa81471 DR |
1958 | those are run for each compilation unit individually, and therefore is |
1959 | not a global interpreter phase. | |
1960 | ||
1961 | Not every program has to go through each of the possible phases, but | |
1962 | transition from one phase to another can only happen in the order | |
1963 | described in the above list. | |
1964 | ||
1965 | An example of all of the phases Perl code can see: | |
1966 | ||
1967 | BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" } | |
1968 | ||
1969 | INIT { print "init-time: ${^GLOBAL_PHASE}\n" } | |
1970 | ||
1971 | CHECK { print "check-time: ${^GLOBAL_PHASE}\n" } | |
1972 | ||
1973 | { | |
1974 | package Print::Phase; | |
1975 | ||
1976 | sub new { | |
1977 | my ($class, $time) = @_; | |
1978 | return bless \$time, $class; | |
1979 | } | |
1980 | ||
1981 | sub DESTROY { | |
1982 | my $self = shift; | |
1983 | print "$$self: ${^GLOBAL_PHASE}\n"; | |
1984 | } | |
1985 | } | |
1986 | ||
1987 | print "run-time: ${^GLOBAL_PHASE}\n"; | |
1988 | ||
1989 | my $runtime = Print::Phase->new( | |
1990 | "lexical variables are garbage collected before END" | |
1991 | ); | |
1992 | ||
1993 | END { print "end-time: ${^GLOBAL_PHASE}\n" } | |
1994 | ||
1995 | our $destruct = Print::Phase->new( | |
1996 | "package variables are garbage collected after END" | |
1997 | ); | |
1998 | ||
1999 | This will print out | |
2000 | ||
2001 | compile-time: START | |
2002 | check-time: CHECK | |
2003 | init-time: INIT | |
2004 | run-time: RUN | |
2005 | lexical variables are garbage collected before END: RUN | |
2006 | end-time: END | |
2007 | package variables are garbage collected after END: DESTRUCT | |
2008 | ||
2009 | This variable was added in Perl 5.14.0. | |
2010 | ||
2011 | =item $^H | |
2012 | X<$^H> | |
2013 | ||
241a59d9 FC |
2014 | WARNING: This variable is strictly for |
2015 | internal use only. Its availability, | |
1fa81471 DR |
2016 | behavior, and contents are subject to change without notice. |
2017 | ||
241a59d9 | 2018 | This variable contains compile-time hints for the Perl interpreter. At the |
1fa81471 DR |
2019 | end of compilation of a BLOCK the value of this variable is restored to the |
2020 | value when the interpreter started to compile the BLOCK. | |
2021 | ||
2022 | When perl begins to parse any block construct that provides a lexical scope | |
2023 | (e.g., eval body, required file, subroutine body, loop body, or conditional | |
2024 | block), the existing value of C<$^H> is saved, but its value is left unchanged. | |
2025 | When the compilation of the block is completed, it regains the saved value. | |
2026 | Between the points where its value is saved and restored, code that | |
2027 | executes within BEGIN blocks is free to change the value of C<$^H>. | |
2028 | ||
2029 | This behavior provides the semantic of lexical scoping, and is used in, | |
2030 | for instance, the C<use strict> pragma. | |
2031 | ||
2032 | The contents should be an integer; different bits of it are used for | |
241a59d9 | 2033 | different pragmatic flags. Here's an example: |
1fa81471 | 2034 | |
9548c15c | 2035 | sub add_100 { $^H |= 0x100 } |
1fa81471 | 2036 | |
9548c15c FC |
2037 | sub foo { |
2038 | BEGIN { add_100() } | |
2039 | bar->baz($boon); | |
2040 | } | |
1fa81471 | 2041 | |
241a59d9 | 2042 | Consider what happens during execution of the BEGIN block. At this point |
1fa81471 | 2043 | the BEGIN block has already been compiled, but the body of C<foo()> is still |
241a59d9 FC |
2044 | being compiled. The new value of C<$^H> |
2045 | will therefore be visible only while | |
1fa81471 DR |
2046 | the body of C<foo()> is being compiled. |
2047 | ||
2048 | Substitution of C<BEGIN { add_100() }> block with: | |
2049 | ||
9548c15c | 2050 | BEGIN { require strict; strict->import('vars') } |
1fa81471 | 2051 | |
241a59d9 | 2052 | demonstrates how C<use strict 'vars'> is implemented. Here's a conditional |
1fa81471 DR |
2053 | version of the same lexical pragma: |
2054 | ||
9548c15c FC |
2055 | BEGIN { |
2056 | require strict; strict->import('vars') if $condition | |
2057 | } | |
1fa81471 DR |
2058 | |
2059 | This variable was added in Perl 5.003. | |
2060 | ||
2061 | =item %^H | |
2062 | X<%^H> | |
2063 | ||
241a59d9 FC |
2064 | The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes |
2065 | it useful for implementation of lexically scoped pragmas. See | |
112284f4 KW |
2066 | L<perlpragma>. All the entries are stringified when accessed at |
2067 | runtime, so only simple values can be accommodated. This means no | |
2068 | pointers to objects, for example. | |
1fa81471 DR |
2069 | |
2070 | When putting items into C<%^H>, in order to avoid conflicting with other | |
2071 | users of the hash there is a convention regarding which keys to use. | |
2072 | A module should use only keys that begin with the module's name (the | |
2073 | name of its main package) and a "/" character. For example, a module | |
2074 | C<Foo::Bar> should use keys such as C<Foo::Bar/baz>. | |
2075 | ||
60cf4914 | 2076 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
2077 | |
2078 | =item ${^OPEN} | |
2079 | X<${^OPEN}> | |
2080 | ||
241a59d9 | 2081 | An internal variable used by PerlIO. A string in two parts, separated |
1fa81471 DR |
2082 | by a C<\0> byte, the first part describes the input layers, the second |
2083 | part describes the output layers. | |
2084 | ||
60cf4914 | 2085 | This variable was added in Perl v5.8.0. |
1fa81471 DR |
2086 | |
2087 | =item $PERLDB | |
2088 | ||
2089 | =item $^P | |
2090 | X<$^P> X<$PERLDB> | |
2091 | ||
241a59d9 | 2092 | The internal variable for debugging support. The meanings of the |
1fa81471 DR |
2093 | various bits are subject to change, but currently indicate: |
2094 | ||
2095 | =over 6 | |
2096 | ||
2097 | =item 0x01 | |
2098 | ||
2099 | Debug subroutine enter/exit. | |
2100 | ||
2101 | =item 0x02 | |
2102 | ||
241a59d9 FC |
2103 | Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for |
2104 | each statement executed. Also causes saving source code lines (like | |
2105 | 0x400). | |
1fa81471 DR |
2106 | |
2107 | =item 0x04 | |
2108 | ||
2109 | Switch off optimizations. | |
2110 | ||
2111 | =item 0x08 | |
2112 | ||
2113 | Preserve more data for future interactive inspections. | |
2114 | ||
2115 | =item 0x10 | |
2116 | ||
2117 | Keep info about source lines on which a subroutine is defined. | |
2118 | ||
2119 | =item 0x20 | |
2120 | ||
2121 | Start with single-step on. | |
2122 | ||
2123 | =item 0x40 | |
2124 | ||
2125 | Use subroutine address instead of name when reporting. | |
2126 | ||
2127 | =item 0x80 | |
2128 | ||
2129 | Report C<goto &subroutine> as well. | |
2130 | ||
2131 | =item 0x100 | |
2132 | ||
2133 | Provide informative "file" names for evals based on the place they were compiled. | |
2134 | ||
2135 | =item 0x200 | |
2136 | ||
2137 | Provide informative names to anonymous subroutines based on the place they | |
2138 | were compiled. | |
2139 | ||
2140 | =item 0x400 | |
2141 | ||
2142 | Save source code lines into C<@{"_<$filename"}>. | |
2143 | ||
aab47982 RS |
2144 | =item 0x800 |
2145 | ||
2146 | When saving source, include evals that generate no subroutines. | |
2147 | ||
2148 | =item 0x1000 | |
2149 | ||
2150 | When saving source, include source that did not compile. | |
2151 | ||
1fa81471 DR |
2152 | =back |
2153 | ||
2154 | Some bits may be relevant at compile-time only, some at | |
241a59d9 | 2155 | run-time only. This is a new mechanism and the details may change. |
1fa81471 DR |
2156 | See also L<perldebguts>. |
2157 | ||
2158 | =item ${^TAINT} | |
2159 | X<${^TAINT}> | |
2160 | ||
241a59d9 | 2161 | Reflects if taint mode is on or off. 1 for on (the program was run with |
1fa81471 DR |
2162 | B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with |
2163 | B<-t> or B<-TU>). | |
2164 | ||
2165 | This variable is read-only. | |
2166 | ||
60cf4914 | 2167 | This variable was added in Perl v5.8.0. |
1fa81471 DR |
2168 | |
2169 | =item ${^UNICODE} | |
2170 | X<${^UNICODE}> | |
2171 | ||
241a59d9 | 2172 | Reflects certain Unicode settings of Perl. See L<perlrun> |
1fa81471 DR |
2173 | documentation for the C<-C> switch for more information about |
2174 | the possible values. | |
2175 | ||
2176 | This variable is set during Perl startup and is thereafter read-only. | |
2177 | ||
60cf4914 | 2178 | This variable was added in Perl v5.8.2. |
1fa81471 DR |
2179 | |
2180 | =item ${^UTF8CACHE} | |
2181 | X<${^UTF8CACHE}> | |
2182 | ||
2183 | This variable controls the state of the internal UTF-8 offset caching code. | |
2184 | 1 for on (the default), 0 for off, -1 to debug the caching code by checking | |
2185 | all its results against linear scans, and panicking on any discrepancy. | |
2186 | ||
94df5432 KW |
2187 | This variable was added in Perl v5.8.9. It is subject to change or |
2188 | removal without notice, but is currently used to avoid recalculating the | |
2189 | boundaries of multi-byte UTF-8-encoded characters. | |
1fa81471 DR |
2190 | |
2191 | =item ${^UTF8LOCALE} | |
2192 | X<${^UTF8LOCALE}> | |
2193 | ||
2194 | This variable indicates whether a UTF-8 locale was detected by perl at | |
241a59d9 | 2195 | startup. This information is used by perl when it's in |
1fa81471 DR |
2196 | adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line |
2197 | switch); see L<perlrun> for more info on this. | |
2198 | ||
60cf4914 | 2199 | This variable was added in Perl v5.8.8. |
1fa81471 DR |
2200 | |
2201 | =back | |
2202 | ||
b0c22438 | 2203 | =head2 Deprecated and removed variables |
7f315d2e | 2204 | |
0b9346e6 | 2205 | Deprecating a variable announces the intent of the perl maintainers to |
241a59d9 FC |
2206 | eventually remove the variable from the language. It may still be |
2207 | available despite its status. Using a deprecated variable triggers | |
b0c22438 | 2208 | a warning. |
7f315d2e | 2209 | |
84dabc03 | 2210 | Once a variable is removed, its use triggers an error telling you |
b0c22438 | 2211 | the variable is unsupported. |
7f315d2e | 2212 | |
84dabc03 | 2213 | See L<perldiag> for details about error messages. |
7f315d2e | 2214 | |
b0c22438 | 2215 | =over 8 |
7f315d2e | 2216 | |
84dabc03 | 2217 | =item $# |
b7a15f05 | 2218 | X<$#> |
84dabc03 | 2219 | |
38e5787b | 2220 | C<$#> was a variable that could be used to format printed numbers. |
60cf4914 | 2221 | After a deprecation cycle, its magic was removed in Perl v5.10.0 and |
84dabc03 | 2222 | using it now triggers a warning: C<$# is no longer supported>. |
2223 | ||
2224 | This is not the sigil you use in front of an array name to get the | |
241a59d9 FC |
2225 | last index, like C<$#array>. That's still how you get the last index |
2226 | of an array in Perl. The two have nothing to do with each other. | |
84dabc03 | 2227 | |
2228 | Deprecated in Perl 5. | |
2229 | ||
60cf4914 | 2230 | Removed in Perl v5.10.0. |
84dabc03 | 2231 | |
7f315d2e CO |
2232 | =item $* |
2233 | X<$*> | |
2234 | ||
84dabc03 | 2235 | C<$*> was a variable that you could use to enable multiline matching. |
60cf4914 | 2236 | After a deprecation cycle, its magic was removed in Perl v5.10.0. |
7f315d2e | 2237 | Using it now triggers a warning: C<$* is no longer supported>. |
84dabc03 | 2238 | You should use the C</s> and C</m> regexp modifiers instead. |
7f315d2e | 2239 | |
b0c22438 | 2240 | Deprecated in Perl 5. |
7f315d2e | 2241 | |
60cf4914 | 2242 | Removed in Perl v5.10.0. |
7f315d2e | 2243 | |
84dabc03 | 2244 | =item $[ |
b7a15f05 | 2245 | X<$[> |
84dabc03 | 2246 | |
b82b06b8 FC |
2247 | This variable stores the index of the first element in an array, and |
2248 | of the first character in a substring. The default is 0, but you could | |
2249 | theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran) | |
2250 | when subscripting and when evaluating the index() and substr() functions. | |
84dabc03 | 2251 | |
b82b06b8 FC |
2252 | As of release 5 of Perl, assignment to C<$[> is treated as a compiler |
2253 | directive, and cannot influence the behavior of any other file. | |
2254 | (That's why you can only assign compile-time constants to it.) | |
2255 | Its use is highly discouraged. | |
2256 | ||
60cf4914 | 2257 | Prior to Perl v5.10.0, assignment to C<$[> could be seen from outer lexical |
b82b06b8 FC |
2258 | scopes in the same file, unlike other compile-time directives (such as |
2259 | L<strict>). Using local() on it would bind its value strictly to a lexical | |
2260 | block. Now it is always lexically scoped. | |
2261 | ||
60cf4914 | 2262 | As of Perl v5.16.0, it is implemented by the L<arybase> module. See |
b82b06b8 | 2263 | L<arybase> for more details on its behaviour. |
84dabc03 | 2264 | |
6b54f8ab FC |
2265 | Under C<use v5.16>, or C<no feature "array_base">, C<$[> no longer has any |
2266 | effect, and always contains 0. Assigning 0 to it is permitted, but any | |
2267 | other value will produce an error. | |
2268 | ||
b82b06b8 FC |
2269 | Mnemonic: [ begins subscripts. |
2270 | ||
60cf4914 | 2271 | Deprecated in Perl v5.12.0. |
e1dccc0d | 2272 | |
b0c22438 | 2273 | =item $] |
b7a15f05 | 2274 | X<$]> |
55602bd2 | 2275 | |
57f6eff5 | 2276 | See L</$^V> for a more modern representation of the Perl version that allows |
d4ba9bf2 | 2277 | accurate string comparisons. |
2278 | ||
241a59d9 | 2279 | The version + patchlevel / 1000 of the Perl interpreter. This variable |
b0c22438 | 2280 | can be used to determine whether the Perl interpreter executing a |
2281 | script is in the right range of versions: | |
55602bd2 | 2282 | |
9016991b | 2283 | warn "No PerlIO!\n" if $] lt '5.008'; |
55602bd2 | 2284 | |
d4ba9bf2 | 2285 | The floating point representation can sometimes lead to inaccurate |
9016991b | 2286 | numeric comparisons, so string comparisons are recommended. |
d4ba9bf2 | 2287 | |
b0c22438 | 2288 | See also the documentation of C<use VERSION> and C<require VERSION> |
2289 | for a convenient way to fail if the running Perl interpreter is too old. | |
55602bd2 | 2290 | |
b0c22438 | 2291 | Mnemonic: Is this version of perl in the right bracket? |
19799a22 | 2292 | |
b0c22438 | 2293 | =back |
2b92dfce | 2294 | |
0b9346e6 | 2295 | =cut |