Commit | Line | Data |
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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>. |
ce4793f1 KW |
15 | A Unicode letter that is not ASCII is not considered to be a letter |
16 | unless S<C<"use utf8">> is in effect, and somewhat more complicated | |
17 | rules apply; see L<perldata/Identifier parsing> for details. | |
b0c22438 | 18 | |
ce4793f1 KW |
19 | Perl variable names may also be a sequence of digits, a single |
20 | punctuation character, or the two-character sequence: C<^> (caret or | |
21 | CIRCUMFLEX ACCENT) followed by any one of the characters C<[][A-Z^_?\]>. | |
22 | These names are all reserved for | |
b0c22438 | 23 | special uses by Perl; for example, the all-digits names are used |
24 | to hold data captured by backreferences after a regular expression | |
ce4793f1 | 25 | match. |
b0c22438 | 26 | |
ce4793f1 KW |
27 | Since Perl v5.6.0, Perl variable names may also be alphanumeric strings |
28 | preceded by a caret. These must all be written in the form C<${^Foo}>; | |
29 | the braces are not optional. C<${^Foo}> denotes the scalar variable | |
30 | whose name is considered to be a control-C<F> followed by two C<o>'s. | |
31 | These variables are | |
b0c22438 | 32 | reserved for future special uses by Perl, except for the ones that |
ce4793f1 KW |
33 | begin with C<^_> (caret-underscore). No |
34 | name that begins with C<^_> will acquire a special | |
b0c22438 | 35 | meaning in any future version of Perl; such names may therefore be |
241a59d9 | 36 | used safely in programs. C<$^_> itself, however, I<is> reserved. |
b0c22438 | 37 | |
ce4793f1 | 38 | Perl identifiers that begin with digits or |
b0c22438 | 39 | punctuation characters are exempt from the effects of the C<package> |
40 | declaration and are always forced to be in package C<main>; they are | |
241a59d9 | 41 | also exempt from C<strict 'vars'> errors. A few other names are also |
b0c22438 | 42 | exempt in these ways: |
43 | ||
9548c15c FC |
44 | ENV STDIN |
45 | INC STDOUT | |
46 | ARGV STDERR | |
47 | ARGVOUT | |
48 | SIG | |
b0c22438 | 49 | |
69520822 | 50 | In particular, the special C<${^_XYZ}> variables are always taken |
b0c22438 | 51 | to be in package C<main>, regardless of any C<package> declarations |
52 | presently in scope. | |
53 | ||
54 | =head1 SPECIAL VARIABLES | |
a0d0e21e | 55 | |
241a59d9 | 56 | The following names have special meaning to Perl. Most punctuation |
0b9346e6 | 57 | names have reasonable mnemonics, or analogs in the shells. |
58 | Nevertheless, if you wish to use long variable names, you need only say: | |
a0d0e21e | 59 | |
9548c15c | 60 | use English; |
a0d0e21e | 61 | |
241a59d9 FC |
62 | at the top of your program. This aliases all the short names to the long |
63 | names in the current package. Some even have medium names, generally | |
1e7d0944 | 64 | borrowed from B<awk>. For more info, please see L<English>. |
a1ce9542 | 65 | |
241a59d9 | 66 | Before you continue, note the sort order for variables. In general, we |
0b9346e6 | 67 | first list the variables in case-insensitive, almost-lexigraphical |
68 | order (ignoring the C<{> or C<^> preceding words, as in C<${^UNICODE}> | |
69 | or C<$^T>), although C<$_> and C<@_> move up to the top of the pile. | |
70 | For variables with the same identifier, we list it in order of scalar, | |
71 | array, hash, and bareword. | |
a1ce9542 | 72 | |
b0c22438 | 73 | =head2 General Variables |
a0d0e21e | 74 | |
84dabc03 | 75 | =over 8 |
76 | ||
a0d0e21e LW |
77 | =item $ARG |
78 | ||
79 | =item $_ | |
a054c801 | 80 | X<$_> X<$ARG> |
a0d0e21e | 81 | |
241a59d9 | 82 | The default input and pattern-searching space. The following pairs are |
a0d0e21e LW |
83 | equivalent: |
84 | ||
9548c15c FC |
85 | while (<>) {...} # equivalent only in while! |
86 | while (defined($_ = <>)) {...} | |
a0d0e21e | 87 | |
9548c15c FC |
88 | /^Subject:/ |
89 | $_ =~ /^Subject:/ | |
a0d0e21e | 90 | |
9548c15c FC |
91 | tr/a-z/A-Z/ |
92 | $_ =~ tr/a-z/A-Z/ | |
a0d0e21e | 93 | |
9548c15c FC |
94 | chomp |
95 | chomp($_) | |
a0d0e21e | 96 | |
0b9346e6 | 97 | Here are the places where Perl will assume C<$_> even if you don't use it: |
cb1a09d0 AD |
98 | |
99 | =over 3 | |
100 | ||
101 | =item * | |
102 | ||
84dabc03 | 103 | The following functions use C<$_> as a default argument: |
db1511c8 | 104 | |
f61f53cc | 105 | abs, alarm, chomp, chop, chr, chroot, |
ae815a4d FC |
106 | cos, defined, eval, evalbytes, exp, fc, glob, hex, int, lc, |
107 | lcfirst, length, log, lstat, mkdir, oct, ord, pos, print, printf, | |
b0169937 | 108 | quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only), |
ae815a4d FC |
109 | rmdir, say, sin, split (for its second |
110 | argument), sqrt, stat, study, uc, ucfirst, | |
b0169937 | 111 | unlink, unpack. |
cb1a09d0 AD |
112 | |
113 | =item * | |
114 | ||
db1511c8 GS |
115 | All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN. |
116 | See L<perlfunc/-X> | |
117 | ||
cb1a09d0 AD |
118 | =item * |
119 | ||
b0169937 GS |
120 | The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>) |
121 | when used without an C<=~> operator. | |
cb1a09d0 | 122 | |
54310121 | 123 | =item * |
cb1a09d0 AD |
124 | |
125 | The default iterator variable in a C<foreach> loop if no other | |
126 | variable is supplied. | |
127 | ||
54310121 | 128 | =item * |
cb1a09d0 | 129 | |
b0c22438 | 130 | The implicit iterator variable in the C<grep()> and C<map()> functions. |
cb1a09d0 | 131 | |
54310121 | 132 | =item * |
cb1a09d0 | 133 | |
b0c22438 | 134 | The implicit variable of C<given()>. |
db1511c8 GS |
135 | |
136 | =item * | |
137 | ||
ae815a4d FC |
138 | The default place to put the next value or input record |
139 | when a C<< <FH> >>, C<readline>, C<readdir> or C<each> | |
cb1a09d0 | 140 | operation's result is tested by itself as the sole criterion of a C<while> |
241a59d9 | 141 | test. Outside a C<while> test, this will not happen. |
cb1a09d0 AD |
142 | |
143 | =back | |
144 | ||
5f6af817 RS |
145 | C<$_> is a global variable. |
146 | ||
147 | However, between perl v5.10.0 and v5.24.0, it could be used lexically by | |
148 | writing C<my $_>. Making C<$_> refer to the global C<$_> in the same scope | |
149 | was then possible with C<our $_>. This experimental feature was removed and is | |
150 | now a fatal error, but you may encounter it in older code. | |
59f00321 | 151 | |
b0c22438 | 152 | Mnemonic: underline is understood in certain operations. |
a0d0e21e | 153 | |
0b9346e6 | 154 | =item @ARG |
cde0cee5 | 155 | |
0b9346e6 | 156 | =item @_ |
157 | X<@_> X<@ARG> | |
a0d0e21e | 158 | |
0b9346e6 | 159 | Within a subroutine the array C<@_> contains the parameters passed to |
241a59d9 | 160 | that subroutine. Inside a subroutine, C<@_> is the default array for |
256ca3d3 | 161 | the array operators C<pop> and C<shift>. |
a0d0e21e | 162 | |
0b9346e6 | 163 | See L<perlsub>. |
a0d0e21e | 164 | |
1311257d | 165 | =item $LIST_SEPARATOR |
166 | ||
167 | =item $" | |
168 | X<$"> X<$LIST_SEPARATOR> | |
169 | ||
69520822 | 170 | When an array or an array slice is interpolated into a double-quoted |
171 | string or a similar context such as C</.../>, its elements are | |
241a59d9 | 172 | separated by this value. Default is a space. For example, this: |
69520822 | 173 | |
9548c15c | 174 | print "The array is: @array\n"; |
69520822 | 175 | |
176 | is equivalent to this: | |
177 | ||
9548c15c | 178 | print "The array is: " . join($", @array) . "\n"; |
69520822 | 179 | |
180 | Mnemonic: works in double-quoted context. | |
1311257d | 181 | |
b0c22438 | 182 | =item $PROCESS_ID |
cde0cee5 | 183 | |
b0c22438 | 184 | =item $PID |
a0d0e21e | 185 | |
b0c22438 | 186 | =item $$ |
187 | X<$$> X<$PID> X<$PROCESS_ID> | |
a0d0e21e | 188 | |
241a59d9 | 189 | The process number of the Perl running this script. Though you I<can> set |
4a904372 | 190 | this variable, doing so is generally discouraged, although it can be |
241a59d9 | 191 | invaluable for some testing purposes. It will be reset automatically |
b0c22438 | 192 | across C<fork()> calls. |
a0d0e21e | 193 | |
d7c042c9 AB |
194 | Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl |
195 | would emulate POSIX semantics on Linux systems using LinuxThreads, a | |
196 | partial implementation of POSIX Threads that has since been superseded | |
197 | by the Native POSIX Thread Library (NPTL). | |
198 | ||
e3f68f70 | 199 | LinuxThreads is now obsolete on Linux, and caching C<getpid()> |
d7c042c9 AB |
200 | like this made embedding perl unnecessarily complex (since you'd have |
201 | to manually update the value of $$), so now C<$$> and C<getppid()> | |
202 | will always return the same values as the underlying C library. | |
203 | ||
204 | Debian GNU/kFreeBSD systems also used LinuxThreads up until and | |
205 | including the 6.0 release, but after that moved to FreeBSD thread | |
206 | semantics, which are POSIX-like. | |
207 | ||
208 | To see if your system is affected by this discrepancy check if | |
209 | C<getconf GNU_LIBPTHREAD_VERSION | grep -q NPTL> returns a false | |
1e7d0944 | 210 | value. NTPL threads preserve the POSIX semantics. |
a0d0e21e | 211 | |
b0c22438 | 212 | Mnemonic: same as shells. |
ad83b128 | 213 | |
66d7055b DR |
214 | =item $PROGRAM_NAME |
215 | ||
216 | =item $0 | |
217 | X<$0> X<$PROGRAM_NAME> | |
218 | ||
219 | Contains the name of the program being executed. | |
220 | ||
221 | On some (but not all) operating systems assigning to C<$0> modifies | |
241a59d9 | 222 | the argument area that the C<ps> program sees. On some platforms you |
66d7055b | 223 | may have to use special C<ps> options or a different C<ps> to see the |
241a59d9 | 224 | changes. Modifying the C<$0> is more useful as a way of indicating the |
66d7055b DR |
225 | current program state than it is for hiding the program you're |
226 | running. | |
227 | ||
228 | Note that there are platform-specific limitations on the maximum | |
241a59d9 | 229 | length of C<$0>. In the most extreme case it may be limited to the |
66d7055b DR |
230 | space occupied by the original C<$0>. |
231 | ||
232 | In some platforms there may be arbitrary amount of padding, for | |
233 | example space characters, after the modified name as shown by C<ps>. | |
234 | In some platforms this padding may extend all the way to the original | |
235 | length of the argument area, no matter what you do (this is the case | |
236 | for example with Linux 2.2). | |
237 | ||
238 | Note for BSD users: setting C<$0> does not completely remove "perl" | |
241a59d9 | 239 | from the ps(1) output. For example, setting C<$0> to C<"foobar"> may |
66d7055b DR |
240 | result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix |
241 | and the " (perl)" suffix are shown depends on your exact BSD variant | |
241a59d9 | 242 | and version). This is an operating system feature, Perl cannot help it. |
66d7055b DR |
243 | |
244 | In multithreaded scripts Perl coordinates the threads so that any | |
245 | thread may modify its copy of the C<$0> and the change becomes visible | |
241a59d9 | 246 | to ps(1) (assuming the operating system plays along). Note that |
66d7055b DR |
247 | the view of C<$0> the other threads have will not change since they |
248 | have their own copies of it. | |
249 | ||
250 | If the program has been given to perl via the switches C<-e> or C<-E>, | |
251 | C<$0> will contain the string C<"-e">. | |
252 | ||
60cf4914 | 253 | On Linux as of perl v5.14.0 the legacy process name will be set with |
66d7055b | 254 | C<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as |
241a59d9 | 255 | perl has done since version 4.000. Now system utilities that read the |
66d7055b | 256 | legacy process name such as ps, top and killall will recognize the |
241a59d9 | 257 | name you set when assigning to C<$0>. The string you supply will be |
66d7055b DR |
258 | cut off at 16 bytes, this is a limitation imposed by Linux. |
259 | ||
260 | Mnemonic: same as B<sh> and B<ksh>. | |
261 | ||
b0c22438 | 262 | =item $REAL_GROUP_ID |
a01268b5 | 263 | |
b0c22438 | 264 | =item $GID |
a01268b5 | 265 | |
b0c22438 | 266 | =item $( |
267 | X<$(> X<$GID> X<$REAL_GROUP_ID> | |
a01268b5 | 268 | |
241a59d9 | 269 | The real gid of this process. If you are on a machine that supports |
b0c22438 | 270 | membership in multiple groups simultaneously, gives a space separated |
241a59d9 | 271 | list of groups you are in. The first number is the one returned by |
b0c22438 | 272 | C<getgid()>, and the subsequent ones by C<getgroups()>, one of which may be |
273 | the same as the first number. | |
a01268b5 | 274 | |
b0c22438 | 275 | However, a value assigned to C<$(> must be a single number used to |
241a59d9 FC |
276 | set the real gid. So the value given by C<$(> should I<not> be assigned |
277 | back to C<$(> without being forced numeric, such as by adding zero. Note | |
b0c22438 | 278 | that this is different to the effective gid (C<$)>) which does take a |
279 | list. | |
fe307981 | 280 | |
b0c22438 | 281 | You can change both the real gid and the effective gid at the same |
241a59d9 FC |
282 | time by using C<POSIX::setgid()>. Changes |
283 | to C<$(> require a check to C<$!> | |
b0c22438 | 284 | to detect any possible errors after an attempted change. |
6cef1e77 | 285 | |
241a59d9 | 286 | Mnemonic: parentheses are used to I<group> things. The real gid is the |
b0c22438 | 287 | group you I<left>, if you're running setgid. |
6cef1e77 | 288 | |
b0c22438 | 289 | =item $EFFECTIVE_GROUP_ID |
8e08999f | 290 | |
b0c22438 | 291 | =item $EGID |
81714fb9 | 292 | |
b0c22438 | 293 | =item $) |
294 | X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID> | |
81714fb9 | 295 | |
241a59d9 | 296 | The effective gid of this process. If you are on a machine that |
b0c22438 | 297 | supports membership in multiple groups simultaneously, gives a space |
241a59d9 | 298 | separated list of groups you are in. The first number is the one |
b0c22438 | 299 | returned by C<getegid()>, and the subsequent ones by C<getgroups()>, |
300 | one of which may be the same as the first number. | |
81714fb9 | 301 | |
b0c22438 | 302 | Similarly, a value assigned to C<$)> must also be a space-separated |
241a59d9 FC |
303 | list of numbers. The first number sets the effective gid, and |
304 | the rest (if any) are passed to C<setgroups()>. To get the effect of an | |
b0c22438 | 305 | empty list for C<setgroups()>, just repeat the new effective gid; that is, |
306 | to force an effective gid of 5 and an effectively empty C<setgroups()> | |
307 | list, say C< $) = "5 5" >. | |
81714fb9 | 308 | |
b0c22438 | 309 | You can change both the effective gid and the real gid at the same |
310 | time by using C<POSIX::setgid()> (use only a single numeric argument). | |
311 | Changes to C<$)> require a check to C<$!> to detect any possible errors | |
312 | after an attempted change. | |
44a2ac75 | 313 | |
b0c22438 | 314 | C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on |
241a59d9 | 315 | machines that support the corresponding I<set[re][ug]id()> routine. C<$(> |
b0c22438 | 316 | and C<$)> can be swapped only on machines supporting C<setregid()>. |
3195cf34 | 317 | |
241a59d9 | 318 | Mnemonic: parentheses are used to I<group> things. The effective gid |
b0c22438 | 319 | is the group that's I<right> for you, if you're running setgid. |
44a2ac75 | 320 | |
c82f2f4e DR |
321 | =item $REAL_USER_ID |
322 | ||
323 | =item $UID | |
324 | ||
325 | =item $< | |
326 | X<< $< >> X<$UID> X<$REAL_USER_ID> | |
327 | ||
241a59d9 FC |
328 | The real uid of this process. You can change both the real uid and the |
329 | effective uid at the same time by using C<POSIX::setuid()>. Since | |
c82f2f4e DR |
330 | changes to C<< $< >> require a system call, check C<$!> after a change |
331 | attempt to detect any possible errors. | |
332 | ||
333 | Mnemonic: it's the uid you came I<from>, if you're running setuid. | |
334 | ||
335 | =item $EFFECTIVE_USER_ID | |
336 | ||
337 | =item $EUID | |
338 | ||
339 | =item $> | |
340 | X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID> | |
341 | ||
241a59d9 | 342 | The effective uid of this process. For example: |
c82f2f4e | 343 | |
9548c15c FC |
344 | $< = $>; # set real to effective uid |
345 | ($<,$>) = ($>,$<); # swap real and effective uids | |
c82f2f4e DR |
346 | |
347 | You can change both the effective uid and the real uid at the same | |
241a59d9 | 348 | time by using C<POSIX::setuid()>. Changes to C<< $> >> require a check |
c82f2f4e DR |
349 | to C<$!> to detect any possible errors after an attempted change. |
350 | ||
351 | C<< $< >> and C<< $> >> can be swapped only on machines | |
352 | supporting C<setreuid()>. | |
353 | ||
354 | Mnemonic: it's the uid you went I<to>, if you're running setuid. | |
355 | ||
0b9346e6 | 356 | =item $SUBSCRIPT_SEPARATOR |
357 | ||
358 | =item $SUBSEP | |
359 | ||
360 | =item $; | |
361 | X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR> | |
362 | ||
241a59d9 | 363 | The subscript separator for multidimensional array emulation. If you |
0b9346e6 | 364 | refer to a hash element as |
365 | ||
592708b4 | 366 | $foo{$x,$y,$z} |
0b9346e6 | 367 | |
368 | it really means | |
369 | ||
592708b4 | 370 | $foo{join($;, $x, $y, $z)} |
0b9346e6 | 371 | |
372 | But don't put | |
373 | ||
592708b4 | 374 | @foo{$x,$y,$z} # a slice--note the @ |
0b9346e6 | 375 | |
376 | which means | |
377 | ||
592708b4 | 378 | ($foo{$x},$foo{$y},$foo{$z}) |
0b9346e6 | 379 | |
241a59d9 | 380 | Default is "\034", the same as SUBSEP in B<awk>. If your keys contain |
0b9346e6 | 381 | binary data there might not be any safe value for C<$;>. |
382 | ||
383 | Consider using "real" multidimensional arrays as described | |
384 | in L<perllol>. | |
385 | ||
386 | Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon. | |
387 | ||
0b9346e6 | 388 | =item $a |
389 | ||
390 | =item $b | |
391 | X<$a> X<$b> | |
392 | ||
393 | Special package variables when using C<sort()>, see L<perlfunc/sort>. | |
394 | Because of this specialness C<$a> and C<$b> don't need to be declared | |
395 | (using C<use vars>, or C<our()>) even when using the C<strict 'vars'> | |
241a59d9 | 396 | pragma. Don't lexicalize them with C<my $a> or C<my $b> if you want to |
0b9346e6 | 397 | be able to use them in the C<sort()> comparison block or function. |
398 | ||
0b9346e6 | 399 | =item %ENV |
400 | X<%ENV> | |
401 | ||
241a59d9 | 402 | The hash C<%ENV> contains your current environment. Setting a |
0b9346e6 | 403 | value in C<ENV> changes the environment for any child processes |
404 | you subsequently C<fork()> off. | |
405 | ||
32e006ac | 406 | As of v5.18.0, both keys and values stored in C<%ENV> are stringified. |
a5effbbc KF |
407 | |
408 | my $foo = 1; | |
409 | $ENV{'bar'} = \$foo; | |
410 | if( ref $ENV{'bar'} ) { | |
32e006ac | 411 | say "Pre 5.18.0 Behaviour"; |
a5effbbc | 412 | } else { |
32e006ac | 413 | say "Post 5.18.0 Behaviour"; |
a5effbbc KF |
414 | } |
415 | ||
416 | Previously, only child processes received stringified values: | |
417 | ||
418 | my $foo = 1; | |
419 | $ENV{'bar'} = \$foo; | |
420 | ||
421 | # Always printed 'non ref' | |
6d3f582d FC |
422 | system($^X, '-e', |
423 | q/print ( ref $ENV{'bar'} ? 'ref' : 'non ref' ) /); | |
a5effbbc KF |
424 | |
425 | This happens because you can't really share arbitrary data structures with | |
426 | foreign processes. | |
427 | ||
d2578154 KE |
428 | =item $OLD_PERL_VERSION |
429 | ||
4ad0ecd4 | 430 | =item $] |
b77ebf74 | 431 | X<$]> X<$OLD_PERL_VERSION> |
4ad0ecd4 KE |
432 | |
433 | The revision, version, and subversion of the Perl interpreter, represented | |
434 | as a decimal of the form 5.XXXYYY, where XXX is the version / 1e3 and YYY | |
435 | is the subversion / 1e6. For example, Perl v5.10.1 would be "5.010001". | |
436 | ||
437 | This variable can be used to determine whether the Perl interpreter | |
438 | executing a script is in the right range of versions: | |
439 | ||
601390ce | 440 | warn "No PerlIO!\n" if "$]" < 5.008; |
4ad0ecd4 | 441 | |
601390ce DB |
442 | When comparing C<$]>, numeric comparison operators should be used, but the |
443 | variable should be stringified first to avoid issues where its original | |
444 | numeric value is inaccurate. | |
4ad0ecd4 KE |
445 | |
446 | See also the documentation of C<use VERSION> and C<require VERSION> | |
447 | for a convenient way to fail if the running Perl interpreter is too old. | |
448 | ||
449 | See L</$^V> for a representation of the Perl version as a L<version> | |
450 | object, which allows more flexible string comparisons. | |
451 | ||
452 | The main advantage of C<$]> over C<$^V> is that it works the same on any | |
453 | version of Perl. The disadvantages are that it can't easily be compared | |
454 | to versions in other formats (e.g. literal v-strings, "v1.2.3" or | |
601390ce DB |
455 | version objects) and numeric comparisons are subject to the binary |
456 | floating point representation; it's good for numeric literal version | |
457 | checks and bad for comparing to a variable that hasn't been | |
458 | sanity-checked. | |
4ad0ecd4 | 459 | |
9fcc2314 AP |
460 | The C<$OLD_PERL_VERSION> form was added in Perl v5.20.0 for historical |
461 | reasons but its use is discouraged. (If your reason to use C<$]> is to | |
462 | run code on old perls then referring to it as C<$OLD_PERL_VERSION> would | |
463 | be self-defeating.) | |
4ad0ecd4 | 464 | |
9fcc2314 | 465 | Mnemonic: Is this version of perl in the right bracket? |
83c1fffe | 466 | |
b0c22438 | 467 | =item $SYSTEM_FD_MAX |
5b2b9c68 | 468 | |
b0c22438 | 469 | =item $^F |
470 | X<$^F> X<$SYSTEM_FD_MAX> | |
5b2b9c68 | 471 | |
241a59d9 | 472 | The maximum system file descriptor, ordinarily 2. System file |
b0c22438 | 473 | descriptors are passed to C<exec()>ed processes, while higher file |
241a59d9 FC |
474 | descriptors are not. Also, during an |
475 | C<open()>, system file descriptors are | |
b0c22438 | 476 | preserved even if the C<open()> fails (ordinary file descriptors are |
241a59d9 | 477 | closed before the C<open()> is attempted). The close-on-exec |
b0c22438 | 478 | status of a file descriptor will be decided according to the value of |
479 | C<$^F> when the corresponding file, pipe, or socket was opened, not the | |
480 | time of the C<exec()>. | |
5b2b9c68 | 481 | |
0b9346e6 | 482 | =item @F |
483 | X<@F> | |
484 | ||
485 | The array C<@F> contains the fields of each line read in when autosplit | |
028611fa DB |
486 | mode is turned on. See L<perlrun|perlrun/-a> for the B<-a> switch. This |
487 | array is package-specific, and must be declared or given a full package | |
488 | name if not in package main when running under C<strict 'vars'>. | |
0b9346e6 | 489 | |
0b9346e6 | 490 | =item @INC |
491 | X<@INC> | |
492 | ||
493 | The array C<@INC> contains the list of places that the C<do EXPR>, | |
241a59d9 | 494 | C<require>, or C<use> constructs look for their library files. It |
0b9346e6 | 495 | initially consists of the arguments to any B<-I> command-line |
496 | switches, followed by the default Perl library, probably | |
87e54f02 N |
497 | F</usr/local/lib/perl>. |
498 | Prior to Perl 5.26, C<.> -which represents the current directory, was included | |
499 | in C<@INC>; it has been removed. This change in behavior is documented | |
500 | in L<C<PERL_USE_UNSAFE_INC>|perlrun/PERL_USE_UNSAFE_INC> and it is | |
501 | not recommended that C<.> be re-added to C<@INC>. | |
502 | If you need to modify C<@INC> at runtime, you should use the C<use lib> pragma | |
503 | to get the machine-dependent library properly loaded as well: | |
0b9346e6 | 504 | |
9548c15c FC |
505 | use lib '/mypath/libdir/'; |
506 | use SomeMod; | |
0b9346e6 | 507 | |
508 | You can also insert hooks into the file inclusion system by putting Perl | |
241a59d9 FC |
509 | code directly into C<@INC>. Those hooks may be subroutine references, |
510 | array references or blessed objects. See L<perlfunc/require> for details. | |
0b9346e6 | 511 | |
512 | =item %INC | |
513 | X<%INC> | |
514 | ||
515 | The hash C<%INC> contains entries for each filename included via the | |
241a59d9 | 516 | C<do>, C<require>, or C<use> operators. The key is the filename |
0b9346e6 | 517 | you specified (with module names converted to pathnames), and the |
241a59d9 | 518 | value is the location of the file found. The C<require> |
0b9346e6 | 519 | operator uses this hash to determine whether a particular file has |
520 | already been included. | |
521 | ||
522 | If the file was loaded via a hook (e.g. a subroutine reference, see | |
523 | L<perlfunc/require> for a description of these hooks), this hook is | |
241a59d9 | 524 | by default inserted into C<%INC> in place of a filename. Note, however, |
0b9346e6 | 525 | that the hook may have set the C<%INC> entry by itself to provide some more |
526 | specific info. | |
527 | ||
b0c22438 | 528 | =item $INPLACE_EDIT |
a0d0e21e | 529 | |
b0c22438 | 530 | =item $^I |
531 | X<$^I> X<$INPLACE_EDIT> | |
a0d0e21e | 532 | |
241a59d9 | 533 | The current value of the inplace-edit extension. Use C<undef> to disable |
b0c22438 | 534 | inplace editing. |
a0d0e21e | 535 | |
b0c22438 | 536 | Mnemonic: value of B<-i> switch. |
a0d0e21e | 537 | |
bf38d944 H |
538 | =item @ISA |
539 | X<@ISA> | |
540 | ||
541 | Each package contains a special array called C<@ISA> which contains a list | |
542 | of that class's parent classes, if any. This array is simply a list of | |
543 | scalars, each of which is a string that corresponds to a package name. The | |
544 | array is examined when Perl does method resolution, which is covered in | |
545 | L<perlobj>. | |
546 | ||
5312fe6c AP |
547 | To load packages while adding them to C<@ISA>, see the L<parent> pragma. The |
548 | discouraged L<base> pragma does this as well, but should not be used except | |
549 | when compatibility with the discouraged L<fields> pragma is required. | |
bf38d944 | 550 | |
b0c22438 | 551 | =item $^M |
552 | X<$^M> | |
a0d0e21e | 553 | |
b0c22438 | 554 | By default, running out of memory is an untrappable, fatal error. |
555 | However, if suitably built, Perl can use the contents of C<$^M> | |
241a59d9 | 556 | as an emergency memory pool after C<die()>ing. Suppose that your Perl |
b0c22438 | 557 | were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc. |
558 | Then | |
a0d0e21e | 559 | |
9548c15c | 560 | $^M = 'a' x (1 << 16); |
a0d0e21e | 561 | |
241a59d9 | 562 | would allocate a 64K buffer for use in an emergency. See the |
b0c22438 | 563 | F<INSTALL> file in the Perl distribution for information on how to |
241a59d9 | 564 | add custom C compilation flags when compiling perl. To discourage casual |
b0c22438 | 565 | use of this advanced feature, there is no L<English|English> long name for |
566 | this variable. | |
a0d0e21e | 567 | |
b0c22438 | 568 | This variable was added in Perl 5.004. |
a0d0e21e | 569 | |
b0c22438 | 570 | =item $OSNAME |
a0d0e21e | 571 | |
b0c22438 | 572 | =item $^O |
573 | X<$^O> X<$OSNAME> | |
a0d0e21e | 574 | |
b0c22438 | 575 | The name of the operating system under which this copy of Perl was |
241a59d9 | 576 | built, as determined during the configuration process. For examples |
b0c22438 | 577 | see L<perlport/PLATFORMS>. |
a0d0e21e | 578 | |
241a59d9 | 579 | The value is identical to C<$Config{'osname'}>. See also L<Config> |
028611fa | 580 | and the B<-V> command-line switch documented in L<perlrun|perlrun/-V>. |
a0d0e21e | 581 | |
b0c22438 | 582 | In Windows platforms, C<$^O> is not very helpful: since it is always |
583 | C<MSWin32>, it doesn't tell the difference between | |
241a59d9 | 584 | 95/98/ME/NT/2000/XP/CE/.NET. Use C<Win32::GetOSName()> or |
b0c22438 | 585 | Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish |
586 | between the variants. | |
a0d0e21e | 587 | |
b0c22438 | 588 | This variable was added in Perl 5.003. |
a0d0e21e | 589 | |
1fa81471 DR |
590 | =item %SIG |
591 | X<%SIG> | |
a0d0e21e | 592 | |
241a59d9 | 593 | The hash C<%SIG> contains signal handlers for signals. For example: |
a0d0e21e | 594 | |
9548c15c FC |
595 | sub handler { # 1st argument is signal name |
596 | my($sig) = @_; | |
597 | print "Caught a SIG$sig--shutting down\n"; | |
598 | close(LOG); | |
599 | exit(0); | |
600 | } | |
a0d0e21e | 601 | |
9548c15c FC |
602 | $SIG{'INT'} = \&handler; |
603 | $SIG{'QUIT'} = \&handler; | |
604 | ... | |
605 | $SIG{'INT'} = 'DEFAULT'; # restore default action | |
606 | $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT | |
a0d0e21e | 607 | |
1fa81471 | 608 | Using a value of C<'IGNORE'> usually has the effect of ignoring the |
241a59d9 | 609 | signal, except for the C<CHLD> signal. See L<perlipc> for more about |
40719f1d C |
610 | this special case. Using an empty string or C<undef> as the value has |
611 | the same effect as C<'DEFAULT'>. | |
a0d0e21e | 612 | |
1fa81471 | 613 | Here are some other examples: |
a0d0e21e | 614 | |
9548c15c FC |
615 | $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not |
616 | # recommended) | |
617 | $SIG{"PIPE"} = \&Plumber; # just fine; assume current | |
618 | # Plumber | |
619 | $SIG{"PIPE"} = *Plumber; # somewhat esoteric | |
620 | $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() | |
621 | # return?? | |
a0d0e21e | 622 | |
1fa81471 DR |
623 | Be sure not to use a bareword as the name of a signal handler, |
624 | lest you inadvertently call it. | |
a0d0e21e | 625 | |
40719f1d C |
626 | Using a string that doesn't correspond to any existing function or a |
627 | glob that doesn't contain a code slot is equivalent to C<'IGNORE'>, | |
628 | but a warning is emitted when the handler is being called (the warning | |
629 | is not emitted for the internal hooks described below). | |
630 | ||
1fa81471 | 631 | If your system has the C<sigaction()> function then signal handlers |
241a59d9 | 632 | are installed using it. This means you get reliable signal handling. |
a0d0e21e | 633 | |
60cf4914 | 634 | The default delivery policy of signals changed in Perl v5.8.0 from |
1fa81471 | 635 | immediate (also known as "unsafe") to deferred, also known as "safe |
241a59d9 | 636 | signals". See L<perlipc> for more information. |
a0d0e21e | 637 | |
241a59d9 | 638 | Certain internal hooks can be also set using the C<%SIG> hash. The |
1fa81471 | 639 | routine indicated by C<$SIG{__WARN__}> is called when a warning |
241a59d9 FC |
640 | message is about to be printed. The warning message is passed as the |
641 | first argument. The presence of a C<__WARN__> hook causes the | |
642 | ordinary printing of warnings to C<STDERR> to be suppressed. You can | |
1fa81471 DR |
643 | use this to save warnings in a variable, or turn warnings into fatal |
644 | errors, like this: | |
a0d0e21e | 645 | |
9548c15c FC |
646 | local $SIG{__WARN__} = sub { die $_[0] }; |
647 | eval $proggie; | |
a8f8344d | 648 | |
40719f1d C |
649 | As the C<'IGNORE'> hook is not supported by C<__WARN__>, its effect is |
650 | the same as using C<'DEFAULT'>. You can disable warnings using the | |
651 | empty subroutine: | |
f86702cc | 652 | |
9548c15c | 653 | local $SIG{__WARN__} = sub {}; |
55602bd2 | 654 | |
b0c22438 | 655 | The routine indicated by C<$SIG{__DIE__}> is called when a fatal |
241a59d9 FC |
656 | exception is about to be thrown. The error message is passed as the |
657 | first argument. When a C<__DIE__> hook routine returns, the exception | |
b0c22438 | 658 | processing continues as it would have in the absence of the hook, |
c94b42ea DM |
659 | unless the hook routine itself exits via a C<goto &sub>, a loop exit, |
660 | or a C<die()>. The C<__DIE__> handler is explicitly disabled during | |
661 | the call, so that you can die from a C<__DIE__> handler. Similarly | |
662 | for C<__WARN__>. | |
e5218da5 | 663 | |
4a29ab5e A |
664 | The C<$SIG{__DIE__}> hook is called even inside an C<eval()>. It was |
665 | never intended to happen this way, but an implementation glitch made | |
666 | this possible. This used to be deprecated, as it allowed strange action | |
667 | at a distance like rewriting a pending exception in C<$@>. Plans to | |
668 | rectify this have been scrapped, as users found that rewriting a | |
669 | pending exception is actually a useful feature, and not a bug. | |
b0c22438 | 670 | |
bba48ac3 | 671 | The C<$SIG{__DIE__}> doesn't support C<'IGNORE'>; it has the same |
40719f1d C |
672 | effect as C<'DEFAULT'>. |
673 | ||
b0c22438 | 674 | C<__DIE__>/C<__WARN__> handlers are very special in one respect: they |
241a59d9 | 675 | may be called to report (probable) errors found by the parser. In such |
b0c22438 | 676 | a case the parser may be in inconsistent state, so any attempt to |
677 | evaluate Perl code from such a handler will probably result in a | |
241a59d9 | 678 | segfault. This means that warnings or errors that result from parsing |
b0c22438 | 679 | Perl should be used with extreme caution, like this: |
e5218da5 | 680 | |
9548c15c FC |
681 | require Carp if defined $^S; |
682 | Carp::confess("Something wrong") if defined &Carp::confess; | |
683 | die "Something wrong, but could not load Carp to give " | |
684 | . "backtrace...\n\t" | |
685 | . "To see backtrace try starting Perl with -MCarp switch"; | |
e5218da5 | 686 | |
b0c22438 | 687 | Here the first line will load C<Carp> I<unless> it is the parser who |
241a59d9 FC |
688 | called the handler. The second line will print backtrace and die if |
689 | C<Carp> was available. The third line will be executed only if C<Carp> was | |
b0c22438 | 690 | not available. |
0a378802 | 691 | |
0b9346e6 | 692 | Having to even think about the C<$^S> variable in your exception |
241a59d9 FC |
693 | handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented |
694 | invites grievous and difficult to track down errors. Avoid it | |
0b9346e6 | 695 | and use an C<END{}> or CORE::GLOBAL::die override instead. |
696 | ||
b0c22438 | 697 | See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and |
698 | L<warnings> for additional information. | |
0a378802 | 699 | |
b0c22438 | 700 | =item $BASETIME |
6ab308ee | 701 | |
b0c22438 | 702 | =item $^T |
703 | X<$^T> X<$BASETIME> | |
6ab308ee | 704 | |
b0c22438 | 705 | The time at which the program began running, in seconds since the |
241a59d9 | 706 | epoch (beginning of 1970). The values returned by the B<-M>, B<-A>, |
b0c22438 | 707 | and B<-C> filetests are based on this value. |
a0d0e21e | 708 | |
b0c22438 | 709 | =item $PERL_VERSION |
a0d0e21e | 710 | |
b0c22438 | 711 | =item $^V |
712 | X<$^V> X<$PERL_VERSION> | |
a0d0e21e | 713 | |
e34263aa KW |
714 | =for comment |
715 | These are documented in the generated file lib/Config.pod. This looks | |
716 | like as good a place as any to give notice that they are documented. | |
717 | ||
b0c22438 | 718 | The revision, version, and subversion of the Perl interpreter, |
eb82332c | 719 | represented as a L<version> object. |
748a9306 | 720 | |
60cf4914 BF |
721 | This variable first appeared in perl v5.6.0; earlier versions of perl |
722 | will see an undefined value. Before perl v5.10.0 C<$^V> was represented | |
f20d3573 | 723 | as a v-string rather than a L<version> object. |
55602bd2 | 724 | |
b0c22438 | 725 | C<$^V> can be used to determine whether the Perl interpreter executing |
241a59d9 | 726 | a script is in the right range of versions. For example: |
a0d0e21e | 727 | |
9548c15c | 728 | warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1 |
a0d0e21e | 729 | |
f20d3573 DG |
730 | While version objects overload stringification, to portably convert |
731 | C<$^V> into its string representation, use C<sprintf()>'s C<"%vd"> | |
732 | conversion, which works for both v-strings or version objects: | |
a0d0e21e | 733 | |
9548c15c | 734 | printf "version is v%vd\n", $^V; # Perl's version |
a0d0e21e | 735 | |
b0c22438 | 736 | See the documentation of C<use VERSION> and C<require VERSION> |
737 | for a convenient way to fail if the running Perl interpreter is too old. | |
4d76a344 | 738 | |
6a29646e | 739 | See also C<L</$]>> for a decimal representation of the Perl version. |
a0d0e21e | 740 | |
f20d3573 DG |
741 | The main advantage of C<$^V> over C<$]> is that, for Perl v5.10.0 or |
742 | later, it overloads operators, allowing easy comparison against other | |
743 | version representations (e.g. decimal, literal v-string, "v1.2.3", or | |
744 | objects). The disadvantage is that prior to v5.10.0, it was only a | |
6a29646e KW |
745 | literal v-string, which can't be easily printed or compared, whereas |
746 | the behavior of C<$]> is unchanged on all versions of Perl. | |
a0d0e21e | 747 | |
eb82332c | 748 | Mnemonic: use ^V for a version object. |
a0d0e21e | 749 | |
b0c22438 | 750 | =item ${^WIN32_SLOPPY_STAT} |
5b442a2a | 751 | X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl> |
a0d0e21e | 752 | |
b0c22438 | 753 | If this variable is set to a true value, then C<stat()> on Windows will |
241a59d9 | 754 | not try to open the file. This means that the link count cannot be |
b0c22438 | 755 | determined and file attributes may be out of date if additional |
241a59d9 | 756 | hardlinks to the file exist. On the other hand, not opening the file |
b0c22438 | 757 | is considerably faster, especially for files on network drives. |
a0d0e21e | 758 | |
b0c22438 | 759 | This variable could be set in the F<sitecustomize.pl> file to |
760 | configure the local Perl installation to use "sloppy" C<stat()> by | |
028611fa DB |
761 | default. See the documentation for B<-f> in L<perlrun|perlrun/-f> |
762 | for more information about site customization. | |
a0d0e21e | 763 | |
60cf4914 | 764 | This variable was added in Perl v5.10.0. |
a0d0e21e | 765 | |
b0c22438 | 766 | =item $EXECUTABLE_NAME |
a0d0e21e | 767 | |
b0c22438 | 768 | =item $^X |
769 | X<$^X> X<$EXECUTABLE_NAME> | |
a0d0e21e | 770 | |
b0c22438 | 771 | The name used to execute the current copy of Perl, from C's |
772 | C<argv[0]> or (where supported) F</proc/self/exe>. | |
a043a685 | 773 | |
b0c22438 | 774 | Depending on the host operating system, the value of C<$^X> may be |
775 | a relative or absolute pathname of the perl program file, or may | |
776 | be the string used to invoke perl but not the pathname of the | |
241a59d9 | 777 | perl program file. Also, most operating systems permit invoking |
b0c22438 | 778 | programs that are not in the PATH environment variable, so there |
241a59d9 | 779 | is no guarantee that the value of C<$^X> is in PATH. For VMS, the |
b0c22438 | 780 | value may or may not include a version number. |
a0d0e21e | 781 | |
b0c22438 | 782 | You usually can use the value of C<$^X> to re-invoke an independent |
783 | copy of the same perl that is currently running, e.g., | |
a0d0e21e | 784 | |
9548c15c | 785 | @first_run = `$^X -le "print int rand 100 for 1..100"`; |
a0d0e21e | 786 | |
b0c22438 | 787 | But recall that not all operating systems support forking or |
788 | capturing of the output of commands, so this complex statement | |
789 | may not be portable. | |
a0d0e21e | 790 | |
b0c22438 | 791 | It is not safe to use the value of C<$^X> as a path name of a file, |
792 | as some operating systems that have a mandatory suffix on | |
793 | executable files do not require use of the suffix when invoking | |
241a59d9 | 794 | a command. To convert the value of C<$^X> to a path name, use the |
b0c22438 | 795 | following statements: |
8cc95fdb | 796 | |
9548c15c FC |
797 | # Build up a set of file names (not command names). |
798 | use Config; | |
799 | my $this_perl = $^X; | |
800 | if ($^O ne 'VMS') { | |
801 | $this_perl .= $Config{_exe} | |
802 | unless $this_perl =~ m/$Config{_exe}$/i; | |
803 | } | |
8cc95fdb | 804 | |
b0c22438 | 805 | Because many operating systems permit anyone with read access to |
806 | the Perl program file to make a copy of it, patch the copy, and | |
807 | then execute the copy, the security-conscious Perl programmer | |
808 | should take care to invoke the installed copy of perl, not the | |
241a59d9 | 809 | copy referenced by C<$^X>. The following statements accomplish |
b0c22438 | 810 | this goal, and produce a pathname that can be invoked as a |
811 | command or referenced as a file. | |
a043a685 | 812 | |
9548c15c FC |
813 | use Config; |
814 | my $secure_perl_path = $Config{perlpath}; | |
815 | if ($^O ne 'VMS') { | |
816 | $secure_perl_path .= $Config{_exe} | |
817 | unless $secure_perl_path =~ m/$Config{_exe}$/i; | |
818 | } | |
a0d0e21e | 819 | |
b0c22438 | 820 | =back |
a0d0e21e | 821 | |
b0c22438 | 822 | =head2 Variables related to regular expressions |
823 | ||
824 | Most of the special variables related to regular expressions are side | |
241a59d9 FC |
825 | effects. Perl sets these variables when it has a successful match, so |
826 | you should check the match result before using them. For instance: | |
b0c22438 | 827 | |
9548c15c FC |
828 | if( /P(A)TT(ER)N/ ) { |
829 | print "I found $1 and $2\n"; | |
830 | } | |
b0c22438 | 831 | |
0b9346e6 | 832 | These variables are read-only and dynamically-scoped, unless we note |
b0c22438 | 833 | otherwise. |
834 | ||
0b9346e6 | 835 | The dynamic nature of the regular expression variables means that |
836 | their value is limited to the block that they are in, as demonstrated | |
837 | by this bit of code: | |
b0c22438 | 838 | |
9548c15c FC |
839 | my $outer = 'Wallace and Grommit'; |
840 | my $inner = 'Mutt and Jeff'; | |
0b9346e6 | 841 | |
9548c15c | 842 | my $pattern = qr/(\S+) and (\S+)/; |
0b9346e6 | 843 | |
9548c15c | 844 | sub show_n { print "\$1 is $1; \$2 is $2\n" } |
0b9346e6 | 845 | |
9548c15c FC |
846 | { |
847 | OUTER: | |
848 | show_n() if $outer =~ m/$pattern/; | |
0b9346e6 | 849 | |
9548c15c FC |
850 | INNER: { |
851 | show_n() if $inner =~ m/$pattern/; | |
852 | } | |
0b9346e6 | 853 | |
9548c15c FC |
854 | show_n(); |
855 | } | |
b0c22438 | 856 | |
0b9346e6 | 857 | The output shows that while in the C<OUTER> block, the values of C<$1> |
241a59d9 | 858 | and C<$2> are from the match against C<$outer>. Inside the C<INNER> |
0b9346e6 | 859 | block, the values of C<$1> and C<$2> are from the match against |
860 | C<$inner>, but only until the end of the block (i.e. the dynamic | |
241a59d9 | 861 | scope). After the C<INNER> block completes, the values of C<$1> and |
0b9346e6 | 862 | C<$2> return to the values for the match against C<$outer> even though |
b0c22438 | 863 | we have not made another match: |
864 | ||
9548c15c FC |
865 | $1 is Wallace; $2 is Grommit |
866 | $1 is Mutt; $2 is Jeff | |
867 | $1 is Wallace; $2 is Grommit | |
a0d0e21e | 868 | |
40445027 | 869 | =head3 Performance issues |
0b9346e6 | 870 | |
40445027 DM |
871 | Traditionally in Perl, any use of any of the three variables C<$`>, C<$&> |
872 | or C<$'> (or their C<use English> equivalents) anywhere in the code, caused | |
873 | all subsequent successful pattern matches to make a copy of the matched | |
874 | string, in case the code might subsequently access one of those variables. | |
875 | This imposed a considerable performance penalty across the whole program, | |
876 | so generally the use of these variables has been discouraged. | |
0b9346e6 | 877 | |
40445027 DM |
878 | In Perl 5.6.0 the C<@-> and C<@+> dynamic arrays were introduced that |
879 | supply the indices of successful matches. So you could for example do | |
880 | this: | |
881 | ||
882 | $str =~ /pattern/; | |
883 | ||
33f0d962 | 884 | print $`, $&, $'; # bad: performance hit |
40445027 | 885 | |
33f0d962 | 886 | print # good: no performance hit |
40445027 DM |
887 | substr($str, 0, $-[0]), |
888 | substr($str, $-[0], $+[0]-$-[0]), | |
889 | substr($str, $+[0]); | |
890 | ||
891 | In Perl 5.10.0 the C</p> match operator flag and the C<${^PREMATCH}>, | |
892 | C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed | |
893 | you to suffer the penalties only on patterns marked with C</p>. | |
894 | ||
895 | In Perl 5.18.0 onwards, perl started noting the presence of each of the | |
896 | three variables separately, and only copied that part of the string | |
897 | required; so in | |
898 | ||
899 | $`; $&; "abcdefgh" =~ /d/ | |
900 | ||
901 | perl would only copy the "abcd" part of the string. That could make a big | |
902 | difference in something like | |
903 | ||
904 | $str = 'x' x 1_000_000; | |
905 | $&; # whoops | |
906 | $str =~ /x/g # one char copied a million times, not a million chars | |
907 | ||
908 | In Perl 5.20.0 a new copy-on-write system was enabled by default, which | |
909 | finally fixes all performance issues with these three variables, and makes | |
910 | them safe to use anywhere. | |
911 | ||
912 | The C<Devel::NYTProf> and C<Devel::FindAmpersand> modules can help you | |
913 | find uses of these problematic match variables in your code. | |
13b0f67d | 914 | |
b0c22438 | 915 | =over 8 |
a0d0e21e | 916 | |
b0c22438 | 917 | =item $<I<digits>> ($1, $2, ...) |
27deb0cf | 918 | X<$1> X<$2> X<$3> X<$I<digits>> |
8cc95fdb | 919 | |
b0c22438 | 920 | Contains the subpattern from the corresponding set of capturing |
921 | parentheses from the last successful pattern match, not counting patterns | |
922 | matched in nested blocks that have been exited already. | |
8cc95fdb | 923 | |
27deb0cf YO |
924 | Note there is a distinction between a capture buffer which matches |
925 | the empty string a capture buffer which is optional. Eg, C<(x?)> and | |
926 | C<(x)?> The latter may be undef, the former not. | |
927 | ||
b0c22438 | 928 | These variables are read-only and dynamically-scoped. |
a043a685 | 929 | |
b0c22438 | 930 | Mnemonic: like \digits. |
a0d0e21e | 931 | |
27deb0cf YO |
932 | =item @{^CAPTURE} |
933 | X<@{^CAPTURE}> X<@^CAPTURE> | |
934 | ||
95013431 YO |
935 | An array which exposes the contents of the capture buffers, if any, of |
936 | the last successful pattern match, not counting patterns matched | |
27deb0cf YO |
937 | in nested blocks that have been exited already. |
938 | ||
939 | Note that the 0 index of @{^CAPTURE} is equivalent to $1, the 1 index | |
940 | is equivalent to $2, etc. | |
941 | ||
942 | if ("foal"=~/(.)(.)(.)(.)/) { | |
943 | print join "-", @{^CAPTURE}; | |
944 | } | |
945 | ||
946 | should output "f-o-a-l". | |
947 | ||
135226fa KW |
948 | See also L<<< /$<I<digits>> ($1, $2, ...) >>>, L</%{^CAPTURE}> and |
949 | L</%{^CAPTURE_ALL}>. | |
27deb0cf | 950 | |
95013431 YO |
951 | Note that unlike most other regex magic variables there is no single |
952 | letter equivalent to C<@{^CAPTURE}>. | |
953 | ||
27deb0cf YO |
954 | This variable was added in 5.25.7 |
955 | ||
b0c22438 | 956 | =item $MATCH |
a0d0e21e | 957 | |
b0c22438 | 958 | =item $& |
959 | X<$&> X<$MATCH> | |
a0d0e21e | 960 | |
b0c22438 | 961 | The string matched by the last successful pattern match (not counting |
962 | any matches hidden within a BLOCK or C<eval()> enclosed by the current | |
963 | BLOCK). | |
a0d0e21e | 964 | |
40445027 DM |
965 | See L</Performance issues> above for the serious performance implications |
966 | of using this variable (even once) in your code. | |
80bca1b4 | 967 | |
b0c22438 | 968 | This variable is read-only and dynamically-scoped. |
f9cbb277 | 969 | |
b0c22438 | 970 | Mnemonic: like C<&> in some editors. |
0b9346e6 | 971 | |
b0c22438 | 972 | =item ${^MATCH} |
973 | X<${^MATCH}> | |
a0d0e21e | 974 | |
b0c22438 | 975 | This is similar to C<$&> (C<$MATCH>) except that it does not incur the |
13b0f67d | 976 | performance penalty associated with that variable. |
40445027 DM |
977 | |
978 | See L</Performance issues> above. | |
979 | ||
13b0f67d | 980 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 981 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
982 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
983 | C<${^MATCH}> does the same thing as C<$MATCH>. | |
80bca1b4 | 984 | |
60cf4914 | 985 | This variable was added in Perl v5.10.0. |
4bc88a62 | 986 | |
b0c22438 | 987 | This variable is read-only and dynamically-scoped. |
e2975953 | 988 | |
b0c22438 | 989 | =item $PREMATCH |
52c447a8 | 990 | |
b0c22438 | 991 | =item $` |
5b442a2a | 992 | X<$`> X<$PREMATCH> X<${^PREMATCH}> |
7636ea95 | 993 | |
b0c22438 | 994 | The string preceding whatever was matched by the last successful |
995 | pattern match, not counting any matches hidden within a BLOCK or C<eval> | |
0b9346e6 | 996 | enclosed by the current BLOCK. |
a0d0e21e | 997 | |
40445027 DM |
998 | See L</Performance issues> above for the serious performance implications |
999 | of using this variable (even once) in your code. | |
a0d0e21e | 1000 | |
b0c22438 | 1001 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 1002 | |
b0c22438 | 1003 | Mnemonic: C<`> often precedes a quoted string. |
f83ed198 | 1004 | |
b0c22438 | 1005 | =item ${^PREMATCH} |
5b442a2a | 1006 | X<$`> X<${^PREMATCH}> |
a0d0e21e | 1007 | |
b0c22438 | 1008 | This is similar to C<$`> ($PREMATCH) except that it does not incur the |
13b0f67d | 1009 | performance penalty associated with that variable. |
40445027 DM |
1010 | |
1011 | See L</Performance issues> above. | |
1012 | ||
13b0f67d | 1013 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 1014 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
1015 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
1016 | C<${^PREMATCH}> does the same thing as C<$PREMATCH>. | |
a0d0e21e | 1017 | |
4a70680a | 1018 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1019 | |
b0c22438 | 1020 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 1021 | |
b0c22438 | 1022 | =item $POSTMATCH |
16070b82 | 1023 | |
b0c22438 | 1024 | =item $' |
5b442a2a | 1025 | X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@-> |
305aace0 | 1026 | |
b0c22438 | 1027 | The string following whatever was matched by the last successful |
1028 | pattern match (not counting any matches hidden within a BLOCK or C<eval()> | |
241a59d9 | 1029 | enclosed by the current BLOCK). Example: |
305aace0 | 1030 | |
9548c15c FC |
1031 | local $_ = 'abcdefghi'; |
1032 | /def/; | |
1033 | print "$`:$&:$'\n"; # prints abc:def:ghi | |
305aace0 | 1034 | |
40445027 DM |
1035 | See L</Performance issues> above for the serious performance implications |
1036 | of using this variable (even once) in your code. | |
a0d0e21e | 1037 | |
b0c22438 | 1038 | This variable is read-only and dynamically-scoped. |
1039 | ||
1040 | Mnemonic: C<'> often follows a quoted string. | |
1041 | ||
1042 | =item ${^POSTMATCH} | |
5b442a2a | 1043 | X<${^POSTMATCH}> X<$'> X<$POSTMATCH> |
b0c22438 | 1044 | |
1045 | This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the | |
13b0f67d | 1046 | performance penalty associated with that variable. |
40445027 DM |
1047 | |
1048 | See L</Performance issues> above. | |
1049 | ||
13b0f67d | 1050 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 1051 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
1052 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
1053 | C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>. | |
b0c22438 | 1054 | |
60cf4914 | 1055 | This variable was added in Perl v5.10.0. |
b0c22438 | 1056 | |
1057 | This variable is read-only and dynamically-scoped. | |
1058 | ||
1059 | =item $LAST_PAREN_MATCH | |
1060 | ||
1061 | =item $+ | |
1062 | X<$+> X<$LAST_PAREN_MATCH> | |
1063 | ||
0b9dad94 DM |
1064 | The text matched by the highest used capture group of the last |
1065 | successful search pattern. It is logically equivalent to the highest | |
1066 | numbered capture variable (C<$1>, C<$2>, ...) which has a defined value. | |
1067 | ||
b0c22438 | 1068 | This is useful if you don't know which one of a set of alternative patterns |
241a59d9 | 1069 | matched. For example: |
b0c22438 | 1070 | |
9548c15c | 1071 | /Version: (.*)|Revision: (.*)/ && ($rev = $+); |
b0c22438 | 1072 | |
1073 | This variable is read-only and dynamically-scoped. | |
1074 | ||
1075 | Mnemonic: be positive and forward looking. | |
1076 | ||
1077 | =item $LAST_SUBMATCH_RESULT | |
1078 | ||
1079 | =item $^N | |
5b442a2a | 1080 | X<$^N> X<$LAST_SUBMATCH_RESULT> |
b0c22438 | 1081 | |
1082 | The text matched by the used group most-recently closed (i.e. the group | |
1083 | with the rightmost closing parenthesis) of the last successful search | |
0b9dad94 DM |
1084 | pattern. This is subtly different from C<$+>. For example in |
1085 | ||
1086 | "ab" =~ /^((.)(.))$/ | |
1087 | ||
1088 | we have | |
1089 | ||
1090 | $1,$^N have the value "ab" | |
1091 | $2 has the value "a" | |
1092 | $3,$+ have the value "b" | |
b0c22438 | 1093 | |
1094 | This is primarily used inside C<(?{...})> blocks for examining text | |
241a59d9 | 1095 | recently matched. For example, to effectively capture text to a variable |
b0c22438 | 1096 | (in addition to C<$1>, C<$2>, etc.), replace C<(...)> with |
1097 | ||
9548c15c | 1098 | (?:(...)(?{ $var = $^N })) |
b0c22438 | 1099 | |
1100 | By setting and then using C<$var> in this way relieves you from having to | |
1101 | worry about exactly which numbered set of parentheses they are. | |
1102 | ||
60cf4914 | 1103 | This variable was added in Perl v5.8.0. |
b0c22438 | 1104 | |
1105 | Mnemonic: the (possibly) Nested parenthesis that most recently closed. | |
1106 | ||
1107 | =item @LAST_MATCH_END | |
1108 | ||
1109 | =item @+ | |
1110 | X<@+> X<@LAST_MATCH_END> | |
1111 | ||
1112 | This array holds the offsets of the ends of the last successful | |
241a59d9 FC |
1113 | submatches in the currently active dynamic scope. C<$+[0]> is |
1114 | the offset into the string of the end of the entire match. This | |
b0c22438 | 1115 | is the same value as what the C<pos> function returns when called |
241a59d9 | 1116 | on the variable that was matched against. The I<n>th element |
b0c22438 | 1117 | of this array holds the offset of the I<n>th submatch, so |
1118 | C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset | |
241a59d9 FC |
1119 | past where C<$2> ends, and so on. You can use C<$#+> to determine |
1120 | how many subgroups were in the last successful match. See the | |
b0c22438 | 1121 | examples given for the C<@-> variable. |
1122 | ||
60cf4914 | 1123 | This variable was added in Perl v5.6.0. |
b0c22438 | 1124 | |
27deb0cf YO |
1125 | =item %{^CAPTURE} |
1126 | ||
b0c22438 | 1127 | =item %LAST_PAREN_MATCH |
1128 | ||
1129 | =item %+ | |
27deb0cf | 1130 | X<%+> X<%LAST_PAREN_MATCH> X<%{^CAPTURE}> |
b0c22438 | 1131 | |
1132 | Similar to C<@+>, the C<%+> hash allows access to the named capture | |
1133 | buffers, should they exist, in the last successful match in the | |
1134 | currently active dynamic scope. | |
1135 | ||
1136 | For example, C<$+{foo}> is equivalent to C<$1> after the following match: | |
1137 | ||
9548c15c | 1138 | 'foo' =~ /(?<foo>foo)/; |
b0c22438 | 1139 | |
1140 | The keys of the C<%+> hash list only the names of buffers that have | |
1141 | captured (and that are thus associated to defined values). | |
1142 | ||
33727e0f LM |
1143 | If multiple distinct capture groups have the same name, then |
1144 | C<$+{NAME}> will refer to the leftmost defined group in the match. | |
1145 | ||
b0c22438 | 1146 | The underlying behaviour of C<%+> is provided by the |
1147 | L<Tie::Hash::NamedCapture> module. | |
1148 | ||
1149 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1150 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1151 | iterative access to them via C<each> may have unpredictable results. |
1152 | Likewise, if the last successful match changes, then the results may be | |
1153 | surprising. | |
1154 | ||
27deb0cf YO |
1155 | This variable was added in Perl v5.10.0. The C<%{^CAPTURE}> alias was |
1156 | added in 5.25.7. | |
a0d0e21e | 1157 | |
b0c22438 | 1158 | This variable is read-only and dynamically-scoped. |
1159 | ||
1160 | =item @LAST_MATCH_START | |
1161 | ||
1162 | =item @- | |
1163 | X<@-> X<@LAST_MATCH_START> | |
1164 | ||
1165 | C<$-[0]> is the offset of the start of the last successful match. | |
8dbb2d95 | 1166 | C<$-[I<n>]> is the offset of the start of the substring matched by |
b0c22438 | 1167 | I<n>-th subpattern, or undef if the subpattern did not match. |
1168 | ||
1169 | Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0], | |
241a59d9 | 1170 | $+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n], |
b0c22438 | 1171 | $+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with |
241a59d9 FC |
1172 | C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the |
1173 | last matched subgroup in the last successful match. Contrast with | |
1174 | C<$#+>, the number of subgroups in the regular expression. Compare | |
b0c22438 | 1175 | with C<@+>. |
1176 | ||
1177 | This array holds the offsets of the beginnings of the last | |
1178 | successful submatches in the currently active dynamic scope. | |
1179 | C<$-[0]> is the offset into the string of the beginning of the | |
241a59d9 | 1180 | entire match. The I<n>th element of this array holds the offset |
b0c22438 | 1181 | of the I<n>th submatch, so C<$-[1]> is the offset where C<$1> |
1182 | begins, C<$-[2]> the offset where C<$2> begins, and so on. | |
1183 | ||
1184 | After a match against some variable C<$var>: | |
1185 | ||
1186 | =over 5 | |
1187 | ||
1188 | =item C<$`> is the same as C<substr($var, 0, $-[0])> | |
1189 | ||
1190 | =item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])> | |
1191 | ||
1192 | =item C<$'> is the same as C<substr($var, $+[0])> | |
1193 | ||
1194 | =item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])> | |
1195 | ||
1196 | =item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])> | |
1197 | ||
1198 | =item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])> | |
1199 | ||
1200 | =back | |
1201 | ||
60cf4914 | 1202 | This variable was added in Perl v5.6.0. |
b0c22438 | 1203 | |
27deb0cf YO |
1204 | =item %{^CAPTURE_ALL} |
1205 | X<%{^CAPTURE_ALL}> | |
1206 | ||
b0c22438 | 1207 | =item %- |
2e67aae7 | 1208 | X<%-> |
b0c22438 | 1209 | |
1210 | Similar to C<%+>, this variable allows access to the named capture groups | |
241a59d9 | 1211 | in the last successful match in the currently active dynamic scope. To |
b0c22438 | 1212 | each capture group name found in the regular expression, it associates a |
1213 | reference to an array containing the list of values captured by all | |
1214 | buffers with that name (should there be several of them), in the order | |
1215 | where they appear. | |
1216 | ||
1217 | Here's an example: | |
1218 | ||
1219 | if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) { | |
1220 | foreach my $bufname (sort keys %-) { | |
1221 | my $ary = $-{$bufname}; | |
1222 | foreach my $idx (0..$#$ary) { | |
1223 | print "\$-{$bufname}[$idx] : ", | |
9548c15c FC |
1224 | (defined($ary->[$idx]) |
1225 | ? "'$ary->[$idx]'" | |
1226 | : "undef"), | |
b0c22438 | 1227 | "\n"; |
1228 | } | |
1229 | } | |
1230 | } | |
1231 | ||
1232 | would print out: | |
1233 | ||
9548c15c FC |
1234 | $-{A}[0] : '1' |
1235 | $-{A}[1] : '3' | |
1236 | $-{B}[0] : '2' | |
1237 | $-{B}[1] : '4' | |
b0c22438 | 1238 | |
1239 | The keys of the C<%-> hash correspond to all buffer names found in | |
1240 | the regular expression. | |
1241 | ||
1242 | The behaviour of C<%-> is implemented via the | |
1243 | L<Tie::Hash::NamedCapture> module. | |
1244 | ||
1245 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1246 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1247 | iterative access to them via C<each> may have unpredictable results. |
1248 | Likewise, if the last successful match changes, then the results may be | |
1249 | surprising. | |
1250 | ||
27deb0cf YO |
1251 | This variable was added in Perl v5.10.0. The C<%{^CAPTURE_ALL}> alias was |
1252 | added in 5.25.7. | |
b0c22438 | 1253 | |
1254 | This variable is read-only and dynamically-scoped. | |
1255 | ||
1256 | =item $LAST_REGEXP_CODE_RESULT | |
1257 | ||
1258 | =item $^R | |
1259 | X<$^R> X<$LAST_REGEXP_CODE_RESULT> | |
1260 | ||
1261 | The result of evaluation of the last successful C<(?{ code })> | |
241a59d9 | 1262 | regular expression assertion (see L<perlre>). May be written to. |
b0c22438 | 1263 | |
1264 | This variable was added in Perl 5.005. | |
a0d0e21e | 1265 | |
6ef7fe53 KW |
1266 | =item ${^RE_COMPILE_RECURSION_LIMIT} |
1267 | X<${^RE_COMPILE_RECURSION_LIMIT}> | |
1268 | ||
1269 | The current value giving the maximum number of open but unclosed | |
1270 | parenthetical groups there may be at any point during a regular | |
1271 | expression compilation. The default is currently 1000 nested groups. | |
1272 | You may adjust it depending on your needs and the amount of memory | |
1273 | available. | |
1274 | ||
1275 | This variable was added in Perl v5.30.0. | |
1276 | ||
a3621e74 | 1277 | =item ${^RE_DEBUG_FLAGS} |
ca1b95ae | 1278 | X<${^RE_DEBUG_FLAGS}> |
a3621e74 | 1279 | |
241a59d9 FC |
1280 | The current value of the regex debugging flags. Set to 0 for no debug output |
1281 | even when the C<re 'debug'> module is loaded. See L<re> for details. | |
b0c22438 | 1282 | |
60cf4914 | 1283 | This variable was added in Perl v5.10.0. |
a3621e74 | 1284 | |
0111c4fd | 1285 | =item ${^RE_TRIE_MAXBUF} |
ca1b95ae | 1286 | X<${^RE_TRIE_MAXBUF}> |
a3621e74 YO |
1287 | |
1288 | Controls how certain regex optimisations are applied and how much memory they | |
241a59d9 FC |
1289 | utilize. This value by default is 65536 which corresponds to a 512kB |
1290 | temporary cache. Set this to a higher value to trade | |
1291 | memory for speed when matching large alternations. Set | |
1292 | it to a lower value if you want the optimisations to | |
a3621e74 YO |
1293 | be as conservative of memory as possible but still occur, and set it to a |
1294 | negative value to prevent the optimisation and conserve the most memory. | |
1295 | Under normal situations this variable should be of no interest to you. | |
1296 | ||
60cf4914 | 1297 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1298 | |
b0c22438 | 1299 | =back |
a0d0e21e | 1300 | |
b0c22438 | 1301 | =head2 Variables related to filehandles |
a0d0e21e | 1302 | |
b0c22438 | 1303 | Variables that depend on the currently selected filehandle may be set |
1304 | by calling an appropriate object method on the C<IO::Handle> object, | |
1305 | although this is less efficient than using the regular built-in | |
241a59d9 | 1306 | variables. (Summary lines below for this contain the word HANDLE.) |
b0c22438 | 1307 | First you must say |
6e2995f4 | 1308 | |
9548c15c | 1309 | use IO::Handle; |
0462a1ab | 1310 | |
b0c22438 | 1311 | after which you may use either |
0462a1ab | 1312 | |
9548c15c | 1313 | method HANDLE EXPR |
0462a1ab | 1314 | |
b0c22438 | 1315 | or more safely, |
0462a1ab | 1316 | |
9548c15c | 1317 | HANDLE->method(EXPR) |
0462a1ab | 1318 | |
241a59d9 | 1319 | Each method returns the old value of the C<IO::Handle> attribute. The |
b0c22438 | 1320 | methods each take an optional EXPR, which, if supplied, specifies the |
241a59d9 | 1321 | new value for the C<IO::Handle> attribute in question. If not |
b0c22438 | 1322 | supplied, most methods do nothing to the current value--except for |
1323 | C<autoflush()>, which will assume a 1 for you, just to be different. | |
0462a1ab | 1324 | |
b0c22438 | 1325 | Because loading in the C<IO::Handle> class is an expensive operation, |
1326 | you should learn how to use the regular built-in variables. | |
1327 | ||
241a59d9 | 1328 | A few of these variables are considered "read-only". This means that |
b0c22438 | 1329 | if you try to assign to this variable, either directly or indirectly |
1330 | through a reference, you'll raise a run-time exception. | |
1331 | ||
1332 | You should be very careful when modifying the default values of most | |
241a59d9 | 1333 | special variables described in this document. In most cases you want |
b0c22438 | 1334 | to localize these variables before changing them, since if you don't, |
1335 | the change may affect other modules which rely on the default values | |
241a59d9 | 1336 | of the special variables that you have changed. This is one of the |
b0c22438 | 1337 | correct ways to read the whole file at once: |
1338 | ||
9548c15c FC |
1339 | open my $fh, "<", "foo" or die $!; |
1340 | local $/; # enable localized slurp mode | |
1341 | my $content = <$fh>; | |
1342 | close $fh; | |
b0c22438 | 1343 | |
1344 | But the following code is quite bad: | |
1345 | ||
9548c15c FC |
1346 | open my $fh, "<", "foo" or die $!; |
1347 | undef $/; # enable slurp mode | |
1348 | my $content = <$fh>; | |
1349 | close $fh; | |
b0c22438 | 1350 | |
1351 | since some other module, may want to read data from some file in the | |
1352 | default "line mode", so if the code we have just presented has been | |
1353 | executed, the global value of C<$/> is now changed for any other code | |
1354 | running inside the same Perl interpreter. | |
1355 | ||
1356 | Usually when a variable is localized you want to make sure that this | |
241a59d9 FC |
1357 | change affects the shortest scope possible. So unless you are already |
1358 | inside some short C<{}> block, you should create one yourself. For | |
b0c22438 | 1359 | example: |
1360 | ||
9548c15c FC |
1361 | my $content = ''; |
1362 | open my $fh, "<", "foo" or die $!; | |
1363 | { | |
1364 | local $/; | |
1365 | $content = <$fh>; | |
1366 | } | |
1367 | close $fh; | |
0462a1ab | 1368 | |
b0c22438 | 1369 | Here is an example of how your own code can go broken: |
0462a1ab | 1370 | |
9548c15c FC |
1371 | for ( 1..3 ){ |
1372 | $\ = "\r\n"; | |
1373 | nasty_break(); | |
1374 | print "$_"; | |
1375 | } | |
0b9346e6 | 1376 | |
9548c15c | 1377 | sub nasty_break { |
0b9346e6 | 1378 | $\ = "\f"; |
1379 | # do something with $_ | |
9548c15c | 1380 | } |
0462a1ab | 1381 | |
0b9346e6 | 1382 | You probably expect this code to print the equivalent of |
0462a1ab | 1383 | |
0b9346e6 | 1384 | "1\r\n2\r\n3\r\n" |
0462a1ab | 1385 | |
b0c22438 | 1386 | but instead you get: |
0462a1ab | 1387 | |
0b9346e6 | 1388 | "1\f2\f3\f" |
0462a1ab | 1389 | |
0b9346e6 | 1390 | Why? Because C<nasty_break()> modifies C<$\> without localizing it |
241a59d9 FC |
1391 | first. The value you set in C<nasty_break()> is still there when you |
1392 | return. The fix is to add C<local()> so the value doesn't leak out of | |
0b9346e6 | 1393 | C<nasty_break()>: |
6e2995f4 | 1394 | |
9548c15c | 1395 | local $\ = "\f"; |
a0d0e21e | 1396 | |
b0c22438 | 1397 | It's easy to notice the problem in such a short example, but in more |
1398 | complicated code you are looking for trouble if you don't localize | |
1399 | changes to the special variables. | |
a0d0e21e | 1400 | |
b0c22438 | 1401 | =over 8 |
a0d0e21e | 1402 | |
b0c22438 | 1403 | =item $ARGV |
1404 | X<$ARGV> | |
fb73857a | 1405 | |
ca1b95ae | 1406 | Contains the name of the current file when reading from C<< <> >>. |
b0c22438 | 1407 | |
1408 | =item @ARGV | |
1409 | X<@ARGV> | |
1410 | ||
ca1b95ae | 1411 | The array C<@ARGV> contains the command-line arguments intended for |
241a59d9 | 1412 | the script. C<$#ARGV> is generally the number of arguments minus |
b0c22438 | 1413 | one, because C<$ARGV[0]> is the first argument, I<not> the program's |
241a59d9 | 1414 | command name itself. See L</$0> for the command name. |
b0c22438 | 1415 | |
84dabc03 | 1416 | =item ARGV |
1417 | X<ARGV> | |
1418 | ||
1419 | The special filehandle that iterates over command-line filenames in | |
241a59d9 FC |
1420 | C<@ARGV>. Usually written as the null filehandle in the angle operator |
1421 | C<< <> >>. Note that currently C<ARGV> only has its magical effect | |
84dabc03 | 1422 | within the C<< <> >> operator; elsewhere it is just a plain filehandle |
241a59d9 | 1423 | corresponding to the last file opened by C<< <> >>. In particular, |
84dabc03 | 1424 | passing C<\*ARGV> as a parameter to a function that expects a filehandle |
1425 | may not cause your function to automatically read the contents of all the | |
1426 | files in C<@ARGV>. | |
1427 | ||
b0c22438 | 1428 | =item ARGVOUT |
1429 | X<ARGVOUT> | |
1430 | ||
1431 | The special filehandle that points to the currently open output file | |
241a59d9 FC |
1432 | when doing edit-in-place processing with B<-i>. Useful when you have |
1433 | to do a lot of inserting and don't want to keep modifying C<$_>. See | |
028611fa | 1434 | L<perlrun|perlrun/-i[extension]> for the B<-i> switch. |
b0c22438 | 1435 | |
96948506 | 1436 | =item IO::Handle->output_field_separator( EXPR ) |
84dabc03 | 1437 | |
1438 | =item $OUTPUT_FIELD_SEPARATOR | |
1439 | ||
1440 | =item $OFS | |
1441 | ||
1442 | =item $, | |
1443 | X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR> | |
1444 | ||
241a59d9 FC |
1445 | The output field separator for the print operator. If defined, this |
1446 | value is printed between each of print's arguments. Default is C<undef>. | |
84dabc03 | 1447 | |
96948506 | 1448 | You cannot call C<output_field_separator()> on a handle, only as a |
008f9687 | 1449 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1450 | |
84dabc03 | 1451 | Mnemonic: what is printed when there is a "," in your print statement. |
1452 | ||
5b442a2a | 1453 | =item HANDLE->input_line_number( EXPR ) |
b0c22438 | 1454 | |
1455 | =item $INPUT_LINE_NUMBER | |
1456 | ||
1457 | =item $NR | |
1458 | ||
1459 | =item $. | |
1460 | X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number> | |
1461 | ||
1462 | Current line number for the last filehandle accessed. | |
1463 | ||
1464 | Each filehandle in Perl counts the number of lines that have been read | |
241a59d9 | 1465 | from it. (Depending on the value of C<$/>, Perl's idea of what |
b0c22438 | 1466 | constitutes a line may not match yours.) When a line is read from a |
1467 | filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or | |
1468 | C<seek()> is called on it, C<$.> becomes an alias to the line counter | |
1469 | for that filehandle. | |
1470 | ||
1471 | You can adjust the counter by assigning to C<$.>, but this will not | |
241a59d9 FC |
1472 | actually move the seek pointer. I<Localizing C<$.> will not localize |
1473 | the filehandle's line count>. Instead, it will localize perl's notion | |
b0c22438 | 1474 | of which filehandle C<$.> is currently aliased to. |
1475 | ||
1476 | C<$.> is reset when the filehandle is closed, but B<not> when an open | |
241a59d9 FC |
1477 | filehandle is reopened without an intervening C<close()>. For more |
1478 | details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does | |
b0c22438 | 1479 | an explicit close, line numbers increase across C<ARGV> files (but see |
1480 | examples in L<perlfunc/eof>). | |
1481 | ||
1482 | You can also use C<< HANDLE->input_line_number(EXPR) >> to access the | |
1483 | line counter for a given filehandle without having to worry about | |
1484 | which handle you last accessed. | |
1485 | ||
1486 | Mnemonic: many programs use "." to mean the current line number. | |
1487 | ||
96948506 | 1488 | =item IO::Handle->input_record_separator( EXPR ) |
b0c22438 | 1489 | |
1490 | =item $INPUT_RECORD_SEPARATOR | |
1491 | ||
1492 | =item $RS | |
1493 | ||
1494 | =item $/ | |
1495 | X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR> | |
1496 | ||
241a59d9 FC |
1497 | The input record separator, newline by default. This influences Perl's |
1498 | idea of what a "line" is. Works like B<awk>'s RS variable, including | |
84dabc03 | 1499 | treating empty lines as a terminator if set to the null string (an |
241a59d9 | 1500 | empty line cannot contain any spaces or tabs). You may set it to a |
84dabc03 | 1501 | multi-character string to match a multi-character terminator, or to |
241a59d9 | 1502 | C<undef> to read through the end of file. Setting it to C<"\n\n"> |
84dabc03 | 1503 | means something slightly different than setting to C<"">, if the file |
241a59d9 FC |
1504 | contains consecutive empty lines. Setting to C<""> will treat two or |
1505 | more consecutive empty lines as a single empty line. Setting to | |
84dabc03 | 1506 | C<"\n\n"> will blindly assume that the next input character belongs to |
1507 | the next paragraph, even if it's a newline. | |
b0c22438 | 1508 | |
1509 | local $/; # enable "slurp" mode | |
1510 | local $_ = <FH>; # whole file now here | |
1511 | s/\n[ \t]+/ /g; | |
1512 | ||
241a59d9 | 1513 | Remember: the value of C<$/> is a string, not a regex. B<awk> has to |
b0c22438 | 1514 | be better for something. :-) |
1515 | ||
440af013 JK |
1516 | Setting C<$/> to an empty string -- the so-called I<paragraph mode> -- merits |
1517 | special attention. When C<$/> is set to C<""> and the entire file is read in | |
1518 | with that setting, any sequence of consecutive newlines C<"\n\n"> at the | |
1519 | beginning of the file is discarded. With the exception of the final record in | |
1520 | the file, each sequence of characters ending in two or more newlines is | |
1521 | treated as one record and is read in to end in exactly two newlines. If the | |
1522 | last record in the file ends in zero or one consecutive newlines, that record | |
1523 | is read in with that number of newlines. If the last record ends in two or | |
1524 | more consecutive newlines, it is read in with two newlines like all preceding | |
1525 | records. | |
1526 | ||
1527 | Suppose we wrote the following string to a file: | |
1528 | ||
1529 | my $string = "\n\n\n"; | |
1530 | $string .= "alpha beta\ngamma delta\n\n\n"; | |
1531 | $string .= "epsilon zeta eta\n\n"; | |
1532 | $string .= "theta\n"; | |
1533 | ||
1534 | my $file = 'simple_file.txt'; | |
1535 | open my $OUT, '>', $file or die; | |
1536 | print $OUT $string; | |
1537 | close $OUT or die; | |
1538 | ||
1539 | Now we read that file in paragraph mode: | |
1540 | ||
1541 | local $/ = ""; # paragraph mode | |
1542 | open my $IN, '<', $file or die; | |
1543 | my @records = <$IN>; | |
1544 | close $IN or die; | |
1545 | ||
1546 | C<@records> will consist of these 3 strings: | |
1547 | ||
1548 | ( | |
1549 | "alpha beta\ngamma delta\n\n", | |
1550 | "epsilon zeta eta\n\n", | |
1551 | "theta\n", | |
1552 | ) | |
1553 | ||
b0c22438 | 1554 | Setting C<$/> to a reference to an integer, scalar containing an |
1555 | integer, or scalar that's convertible to an integer will attempt to | |
1556 | read records instead of lines, with the maximum record size being the | |
3d249121 | 1557 | referenced integer number of characters. So this: |
b0c22438 | 1558 | |
1559 | local $/ = \32768; # or \"32768", or \$var_containing_32768 | |
1560 | open my $fh, "<", $myfile or die $!; | |
1561 | local $_ = <$fh>; | |
fb73857a | 1562 | |
f1ee460b | 1563 | will read a record of no more than 32768 characters from $fh. If you're |
b0c22438 | 1564 | not reading from a record-oriented file (or your OS doesn't have |
1565 | record-oriented files), then you'll likely get a full chunk of data | |
241a59d9 FC |
1566 | with every read. If a record is larger than the record size you've |
1567 | set, you'll get the record back in pieces. Trying to set the record | |
b3a2acfa YO |
1568 | size to zero or less is deprecated and will cause $/ to have the value |
1569 | of "undef", which will cause reading in the (rest of the) whole file. | |
1570 | ||
1571 | As of 5.19.9 setting C<$/> to any other form of reference will throw a | |
1572 | fatal exception. This is in preparation for supporting new ways to set | |
1573 | C<$/> in the future. | |
6e2995f4 | 1574 | |
78c28381 | 1575 | On VMS only, record reads bypass PerlIO layers and any associated |
3d249121 | 1576 | buffering, so you must not mix record and non-record reads on the |
78c28381 CB |
1577 | same filehandle. Record mode mixes with line mode only when the |
1578 | same buffering layer is in use for both modes. | |
5c055ba3 | 1579 | |
96948506 | 1580 | You cannot call C<input_record_separator()> on a handle, only as a |
008f9687 | 1581 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1582 | |
008f9687 | 1583 | See also L<perlport/"Newlines">. Also see L</$.>. |
9bf22702 | 1584 | |
b0c22438 | 1585 | Mnemonic: / delimits line boundaries when quoting poetry. |
5c055ba3 | 1586 | |
96948506 | 1587 | =item IO::Handle->output_record_separator( EXPR ) |
84902520 | 1588 | |
b0c22438 | 1589 | =item $OUTPUT_RECORD_SEPARATOR |
84902520 | 1590 | |
b0c22438 | 1591 | =item $ORS |
84902520 | 1592 | |
b0c22438 | 1593 | =item $\ |
1594 | X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR> | |
84902520 | 1595 | |
241a59d9 FC |
1596 | The output record separator for the print operator. If defined, this |
1597 | value is printed after the last of print's arguments. Default is C<undef>. | |
84902520 | 1598 | |
96948506 | 1599 | You cannot call C<output_record_separator()> on a handle, only as a |
008f9687 | 1600 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1601 | |
b0c22438 | 1602 | Mnemonic: you set C<$\> instead of adding "\n" at the end of the print. |
1603 | Also, it's just like C<$/>, but it's what you get "back" from Perl. | |
84902520 | 1604 | |
5b442a2a | 1605 | =item HANDLE->autoflush( EXPR ) |
1606 | ||
1607 | =item $OUTPUT_AUTOFLUSH | |
1608 | ||
84dabc03 | 1609 | =item $| |
1610 | X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH> | |
84902520 | 1611 | |
84dabc03 | 1612 | If set to nonzero, forces a flush right away and after every write or |
241a59d9 | 1613 | print on the currently selected output channel. Default is 0 |
84dabc03 | 1614 | (regardless of whether the channel is really buffered by the system or |
1615 | not; C<$|> tells you only whether you've asked Perl explicitly to | |
241a59d9 FC |
1616 | flush after each write). STDOUT will typically be line buffered if |
1617 | output is to the terminal and block buffered otherwise. Setting this | |
84dabc03 | 1618 | variable is useful primarily when you are outputting to a pipe or |
1619 | socket, such as when you are running a Perl program under B<rsh> and | |
241a59d9 FC |
1620 | want to see the output as it's happening. This has no effect on input |
1621 | buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on | |
1622 | how to select the output channel. See also L<IO::Handle>. | |
84dabc03 | 1623 | |
1624 | Mnemonic: when you want your pipes to be piping hot. | |
1625 | ||
8561ea1d FC |
1626 | =item ${^LAST_FH} |
1627 | X<${^LAST_FH}> | |
1628 | ||
1629 | This read-only variable contains a reference to the last-read filehandle. | |
1630 | This is set by C<< <HANDLE> >>, C<readline>, C<tell>, C<eof> and C<seek>. | |
1631 | This is the same handle that C<$.> and C<tell> and C<eof> without arguments | |
1632 | use. It is also the handle used when Perl appends ", <STDIN> line 1" to | |
1633 | an error or warning message. | |
1634 | ||
1635 | This variable was added in Perl v5.18.0. | |
1636 | ||
84dabc03 | 1637 | =back |
84902520 | 1638 | |
b0c22438 | 1639 | =head3 Variables related to formats |
83ee9e09 | 1640 | |
b0c22438 | 1641 | The special variables for formats are a subset of those for |
241a59d9 | 1642 | filehandles. See L<perlform> for more information about Perl's |
69b55ccc | 1643 | formats. |
83ee9e09 | 1644 | |
b0c22438 | 1645 | =over 8 |
83ee9e09 | 1646 | |
84dabc03 | 1647 | =item $ACCUMULATOR |
1648 | ||
1649 | =item $^A | |
1650 | X<$^A> X<$ACCUMULATOR> | |
1651 | ||
1652 | The current value of the C<write()> accumulator for C<format()> lines. | |
1653 | A format contains C<formline()> calls that put their result into | |
241a59d9 FC |
1654 | C<$^A>. After calling its format, C<write()> prints out the contents |
1655 | of C<$^A> and empties. So you never really see the contents of C<$^A> | |
1656 | unless you call C<formline()> yourself and then look at it. See | |
96090e4f | 1657 | L<perlform> and L<perlfunc/"formline PICTURE,LIST">. |
84dabc03 | 1658 | |
96948506 | 1659 | =item IO::Handle->format_formfeed(EXPR) |
5b442a2a | 1660 | |
1661 | =item $FORMAT_FORMFEED | |
1662 | ||
84dabc03 | 1663 | =item $^L |
1664 | X<$^L> X<$FORMAT_FORMFEED> | |
1665 | ||
241a59d9 | 1666 | What formats output as a form feed. The default is C<\f>. |
84dabc03 | 1667 | |
96948506 | 1668 | You cannot call C<format_formfeed()> on a handle, only as a static |
008f9687 | 1669 | method. See L<IO::Handle|IO::Handle>. |
96948506 | 1670 | |
b0c22438 | 1671 | =item HANDLE->format_page_number(EXPR) |
83ee9e09 | 1672 | |
b0c22438 | 1673 | =item $FORMAT_PAGE_NUMBER |
83ee9e09 | 1674 | |
b0c22438 | 1675 | =item $% |
1676 | X<$%> X<$FORMAT_PAGE_NUMBER> | |
83ee9e09 | 1677 | |
b0c22438 | 1678 | The current page number of the currently selected output channel. |
83ee9e09 | 1679 | |
b0c22438 | 1680 | Mnemonic: C<%> is page number in B<nroff>. |
7619c85e | 1681 | |
b0c22438 | 1682 | =item HANDLE->format_lines_left(EXPR) |
b9ac3b5b | 1683 | |
b0c22438 | 1684 | =item $FORMAT_LINES_LEFT |
66558a10 | 1685 | |
b0c22438 | 1686 | =item $- |
1687 | X<$-> X<$FORMAT_LINES_LEFT> | |
fb73857a | 1688 | |
b0c22438 | 1689 | The number of lines left on the page of the currently selected output |
1690 | channel. | |
fa05a9fd | 1691 | |
b0c22438 | 1692 | Mnemonic: lines_on_page - lines_printed. |
fa05a9fd | 1693 | |
96948506 | 1694 | =item IO::Handle->format_line_break_characters EXPR |
fb73857a | 1695 | |
84dabc03 | 1696 | =item $FORMAT_LINE_BREAK_CHARACTERS |
a0d0e21e | 1697 | |
84dabc03 | 1698 | =item $: |
1699 | X<$:> X<FORMAT_LINE_BREAK_CHARACTERS> | |
a0d0e21e | 1700 | |
84dabc03 | 1701 | The current set of characters after which a string may be broken to |
241a59d9 | 1702 | fill continuation fields (starting with C<^>) in a format. The default is |
84dabc03 | 1703 | S<" \n-">, to break on a space, newline, or a hyphen. |
a0d0e21e | 1704 | |
96948506 | 1705 | You cannot call C<format_line_break_characters()> on a handle, only as |
008f9687 | 1706 | a static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1707 | |
84dabc03 | 1708 | Mnemonic: a "colon" in poetry is a part of a line. |
1709 | ||
1710 | =item HANDLE->format_lines_per_page(EXPR) | |
1711 | ||
1712 | =item $FORMAT_LINES_PER_PAGE | |
1713 | ||
1714 | =item $= | |
1715 | X<$=> X<$FORMAT_LINES_PER_PAGE> | |
1716 | ||
1717 | The current page length (printable lines) of the currently selected | |
241a59d9 | 1718 | output channel. The default is 60. |
84dabc03 | 1719 | |
1720 | Mnemonic: = has horizontal lines. | |
7c36658b | 1721 | |
b0c22438 | 1722 | =item HANDLE->format_top_name(EXPR) |
7c36658b | 1723 | |
b0c22438 | 1724 | =item $FORMAT_TOP_NAME |
a05d7ebb | 1725 | |
b0c22438 | 1726 | =item $^ |
1727 | X<$^> X<$FORMAT_TOP_NAME> | |
fde18df1 | 1728 | |
b0c22438 | 1729 | The name of the current top-of-page format for the currently selected |
241a59d9 FC |
1730 | output channel. The default is the name of the filehandle with C<_TOP> |
1731 | appended. For example, the default format top name for the C<STDOUT> | |
12abbafd | 1732 | filehandle is C<STDOUT_TOP>. |
e07ea26a | 1733 | |
b0c22438 | 1734 | Mnemonic: points to top of page. |
e07ea26a | 1735 | |
84dabc03 | 1736 | =item HANDLE->format_name(EXPR) |
16070b82 | 1737 | |
84dabc03 | 1738 | =item $FORMAT_NAME |
aa2f2a36 | 1739 | |
84dabc03 | 1740 | =item $~ |
1741 | X<$~> X<$FORMAT_NAME> | |
aa2f2a36 | 1742 | |
84dabc03 | 1743 | The name of the current report format for the currently selected |
241a59d9 FC |
1744 | output channel. The default format name is the same as the filehandle |
1745 | name. For example, the default format name for the C<STDOUT> | |
84dabc03 | 1746 | filehandle is just C<STDOUT>. |
16070b82 | 1747 | |
84dabc03 | 1748 | Mnemonic: brother to C<$^>. |
16070b82 | 1749 | |
b0c22438 | 1750 | =back |
a0d0e21e | 1751 | |
84dabc03 | 1752 | =head2 Error Variables |
b0c22438 | 1753 | X<error> X<exception> |
a0d0e21e | 1754 | |
b0c22438 | 1755 | The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information |
1756 | about different types of error conditions that may appear during | |
241a59d9 | 1757 | execution of a Perl program. The variables are shown ordered by |
b0c22438 | 1758 | the "distance" between the subsystem which reported the error and |
241a59d9 | 1759 | the Perl process. They correspond to errors detected by the Perl |
b0c22438 | 1760 | interpreter, C library, operating system, or an external program, |
1761 | respectively. | |
4438c4b7 | 1762 | |
b0c22438 | 1763 | To illustrate the differences between these variables, consider the |
241a59d9 | 1764 | following Perl expression, which uses a single-quoted string. After |
7fd683ff | 1765 | execution of this statement, perl may have set all four special error |
7333b1c4 | 1766 | variables: |
4438c4b7 | 1767 | |
9548c15c FC |
1768 | eval q{ |
1769 | open my $pipe, "/cdrom/install |" or die $!; | |
1770 | my @res = <$pipe>; | |
1771 | close $pipe or die "bad pipe: $?, $!"; | |
1772 | }; | |
a0d0e21e | 1773 | |
7333b1c4 | 1774 | When perl executes the C<eval()> expression, it translates the |
1775 | C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library | |
241a59d9 | 1776 | and thence to the operating system kernel. perl sets C<$!> to |
7333b1c4 | 1777 | the C library's C<errno> if one of these calls fails. |
2a8c8378 | 1778 | |
84dabc03 | 1779 | C<$@> is set if the string to be C<eval>-ed did not compile (this may |
1780 | happen if C<open> or C<close> were imported with bad prototypes), or | |
241a59d9 | 1781 | if Perl code executed during evaluation C<die()>d. In these cases the |
0b9346e6 | 1782 | value of C<$@> is the compile error, or the argument to C<die> (which |
241a59d9 | 1783 | will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.) |
2a8c8378 | 1784 | |
84dabc03 | 1785 | Under a few operating systems, C<$^E> may contain a more verbose error |
241a59d9 | 1786 | indicator, such as in this case, "CDROM tray not closed." Systems that |
84dabc03 | 1787 | do not support extended error messages leave C<$^E> the same as C<$!>. |
a0d0e21e | 1788 | |
2e6ba115 | 1789 | Finally, C<$?> may be set to a non-0 value if the external program |
241a59d9 | 1790 | F</cdrom/install> fails. The upper eight bits reflect specific error |
84dabc03 | 1791 | conditions encountered by the program (the program's C<exit()> value). |
1792 | The lower eight bits reflect mode of failure, like signal death and | |
241a59d9 | 1793 | core dump information. See L<wait(2)> for details. In contrast to |
2e6ba115 | 1794 | C<$!> and C<$^E>, which are set only if an error condition is detected, |
84dabc03 | 1795 | the variable C<$?> is set on each C<wait> or pipe C<close>, |
241a59d9 | 1796 | overwriting the old value. This is more like C<$@>, which on every |
84dabc03 | 1797 | C<eval()> is always set on failure and cleared on success. |
a0d0e21e | 1798 | |
b0c22438 | 1799 | For more details, see the individual descriptions at C<$@>, C<$!>, |
1800 | C<$^E>, and C<$?>. | |
38e4f4ae | 1801 | |
0b9346e6 | 1802 | =over 8 |
1803 | ||
b0c22438 | 1804 | =item ${^CHILD_ERROR_NATIVE} |
1805 | X<$^CHILD_ERROR_NATIVE> | |
a0d0e21e | 1806 | |
b0c22438 | 1807 | The native status returned by the last pipe close, backtick (C<``>) |
1808 | command, successful call to C<wait()> or C<waitpid()>, or from the | |
241a59d9 | 1809 | C<system()> operator. On POSIX-like systems this value can be decoded |
f2febc77 KW |
1810 | with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, and |
1811 | WSTOPSIG functions provided by the L<POSIX> module. | |
a0d0e21e | 1812 | |
b0c22438 | 1813 | Under VMS this reflects the actual VMS exit status; i.e. it is the |
1814 | same as C<$?> when the pragma C<use vmsish 'status'> is in effect. | |
a0d0e21e | 1815 | |
60cf4914 | 1816 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1817 | |
5b442a2a | 1818 | =item $EXTENDED_OS_ERROR |
1819 | ||
84dabc03 | 1820 | =item $^E |
1821 | X<$^E> X<$EXTENDED_OS_ERROR> | |
1822 | ||
241a59d9 | 1823 | Error information specific to the current operating system. At the |
a804e657 | 1824 | moment, this differs from C<L</$!>> under only VMS, OS/2, and Win32 (and |
241a59d9 | 1825 | for MacPerl). On all other platforms, C<$^E> is always just the same |
84dabc03 | 1826 | as C<$!>. |
1827 | ||
1828 | Under VMS, C<$^E> provides the VMS status value from the last system | |
241a59d9 FC |
1829 | error. This is more specific information about the last system error |
1830 | than that provided by C<$!>. This is particularly important when C<$!> | |
84dabc03 | 1831 | is set to B<EVMSERR>. |
1832 | ||
1833 | Under OS/2, C<$^E> is set to the error code of the last call to OS/2 | |
1834 | API either via CRT, or directly from perl. | |
1835 | ||
1836 | Under Win32, C<$^E> always returns the last error information reported | |
1837 | by the Win32 call C<GetLastError()> which describes the last error | |
241a59d9 FC |
1838 | from within the Win32 API. Most Win32-specific code will report errors |
1839 | via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most | |
84dabc03 | 1840 | portable Perl code will report errors via C<$!>. |
1841 | ||
a95b3d6a | 1842 | Caveats mentioned in the description of C<L</$!>> generally apply to |
84dabc03 | 1843 | C<$^E>, also. |
1844 | ||
1845 | This variable was added in Perl 5.003. | |
1846 | ||
1847 | Mnemonic: Extra error explanation. | |
0b9346e6 | 1848 | |
84dabc03 | 1849 | =item $EXCEPTIONS_BEING_CAUGHT |
1850 | ||
1851 | =item $^S | |
1852 | X<$^S> X<$EXCEPTIONS_BEING_CAUGHT> | |
1853 | ||
1854 | Current state of the interpreter. | |
1855 | ||
ca1b95ae | 1856 | $^S State |
aa959a20 FC |
1857 | --------- ------------------------------------- |
1858 | undef Parsing module, eval, or main program | |
ca1b95ae | 1859 | true (1) Executing an eval |
1860 | false (0) Otherwise | |
84dabc03 | 1861 | |
1862 | The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}> | |
1863 | handlers. | |
1864 | ||
aa959a20 FC |
1865 | The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because |
1866 | the C<undef> value does not indicate whether exceptions are being caught, | |
1867 | since compilation of the main program does not catch exceptions. | |
1868 | ||
84dabc03 | 1869 | This variable was added in Perl 5.004. |
1870 | ||
1871 | =item $WARNING | |
1872 | ||
1873 | =item $^W | |
1874 | X<$^W> X<$WARNING> | |
1875 | ||
1876 | The current value of the warning switch, initially true if B<-w> was | |
1877 | used, false otherwise, but directly modifiable. | |
1878 | ||
1879 | See also L<warnings>. | |
1880 | ||
0b9346e6 | 1881 | Mnemonic: related to the B<-w> switch. |
84dabc03 | 1882 | |
1883 | =item ${^WARNING_BITS} | |
ca1b95ae | 1884 | X<${^WARNING_BITS}> |
84dabc03 | 1885 | |
1886 | The current set of warning checks enabled by the C<use warnings> pragma. | |
44567c86 FC |
1887 | It has the same scoping as the C<$^H> and C<%^H> variables. The exact |
1888 | values are considered internal to the L<warnings> pragma and may change | |
1889 | between versions of Perl. | |
84dabc03 | 1890 | |
60cf4914 | 1891 | This variable was added in Perl v5.6.0. |
84dabc03 | 1892 | |
b0c22438 | 1893 | =item $OS_ERROR |
5ccee41e | 1894 | |
b0c22438 | 1895 | =item $ERRNO |
5ccee41e | 1896 | |
b0c22438 | 1897 | =item $! |
1898 | X<$!> X<$ERRNO> X<$OS_ERROR> | |
9b0e6e7a | 1899 | |
a73bef78 JL |
1900 | When referenced, C<$!> retrieves the current value |
1901 | of the C C<errno> integer variable. | |
1902 | If C<$!> is assigned a numerical value, that value is stored in C<errno>. | |
1903 | When referenced as a string, C<$!> yields the system error string | |
1904 | corresponding to C<errno>. | |
1905 | ||
1906 | Many system or library calls set C<errno> if they fail, | |
1907 | to indicate the cause of failure. They usually do B<not> | |
e275abc0 TC |
1908 | set C<errno> to zero if they succeed and may set C<errno> to a |
1909 | non-zero value on success. This means C<errno>, hence C<$!>, is | |
1910 | meaningful only I<immediately> after a B<failure>: | |
a73bef78 JL |
1911 | |
1912 | if (open my $fh, "<", $filename) { | |
ca1b95ae | 1913 | # Here $! is meaningless. |
1914 | ... | |
7fd683ff | 1915 | } |
ca1b95ae | 1916 | else { |
1917 | # ONLY here is $! meaningful. | |
1918 | ... | |
1919 | # Already here $! might be meaningless. | |
b0c22438 | 1920 | } |
1921 | # Since here we might have either success or failure, | |
a73bef78 | 1922 | # $! is meaningless. |
a0d0e21e | 1923 | |
a73bef78 JL |
1924 | Here, I<meaningless> means that C<$!> may be unrelated to the outcome |
1925 | of the C<open()> operator. Assignment to C<$!> is similarly ephemeral. | |
1926 | It can be used immediately before invoking the C<die()> operator, | |
1927 | to set the exit value, or to inspect the system error string | |
1928 | corresponding to error I<n>, or to restore C<$!> to a meaningful state. | |
d54b56d5 | 1929 | |
8a65a5dc TC |
1930 | Perl itself may set C<errno> to a non-zero on failure even if no |
1931 | system call is performed. | |
1932 | ||
b0c22438 | 1933 | Mnemonic: What just went bang? |
314d39ce | 1934 | |
b0c22438 | 1935 | =item %OS_ERROR |
fb73857a | 1936 | |
b0c22438 | 1937 | =item %ERRNO |
fb73857a | 1938 | |
b0c22438 | 1939 | =item %! |
5b442a2a | 1940 | X<%!> X<%OS_ERROR> X<%ERRNO> |
a0d0e21e | 1941 | |
b0c22438 | 1942 | Each element of C<%!> has a true value only if C<$!> is set to that |
241a59d9 | 1943 | value. For example, C<$!{ENOENT}> is true if and only if the current |
84dabc03 | 1944 | value of C<$!> is C<ENOENT>; that is, if the most recent error was "No |
1945 | such file or directory" (or its moral equivalent: not all operating | |
3b90fd91 RS |
1946 | systems give that exact error, and certainly not all languages). The |
1947 | specific true value is not guaranteed, but in the past has generally | |
1948 | been the numeric value of C<$!>. To check if a particular key is | |
1949 | meaningful on your system, use C<exists $!{the_key}>; for a list of legal | |
1950 | keys, use C<keys %!>. See L<Errno> for more information, and also see | |
1951 | L</$!>. | |
a0d0e21e | 1952 | |
b0c22438 | 1953 | This variable was added in Perl 5.005. |
44f0be63 | 1954 | |
84dabc03 | 1955 | =item $CHILD_ERROR |
b687b08b | 1956 | |
84dabc03 | 1957 | =item $? |
1958 | X<$?> X<$CHILD_ERROR> | |
a0d0e21e | 1959 | |
84dabc03 | 1960 | The status returned by the last pipe close, backtick (C<``>) command, |
1961 | successful call to C<wait()> or C<waitpid()>, or from the C<system()> | |
241a59d9 | 1962 | operator. This is just the 16-bit status word returned by the |
84dabc03 | 1963 | traditional Unix C<wait()> system call (or else is made up to look |
241a59d9 | 1964 | like it). Thus, the exit value of the subprocess is really (C<<< $? >> |
84dabc03 | 1965 | 8 >>>), and C<$? & 127> gives which signal, if any, the process died |
1966 | from, and C<$? & 128> reports whether there was a core dump. | |
a0d0e21e | 1967 | |
84dabc03 | 1968 | Additionally, if the C<h_errno> variable is supported in C, its value |
1969 | is returned via C<$?> if any C<gethost*()> function fails. | |
b687b08b | 1970 | |
84dabc03 | 1971 | If you have installed a signal handler for C<SIGCHLD>, the |
1972 | value of C<$?> will usually be wrong outside that handler. | |
a0d0e21e | 1973 | |
84dabc03 | 1974 | Inside an C<END> subroutine C<$?> contains the value that is going to be |
241a59d9 FC |
1975 | given to C<exit()>. You can modify C<$?> in an C<END> subroutine to |
1976 | change the exit status of your program. For example: | |
a0d0e21e | 1977 | |
84dabc03 | 1978 | END { |
1979 | $? = 1 if $? == 255; # die would make it 255 | |
1980 | } | |
a0d0e21e | 1981 | |
84dabc03 | 1982 | Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the |
1983 | actual VMS exit status, instead of the default emulation of POSIX | |
1984 | status; see L<perlvms/$?> for details. | |
1985 | ||
1986 | Mnemonic: similar to B<sh> and B<ksh>. | |
a0d0e21e | 1987 | |
b0c22438 | 1988 | =item $EVAL_ERROR |
f648820c | 1989 | |
b0c22438 | 1990 | =item $@ |
1991 | X<$@> X<$EVAL_ERROR> | |
a0d0e21e | 1992 | |
2e6ba115 LM |
1993 | The Perl error from the last C<eval> operator, i.e. the last exception that |
1994 | was caught. For C<eval BLOCK>, this is either a runtime error message or the | |
1995 | string or reference C<die> was called with. The C<eval STRING> form also | |
1996 | catches syntax errors and other compile time exceptions. | |
1997 | ||
1998 | If no error occurs, C<eval> sets C<$@> to the empty string. | |
a0d0e21e | 1999 | |
241a59d9 | 2000 | Warning messages are not collected in this variable. You can, however, |
b0c22438 | 2001 | set up a routine to process warnings by setting C<$SIG{__WARN__}> as |
7333b1c4 | 2002 | described in L</%SIG>. |
748a9306 | 2003 | |
2e6ba115 | 2004 | Mnemonic: Where was the error "at"? |
7f315d2e | 2005 | |
b0c22438 | 2006 | =back |
7f315d2e | 2007 | |
1fa81471 DR |
2008 | =head2 Variables related to the interpreter state |
2009 | ||
2010 | These variables provide information about the current interpreter state. | |
2011 | ||
2012 | =over 8 | |
2013 | ||
2014 | =item $COMPILING | |
2015 | ||
2016 | =item $^C | |
2017 | X<$^C> X<$COMPILING> | |
2018 | ||
2019 | The current value of the flag associated with the B<-c> switch. | |
2020 | Mainly of use with B<-MO=...> to allow code to alter its behavior | |
2021 | when being compiled, such as for example to C<AUTOLOAD> at compile | |
241a59d9 | 2022 | time rather than normal, deferred loading. Setting |
1fa81471 DR |
2023 | C<$^C = 1> is similar to calling C<B::minus_c>. |
2024 | ||
60cf4914 | 2025 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
2026 | |
2027 | =item $DEBUGGING | |
2028 | ||
2029 | =item $^D | |
2030 | X<$^D> X<$DEBUGGING> | |
2031 | ||
241a59d9 | 2032 | The current value of the debugging flags. May be read or set. Like its |
a975eeba | 2033 | L<command-line equivalent|perlrun/B<-D>I<letters>>, you can use numeric |
8af589bf KW |
2034 | or symbolic values, e.g. C<$^D = 10> or C<$^D = "st">. See |
2035 | L<perlrun/B<-D>I<number>>. The contents of this variable also affects the | |
2036 | debugger operation. See L<perldebguts/Debugger Internals>. | |
1fa81471 DR |
2037 | |
2038 | Mnemonic: value of B<-D> switch. | |
2039 | ||
2040 | =item ${^ENCODING} | |
2041 | X<${^ENCODING}> | |
2042 | ||
981b911e | 2043 | This variable is no longer supported. |
a3ee04ba | 2044 | |
981b911e FC |
2045 | It used to hold the I<object reference> to the C<Encode> object that was |
2046 | used to convert the source code to Unicode. | |
a3ee04ba | 2047 | |
981b911e FC |
2048 | Its purpose was to allow your non-ASCII Perl |
2049 | scripts not to have to be written in UTF-8; this was | |
a3ee04ba | 2050 | useful before editors that worked on UTF-8 encoded text were common, but |
981b911e FC |
2051 | that was long ago. It caused problems, such as affecting the operation |
2052 | of other modules that weren't expecting it, causing general mayhem. | |
a3ee04ba | 2053 | |
981b911e FC |
2054 | If you need something like this functionality, it is recommended that use |
2055 | you a simple source filter, such as L<Filter::Encoding>. | |
a3ee04ba KW |
2056 | |
2057 | If you are coming here because code of yours is being adversely affected | |
2058 | by someone's use of this variable, you can usually work around it by | |
2059 | doing this: | |
2060 | ||
2061 | local ${^ENCODING}; | |
2062 | ||
2063 | near the beginning of the functions that are getting broken. This | |
2064 | undefines the variable during the scope of execution of the including | |
2065 | function. | |
1fa81471 | 2066 | |
981b911e | 2067 | This variable was added in Perl 5.8.2 and removed in 5.26.0. |
fd503f5c | 2068 | Setting it to anything other than C<undef> was made fatal in Perl 5.28.0. |
1fa81471 DR |
2069 | |
2070 | =item ${^GLOBAL_PHASE} | |
2071 | X<${^GLOBAL_PHASE}> | |
2072 | ||
2073 | The current phase of the perl interpreter. | |
2074 | ||
2075 | Possible values are: | |
2076 | ||
2077 | =over 8 | |
2078 | ||
2079 | =item CONSTRUCT | |
2080 | ||
241a59d9 | 2081 | The C<PerlInterpreter*> is being constructed via C<perl_construct>. This |
1fa81471 | 2082 | value is mostly there for completeness and for use via the |
241a59d9 | 2083 | underlying C variable C<PL_phase>. It's not really possible for Perl |
1fa81471 DR |
2084 | code to be executed unless construction of the interpreter is |
2085 | finished. | |
2086 | ||
2087 | =item START | |
2088 | ||
241a59d9 | 2089 | This is the global compile-time. That includes, basically, every |
1fa81471 DR |
2090 | C<BEGIN> block executed directly or indirectly from during the |
2091 | compile-time of the top-level program. | |
2092 | ||
2093 | This phase is not called "BEGIN" to avoid confusion with | |
2094 | C<BEGIN>-blocks, as those are executed during compile-time of any | |
241a59d9 | 2095 | compilation unit, not just the top-level program. A new, localised |
1fa81471 DR |
2096 | compile-time entered at run-time, for example by constructs as |
2097 | C<eval "use SomeModule"> are not global interpreter phases, and | |
2098 | therefore aren't reflected by C<${^GLOBAL_PHASE}>. | |
2099 | ||
2100 | =item CHECK | |
2101 | ||
2102 | Execution of any C<CHECK> blocks. | |
2103 | ||
2104 | =item INIT | |
2105 | ||
2106 | Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks. | |
2107 | ||
2108 | =item RUN | |
2109 | ||
2110 | The main run-time, i.e. the execution of C<PL_main_root>. | |
2111 | ||
2112 | =item END | |
2113 | ||
2114 | Execution of any C<END> blocks. | |
2115 | ||
2116 | =item DESTRUCT | |
2117 | ||
2118 | Global destruction. | |
2119 | ||
2120 | =back | |
2121 | ||
241a59d9 | 2122 | Also note that there's no value for UNITCHECK-blocks. That's because |
1fa81471 DR |
2123 | those are run for each compilation unit individually, and therefore is |
2124 | not a global interpreter phase. | |
2125 | ||
2126 | Not every program has to go through each of the possible phases, but | |
2127 | transition from one phase to another can only happen in the order | |
2128 | described in the above list. | |
2129 | ||
2130 | An example of all of the phases Perl code can see: | |
2131 | ||
2132 | BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" } | |
2133 | ||
2134 | INIT { print "init-time: ${^GLOBAL_PHASE}\n" } | |
2135 | ||
2136 | CHECK { print "check-time: ${^GLOBAL_PHASE}\n" } | |
2137 | ||
2138 | { | |
2139 | package Print::Phase; | |
2140 | ||
2141 | sub new { | |
2142 | my ($class, $time) = @_; | |
2143 | return bless \$time, $class; | |
2144 | } | |
2145 | ||
2146 | sub DESTROY { | |
2147 | my $self = shift; | |
2148 | print "$$self: ${^GLOBAL_PHASE}\n"; | |
2149 | } | |
2150 | } | |
2151 | ||
2152 | print "run-time: ${^GLOBAL_PHASE}\n"; | |
2153 | ||
2154 | my $runtime = Print::Phase->new( | |
2155 | "lexical variables are garbage collected before END" | |
2156 | ); | |
2157 | ||
2158 | END { print "end-time: ${^GLOBAL_PHASE}\n" } | |
2159 | ||
2160 | our $destruct = Print::Phase->new( | |
2161 | "package variables are garbage collected after END" | |
2162 | ); | |
2163 | ||
2164 | This will print out | |
2165 | ||
2166 | compile-time: START | |
2167 | check-time: CHECK | |
2168 | init-time: INIT | |
2169 | run-time: RUN | |
2170 | lexical variables are garbage collected before END: RUN | |
2171 | end-time: END | |
2172 | package variables are garbage collected after END: DESTRUCT | |
2173 | ||
2174 | This variable was added in Perl 5.14.0. | |
2175 | ||
2176 | =item $^H | |
2177 | X<$^H> | |
2178 | ||
241a59d9 FC |
2179 | WARNING: This variable is strictly for |
2180 | internal use only. Its availability, | |
1fa81471 DR |
2181 | behavior, and contents are subject to change without notice. |
2182 | ||
241a59d9 | 2183 | This variable contains compile-time hints for the Perl interpreter. At the |
1fa81471 DR |
2184 | end of compilation of a BLOCK the value of this variable is restored to the |
2185 | value when the interpreter started to compile the BLOCK. | |
2186 | ||
2187 | When perl begins to parse any block construct that provides a lexical scope | |
2188 | (e.g., eval body, required file, subroutine body, loop body, or conditional | |
2189 | block), the existing value of C<$^H> is saved, but its value is left unchanged. | |
2190 | When the compilation of the block is completed, it regains the saved value. | |
2191 | Between the points where its value is saved and restored, code that | |
2192 | executes within BEGIN blocks is free to change the value of C<$^H>. | |
2193 | ||
2194 | This behavior provides the semantic of lexical scoping, and is used in, | |
2195 | for instance, the C<use strict> pragma. | |
2196 | ||
2197 | The contents should be an integer; different bits of it are used for | |
241a59d9 | 2198 | different pragmatic flags. Here's an example: |
1fa81471 | 2199 | |
9548c15c | 2200 | sub add_100 { $^H |= 0x100 } |
1fa81471 | 2201 | |
9548c15c FC |
2202 | sub foo { |
2203 | BEGIN { add_100() } | |
2204 | bar->baz($boon); | |
2205 | } | |
1fa81471 | 2206 | |
241a59d9 | 2207 | Consider what happens during execution of the BEGIN block. At this point |
1fa81471 | 2208 | the BEGIN block has already been compiled, but the body of C<foo()> is still |
241a59d9 FC |
2209 | being compiled. The new value of C<$^H> |
2210 | will therefore be visible only while | |
1fa81471 DR |
2211 | the body of C<foo()> is being compiled. |
2212 | ||
2213 | Substitution of C<BEGIN { add_100() }> block with: | |
2214 | ||
9548c15c | 2215 | BEGIN { require strict; strict->import('vars') } |
1fa81471 | 2216 | |
241a59d9 | 2217 | demonstrates how C<use strict 'vars'> is implemented. Here's a conditional |
1fa81471 DR |
2218 | version of the same lexical pragma: |
2219 | ||
9548c15c FC |
2220 | BEGIN { |
2221 | require strict; strict->import('vars') if $condition | |
2222 | } | |
1fa81471 DR |
2223 | |
2224 | This variable was added in Perl 5.003. | |
2225 | ||
2226 | =item %^H | |
2227 | X<%^H> | |
2228 | ||
241a59d9 FC |
2229 | The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes |
2230 | it useful for implementation of lexically scoped pragmas. See | |
112284f4 KW |
2231 | L<perlpragma>. All the entries are stringified when accessed at |
2232 | runtime, so only simple values can be accommodated. This means no | |
2233 | pointers to objects, for example. | |
1fa81471 DR |
2234 | |
2235 | When putting items into C<%^H>, in order to avoid conflicting with other | |
2236 | users of the hash there is a convention regarding which keys to use. | |
2237 | A module should use only keys that begin with the module's name (the | |
2238 | name of its main package) and a "/" character. For example, a module | |
2239 | C<Foo::Bar> should use keys such as C<Foo::Bar/baz>. | |
2240 | ||
60cf4914 | 2241 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
2242 | |
2243 | =item ${^OPEN} | |
2244 | X<${^OPEN}> | |
2245 | ||
e038729f | 2246 | An internal variable used by L<PerlIO>. A string in two parts, separated |
1fa81471 DR |
2247 | by a C<\0> byte, the first part describes the input layers, the second |
2248 | part describes the output layers. | |
2249 | ||
e038729f DB |
2250 | This is the mechanism that applies the lexical effects of the L<open> |
2251 | pragma, and the main program scope effects of the C<io> or C<D> options | |
2252 | for the L<-C command-line switch|perlrun/-C [I<numberE<sol>list>]> and | |
2253 | L<PERL_UNICODE environment variable|perlrun/PERL_UNICODE>. | |
2254 | ||
2255 | The functions C<accept()>, C<open()>, C<pipe()>, C<readpipe()> (as well | |
2256 | as the related C<qx> and C<`STRING`> operators), C<socket()>, | |
2257 | C<socketpair()>, and C<sysopen()> are affected by the lexical value of | |
2258 | this variable. The implicit L</ARGV> handle opened by C<readline()> (or | |
2259 | the related C<< <> >> and C<<< <<>> >>> operators) on passed filenames is | |
2260 | also affected (but not if it opens C<STDIN>). If this variable is not | |
2261 | set, these functions will set the default layers as described in | |
2262 | L<PerlIO/Defaults and how to override them>. | |
2263 | ||
2264 | C<open()> ignores this variable (and the default layers) when called with | |
2265 | 3 arguments and explicit layers are specified. Indirect calls to these | |
2266 | functions via modules like L<IO::Handle> are not affected as they occur | |
2267 | in a different lexical scope. Directory handles such as opened by | |
2268 | C<opendir()> are not currently affected. | |
2269 | ||
60cf4914 | 2270 | This variable was added in Perl v5.8.0. |
1fa81471 DR |
2271 | |
2272 | =item $PERLDB | |
2273 | ||
2274 | =item $^P | |
2275 | X<$^P> X<$PERLDB> | |
2276 | ||
241a59d9 | 2277 | The internal variable for debugging support. The meanings of the |
1fa81471 DR |
2278 | various bits are subject to change, but currently indicate: |
2279 | ||
2280 | =over 6 | |
2281 | ||
2282 | =item 0x01 | |
2283 | ||
2284 | Debug subroutine enter/exit. | |
2285 | ||
2286 | =item 0x02 | |
2287 | ||
241a59d9 FC |
2288 | Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for |
2289 | each statement executed. Also causes saving source code lines (like | |
2290 | 0x400). | |
1fa81471 DR |
2291 | |
2292 | =item 0x04 | |
2293 | ||
2294 | Switch off optimizations. | |
2295 | ||
2296 | =item 0x08 | |
2297 | ||
2298 | Preserve more data for future interactive inspections. | |
2299 | ||
2300 | =item 0x10 | |
2301 | ||
2302 | Keep info about source lines on which a subroutine is defined. | |
2303 | ||
2304 | =item 0x20 | |
2305 | ||
2306 | Start with single-step on. | |
2307 | ||
2308 | =item 0x40 | |
2309 | ||
2310 | Use subroutine address instead of name when reporting. | |
2311 | ||
2312 | =item 0x80 | |
2313 | ||
2314 | Report C<goto &subroutine> as well. | |
2315 | ||
2316 | =item 0x100 | |
2317 | ||
2318 | Provide informative "file" names for evals based on the place they were compiled. | |
2319 | ||
2320 | =item 0x200 | |
2321 | ||
2322 | Provide informative names to anonymous subroutines based on the place they | |
2323 | were compiled. | |
2324 | ||
2325 | =item 0x400 | |
2326 | ||
2327 | Save source code lines into C<@{"_<$filename"}>. | |
2328 | ||
aab47982 RS |
2329 | =item 0x800 |
2330 | ||
2331 | When saving source, include evals that generate no subroutines. | |
2332 | ||
2333 | =item 0x1000 | |
2334 | ||
2335 | When saving source, include source that did not compile. | |
2336 | ||
1fa81471 DR |
2337 | =back |
2338 | ||
2339 | Some bits may be relevant at compile-time only, some at | |
241a59d9 | 2340 | run-time only. This is a new mechanism and the details may change. |
1fa81471 DR |
2341 | See also L<perldebguts>. |
2342 | ||
2343 | =item ${^TAINT} | |
2344 | X<${^TAINT}> | |
2345 | ||
241a59d9 | 2346 | Reflects if taint mode is on or off. 1 for on (the program was run with |
1fa81471 DR |
2347 | B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with |
2348 | B<-t> or B<-TU>). | |
2349 | ||
2350 | This variable is read-only. | |
2351 | ||
60cf4914 | 2352 | This variable was added in Perl v5.8.0. |
1fa81471 | 2353 | |
f512d242 KW |
2354 | =item ${^SAFE_LOCALES} |
2355 | X<${^SAFE_LOCALES}> | |
2356 | ||
2357 | Reflects if safe locale operations are available to this perl (when the | |
2358 | value is 1) or not (the value is 0). This variable is always 1 if the | |
e9bc6d6b KW |
2359 | perl has been compiled without threads. It is also 1 if this perl is |
2360 | using thread-safe locale operations. Note that an individual thread may | |
2361 | choose to use the global locale (generally unsafe) by calling | |
58e641fb | 2362 | L<perlapi/switch_to_global_locale>. This variable currently is still |
e9bc6d6b | 2363 | set to 1 in such threads. |
f512d242 KW |
2364 | |
2365 | This variable is read-only. | |
2366 | ||
2367 | This variable was added in Perl v5.28.0. | |
2368 | ||
1fa81471 DR |
2369 | =item ${^UNICODE} |
2370 | X<${^UNICODE}> | |
2371 | ||
028611fa DB |
2372 | Reflects certain Unicode settings of Perl. See |
2373 | L<perlrun|perlrun/-C [numberE<sol>list]> documentation for the C<-C> | |
2374 | switch for more information about the possible values. | |
1fa81471 DR |
2375 | |
2376 | This variable is set during Perl startup and is thereafter read-only. | |
2377 | ||
60cf4914 | 2378 | This variable was added in Perl v5.8.2. |
1fa81471 DR |
2379 | |
2380 | =item ${^UTF8CACHE} | |
2381 | X<${^UTF8CACHE}> | |
2382 | ||
2383 | This variable controls the state of the internal UTF-8 offset caching code. | |
2384 | 1 for on (the default), 0 for off, -1 to debug the caching code by checking | |
2385 | all its results against linear scans, and panicking on any discrepancy. | |
2386 | ||
94df5432 KW |
2387 | This variable was added in Perl v5.8.9. It is subject to change or |
2388 | removal without notice, but is currently used to avoid recalculating the | |
2389 | boundaries of multi-byte UTF-8-encoded characters. | |
1fa81471 DR |
2390 | |
2391 | =item ${^UTF8LOCALE} | |
2392 | X<${^UTF8LOCALE}> | |
2393 | ||
2394 | This variable indicates whether a UTF-8 locale was detected by perl at | |
241a59d9 | 2395 | startup. This information is used by perl when it's in |
1fa81471 | 2396 | adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line |
028611fa DB |
2397 | switch); see L<perlrun|perlrun/-C [numberE<sol>list]> for more info on |
2398 | this. | |
1fa81471 | 2399 | |
60cf4914 | 2400 | This variable was added in Perl v5.8.8. |
1fa81471 DR |
2401 | |
2402 | =back | |
2403 | ||
b0c22438 | 2404 | =head2 Deprecated and removed variables |
7f315d2e | 2405 | |
0b9346e6 | 2406 | Deprecating a variable announces the intent of the perl maintainers to |
241a59d9 FC |
2407 | eventually remove the variable from the language. It may still be |
2408 | available despite its status. Using a deprecated variable triggers | |
b0c22438 | 2409 | a warning. |
7f315d2e | 2410 | |
84dabc03 | 2411 | Once a variable is removed, its use triggers an error telling you |
b0c22438 | 2412 | the variable is unsupported. |
7f315d2e | 2413 | |
84dabc03 | 2414 | See L<perldiag> for details about error messages. |
7f315d2e | 2415 | |
b0c22438 | 2416 | =over 8 |
7f315d2e | 2417 | |
84dabc03 | 2418 | =item $# |
b7a15f05 | 2419 | X<$#> |
84dabc03 | 2420 | |
38e5787b | 2421 | C<$#> was a variable that could be used to format printed numbers. |
60cf4914 | 2422 | After a deprecation cycle, its magic was removed in Perl v5.10.0 and |
84dabc03 | 2423 | using it now triggers a warning: C<$# is no longer supported>. |
2424 | ||
2425 | This is not the sigil you use in front of an array name to get the | |
241a59d9 FC |
2426 | last index, like C<$#array>. That's still how you get the last index |
2427 | of an array in Perl. The two have nothing to do with each other. | |
84dabc03 | 2428 | |
2429 | Deprecated in Perl 5. | |
2430 | ||
60cf4914 | 2431 | Removed in Perl v5.10.0. |
84dabc03 | 2432 | |
7f315d2e CO |
2433 | =item $* |
2434 | X<$*> | |
2435 | ||
84dabc03 | 2436 | C<$*> was a variable that you could use to enable multiline matching. |
60cf4914 | 2437 | After a deprecation cycle, its magic was removed in Perl v5.10.0. |
7f315d2e | 2438 | Using it now triggers a warning: C<$* is no longer supported>. |
84dabc03 | 2439 | You should use the C</s> and C</m> regexp modifiers instead. |
7f315d2e | 2440 | |
b0c22438 | 2441 | Deprecated in Perl 5. |
7f315d2e | 2442 | |
60cf4914 | 2443 | Removed in Perl v5.10.0. |
7f315d2e | 2444 | |
84dabc03 | 2445 | =item $[ |
b7a15f05 | 2446 | X<$[> |
84dabc03 | 2447 | |
b82b06b8 FC |
2448 | This variable stores the index of the first element in an array, and |
2449 | of the first character in a substring. The default is 0, but you could | |
2450 | theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran) | |
2451 | when subscripting and when evaluating the index() and substr() functions. | |
84dabc03 | 2452 | |
b82b06b8 FC |
2453 | As of release 5 of Perl, assignment to C<$[> is treated as a compiler |
2454 | directive, and cannot influence the behavior of any other file. | |
2455 | (That's why you can only assign compile-time constants to it.) | |
2456 | Its use is highly discouraged. | |
2457 | ||
60cf4914 | 2458 | Prior to Perl v5.10.0, assignment to C<$[> could be seen from outer lexical |
b82b06b8 FC |
2459 | scopes in the same file, unlike other compile-time directives (such as |
2460 | L<strict>). Using local() on it would bind its value strictly to a lexical | |
2461 | block. Now it is always lexically scoped. | |
2462 | ||
c22e17d0 | 2463 | As of Perl v5.16.0, it is implemented by the L<arybase> module. |
84dabc03 | 2464 | |
c22e17d0 DIM |
2465 | As of Perl v5.30.0, or under C<use v5.16>, or C<no feature "array_base">, |
2466 | C<$[> no longer has any effect, and always contains 0. | |
2467 | Assigning 0 to it is permitted, but any other value will produce an error. | |
6b54f8ab | 2468 | |
b82b06b8 FC |
2469 | Mnemonic: [ begins subscripts. |
2470 | ||
60cf4914 | 2471 | Deprecated in Perl v5.12.0. |
e1dccc0d | 2472 | |
b0c22438 | 2473 | =back |
2b92dfce | 2474 | |
0b9346e6 | 2475 | =cut |