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 | ||
fc33dad2 FC |
145 | C<$_> is by default a global variable. However, as |
146 | of perl v5.10.0, you can use a lexical version of | |
241a59d9 | 147 | C<$_> by declaring it in a file or in a block with C<my>. Moreover, |
fc33dad2 FC |
148 | declaring C<our $_> restores the global C<$_> in the current scope. Though |
149 | this seemed like a good idea at the time it was introduced, lexical C<$_> | |
150 | actually causes more problems than it solves. If you call a function that | |
151 | expects to be passed information via C<$_>, it may or may not work, | |
152 | depending on how the function is written, there not being any easy way to | |
153 | solve this. Just avoid lexical C<$_>, unless you are feeling particularly | |
dd73cf18 RS |
154 | masochistic. For this reason lexical C<$_> is still experimental and will |
155 | produce a warning unless warnings have been disabled. As with other | |
156 | experimental features, the behavior of lexical C<$_> is subject to change | |
157 | without notice, including change into a fatal error. | |
59f00321 | 158 | |
b0c22438 | 159 | Mnemonic: underline is understood in certain operations. |
a0d0e21e | 160 | |
0b9346e6 | 161 | =item @ARG |
cde0cee5 | 162 | |
0b9346e6 | 163 | =item @_ |
164 | X<@_> X<@ARG> | |
a0d0e21e | 165 | |
0b9346e6 | 166 | Within a subroutine the array C<@_> contains the parameters passed to |
241a59d9 | 167 | that subroutine. Inside a subroutine, C<@_> is the default array for |
256ca3d3 | 168 | the array operators C<pop> and C<shift>. |
a0d0e21e | 169 | |
0b9346e6 | 170 | See L<perlsub>. |
a0d0e21e | 171 | |
1311257d | 172 | =item $LIST_SEPARATOR |
173 | ||
174 | =item $" | |
175 | X<$"> X<$LIST_SEPARATOR> | |
176 | ||
69520822 | 177 | When an array or an array slice is interpolated into a double-quoted |
178 | string or a similar context such as C</.../>, its elements are | |
241a59d9 | 179 | separated by this value. Default is a space. For example, this: |
69520822 | 180 | |
9548c15c | 181 | print "The array is: @array\n"; |
69520822 | 182 | |
183 | is equivalent to this: | |
184 | ||
9548c15c | 185 | print "The array is: " . join($", @array) . "\n"; |
69520822 | 186 | |
187 | Mnemonic: works in double-quoted context. | |
1311257d | 188 | |
b0c22438 | 189 | =item $PROCESS_ID |
cde0cee5 | 190 | |
b0c22438 | 191 | =item $PID |
a0d0e21e | 192 | |
b0c22438 | 193 | =item $$ |
194 | X<$$> X<$PID> X<$PROCESS_ID> | |
a0d0e21e | 195 | |
241a59d9 | 196 | The process number of the Perl running this script. Though you I<can> set |
4a904372 | 197 | this variable, doing so is generally discouraged, although it can be |
241a59d9 | 198 | invaluable for some testing purposes. It will be reset automatically |
b0c22438 | 199 | across C<fork()> calls. |
a0d0e21e | 200 | |
d7c042c9 AB |
201 | Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl |
202 | would emulate POSIX semantics on Linux systems using LinuxThreads, a | |
203 | partial implementation of POSIX Threads that has since been superseded | |
204 | by the Native POSIX Thread Library (NPTL). | |
205 | ||
e3f68f70 | 206 | LinuxThreads is now obsolete on Linux, and caching C<getpid()> |
d7c042c9 AB |
207 | like this made embedding perl unnecessarily complex (since you'd have |
208 | to manually update the value of $$), so now C<$$> and C<getppid()> | |
209 | will always return the same values as the underlying C library. | |
210 | ||
211 | Debian GNU/kFreeBSD systems also used LinuxThreads up until and | |
212 | including the 6.0 release, but after that moved to FreeBSD thread | |
213 | semantics, which are POSIX-like. | |
214 | ||
215 | To see if your system is affected by this discrepancy check if | |
216 | C<getconf GNU_LIBPTHREAD_VERSION | grep -q NPTL> returns a false | |
1e7d0944 | 217 | value. NTPL threads preserve the POSIX semantics. |
a0d0e21e | 218 | |
b0c22438 | 219 | Mnemonic: same as shells. |
ad83b128 | 220 | |
66d7055b DR |
221 | =item $PROGRAM_NAME |
222 | ||
223 | =item $0 | |
224 | X<$0> X<$PROGRAM_NAME> | |
225 | ||
226 | Contains the name of the program being executed. | |
227 | ||
228 | On some (but not all) operating systems assigning to C<$0> modifies | |
241a59d9 | 229 | the argument area that the C<ps> program sees. On some platforms you |
66d7055b | 230 | may have to use special C<ps> options or a different C<ps> to see the |
241a59d9 | 231 | changes. Modifying the C<$0> is more useful as a way of indicating the |
66d7055b DR |
232 | current program state than it is for hiding the program you're |
233 | running. | |
234 | ||
235 | Note that there are platform-specific limitations on the maximum | |
241a59d9 | 236 | length of C<$0>. In the most extreme case it may be limited to the |
66d7055b DR |
237 | space occupied by the original C<$0>. |
238 | ||
239 | In some platforms there may be arbitrary amount of padding, for | |
240 | example space characters, after the modified name as shown by C<ps>. | |
241 | In some platforms this padding may extend all the way to the original | |
242 | length of the argument area, no matter what you do (this is the case | |
243 | for example with Linux 2.2). | |
244 | ||
245 | Note for BSD users: setting C<$0> does not completely remove "perl" | |
241a59d9 | 246 | from the ps(1) output. For example, setting C<$0> to C<"foobar"> may |
66d7055b DR |
247 | result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix |
248 | and the " (perl)" suffix are shown depends on your exact BSD variant | |
241a59d9 | 249 | and version). This is an operating system feature, Perl cannot help it. |
66d7055b DR |
250 | |
251 | In multithreaded scripts Perl coordinates the threads so that any | |
252 | thread may modify its copy of the C<$0> and the change becomes visible | |
241a59d9 | 253 | to ps(1) (assuming the operating system plays along). Note that |
66d7055b DR |
254 | the view of C<$0> the other threads have will not change since they |
255 | have their own copies of it. | |
256 | ||
257 | If the program has been given to perl via the switches C<-e> or C<-E>, | |
258 | C<$0> will contain the string C<"-e">. | |
259 | ||
60cf4914 | 260 | On Linux as of perl v5.14.0 the legacy process name will be set with |
66d7055b | 261 | C<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as |
241a59d9 | 262 | perl has done since version 4.000. Now system utilities that read the |
66d7055b | 263 | legacy process name such as ps, top and killall will recognize the |
241a59d9 | 264 | name you set when assigning to C<$0>. The string you supply will be |
66d7055b DR |
265 | cut off at 16 bytes, this is a limitation imposed by Linux. |
266 | ||
267 | Mnemonic: same as B<sh> and B<ksh>. | |
268 | ||
b0c22438 | 269 | =item $REAL_GROUP_ID |
a01268b5 | 270 | |
b0c22438 | 271 | =item $GID |
a01268b5 | 272 | |
b0c22438 | 273 | =item $( |
274 | X<$(> X<$GID> X<$REAL_GROUP_ID> | |
a01268b5 | 275 | |
241a59d9 | 276 | The real gid of this process. If you are on a machine that supports |
b0c22438 | 277 | membership in multiple groups simultaneously, gives a space separated |
241a59d9 | 278 | list of groups you are in. The first number is the one returned by |
b0c22438 | 279 | C<getgid()>, and the subsequent ones by C<getgroups()>, one of which may be |
280 | the same as the first number. | |
a01268b5 | 281 | |
b0c22438 | 282 | However, a value assigned to C<$(> must be a single number used to |
241a59d9 FC |
283 | set the real gid. So the value given by C<$(> should I<not> be assigned |
284 | back to C<$(> without being forced numeric, such as by adding zero. Note | |
b0c22438 | 285 | that this is different to the effective gid (C<$)>) which does take a |
286 | list. | |
fe307981 | 287 | |
b0c22438 | 288 | You can change both the real gid and the effective gid at the same |
241a59d9 FC |
289 | time by using C<POSIX::setgid()>. Changes |
290 | to C<$(> require a check to C<$!> | |
b0c22438 | 291 | to detect any possible errors after an attempted change. |
6cef1e77 | 292 | |
241a59d9 | 293 | Mnemonic: parentheses are used to I<group> things. The real gid is the |
b0c22438 | 294 | group you I<left>, if you're running setgid. |
6cef1e77 | 295 | |
b0c22438 | 296 | =item $EFFECTIVE_GROUP_ID |
8e08999f | 297 | |
b0c22438 | 298 | =item $EGID |
81714fb9 | 299 | |
b0c22438 | 300 | =item $) |
301 | X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID> | |
81714fb9 | 302 | |
241a59d9 | 303 | The effective gid of this process. If you are on a machine that |
b0c22438 | 304 | supports membership in multiple groups simultaneously, gives a space |
241a59d9 | 305 | separated list of groups you are in. The first number is the one |
b0c22438 | 306 | returned by C<getegid()>, and the subsequent ones by C<getgroups()>, |
307 | one of which may be the same as the first number. | |
81714fb9 | 308 | |
b0c22438 | 309 | Similarly, a value assigned to C<$)> must also be a space-separated |
241a59d9 FC |
310 | list of numbers. The first number sets the effective gid, and |
311 | the rest (if any) are passed to C<setgroups()>. To get the effect of an | |
b0c22438 | 312 | empty list for C<setgroups()>, just repeat the new effective gid; that is, |
313 | to force an effective gid of 5 and an effectively empty C<setgroups()> | |
314 | list, say C< $) = "5 5" >. | |
81714fb9 | 315 | |
b0c22438 | 316 | You can change both the effective gid and the real gid at the same |
317 | time by using C<POSIX::setgid()> (use only a single numeric argument). | |
318 | Changes to C<$)> require a check to C<$!> to detect any possible errors | |
319 | after an attempted change. | |
44a2ac75 | 320 | |
b0c22438 | 321 | C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on |
241a59d9 | 322 | machines that support the corresponding I<set[re][ug]id()> routine. C<$(> |
b0c22438 | 323 | and C<$)> can be swapped only on machines supporting C<setregid()>. |
3195cf34 | 324 | |
241a59d9 | 325 | Mnemonic: parentheses are used to I<group> things. The effective gid |
b0c22438 | 326 | is the group that's I<right> for you, if you're running setgid. |
44a2ac75 | 327 | |
c82f2f4e DR |
328 | =item $REAL_USER_ID |
329 | ||
330 | =item $UID | |
331 | ||
332 | =item $< | |
333 | X<< $< >> X<$UID> X<$REAL_USER_ID> | |
334 | ||
241a59d9 FC |
335 | The real uid of this process. You can change both the real uid and the |
336 | effective uid at the same time by using C<POSIX::setuid()>. Since | |
c82f2f4e DR |
337 | changes to C<< $< >> require a system call, check C<$!> after a change |
338 | attempt to detect any possible errors. | |
339 | ||
340 | Mnemonic: it's the uid you came I<from>, if you're running setuid. | |
341 | ||
342 | =item $EFFECTIVE_USER_ID | |
343 | ||
344 | =item $EUID | |
345 | ||
346 | =item $> | |
347 | X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID> | |
348 | ||
241a59d9 | 349 | The effective uid of this process. For example: |
c82f2f4e | 350 | |
9548c15c FC |
351 | $< = $>; # set real to effective uid |
352 | ($<,$>) = ($>,$<); # swap real and effective uids | |
c82f2f4e DR |
353 | |
354 | You can change both the effective uid and the real uid at the same | |
241a59d9 | 355 | time by using C<POSIX::setuid()>. Changes to C<< $> >> require a check |
c82f2f4e DR |
356 | to C<$!> to detect any possible errors after an attempted change. |
357 | ||
358 | C<< $< >> and C<< $> >> can be swapped only on machines | |
359 | supporting C<setreuid()>. | |
360 | ||
361 | Mnemonic: it's the uid you went I<to>, if you're running setuid. | |
362 | ||
0b9346e6 | 363 | =item $SUBSCRIPT_SEPARATOR |
364 | ||
365 | =item $SUBSEP | |
366 | ||
367 | =item $; | |
368 | X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR> | |
369 | ||
241a59d9 | 370 | The subscript separator for multidimensional array emulation. If you |
0b9346e6 | 371 | refer to a hash element as |
372 | ||
592708b4 | 373 | $foo{$x,$y,$z} |
0b9346e6 | 374 | |
375 | it really means | |
376 | ||
592708b4 | 377 | $foo{join($;, $x, $y, $z)} |
0b9346e6 | 378 | |
379 | But don't put | |
380 | ||
592708b4 | 381 | @foo{$x,$y,$z} # a slice--note the @ |
0b9346e6 | 382 | |
383 | which means | |
384 | ||
592708b4 | 385 | ($foo{$x},$foo{$y},$foo{$z}) |
0b9346e6 | 386 | |
241a59d9 | 387 | Default is "\034", the same as SUBSEP in B<awk>. If your keys contain |
0b9346e6 | 388 | binary data there might not be any safe value for C<$;>. |
389 | ||
390 | Consider using "real" multidimensional arrays as described | |
391 | in L<perllol>. | |
392 | ||
393 | Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon. | |
394 | ||
0b9346e6 | 395 | =item $a |
396 | ||
397 | =item $b | |
398 | X<$a> X<$b> | |
399 | ||
400 | Special package variables when using C<sort()>, see L<perlfunc/sort>. | |
401 | Because of this specialness C<$a> and C<$b> don't need to be declared | |
402 | (using C<use vars>, or C<our()>) even when using the C<strict 'vars'> | |
241a59d9 | 403 | pragma. Don't lexicalize them with C<my $a> or C<my $b> if you want to |
0b9346e6 | 404 | be able to use them in the C<sort()> comparison block or function. |
405 | ||
0b9346e6 | 406 | =item %ENV |
407 | X<%ENV> | |
408 | ||
241a59d9 | 409 | The hash C<%ENV> contains your current environment. Setting a |
0b9346e6 | 410 | value in C<ENV> changes the environment for any child processes |
411 | you subsequently C<fork()> off. | |
412 | ||
32e006ac | 413 | As of v5.18.0, both keys and values stored in C<%ENV> are stringified. |
a5effbbc KF |
414 | |
415 | my $foo = 1; | |
416 | $ENV{'bar'} = \$foo; | |
417 | if( ref $ENV{'bar'} ) { | |
32e006ac | 418 | say "Pre 5.18.0 Behaviour"; |
a5effbbc | 419 | } else { |
32e006ac | 420 | say "Post 5.18.0 Behaviour"; |
a5effbbc KF |
421 | } |
422 | ||
423 | Previously, only child processes received stringified values: | |
424 | ||
425 | my $foo = 1; | |
426 | $ENV{'bar'} = \$foo; | |
427 | ||
428 | # Always printed 'non ref' | |
6d3f582d FC |
429 | system($^X, '-e', |
430 | q/print ( ref $ENV{'bar'} ? 'ref' : 'non ref' ) /); | |
a5effbbc KF |
431 | |
432 | This happens because you can't really share arbitrary data structures with | |
433 | foreign processes. | |
434 | ||
d2578154 KE |
435 | =item $OLD_PERL_VERSION |
436 | ||
4ad0ecd4 | 437 | =item $] |
b77ebf74 | 438 | X<$]> X<$OLD_PERL_VERSION> |
4ad0ecd4 KE |
439 | |
440 | The revision, version, and subversion of the Perl interpreter, represented | |
441 | as a decimal of the form 5.XXXYYY, where XXX is the version / 1e3 and YYY | |
442 | is the subversion / 1e6. For example, Perl v5.10.1 would be "5.010001". | |
443 | ||
444 | This variable can be used to determine whether the Perl interpreter | |
445 | executing a script is in the right range of versions: | |
446 | ||
447 | warn "No PerlIO!\n" if $] lt '5.008'; | |
448 | ||
449 | When comparing C<$]>, string comparison operators are B<highly | |
450 | recommended>. The inherent limitations of binary floating point | |
451 | representation can sometimes lead to incorrect comparisons for some | |
452 | numbers on some architectures. | |
453 | ||
454 | See also the documentation of C<use VERSION> and C<require VERSION> | |
455 | for a convenient way to fail if the running Perl interpreter is too old. | |
456 | ||
457 | See L</$^V> for a representation of the Perl version as a L<version> | |
458 | object, which allows more flexible string comparisons. | |
459 | ||
460 | The main advantage of C<$]> over C<$^V> is that it works the same on any | |
461 | version of Perl. The disadvantages are that it can't easily be compared | |
462 | to versions in other formats (e.g. literal v-strings, "v1.2.3" or | |
463 | version objects) and numeric comparisons can occasionally fail; it's good | |
464 | for string literal version checks and bad for comparing to a variable | |
465 | that hasn't been sanity-checked. | |
466 | ||
9fcc2314 AP |
467 | The C<$OLD_PERL_VERSION> form was added in Perl v5.20.0 for historical |
468 | reasons but its use is discouraged. (If your reason to use C<$]> is to | |
469 | run code on old perls then referring to it as C<$OLD_PERL_VERSION> would | |
470 | be self-defeating.) | |
4ad0ecd4 | 471 | |
9fcc2314 | 472 | Mnemonic: Is this version of perl in the right bracket? |
83c1fffe | 473 | |
b0c22438 | 474 | =item $SYSTEM_FD_MAX |
5b2b9c68 | 475 | |
b0c22438 | 476 | =item $^F |
477 | X<$^F> X<$SYSTEM_FD_MAX> | |
5b2b9c68 | 478 | |
241a59d9 | 479 | The maximum system file descriptor, ordinarily 2. System file |
b0c22438 | 480 | descriptors are passed to C<exec()>ed processes, while higher file |
241a59d9 FC |
481 | descriptors are not. Also, during an |
482 | C<open()>, system file descriptors are | |
b0c22438 | 483 | preserved even if the C<open()> fails (ordinary file descriptors are |
241a59d9 | 484 | closed before the C<open()> is attempted). The close-on-exec |
b0c22438 | 485 | status of a file descriptor will be decided according to the value of |
486 | C<$^F> when the corresponding file, pipe, or socket was opened, not the | |
487 | time of the C<exec()>. | |
5b2b9c68 | 488 | |
0b9346e6 | 489 | =item @F |
490 | X<@F> | |
491 | ||
492 | The array C<@F> contains the fields of each line read in when autosplit | |
241a59d9 | 493 | mode is turned on. See L<perlrun> for the B<-a> switch. This array |
0b9346e6 | 494 | is package-specific, and must be declared or given a full package name |
495 | if not in package main when running under C<strict 'vars'>. | |
496 | ||
0b9346e6 | 497 | =item @INC |
498 | X<@INC> | |
499 | ||
500 | The array C<@INC> contains the list of places that the C<do EXPR>, | |
241a59d9 | 501 | C<require>, or C<use> constructs look for their library files. It |
0b9346e6 | 502 | initially consists of the arguments to any B<-I> command-line |
503 | switches, followed by the default Perl library, probably | |
504 | F</usr/local/lib/perl>, followed by ".", to represent the current | |
241a59d9 | 505 | directory. ("." will not be appended if taint checks are enabled, |
0b9346e6 | 506 | either by C<-T> or by C<-t>.) If you need to modify this at runtime, |
507 | you should use the C<use lib> pragma to get the machine-dependent | |
508 | library properly loaded also: | |
509 | ||
9548c15c FC |
510 | use lib '/mypath/libdir/'; |
511 | use SomeMod; | |
0b9346e6 | 512 | |
513 | You can also insert hooks into the file inclusion system by putting Perl | |
241a59d9 FC |
514 | code directly into C<@INC>. Those hooks may be subroutine references, |
515 | array references or blessed objects. See L<perlfunc/require> for details. | |
0b9346e6 | 516 | |
517 | =item %INC | |
518 | X<%INC> | |
519 | ||
520 | The hash C<%INC> contains entries for each filename included via the | |
241a59d9 | 521 | C<do>, C<require>, or C<use> operators. The key is the filename |
0b9346e6 | 522 | you specified (with module names converted to pathnames), and the |
241a59d9 | 523 | value is the location of the file found. The C<require> |
0b9346e6 | 524 | operator uses this hash to determine whether a particular file has |
525 | already been included. | |
526 | ||
527 | If the file was loaded via a hook (e.g. a subroutine reference, see | |
528 | L<perlfunc/require> for a description of these hooks), this hook is | |
241a59d9 | 529 | by default inserted into C<%INC> in place of a filename. Note, however, |
0b9346e6 | 530 | that the hook may have set the C<%INC> entry by itself to provide some more |
531 | specific info. | |
532 | ||
b0c22438 | 533 | =item $INPLACE_EDIT |
a0d0e21e | 534 | |
b0c22438 | 535 | =item $^I |
536 | X<$^I> X<$INPLACE_EDIT> | |
a0d0e21e | 537 | |
241a59d9 | 538 | The current value of the inplace-edit extension. Use C<undef> to disable |
b0c22438 | 539 | inplace editing. |
a0d0e21e | 540 | |
b0c22438 | 541 | Mnemonic: value of B<-i> switch. |
a0d0e21e | 542 | |
bf38d944 H |
543 | =item @ISA |
544 | X<@ISA> | |
545 | ||
546 | Each package contains a special array called C<@ISA> which contains a list | |
547 | of that class's parent classes, if any. This array is simply a list of | |
548 | scalars, each of which is a string that corresponds to a package name. The | |
549 | array is examined when Perl does method resolution, which is covered in | |
550 | L<perlobj>. | |
551 | ||
5312fe6c AP |
552 | To load packages while adding them to C<@ISA>, see the L<parent> pragma. The |
553 | discouraged L<base> pragma does this as well, but should not be used except | |
554 | when compatibility with the discouraged L<fields> pragma is required. | |
bf38d944 | 555 | |
b0c22438 | 556 | =item $^M |
557 | X<$^M> | |
a0d0e21e | 558 | |
b0c22438 | 559 | By default, running out of memory is an untrappable, fatal error. |
560 | However, if suitably built, Perl can use the contents of C<$^M> | |
241a59d9 | 561 | as an emergency memory pool after C<die()>ing. Suppose that your Perl |
b0c22438 | 562 | were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc. |
563 | Then | |
a0d0e21e | 564 | |
9548c15c | 565 | $^M = 'a' x (1 << 16); |
a0d0e21e | 566 | |
241a59d9 | 567 | would allocate a 64K buffer for use in an emergency. See the |
b0c22438 | 568 | F<INSTALL> file in the Perl distribution for information on how to |
241a59d9 | 569 | add custom C compilation flags when compiling perl. To discourage casual |
b0c22438 | 570 | use of this advanced feature, there is no L<English|English> long name for |
571 | this variable. | |
a0d0e21e | 572 | |
b0c22438 | 573 | This variable was added in Perl 5.004. |
a0d0e21e | 574 | |
b0c22438 | 575 | =item $OSNAME |
a0d0e21e | 576 | |
b0c22438 | 577 | =item $^O |
578 | X<$^O> X<$OSNAME> | |
a0d0e21e | 579 | |
b0c22438 | 580 | The name of the operating system under which this copy of Perl was |
241a59d9 | 581 | built, as determined during the configuration process. For examples |
b0c22438 | 582 | see L<perlport/PLATFORMS>. |
a0d0e21e | 583 | |
241a59d9 | 584 | The value is identical to C<$Config{'osname'}>. See also L<Config> |
b0c22438 | 585 | and the B<-V> command-line switch documented in L<perlrun>. |
a0d0e21e | 586 | |
b0c22438 | 587 | In Windows platforms, C<$^O> is not very helpful: since it is always |
588 | C<MSWin32>, it doesn't tell the difference between | |
241a59d9 | 589 | 95/98/ME/NT/2000/XP/CE/.NET. Use C<Win32::GetOSName()> or |
b0c22438 | 590 | Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish |
591 | between the variants. | |
a0d0e21e | 592 | |
b0c22438 | 593 | This variable was added in Perl 5.003. |
a0d0e21e | 594 | |
1fa81471 DR |
595 | =item %SIG |
596 | X<%SIG> | |
a0d0e21e | 597 | |
241a59d9 | 598 | The hash C<%SIG> contains signal handlers for signals. For example: |
a0d0e21e | 599 | |
9548c15c FC |
600 | sub handler { # 1st argument is signal name |
601 | my($sig) = @_; | |
602 | print "Caught a SIG$sig--shutting down\n"; | |
603 | close(LOG); | |
604 | exit(0); | |
605 | } | |
a0d0e21e | 606 | |
9548c15c FC |
607 | $SIG{'INT'} = \&handler; |
608 | $SIG{'QUIT'} = \&handler; | |
609 | ... | |
610 | $SIG{'INT'} = 'DEFAULT'; # restore default action | |
611 | $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT | |
a0d0e21e | 612 | |
1fa81471 | 613 | Using a value of C<'IGNORE'> usually has the effect of ignoring the |
241a59d9 | 614 | signal, except for the C<CHLD> signal. See L<perlipc> for more about |
1fa81471 | 615 | this special case. |
a0d0e21e | 616 | |
1fa81471 | 617 | Here are some other examples: |
a0d0e21e | 618 | |
9548c15c FC |
619 | $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not |
620 | # recommended) | |
621 | $SIG{"PIPE"} = \&Plumber; # just fine; assume current | |
622 | # Plumber | |
623 | $SIG{"PIPE"} = *Plumber; # somewhat esoteric | |
624 | $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() | |
625 | # return?? | |
a0d0e21e | 626 | |
1fa81471 DR |
627 | Be sure not to use a bareword as the name of a signal handler, |
628 | lest you inadvertently call it. | |
a0d0e21e | 629 | |
1fa81471 | 630 | If your system has the C<sigaction()> function then signal handlers |
241a59d9 | 631 | are installed using it. This means you get reliable signal handling. |
a0d0e21e | 632 | |
60cf4914 | 633 | The default delivery policy of signals changed in Perl v5.8.0 from |
1fa81471 | 634 | immediate (also known as "unsafe") to deferred, also known as "safe |
241a59d9 | 635 | signals". See L<perlipc> for more information. |
a0d0e21e | 636 | |
241a59d9 | 637 | Certain internal hooks can be also set using the C<%SIG> hash. The |
1fa81471 | 638 | routine indicated by C<$SIG{__WARN__}> is called when a warning |
241a59d9 FC |
639 | message is about to be printed. The warning message is passed as the |
640 | first argument. The presence of a C<__WARN__> hook causes the | |
641 | ordinary printing of warnings to C<STDERR> to be suppressed. You can | |
1fa81471 DR |
642 | use this to save warnings in a variable, or turn warnings into fatal |
643 | errors, like this: | |
a0d0e21e | 644 | |
9548c15c FC |
645 | local $SIG{__WARN__} = sub { die $_[0] }; |
646 | eval $proggie; | |
a8f8344d | 647 | |
b0c22438 | 648 | As the C<'IGNORE'> hook is not supported by C<__WARN__>, you can |
649 | disable warnings using the empty subroutine: | |
f86702cc | 650 | |
9548c15c | 651 | local $SIG{__WARN__} = sub {}; |
55602bd2 | 652 | |
b0c22438 | 653 | The routine indicated by C<$SIG{__DIE__}> is called when a fatal |
241a59d9 FC |
654 | exception is about to be thrown. The error message is passed as the |
655 | first argument. When a C<__DIE__> hook routine returns, the exception | |
b0c22438 | 656 | processing continues as it would have in the absence of the hook, |
c94b42ea DM |
657 | unless the hook routine itself exits via a C<goto &sub>, a loop exit, |
658 | or a C<die()>. The C<__DIE__> handler is explicitly disabled during | |
659 | the call, so that you can die from a C<__DIE__> handler. Similarly | |
660 | for C<__WARN__>. | |
e5218da5 | 661 | |
b0c22438 | 662 | Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called |
241a59d9 | 663 | even inside an C<eval()>. Do not use this to rewrite a pending |
b0c22438 | 664 | exception in C<$@>, or as a bizarre substitute for overriding |
241a59d9 | 665 | C<CORE::GLOBAL::die()>. This strange action at a distance may be fixed |
b0c22438 | 666 | in a future release so that C<$SIG{__DIE__}> is only called if your |
241a59d9 | 667 | program is about to exit, as was the original intent. Any other use is |
b0c22438 | 668 | deprecated. |
669 | ||
670 | C<__DIE__>/C<__WARN__> handlers are very special in one respect: they | |
241a59d9 | 671 | may be called to report (probable) errors found by the parser. In such |
b0c22438 | 672 | a case the parser may be in inconsistent state, so any attempt to |
673 | evaluate Perl code from such a handler will probably result in a | |
241a59d9 | 674 | segfault. This means that warnings or errors that result from parsing |
b0c22438 | 675 | Perl should be used with extreme caution, like this: |
e5218da5 | 676 | |
9548c15c FC |
677 | require Carp if defined $^S; |
678 | Carp::confess("Something wrong") if defined &Carp::confess; | |
679 | die "Something wrong, but could not load Carp to give " | |
680 | . "backtrace...\n\t" | |
681 | . "To see backtrace try starting Perl with -MCarp switch"; | |
e5218da5 | 682 | |
b0c22438 | 683 | Here the first line will load C<Carp> I<unless> it is the parser who |
241a59d9 FC |
684 | called the handler. The second line will print backtrace and die if |
685 | C<Carp> was available. The third line will be executed only if C<Carp> was | |
b0c22438 | 686 | not available. |
0a378802 | 687 | |
0b9346e6 | 688 | Having to even think about the C<$^S> variable in your exception |
241a59d9 FC |
689 | handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented |
690 | invites grievous and difficult to track down errors. Avoid it | |
0b9346e6 | 691 | and use an C<END{}> or CORE::GLOBAL::die override instead. |
692 | ||
b0c22438 | 693 | See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and |
694 | L<warnings> for additional information. | |
0a378802 | 695 | |
b0c22438 | 696 | =item $BASETIME |
6ab308ee | 697 | |
b0c22438 | 698 | =item $^T |
699 | X<$^T> X<$BASETIME> | |
6ab308ee | 700 | |
b0c22438 | 701 | The time at which the program began running, in seconds since the |
241a59d9 | 702 | epoch (beginning of 1970). The values returned by the B<-M>, B<-A>, |
b0c22438 | 703 | and B<-C> filetests are based on this value. |
a0d0e21e | 704 | |
b0c22438 | 705 | =item $PERL_VERSION |
a0d0e21e | 706 | |
b0c22438 | 707 | =item $^V |
708 | X<$^V> X<$PERL_VERSION> | |
a0d0e21e | 709 | |
b0c22438 | 710 | The revision, version, and subversion of the Perl interpreter, |
eb82332c | 711 | represented as a L<version> object. |
748a9306 | 712 | |
60cf4914 BF |
713 | This variable first appeared in perl v5.6.0; earlier versions of perl |
714 | will see an undefined value. Before perl v5.10.0 C<$^V> was represented | |
f20d3573 | 715 | as a v-string rather than a L<version> object. |
55602bd2 | 716 | |
b0c22438 | 717 | C<$^V> can be used to determine whether the Perl interpreter executing |
241a59d9 | 718 | a script is in the right range of versions. For example: |
a0d0e21e | 719 | |
9548c15c | 720 | warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1 |
a0d0e21e | 721 | |
f20d3573 DG |
722 | While version objects overload stringification, to portably convert |
723 | C<$^V> into its string representation, use C<sprintf()>'s C<"%vd"> | |
724 | conversion, which works for both v-strings or version objects: | |
a0d0e21e | 725 | |
9548c15c | 726 | printf "version is v%vd\n", $^V; # Perl's version |
a0d0e21e | 727 | |
b0c22438 | 728 | See the documentation of C<use VERSION> and C<require VERSION> |
729 | for a convenient way to fail if the running Perl interpreter is too old. | |
4d76a344 | 730 | |
6a29646e | 731 | See also C<L</$]>> for a decimal representation of the Perl version. |
a0d0e21e | 732 | |
f20d3573 DG |
733 | The main advantage of C<$^V> over C<$]> is that, for Perl v5.10.0 or |
734 | later, it overloads operators, allowing easy comparison against other | |
735 | version representations (e.g. decimal, literal v-string, "v1.2.3", or | |
736 | objects). The disadvantage is that prior to v5.10.0, it was only a | |
6a29646e KW |
737 | literal v-string, which can't be easily printed or compared, whereas |
738 | the behavior of C<$]> is unchanged on all versions of Perl. | |
a0d0e21e | 739 | |
eb82332c | 740 | Mnemonic: use ^V for a version object. |
a0d0e21e | 741 | |
b0c22438 | 742 | =item ${^WIN32_SLOPPY_STAT} |
5b442a2a | 743 | X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl> |
a0d0e21e | 744 | |
b0c22438 | 745 | If this variable is set to a true value, then C<stat()> on Windows will |
241a59d9 | 746 | not try to open the file. This means that the link count cannot be |
b0c22438 | 747 | determined and file attributes may be out of date if additional |
241a59d9 | 748 | hardlinks to the file exist. On the other hand, not opening the file |
b0c22438 | 749 | is considerably faster, especially for files on network drives. |
a0d0e21e | 750 | |
b0c22438 | 751 | This variable could be set in the F<sitecustomize.pl> file to |
752 | configure the local Perl installation to use "sloppy" C<stat()> by | |
241a59d9 | 753 | default. See the documentation for B<-f> in |
b0c22438 | 754 | L<perlrun|perlrun/"Command Switches"> for more information about site |
755 | customization. | |
a0d0e21e | 756 | |
60cf4914 | 757 | This variable was added in Perl v5.10.0. |
a0d0e21e | 758 | |
b0c22438 | 759 | =item $EXECUTABLE_NAME |
a0d0e21e | 760 | |
b0c22438 | 761 | =item $^X |
762 | X<$^X> X<$EXECUTABLE_NAME> | |
a0d0e21e | 763 | |
b0c22438 | 764 | The name used to execute the current copy of Perl, from C's |
765 | C<argv[0]> or (where supported) F</proc/self/exe>. | |
a043a685 | 766 | |
b0c22438 | 767 | Depending on the host operating system, the value of C<$^X> may be |
768 | a relative or absolute pathname of the perl program file, or may | |
769 | be the string used to invoke perl but not the pathname of the | |
241a59d9 | 770 | perl program file. Also, most operating systems permit invoking |
b0c22438 | 771 | programs that are not in the PATH environment variable, so there |
241a59d9 | 772 | is no guarantee that the value of C<$^X> is in PATH. For VMS, the |
b0c22438 | 773 | value may or may not include a version number. |
a0d0e21e | 774 | |
b0c22438 | 775 | You usually can use the value of C<$^X> to re-invoke an independent |
776 | copy of the same perl that is currently running, e.g., | |
a0d0e21e | 777 | |
9548c15c | 778 | @first_run = `$^X -le "print int rand 100 for 1..100"`; |
a0d0e21e | 779 | |
b0c22438 | 780 | But recall that not all operating systems support forking or |
781 | capturing of the output of commands, so this complex statement | |
782 | may not be portable. | |
a0d0e21e | 783 | |
b0c22438 | 784 | It is not safe to use the value of C<$^X> as a path name of a file, |
785 | as some operating systems that have a mandatory suffix on | |
786 | executable files do not require use of the suffix when invoking | |
241a59d9 | 787 | a command. To convert the value of C<$^X> to a path name, use the |
b0c22438 | 788 | following statements: |
8cc95fdb | 789 | |
9548c15c FC |
790 | # Build up a set of file names (not command names). |
791 | use Config; | |
792 | my $this_perl = $^X; | |
793 | if ($^O ne 'VMS') { | |
794 | $this_perl .= $Config{_exe} | |
795 | unless $this_perl =~ m/$Config{_exe}$/i; | |
796 | } | |
8cc95fdb | 797 | |
b0c22438 | 798 | Because many operating systems permit anyone with read access to |
799 | the Perl program file to make a copy of it, patch the copy, and | |
800 | then execute the copy, the security-conscious Perl programmer | |
801 | should take care to invoke the installed copy of perl, not the | |
241a59d9 | 802 | copy referenced by C<$^X>. The following statements accomplish |
b0c22438 | 803 | this goal, and produce a pathname that can be invoked as a |
804 | command or referenced as a file. | |
a043a685 | 805 | |
9548c15c FC |
806 | use Config; |
807 | my $secure_perl_path = $Config{perlpath}; | |
808 | if ($^O ne 'VMS') { | |
809 | $secure_perl_path .= $Config{_exe} | |
810 | unless $secure_perl_path =~ m/$Config{_exe}$/i; | |
811 | } | |
a0d0e21e | 812 | |
b0c22438 | 813 | =back |
a0d0e21e | 814 | |
b0c22438 | 815 | =head2 Variables related to regular expressions |
816 | ||
817 | Most of the special variables related to regular expressions are side | |
241a59d9 FC |
818 | effects. Perl sets these variables when it has a successful match, so |
819 | you should check the match result before using them. For instance: | |
b0c22438 | 820 | |
9548c15c FC |
821 | if( /P(A)TT(ER)N/ ) { |
822 | print "I found $1 and $2\n"; | |
823 | } | |
b0c22438 | 824 | |
0b9346e6 | 825 | These variables are read-only and dynamically-scoped, unless we note |
b0c22438 | 826 | otherwise. |
827 | ||
0b9346e6 | 828 | The dynamic nature of the regular expression variables means that |
829 | their value is limited to the block that they are in, as demonstrated | |
830 | by this bit of code: | |
b0c22438 | 831 | |
9548c15c FC |
832 | my $outer = 'Wallace and Grommit'; |
833 | my $inner = 'Mutt and Jeff'; | |
0b9346e6 | 834 | |
9548c15c | 835 | my $pattern = qr/(\S+) and (\S+)/; |
0b9346e6 | 836 | |
9548c15c | 837 | sub show_n { print "\$1 is $1; \$2 is $2\n" } |
0b9346e6 | 838 | |
9548c15c FC |
839 | { |
840 | OUTER: | |
841 | show_n() if $outer =~ m/$pattern/; | |
0b9346e6 | 842 | |
9548c15c FC |
843 | INNER: { |
844 | show_n() if $inner =~ m/$pattern/; | |
845 | } | |
0b9346e6 | 846 | |
9548c15c FC |
847 | show_n(); |
848 | } | |
b0c22438 | 849 | |
0b9346e6 | 850 | The output shows that while in the C<OUTER> block, the values of C<$1> |
241a59d9 | 851 | and C<$2> are from the match against C<$outer>. Inside the C<INNER> |
0b9346e6 | 852 | block, the values of C<$1> and C<$2> are from the match against |
853 | C<$inner>, but only until the end of the block (i.e. the dynamic | |
241a59d9 | 854 | scope). After the C<INNER> block completes, the values of C<$1> and |
0b9346e6 | 855 | C<$2> return to the values for the match against C<$outer> even though |
b0c22438 | 856 | we have not made another match: |
857 | ||
9548c15c FC |
858 | $1 is Wallace; $2 is Grommit |
859 | $1 is Mutt; $2 is Jeff | |
860 | $1 is Wallace; $2 is Grommit | |
a0d0e21e | 861 | |
40445027 | 862 | =head3 Performance issues |
0b9346e6 | 863 | |
40445027 DM |
864 | Traditionally in Perl, any use of any of the three variables C<$`>, C<$&> |
865 | or C<$'> (or their C<use English> equivalents) anywhere in the code, caused | |
866 | all subsequent successful pattern matches to make a copy of the matched | |
867 | string, in case the code might subsequently access one of those variables. | |
868 | This imposed a considerable performance penalty across the whole program, | |
869 | so generally the use of these variables has been discouraged. | |
0b9346e6 | 870 | |
40445027 DM |
871 | In Perl 5.6.0 the C<@-> and C<@+> dynamic arrays were introduced that |
872 | supply the indices of successful matches. So you could for example do | |
873 | this: | |
874 | ||
875 | $str =~ /pattern/; | |
876 | ||
877 | print $`, $&, $'; # bad: perfomance hit | |
878 | ||
879 | print # good: no perfomance hit | |
880 | substr($str, 0, $-[0]), | |
881 | substr($str, $-[0], $+[0]-$-[0]), | |
882 | substr($str, $+[0]); | |
883 | ||
884 | In Perl 5.10.0 the C</p> match operator flag and the C<${^PREMATCH}>, | |
885 | C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed | |
886 | you to suffer the penalties only on patterns marked with C</p>. | |
887 | ||
888 | In Perl 5.18.0 onwards, perl started noting the presence of each of the | |
889 | three variables separately, and only copied that part of the string | |
890 | required; so in | |
891 | ||
892 | $`; $&; "abcdefgh" =~ /d/ | |
893 | ||
894 | perl would only copy the "abcd" part of the string. That could make a big | |
895 | difference in something like | |
896 | ||
897 | $str = 'x' x 1_000_000; | |
898 | $&; # whoops | |
899 | $str =~ /x/g # one char copied a million times, not a million chars | |
900 | ||
901 | In Perl 5.20.0 a new copy-on-write system was enabled by default, which | |
902 | finally fixes all performance issues with these three variables, and makes | |
903 | them safe to use anywhere. | |
904 | ||
905 | The C<Devel::NYTProf> and C<Devel::FindAmpersand> modules can help you | |
906 | find uses of these problematic match variables in your code. | |
13b0f67d | 907 | |
b0c22438 | 908 | =over 8 |
a0d0e21e | 909 | |
b0c22438 | 910 | =item $<I<digits>> ($1, $2, ...) |
27deb0cf | 911 | X<$1> X<$2> X<$3> X<$I<digits>> |
8cc95fdb | 912 | |
b0c22438 | 913 | Contains the subpattern from the corresponding set of capturing |
914 | parentheses from the last successful pattern match, not counting patterns | |
915 | matched in nested blocks that have been exited already. | |
8cc95fdb | 916 | |
27deb0cf YO |
917 | Note there is a distinction between a capture buffer which matches |
918 | the empty string a capture buffer which is optional. Eg, C<(x?)> and | |
919 | C<(x)?> The latter may be undef, the former not. | |
920 | ||
b0c22438 | 921 | These variables are read-only and dynamically-scoped. |
a043a685 | 922 | |
b0c22438 | 923 | Mnemonic: like \digits. |
a0d0e21e | 924 | |
27deb0cf YO |
925 | =item @{^CAPTURE} |
926 | X<@{^CAPTURE}> X<@^CAPTURE> | |
927 | ||
928 | An array which contains the capture buffers, if any, of the last | |
929 | successful pattern match, not counting patterns matched | |
930 | in nested blocks that have been exited already. | |
931 | ||
932 | Note that the 0 index of @{^CAPTURE} is equivalent to $1, the 1 index | |
933 | is equivalent to $2, etc. | |
934 | ||
935 | if ("foal"=~/(.)(.)(.)(.)/) { | |
936 | print join "-", @{^CAPTURE}; | |
937 | } | |
938 | ||
939 | should output "f-o-a-l". | |
940 | ||
941 | See also L</$I<digits>>, L</%{^CAPTURE}> and L</%{^CAPTURE_ALL}>. | |
942 | ||
943 | This variable was added in 5.25.7 | |
944 | ||
b0c22438 | 945 | =item $MATCH |
a0d0e21e | 946 | |
b0c22438 | 947 | =item $& |
948 | X<$&> X<$MATCH> | |
a0d0e21e | 949 | |
b0c22438 | 950 | The string matched by the last successful pattern match (not counting |
951 | any matches hidden within a BLOCK or C<eval()> enclosed by the current | |
952 | BLOCK). | |
a0d0e21e | 953 | |
40445027 DM |
954 | See L</Performance issues> above for the serious performance implications |
955 | of using this variable (even once) in your code. | |
80bca1b4 | 956 | |
b0c22438 | 957 | This variable is read-only and dynamically-scoped. |
f9cbb277 | 958 | |
b0c22438 | 959 | Mnemonic: like C<&> in some editors. |
0b9346e6 | 960 | |
b0c22438 | 961 | =item ${^MATCH} |
962 | X<${^MATCH}> | |
a0d0e21e | 963 | |
b0c22438 | 964 | This is similar to C<$&> (C<$MATCH>) except that it does not incur the |
13b0f67d | 965 | performance penalty associated with that variable. |
40445027 DM |
966 | |
967 | See L</Performance issues> above. | |
968 | ||
13b0f67d | 969 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 970 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
971 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
972 | C<${^MATCH}> does the same thing as C<$MATCH>. | |
80bca1b4 | 973 | |
60cf4914 | 974 | This variable was added in Perl v5.10.0. |
4bc88a62 | 975 | |
b0c22438 | 976 | This variable is read-only and dynamically-scoped. |
e2975953 | 977 | |
b0c22438 | 978 | =item $PREMATCH |
52c447a8 | 979 | |
b0c22438 | 980 | =item $` |
5b442a2a | 981 | X<$`> X<$PREMATCH> X<${^PREMATCH}> |
7636ea95 | 982 | |
b0c22438 | 983 | The string preceding whatever was matched by the last successful |
984 | pattern match, not counting any matches hidden within a BLOCK or C<eval> | |
0b9346e6 | 985 | enclosed by the current BLOCK. |
a0d0e21e | 986 | |
40445027 DM |
987 | See L</Performance issues> above for the serious performance implications |
988 | of using this variable (even once) in your code. | |
a0d0e21e | 989 | |
b0c22438 | 990 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 991 | |
b0c22438 | 992 | Mnemonic: C<`> often precedes a quoted string. |
f83ed198 | 993 | |
b0c22438 | 994 | =item ${^PREMATCH} |
5b442a2a | 995 | X<$`> X<${^PREMATCH}> |
a0d0e21e | 996 | |
b0c22438 | 997 | This is similar to C<$`> ($PREMATCH) except that it does not incur the |
13b0f67d | 998 | performance penalty associated with that variable. |
40445027 DM |
999 | |
1000 | See L</Performance issues> above. | |
1001 | ||
13b0f67d | 1002 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 1003 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
1004 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
1005 | C<${^PREMATCH}> does the same thing as C<$PREMATCH>. | |
a0d0e21e | 1006 | |
4a70680a | 1007 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1008 | |
b0c22438 | 1009 | This variable is read-only and dynamically-scoped. |
a0d0e21e | 1010 | |
b0c22438 | 1011 | =item $POSTMATCH |
16070b82 | 1012 | |
b0c22438 | 1013 | =item $' |
5b442a2a | 1014 | X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@-> |
305aace0 | 1015 | |
b0c22438 | 1016 | The string following whatever was matched by the last successful |
1017 | pattern match (not counting any matches hidden within a BLOCK or C<eval()> | |
241a59d9 | 1018 | enclosed by the current BLOCK). Example: |
305aace0 | 1019 | |
9548c15c FC |
1020 | local $_ = 'abcdefghi'; |
1021 | /def/; | |
1022 | print "$`:$&:$'\n"; # prints abc:def:ghi | |
305aace0 | 1023 | |
40445027 DM |
1024 | See L</Performance issues> above for the serious performance implications |
1025 | of using this variable (even once) in your code. | |
a0d0e21e | 1026 | |
b0c22438 | 1027 | This variable is read-only and dynamically-scoped. |
1028 | ||
1029 | Mnemonic: C<'> often follows a quoted string. | |
1030 | ||
1031 | =item ${^POSTMATCH} | |
5b442a2a | 1032 | X<${^POSTMATCH}> X<$'> X<$POSTMATCH> |
b0c22438 | 1033 | |
1034 | This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the | |
13b0f67d | 1035 | performance penalty associated with that variable. |
40445027 DM |
1036 | |
1037 | See L</Performance issues> above. | |
1038 | ||
13b0f67d | 1039 | In Perl v5.18 and earlier, it is only guaranteed |
b0c22438 | 1040 | to return a defined value when the pattern was compiled or executed with |
13b0f67d DM |
1041 | the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so |
1042 | C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>. | |
b0c22438 | 1043 | |
60cf4914 | 1044 | This variable was added in Perl v5.10.0. |
b0c22438 | 1045 | |
1046 | This variable is read-only and dynamically-scoped. | |
1047 | ||
1048 | =item $LAST_PAREN_MATCH | |
1049 | ||
1050 | =item $+ | |
1051 | X<$+> X<$LAST_PAREN_MATCH> | |
1052 | ||
1053 | The text matched by the last bracket of the last successful search pattern. | |
1054 | This is useful if you don't know which one of a set of alternative patterns | |
241a59d9 | 1055 | matched. For example: |
b0c22438 | 1056 | |
9548c15c | 1057 | /Version: (.*)|Revision: (.*)/ && ($rev = $+); |
b0c22438 | 1058 | |
1059 | This variable is read-only and dynamically-scoped. | |
1060 | ||
1061 | Mnemonic: be positive and forward looking. | |
1062 | ||
1063 | =item $LAST_SUBMATCH_RESULT | |
1064 | ||
1065 | =item $^N | |
5b442a2a | 1066 | X<$^N> X<$LAST_SUBMATCH_RESULT> |
b0c22438 | 1067 | |
1068 | The text matched by the used group most-recently closed (i.e. the group | |
1069 | with the rightmost closing parenthesis) of the last successful search | |
1070 | pattern. | |
1071 | ||
1072 | This is primarily used inside C<(?{...})> blocks for examining text | |
241a59d9 | 1073 | recently matched. For example, to effectively capture text to a variable |
b0c22438 | 1074 | (in addition to C<$1>, C<$2>, etc.), replace C<(...)> with |
1075 | ||
9548c15c | 1076 | (?:(...)(?{ $var = $^N })) |
b0c22438 | 1077 | |
1078 | By setting and then using C<$var> in this way relieves you from having to | |
1079 | worry about exactly which numbered set of parentheses they are. | |
1080 | ||
60cf4914 | 1081 | This variable was added in Perl v5.8.0. |
b0c22438 | 1082 | |
1083 | Mnemonic: the (possibly) Nested parenthesis that most recently closed. | |
1084 | ||
1085 | =item @LAST_MATCH_END | |
1086 | ||
1087 | =item @+ | |
1088 | X<@+> X<@LAST_MATCH_END> | |
1089 | ||
1090 | This array holds the offsets of the ends of the last successful | |
241a59d9 FC |
1091 | submatches in the currently active dynamic scope. C<$+[0]> is |
1092 | the offset into the string of the end of the entire match. This | |
b0c22438 | 1093 | is the same value as what the C<pos> function returns when called |
241a59d9 | 1094 | on the variable that was matched against. The I<n>th element |
b0c22438 | 1095 | of this array holds the offset of the I<n>th submatch, so |
1096 | C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset | |
241a59d9 FC |
1097 | past where C<$2> ends, and so on. You can use C<$#+> to determine |
1098 | how many subgroups were in the last successful match. See the | |
b0c22438 | 1099 | examples given for the C<@-> variable. |
1100 | ||
60cf4914 | 1101 | This variable was added in Perl v5.6.0. |
b0c22438 | 1102 | |
27deb0cf YO |
1103 | =item %{^CAPTURE} |
1104 | ||
b0c22438 | 1105 | =item %LAST_PAREN_MATCH |
1106 | ||
1107 | =item %+ | |
27deb0cf | 1108 | X<%+> X<%LAST_PAREN_MATCH> X<%{^CAPTURE}> |
b0c22438 | 1109 | |
1110 | Similar to C<@+>, the C<%+> hash allows access to the named capture | |
1111 | buffers, should they exist, in the last successful match in the | |
1112 | currently active dynamic scope. | |
1113 | ||
1114 | For example, C<$+{foo}> is equivalent to C<$1> after the following match: | |
1115 | ||
9548c15c | 1116 | 'foo' =~ /(?<foo>foo)/; |
b0c22438 | 1117 | |
1118 | The keys of the C<%+> hash list only the names of buffers that have | |
1119 | captured (and that are thus associated to defined values). | |
1120 | ||
1121 | The underlying behaviour of C<%+> is provided by the | |
1122 | L<Tie::Hash::NamedCapture> module. | |
1123 | ||
1124 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1125 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1126 | iterative access to them via C<each> may have unpredictable results. |
1127 | Likewise, if the last successful match changes, then the results may be | |
1128 | surprising. | |
1129 | ||
27deb0cf YO |
1130 | This variable was added in Perl v5.10.0. The C<%{^CAPTURE}> alias was |
1131 | added in 5.25.7. | |
a0d0e21e | 1132 | |
b0c22438 | 1133 | This variable is read-only and dynamically-scoped. |
1134 | ||
1135 | =item @LAST_MATCH_START | |
1136 | ||
1137 | =item @- | |
1138 | X<@-> X<@LAST_MATCH_START> | |
1139 | ||
1140 | C<$-[0]> is the offset of the start of the last successful match. | |
1141 | C<$-[>I<n>C<]> is the offset of the start of the substring matched by | |
1142 | I<n>-th subpattern, or undef if the subpattern did not match. | |
1143 | ||
1144 | Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0], | |
241a59d9 | 1145 | $+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n], |
b0c22438 | 1146 | $+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with |
241a59d9 FC |
1147 | C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the |
1148 | last matched subgroup in the last successful match. Contrast with | |
1149 | C<$#+>, the number of subgroups in the regular expression. Compare | |
b0c22438 | 1150 | with C<@+>. |
1151 | ||
1152 | This array holds the offsets of the beginnings of the last | |
1153 | successful submatches in the currently active dynamic scope. | |
1154 | C<$-[0]> is the offset into the string of the beginning of the | |
241a59d9 | 1155 | entire match. The I<n>th element of this array holds the offset |
b0c22438 | 1156 | of the I<n>th submatch, so C<$-[1]> is the offset where C<$1> |
1157 | begins, C<$-[2]> the offset where C<$2> begins, and so on. | |
1158 | ||
1159 | After a match against some variable C<$var>: | |
1160 | ||
1161 | =over 5 | |
1162 | ||
1163 | =item C<$`> is the same as C<substr($var, 0, $-[0])> | |
1164 | ||
1165 | =item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])> | |
1166 | ||
1167 | =item C<$'> is the same as C<substr($var, $+[0])> | |
1168 | ||
1169 | =item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])> | |
1170 | ||
1171 | =item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])> | |
1172 | ||
1173 | =item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])> | |
1174 | ||
1175 | =back | |
1176 | ||
60cf4914 | 1177 | This variable was added in Perl v5.6.0. |
b0c22438 | 1178 | |
27deb0cf YO |
1179 | =item %{^CAPTURE_ALL} |
1180 | X<%{^CAPTURE_ALL}> | |
1181 | ||
b0c22438 | 1182 | =item %- |
2e67aae7 | 1183 | X<%-> |
b0c22438 | 1184 | |
1185 | Similar to C<%+>, this variable allows access to the named capture groups | |
241a59d9 | 1186 | in the last successful match in the currently active dynamic scope. To |
b0c22438 | 1187 | each capture group name found in the regular expression, it associates a |
1188 | reference to an array containing the list of values captured by all | |
1189 | buffers with that name (should there be several of them), in the order | |
1190 | where they appear. | |
1191 | ||
1192 | Here's an example: | |
1193 | ||
1194 | if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) { | |
1195 | foreach my $bufname (sort keys %-) { | |
1196 | my $ary = $-{$bufname}; | |
1197 | foreach my $idx (0..$#$ary) { | |
1198 | print "\$-{$bufname}[$idx] : ", | |
9548c15c FC |
1199 | (defined($ary->[$idx]) |
1200 | ? "'$ary->[$idx]'" | |
1201 | : "undef"), | |
b0c22438 | 1202 | "\n"; |
1203 | } | |
1204 | } | |
1205 | } | |
1206 | ||
1207 | would print out: | |
1208 | ||
9548c15c FC |
1209 | $-{A}[0] : '1' |
1210 | $-{A}[1] : '3' | |
1211 | $-{B}[0] : '2' | |
1212 | $-{B}[1] : '4' | |
b0c22438 | 1213 | |
1214 | The keys of the C<%-> hash correspond to all buffer names found in | |
1215 | the regular expression. | |
1216 | ||
1217 | The behaviour of C<%-> is implemented via the | |
1218 | L<Tie::Hash::NamedCapture> module. | |
1219 | ||
1220 | B<Note:> C<%-> and C<%+> are tied views into a common internal hash | |
241a59d9 | 1221 | associated with the last successful regular expression. Therefore mixing |
b0c22438 | 1222 | iterative access to them via C<each> may have unpredictable results. |
1223 | Likewise, if the last successful match changes, then the results may be | |
1224 | surprising. | |
1225 | ||
27deb0cf YO |
1226 | This variable was added in Perl v5.10.0. The C<%{^CAPTURE_ALL}> alias was |
1227 | added in 5.25.7. | |
b0c22438 | 1228 | |
1229 | This variable is read-only and dynamically-scoped. | |
1230 | ||
1231 | =item $LAST_REGEXP_CODE_RESULT | |
1232 | ||
1233 | =item $^R | |
1234 | X<$^R> X<$LAST_REGEXP_CODE_RESULT> | |
1235 | ||
1236 | The result of evaluation of the last successful C<(?{ code })> | |
241a59d9 | 1237 | regular expression assertion (see L<perlre>). May be written to. |
b0c22438 | 1238 | |
1239 | This variable was added in Perl 5.005. | |
a0d0e21e | 1240 | |
a3621e74 | 1241 | =item ${^RE_DEBUG_FLAGS} |
ca1b95ae | 1242 | X<${^RE_DEBUG_FLAGS}> |
a3621e74 | 1243 | |
241a59d9 FC |
1244 | The current value of the regex debugging flags. Set to 0 for no debug output |
1245 | even when the C<re 'debug'> module is loaded. See L<re> for details. | |
b0c22438 | 1246 | |
60cf4914 | 1247 | This variable was added in Perl v5.10.0. |
a3621e74 | 1248 | |
0111c4fd | 1249 | =item ${^RE_TRIE_MAXBUF} |
ca1b95ae | 1250 | X<${^RE_TRIE_MAXBUF}> |
a3621e74 YO |
1251 | |
1252 | Controls how certain regex optimisations are applied and how much memory they | |
241a59d9 FC |
1253 | utilize. This value by default is 65536 which corresponds to a 512kB |
1254 | temporary cache. Set this to a higher value to trade | |
1255 | memory for speed when matching large alternations. Set | |
1256 | it to a lower value if you want the optimisations to | |
a3621e74 YO |
1257 | be as conservative of memory as possible but still occur, and set it to a |
1258 | negative value to prevent the optimisation and conserve the most memory. | |
1259 | Under normal situations this variable should be of no interest to you. | |
1260 | ||
60cf4914 | 1261 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1262 | |
b0c22438 | 1263 | =back |
a0d0e21e | 1264 | |
b0c22438 | 1265 | =head2 Variables related to filehandles |
a0d0e21e | 1266 | |
b0c22438 | 1267 | Variables that depend on the currently selected filehandle may be set |
1268 | by calling an appropriate object method on the C<IO::Handle> object, | |
1269 | although this is less efficient than using the regular built-in | |
241a59d9 | 1270 | variables. (Summary lines below for this contain the word HANDLE.) |
b0c22438 | 1271 | First you must say |
6e2995f4 | 1272 | |
9548c15c | 1273 | use IO::Handle; |
0462a1ab | 1274 | |
b0c22438 | 1275 | after which you may use either |
0462a1ab | 1276 | |
9548c15c | 1277 | method HANDLE EXPR |
0462a1ab | 1278 | |
b0c22438 | 1279 | or more safely, |
0462a1ab | 1280 | |
9548c15c | 1281 | HANDLE->method(EXPR) |
0462a1ab | 1282 | |
241a59d9 | 1283 | Each method returns the old value of the C<IO::Handle> attribute. The |
b0c22438 | 1284 | methods each take an optional EXPR, which, if supplied, specifies the |
241a59d9 | 1285 | new value for the C<IO::Handle> attribute in question. If not |
b0c22438 | 1286 | supplied, most methods do nothing to the current value--except for |
1287 | C<autoflush()>, which will assume a 1 for you, just to be different. | |
0462a1ab | 1288 | |
b0c22438 | 1289 | Because loading in the C<IO::Handle> class is an expensive operation, |
1290 | you should learn how to use the regular built-in variables. | |
1291 | ||
241a59d9 | 1292 | A few of these variables are considered "read-only". This means that |
b0c22438 | 1293 | if you try to assign to this variable, either directly or indirectly |
1294 | through a reference, you'll raise a run-time exception. | |
1295 | ||
1296 | You should be very careful when modifying the default values of most | |
241a59d9 | 1297 | special variables described in this document. In most cases you want |
b0c22438 | 1298 | to localize these variables before changing them, since if you don't, |
1299 | the change may affect other modules which rely on the default values | |
241a59d9 | 1300 | of the special variables that you have changed. This is one of the |
b0c22438 | 1301 | correct ways to read the whole file at once: |
1302 | ||
9548c15c FC |
1303 | open my $fh, "<", "foo" or die $!; |
1304 | local $/; # enable localized slurp mode | |
1305 | my $content = <$fh>; | |
1306 | close $fh; | |
b0c22438 | 1307 | |
1308 | But the following code is quite bad: | |
1309 | ||
9548c15c FC |
1310 | open my $fh, "<", "foo" or die $!; |
1311 | undef $/; # enable slurp mode | |
1312 | my $content = <$fh>; | |
1313 | close $fh; | |
b0c22438 | 1314 | |
1315 | since some other module, may want to read data from some file in the | |
1316 | default "line mode", so if the code we have just presented has been | |
1317 | executed, the global value of C<$/> is now changed for any other code | |
1318 | running inside the same Perl interpreter. | |
1319 | ||
1320 | Usually when a variable is localized you want to make sure that this | |
241a59d9 FC |
1321 | change affects the shortest scope possible. So unless you are already |
1322 | inside some short C<{}> block, you should create one yourself. For | |
b0c22438 | 1323 | example: |
1324 | ||
9548c15c FC |
1325 | my $content = ''; |
1326 | open my $fh, "<", "foo" or die $!; | |
1327 | { | |
1328 | local $/; | |
1329 | $content = <$fh>; | |
1330 | } | |
1331 | close $fh; | |
0462a1ab | 1332 | |
b0c22438 | 1333 | Here is an example of how your own code can go broken: |
0462a1ab | 1334 | |
9548c15c FC |
1335 | for ( 1..3 ){ |
1336 | $\ = "\r\n"; | |
1337 | nasty_break(); | |
1338 | print "$_"; | |
1339 | } | |
0b9346e6 | 1340 | |
9548c15c | 1341 | sub nasty_break { |
0b9346e6 | 1342 | $\ = "\f"; |
1343 | # do something with $_ | |
9548c15c | 1344 | } |
0462a1ab | 1345 | |
0b9346e6 | 1346 | You probably expect this code to print the equivalent of |
0462a1ab | 1347 | |
0b9346e6 | 1348 | "1\r\n2\r\n3\r\n" |
0462a1ab | 1349 | |
b0c22438 | 1350 | but instead you get: |
0462a1ab | 1351 | |
0b9346e6 | 1352 | "1\f2\f3\f" |
0462a1ab | 1353 | |
0b9346e6 | 1354 | Why? Because C<nasty_break()> modifies C<$\> without localizing it |
241a59d9 FC |
1355 | first. The value you set in C<nasty_break()> is still there when you |
1356 | return. The fix is to add C<local()> so the value doesn't leak out of | |
0b9346e6 | 1357 | C<nasty_break()>: |
6e2995f4 | 1358 | |
9548c15c | 1359 | local $\ = "\f"; |
a0d0e21e | 1360 | |
b0c22438 | 1361 | It's easy to notice the problem in such a short example, but in more |
1362 | complicated code you are looking for trouble if you don't localize | |
1363 | changes to the special variables. | |
a0d0e21e | 1364 | |
b0c22438 | 1365 | =over 8 |
a0d0e21e | 1366 | |
b0c22438 | 1367 | =item $ARGV |
1368 | X<$ARGV> | |
fb73857a | 1369 | |
ca1b95ae | 1370 | Contains the name of the current file when reading from C<< <> >>. |
b0c22438 | 1371 | |
1372 | =item @ARGV | |
1373 | X<@ARGV> | |
1374 | ||
ca1b95ae | 1375 | The array C<@ARGV> contains the command-line arguments intended for |
241a59d9 | 1376 | the script. C<$#ARGV> is generally the number of arguments minus |
b0c22438 | 1377 | one, because C<$ARGV[0]> is the first argument, I<not> the program's |
241a59d9 | 1378 | command name itself. See L</$0> for the command name. |
b0c22438 | 1379 | |
84dabc03 | 1380 | =item ARGV |
1381 | X<ARGV> | |
1382 | ||
1383 | The special filehandle that iterates over command-line filenames in | |
241a59d9 FC |
1384 | C<@ARGV>. Usually written as the null filehandle in the angle operator |
1385 | C<< <> >>. Note that currently C<ARGV> only has its magical effect | |
84dabc03 | 1386 | within the C<< <> >> operator; elsewhere it is just a plain filehandle |
241a59d9 | 1387 | corresponding to the last file opened by C<< <> >>. In particular, |
84dabc03 | 1388 | passing C<\*ARGV> as a parameter to a function that expects a filehandle |
1389 | may not cause your function to automatically read the contents of all the | |
1390 | files in C<@ARGV>. | |
1391 | ||
b0c22438 | 1392 | =item ARGVOUT |
1393 | X<ARGVOUT> | |
1394 | ||
1395 | The special filehandle that points to the currently open output file | |
241a59d9 FC |
1396 | when doing edit-in-place processing with B<-i>. Useful when you have |
1397 | to do a lot of inserting and don't want to keep modifying C<$_>. See | |
b0c22438 | 1398 | L<perlrun> for the B<-i> switch. |
1399 | ||
96948506 | 1400 | =item IO::Handle->output_field_separator( EXPR ) |
84dabc03 | 1401 | |
1402 | =item $OUTPUT_FIELD_SEPARATOR | |
1403 | ||
1404 | =item $OFS | |
1405 | ||
1406 | =item $, | |
1407 | X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR> | |
1408 | ||
241a59d9 FC |
1409 | The output field separator for the print operator. If defined, this |
1410 | value is printed between each of print's arguments. Default is C<undef>. | |
84dabc03 | 1411 | |
96948506 | 1412 | You cannot call C<output_field_separator()> on a handle, only as a |
008f9687 | 1413 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1414 | |
84dabc03 | 1415 | Mnemonic: what is printed when there is a "," in your print statement. |
1416 | ||
5b442a2a | 1417 | =item HANDLE->input_line_number( EXPR ) |
b0c22438 | 1418 | |
1419 | =item $INPUT_LINE_NUMBER | |
1420 | ||
1421 | =item $NR | |
1422 | ||
1423 | =item $. | |
1424 | X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number> | |
1425 | ||
1426 | Current line number for the last filehandle accessed. | |
1427 | ||
1428 | Each filehandle in Perl counts the number of lines that have been read | |
241a59d9 | 1429 | from it. (Depending on the value of C<$/>, Perl's idea of what |
b0c22438 | 1430 | constitutes a line may not match yours.) When a line is read from a |
1431 | filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or | |
1432 | C<seek()> is called on it, C<$.> becomes an alias to the line counter | |
1433 | for that filehandle. | |
1434 | ||
1435 | You can adjust the counter by assigning to C<$.>, but this will not | |
241a59d9 FC |
1436 | actually move the seek pointer. I<Localizing C<$.> will not localize |
1437 | the filehandle's line count>. Instead, it will localize perl's notion | |
b0c22438 | 1438 | of which filehandle C<$.> is currently aliased to. |
1439 | ||
1440 | C<$.> is reset when the filehandle is closed, but B<not> when an open | |
241a59d9 FC |
1441 | filehandle is reopened without an intervening C<close()>. For more |
1442 | details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does | |
b0c22438 | 1443 | an explicit close, line numbers increase across C<ARGV> files (but see |
1444 | examples in L<perlfunc/eof>). | |
1445 | ||
1446 | You can also use C<< HANDLE->input_line_number(EXPR) >> to access the | |
1447 | line counter for a given filehandle without having to worry about | |
1448 | which handle you last accessed. | |
1449 | ||
1450 | Mnemonic: many programs use "." to mean the current line number. | |
1451 | ||
96948506 | 1452 | =item IO::Handle->input_record_separator( EXPR ) |
b0c22438 | 1453 | |
1454 | =item $INPUT_RECORD_SEPARATOR | |
1455 | ||
1456 | =item $RS | |
1457 | ||
1458 | =item $/ | |
1459 | X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR> | |
1460 | ||
241a59d9 FC |
1461 | The input record separator, newline by default. This influences Perl's |
1462 | idea of what a "line" is. Works like B<awk>'s RS variable, including | |
84dabc03 | 1463 | treating empty lines as a terminator if set to the null string (an |
241a59d9 | 1464 | empty line cannot contain any spaces or tabs). You may set it to a |
84dabc03 | 1465 | multi-character string to match a multi-character terminator, or to |
241a59d9 | 1466 | C<undef> to read through the end of file. Setting it to C<"\n\n"> |
84dabc03 | 1467 | means something slightly different than setting to C<"">, if the file |
241a59d9 FC |
1468 | contains consecutive empty lines. Setting to C<""> will treat two or |
1469 | more consecutive empty lines as a single empty line. Setting to | |
84dabc03 | 1470 | C<"\n\n"> will blindly assume that the next input character belongs to |
1471 | the next paragraph, even if it's a newline. | |
b0c22438 | 1472 | |
1473 | local $/; # enable "slurp" mode | |
1474 | local $_ = <FH>; # whole file now here | |
1475 | s/\n[ \t]+/ /g; | |
1476 | ||
241a59d9 | 1477 | Remember: the value of C<$/> is a string, not a regex. B<awk> has to |
b0c22438 | 1478 | be better for something. :-) |
1479 | ||
1480 | Setting C<$/> to a reference to an integer, scalar containing an | |
1481 | integer, or scalar that's convertible to an integer will attempt to | |
1482 | read records instead of lines, with the maximum record size being the | |
3d249121 | 1483 | referenced integer number of characters. So this: |
b0c22438 | 1484 | |
1485 | local $/ = \32768; # or \"32768", or \$var_containing_32768 | |
1486 | open my $fh, "<", $myfile or die $!; | |
1487 | local $_ = <$fh>; | |
fb73857a | 1488 | |
f1ee460b | 1489 | will read a record of no more than 32768 characters from $fh. If you're |
b0c22438 | 1490 | not reading from a record-oriented file (or your OS doesn't have |
1491 | record-oriented files), then you'll likely get a full chunk of data | |
241a59d9 FC |
1492 | with every read. If a record is larger than the record size you've |
1493 | set, you'll get the record back in pieces. Trying to set the record | |
b3a2acfa YO |
1494 | size to zero or less is deprecated and will cause $/ to have the value |
1495 | of "undef", which will cause reading in the (rest of the) whole file. | |
1496 | ||
1497 | As of 5.19.9 setting C<$/> to any other form of reference will throw a | |
1498 | fatal exception. This is in preparation for supporting new ways to set | |
1499 | C<$/> in the future. | |
6e2995f4 | 1500 | |
78c28381 | 1501 | On VMS only, record reads bypass PerlIO layers and any associated |
3d249121 | 1502 | buffering, so you must not mix record and non-record reads on the |
78c28381 CB |
1503 | same filehandle. Record mode mixes with line mode only when the |
1504 | same buffering layer is in use for both modes. | |
5c055ba3 | 1505 | |
96948506 | 1506 | You cannot call C<input_record_separator()> on a handle, only as a |
008f9687 | 1507 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1508 | |
008f9687 | 1509 | See also L<perlport/"Newlines">. Also see L</$.>. |
9bf22702 | 1510 | |
b0c22438 | 1511 | Mnemonic: / delimits line boundaries when quoting poetry. |
5c055ba3 | 1512 | |
96948506 | 1513 | =item IO::Handle->output_record_separator( EXPR ) |
84902520 | 1514 | |
b0c22438 | 1515 | =item $OUTPUT_RECORD_SEPARATOR |
84902520 | 1516 | |
b0c22438 | 1517 | =item $ORS |
84902520 | 1518 | |
b0c22438 | 1519 | =item $\ |
1520 | X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR> | |
84902520 | 1521 | |
241a59d9 FC |
1522 | The output record separator for the print operator. If defined, this |
1523 | value is printed after the last of print's arguments. Default is C<undef>. | |
84902520 | 1524 | |
96948506 | 1525 | You cannot call C<output_record_separator()> on a handle, only as a |
008f9687 | 1526 | static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1527 | |
b0c22438 | 1528 | Mnemonic: you set C<$\> instead of adding "\n" at the end of the print. |
1529 | Also, it's just like C<$/>, but it's what you get "back" from Perl. | |
84902520 | 1530 | |
5b442a2a | 1531 | =item HANDLE->autoflush( EXPR ) |
1532 | ||
1533 | =item $OUTPUT_AUTOFLUSH | |
1534 | ||
84dabc03 | 1535 | =item $| |
1536 | X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH> | |
84902520 | 1537 | |
84dabc03 | 1538 | If set to nonzero, forces a flush right away and after every write or |
241a59d9 | 1539 | print on the currently selected output channel. Default is 0 |
84dabc03 | 1540 | (regardless of whether the channel is really buffered by the system or |
1541 | not; C<$|> tells you only whether you've asked Perl explicitly to | |
241a59d9 FC |
1542 | flush after each write). STDOUT will typically be line buffered if |
1543 | output is to the terminal and block buffered otherwise. Setting this | |
84dabc03 | 1544 | variable is useful primarily when you are outputting to a pipe or |
1545 | socket, such as when you are running a Perl program under B<rsh> and | |
241a59d9 FC |
1546 | want to see the output as it's happening. This has no effect on input |
1547 | buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on | |
1548 | how to select the output channel. See also L<IO::Handle>. | |
84dabc03 | 1549 | |
1550 | Mnemonic: when you want your pipes to be piping hot. | |
1551 | ||
8561ea1d FC |
1552 | =item ${^LAST_FH} |
1553 | X<${^LAST_FH}> | |
1554 | ||
1555 | This read-only variable contains a reference to the last-read filehandle. | |
1556 | This is set by C<< <HANDLE> >>, C<readline>, C<tell>, C<eof> and C<seek>. | |
1557 | This is the same handle that C<$.> and C<tell> and C<eof> without arguments | |
1558 | use. It is also the handle used when Perl appends ", <STDIN> line 1" to | |
1559 | an error or warning message. | |
1560 | ||
1561 | This variable was added in Perl v5.18.0. | |
1562 | ||
84dabc03 | 1563 | =back |
84902520 | 1564 | |
b0c22438 | 1565 | =head3 Variables related to formats |
83ee9e09 | 1566 | |
b0c22438 | 1567 | The special variables for formats are a subset of those for |
241a59d9 | 1568 | filehandles. See L<perlform> for more information about Perl's |
69b55ccc | 1569 | formats. |
83ee9e09 | 1570 | |
b0c22438 | 1571 | =over 8 |
83ee9e09 | 1572 | |
84dabc03 | 1573 | =item $ACCUMULATOR |
1574 | ||
1575 | =item $^A | |
1576 | X<$^A> X<$ACCUMULATOR> | |
1577 | ||
1578 | The current value of the C<write()> accumulator for C<format()> lines. | |
1579 | A format contains C<formline()> calls that put their result into | |
241a59d9 FC |
1580 | C<$^A>. After calling its format, C<write()> prints out the contents |
1581 | of C<$^A> and empties. So you never really see the contents of C<$^A> | |
1582 | unless you call C<formline()> yourself and then look at it. See | |
96090e4f | 1583 | L<perlform> and L<perlfunc/"formline PICTURE,LIST">. |
84dabc03 | 1584 | |
96948506 | 1585 | =item IO::Handle->format_formfeed(EXPR) |
5b442a2a | 1586 | |
1587 | =item $FORMAT_FORMFEED | |
1588 | ||
84dabc03 | 1589 | =item $^L |
1590 | X<$^L> X<$FORMAT_FORMFEED> | |
1591 | ||
241a59d9 | 1592 | What formats output as a form feed. The default is C<\f>. |
84dabc03 | 1593 | |
96948506 | 1594 | You cannot call C<format_formfeed()> on a handle, only as a static |
008f9687 | 1595 | method. See L<IO::Handle|IO::Handle>. |
96948506 | 1596 | |
b0c22438 | 1597 | =item HANDLE->format_page_number(EXPR) |
83ee9e09 | 1598 | |
b0c22438 | 1599 | =item $FORMAT_PAGE_NUMBER |
83ee9e09 | 1600 | |
b0c22438 | 1601 | =item $% |
1602 | X<$%> X<$FORMAT_PAGE_NUMBER> | |
83ee9e09 | 1603 | |
b0c22438 | 1604 | The current page number of the currently selected output channel. |
83ee9e09 | 1605 | |
b0c22438 | 1606 | Mnemonic: C<%> is page number in B<nroff>. |
7619c85e | 1607 | |
b0c22438 | 1608 | =item HANDLE->format_lines_left(EXPR) |
b9ac3b5b | 1609 | |
b0c22438 | 1610 | =item $FORMAT_LINES_LEFT |
66558a10 | 1611 | |
b0c22438 | 1612 | =item $- |
1613 | X<$-> X<$FORMAT_LINES_LEFT> | |
fb73857a | 1614 | |
b0c22438 | 1615 | The number of lines left on the page of the currently selected output |
1616 | channel. | |
fa05a9fd | 1617 | |
b0c22438 | 1618 | Mnemonic: lines_on_page - lines_printed. |
fa05a9fd | 1619 | |
96948506 | 1620 | =item IO::Handle->format_line_break_characters EXPR |
fb73857a | 1621 | |
84dabc03 | 1622 | =item $FORMAT_LINE_BREAK_CHARACTERS |
a0d0e21e | 1623 | |
84dabc03 | 1624 | =item $: |
1625 | X<$:> X<FORMAT_LINE_BREAK_CHARACTERS> | |
a0d0e21e | 1626 | |
84dabc03 | 1627 | The current set of characters after which a string may be broken to |
241a59d9 | 1628 | fill continuation fields (starting with C<^>) in a format. The default is |
84dabc03 | 1629 | S<" \n-">, to break on a space, newline, or a hyphen. |
a0d0e21e | 1630 | |
96948506 | 1631 | You cannot call C<format_line_break_characters()> on a handle, only as |
008f9687 | 1632 | a static method. See L<IO::Handle|IO::Handle>. |
96948506 | 1633 | |
84dabc03 | 1634 | Mnemonic: a "colon" in poetry is a part of a line. |
1635 | ||
1636 | =item HANDLE->format_lines_per_page(EXPR) | |
1637 | ||
1638 | =item $FORMAT_LINES_PER_PAGE | |
1639 | ||
1640 | =item $= | |
1641 | X<$=> X<$FORMAT_LINES_PER_PAGE> | |
1642 | ||
1643 | The current page length (printable lines) of the currently selected | |
241a59d9 | 1644 | output channel. The default is 60. |
84dabc03 | 1645 | |
1646 | Mnemonic: = has horizontal lines. | |
7c36658b | 1647 | |
b0c22438 | 1648 | =item HANDLE->format_top_name(EXPR) |
7c36658b | 1649 | |
b0c22438 | 1650 | =item $FORMAT_TOP_NAME |
a05d7ebb | 1651 | |
b0c22438 | 1652 | =item $^ |
1653 | X<$^> X<$FORMAT_TOP_NAME> | |
fde18df1 | 1654 | |
b0c22438 | 1655 | The name of the current top-of-page format for the currently selected |
241a59d9 FC |
1656 | output channel. The default is the name of the filehandle with C<_TOP> |
1657 | appended. For example, the default format top name for the C<STDOUT> | |
12abbafd | 1658 | filehandle is C<STDOUT_TOP>. |
e07ea26a | 1659 | |
b0c22438 | 1660 | Mnemonic: points to top of page. |
e07ea26a | 1661 | |
84dabc03 | 1662 | =item HANDLE->format_name(EXPR) |
16070b82 | 1663 | |
84dabc03 | 1664 | =item $FORMAT_NAME |
aa2f2a36 | 1665 | |
84dabc03 | 1666 | =item $~ |
1667 | X<$~> X<$FORMAT_NAME> | |
aa2f2a36 | 1668 | |
84dabc03 | 1669 | The name of the current report format for the currently selected |
241a59d9 FC |
1670 | output channel. The default format name is the same as the filehandle |
1671 | name. For example, the default format name for the C<STDOUT> | |
84dabc03 | 1672 | filehandle is just C<STDOUT>. |
16070b82 | 1673 | |
84dabc03 | 1674 | Mnemonic: brother to C<$^>. |
16070b82 | 1675 | |
b0c22438 | 1676 | =back |
a0d0e21e | 1677 | |
84dabc03 | 1678 | =head2 Error Variables |
b0c22438 | 1679 | X<error> X<exception> |
a0d0e21e | 1680 | |
b0c22438 | 1681 | The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information |
1682 | about different types of error conditions that may appear during | |
241a59d9 | 1683 | execution of a Perl program. The variables are shown ordered by |
b0c22438 | 1684 | the "distance" between the subsystem which reported the error and |
241a59d9 | 1685 | the Perl process. They correspond to errors detected by the Perl |
b0c22438 | 1686 | interpreter, C library, operating system, or an external program, |
1687 | respectively. | |
4438c4b7 | 1688 | |
b0c22438 | 1689 | To illustrate the differences between these variables, consider the |
241a59d9 | 1690 | following Perl expression, which uses a single-quoted string. After |
7fd683ff | 1691 | execution of this statement, perl may have set all four special error |
7333b1c4 | 1692 | variables: |
4438c4b7 | 1693 | |
9548c15c FC |
1694 | eval q{ |
1695 | open my $pipe, "/cdrom/install |" or die $!; | |
1696 | my @res = <$pipe>; | |
1697 | close $pipe or die "bad pipe: $?, $!"; | |
1698 | }; | |
a0d0e21e | 1699 | |
7333b1c4 | 1700 | When perl executes the C<eval()> expression, it translates the |
1701 | C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library | |
241a59d9 | 1702 | and thence to the operating system kernel. perl sets C<$!> to |
7333b1c4 | 1703 | the C library's C<errno> if one of these calls fails. |
2a8c8378 | 1704 | |
84dabc03 | 1705 | C<$@> is set if the string to be C<eval>-ed did not compile (this may |
1706 | happen if C<open> or C<close> were imported with bad prototypes), or | |
241a59d9 | 1707 | if Perl code executed during evaluation C<die()>d. In these cases the |
0b9346e6 | 1708 | value of C<$@> is the compile error, or the argument to C<die> (which |
241a59d9 | 1709 | will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.) |
2a8c8378 | 1710 | |
84dabc03 | 1711 | Under a few operating systems, C<$^E> may contain a more verbose error |
241a59d9 | 1712 | indicator, such as in this case, "CDROM tray not closed." Systems that |
84dabc03 | 1713 | do not support extended error messages leave C<$^E> the same as C<$!>. |
a0d0e21e | 1714 | |
2e6ba115 | 1715 | Finally, C<$?> may be set to a non-0 value if the external program |
241a59d9 | 1716 | F</cdrom/install> fails. The upper eight bits reflect specific error |
84dabc03 | 1717 | conditions encountered by the program (the program's C<exit()> value). |
1718 | The lower eight bits reflect mode of failure, like signal death and | |
241a59d9 | 1719 | core dump information. See L<wait(2)> for details. In contrast to |
2e6ba115 | 1720 | C<$!> and C<$^E>, which are set only if an error condition is detected, |
84dabc03 | 1721 | the variable C<$?> is set on each C<wait> or pipe C<close>, |
241a59d9 | 1722 | overwriting the old value. This is more like C<$@>, which on every |
84dabc03 | 1723 | C<eval()> is always set on failure and cleared on success. |
a0d0e21e | 1724 | |
b0c22438 | 1725 | For more details, see the individual descriptions at C<$@>, C<$!>, |
1726 | C<$^E>, and C<$?>. | |
38e4f4ae | 1727 | |
0b9346e6 | 1728 | =over 8 |
1729 | ||
b0c22438 | 1730 | =item ${^CHILD_ERROR_NATIVE} |
1731 | X<$^CHILD_ERROR_NATIVE> | |
a0d0e21e | 1732 | |
b0c22438 | 1733 | The native status returned by the last pipe close, backtick (C<``>) |
1734 | command, successful call to C<wait()> or C<waitpid()>, or from the | |
241a59d9 | 1735 | C<system()> operator. On POSIX-like systems this value can be decoded |
b0c22438 | 1736 | with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, |
1737 | WSTOPSIG and WIFCONTINUED functions provided by the L<POSIX> module. | |
a0d0e21e | 1738 | |
b0c22438 | 1739 | Under VMS this reflects the actual VMS exit status; i.e. it is the |
1740 | same as C<$?> when the pragma C<use vmsish 'status'> is in effect. | |
a0d0e21e | 1741 | |
60cf4914 | 1742 | This variable was added in Perl v5.10.0. |
a0d0e21e | 1743 | |
5b442a2a | 1744 | =item $EXTENDED_OS_ERROR |
1745 | ||
84dabc03 | 1746 | =item $^E |
1747 | X<$^E> X<$EXTENDED_OS_ERROR> | |
1748 | ||
241a59d9 | 1749 | Error information specific to the current operating system. At the |
a804e657 | 1750 | moment, this differs from C<L</$!>> under only VMS, OS/2, and Win32 (and |
241a59d9 | 1751 | for MacPerl). On all other platforms, C<$^E> is always just the same |
84dabc03 | 1752 | as C<$!>. |
1753 | ||
1754 | Under VMS, C<$^E> provides the VMS status value from the last system | |
241a59d9 FC |
1755 | error. This is more specific information about the last system error |
1756 | than that provided by C<$!>. This is particularly important when C<$!> | |
84dabc03 | 1757 | is set to B<EVMSERR>. |
1758 | ||
1759 | Under OS/2, C<$^E> is set to the error code of the last call to OS/2 | |
1760 | API either via CRT, or directly from perl. | |
1761 | ||
1762 | Under Win32, C<$^E> always returns the last error information reported | |
1763 | by the Win32 call C<GetLastError()> which describes the last error | |
241a59d9 FC |
1764 | from within the Win32 API. Most Win32-specific code will report errors |
1765 | via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most | |
84dabc03 | 1766 | portable Perl code will report errors via C<$!>. |
1767 | ||
a95b3d6a | 1768 | Caveats mentioned in the description of C<L</$!>> generally apply to |
84dabc03 | 1769 | C<$^E>, also. |
1770 | ||
1771 | This variable was added in Perl 5.003. | |
1772 | ||
1773 | Mnemonic: Extra error explanation. | |
0b9346e6 | 1774 | |
84dabc03 | 1775 | =item $EXCEPTIONS_BEING_CAUGHT |
1776 | ||
1777 | =item $^S | |
1778 | X<$^S> X<$EXCEPTIONS_BEING_CAUGHT> | |
1779 | ||
1780 | Current state of the interpreter. | |
1781 | ||
ca1b95ae | 1782 | $^S State |
aa959a20 FC |
1783 | --------- ------------------------------------- |
1784 | undef Parsing module, eval, or main program | |
ca1b95ae | 1785 | true (1) Executing an eval |
1786 | false (0) Otherwise | |
84dabc03 | 1787 | |
1788 | The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}> | |
1789 | handlers. | |
1790 | ||
aa959a20 FC |
1791 | The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because |
1792 | the C<undef> value does not indicate whether exceptions are being caught, | |
1793 | since compilation of the main program does not catch exceptions. | |
1794 | ||
84dabc03 | 1795 | This variable was added in Perl 5.004. |
1796 | ||
1797 | =item $WARNING | |
1798 | ||
1799 | =item $^W | |
1800 | X<$^W> X<$WARNING> | |
1801 | ||
1802 | The current value of the warning switch, initially true if B<-w> was | |
1803 | used, false otherwise, but directly modifiable. | |
1804 | ||
1805 | See also L<warnings>. | |
1806 | ||
0b9346e6 | 1807 | Mnemonic: related to the B<-w> switch. |
84dabc03 | 1808 | |
1809 | =item ${^WARNING_BITS} | |
ca1b95ae | 1810 | X<${^WARNING_BITS}> |
84dabc03 | 1811 | |
1812 | The current set of warning checks enabled by the C<use warnings> pragma. | |
44567c86 FC |
1813 | It has the same scoping as the C<$^H> and C<%^H> variables. The exact |
1814 | values are considered internal to the L<warnings> pragma and may change | |
1815 | between versions of Perl. | |
84dabc03 | 1816 | |
60cf4914 | 1817 | This variable was added in Perl v5.6.0. |
84dabc03 | 1818 | |
b0c22438 | 1819 | =item $OS_ERROR |
5ccee41e | 1820 | |
b0c22438 | 1821 | =item $ERRNO |
5ccee41e | 1822 | |
b0c22438 | 1823 | =item $! |
1824 | X<$!> X<$ERRNO> X<$OS_ERROR> | |
9b0e6e7a | 1825 | |
a73bef78 JL |
1826 | When referenced, C<$!> retrieves the current value |
1827 | of the C C<errno> integer variable. | |
1828 | If C<$!> is assigned a numerical value, that value is stored in C<errno>. | |
1829 | When referenced as a string, C<$!> yields the system error string | |
1830 | corresponding to C<errno>. | |
1831 | ||
1832 | Many system or library calls set C<errno> if they fail, | |
1833 | to indicate the cause of failure. They usually do B<not> | |
1834 | set C<errno> to zero if they succeed. This means C<errno>, | |
1835 | hence C<$!>, is meaningful only I<immediately> after a B<failure>: | |
1836 | ||
1837 | if (open my $fh, "<", $filename) { | |
ca1b95ae | 1838 | # Here $! is meaningless. |
1839 | ... | |
7fd683ff | 1840 | } |
ca1b95ae | 1841 | else { |
1842 | # ONLY here is $! meaningful. | |
1843 | ... | |
1844 | # Already here $! might be meaningless. | |
b0c22438 | 1845 | } |
1846 | # Since here we might have either success or failure, | |
a73bef78 | 1847 | # $! is meaningless. |
a0d0e21e | 1848 | |
a73bef78 JL |
1849 | Here, I<meaningless> means that C<$!> may be unrelated to the outcome |
1850 | of the C<open()> operator. Assignment to C<$!> is similarly ephemeral. | |
1851 | It can be used immediately before invoking the C<die()> operator, | |
1852 | to set the exit value, or to inspect the system error string | |
1853 | corresponding to error I<n>, or to restore C<$!> to a meaningful state. | |
d54b56d5 | 1854 | |
b0c22438 | 1855 | Mnemonic: What just went bang? |
314d39ce | 1856 | |
b0c22438 | 1857 | =item %OS_ERROR |
fb73857a | 1858 | |
b0c22438 | 1859 | =item %ERRNO |
fb73857a | 1860 | |
b0c22438 | 1861 | =item %! |
5b442a2a | 1862 | X<%!> X<%OS_ERROR> X<%ERRNO> |
a0d0e21e | 1863 | |
b0c22438 | 1864 | Each element of C<%!> has a true value only if C<$!> is set to that |
241a59d9 | 1865 | value. For example, C<$!{ENOENT}> is true if and only if the current |
84dabc03 | 1866 | value of C<$!> is C<ENOENT>; that is, if the most recent error was "No |
1867 | such file or directory" (or its moral equivalent: not all operating | |
3b90fd91 RS |
1868 | systems give that exact error, and certainly not all languages). The |
1869 | specific true value is not guaranteed, but in the past has generally | |
1870 | been the numeric value of C<$!>. To check if a particular key is | |
1871 | meaningful on your system, use C<exists $!{the_key}>; for a list of legal | |
1872 | keys, use C<keys %!>. See L<Errno> for more information, and also see | |
1873 | L</$!>. | |
a0d0e21e | 1874 | |
b0c22438 | 1875 | This variable was added in Perl 5.005. |
44f0be63 | 1876 | |
84dabc03 | 1877 | =item $CHILD_ERROR |
b687b08b | 1878 | |
84dabc03 | 1879 | =item $? |
1880 | X<$?> X<$CHILD_ERROR> | |
a0d0e21e | 1881 | |
84dabc03 | 1882 | The status returned by the last pipe close, backtick (C<``>) command, |
1883 | successful call to C<wait()> or C<waitpid()>, or from the C<system()> | |
241a59d9 | 1884 | operator. This is just the 16-bit status word returned by the |
84dabc03 | 1885 | traditional Unix C<wait()> system call (or else is made up to look |
241a59d9 | 1886 | like it). Thus, the exit value of the subprocess is really (C<<< $? >> |
84dabc03 | 1887 | 8 >>>), and C<$? & 127> gives which signal, if any, the process died |
1888 | from, and C<$? & 128> reports whether there was a core dump. | |
a0d0e21e | 1889 | |
84dabc03 | 1890 | Additionally, if the C<h_errno> variable is supported in C, its value |
1891 | is returned via C<$?> if any C<gethost*()> function fails. | |
b687b08b | 1892 | |
84dabc03 | 1893 | If you have installed a signal handler for C<SIGCHLD>, the |
1894 | value of C<$?> will usually be wrong outside that handler. | |
a0d0e21e | 1895 | |
84dabc03 | 1896 | Inside an C<END> subroutine C<$?> contains the value that is going to be |
241a59d9 FC |
1897 | given to C<exit()>. You can modify C<$?> in an C<END> subroutine to |
1898 | change the exit status of your program. For example: | |
a0d0e21e | 1899 | |
84dabc03 | 1900 | END { |
1901 | $? = 1 if $? == 255; # die would make it 255 | |
1902 | } | |
a0d0e21e | 1903 | |
84dabc03 | 1904 | Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the |
1905 | actual VMS exit status, instead of the default emulation of POSIX | |
1906 | status; see L<perlvms/$?> for details. | |
1907 | ||
1908 | Mnemonic: similar to B<sh> and B<ksh>. | |
a0d0e21e | 1909 | |
b0c22438 | 1910 | =item $EVAL_ERROR |
f648820c | 1911 | |
b0c22438 | 1912 | =item $@ |
1913 | X<$@> X<$EVAL_ERROR> | |
a0d0e21e | 1914 | |
2e6ba115 LM |
1915 | The Perl error from the last C<eval> operator, i.e. the last exception that |
1916 | was caught. For C<eval BLOCK>, this is either a runtime error message or the | |
1917 | string or reference C<die> was called with. The C<eval STRING> form also | |
1918 | catches syntax errors and other compile time exceptions. | |
1919 | ||
1920 | If no error occurs, C<eval> sets C<$@> to the empty string. | |
a0d0e21e | 1921 | |
241a59d9 | 1922 | Warning messages are not collected in this variable. You can, however, |
b0c22438 | 1923 | set up a routine to process warnings by setting C<$SIG{__WARN__}> as |
7333b1c4 | 1924 | described in L</%SIG>. |
748a9306 | 1925 | |
2e6ba115 | 1926 | Mnemonic: Where was the error "at"? |
7f315d2e | 1927 | |
b0c22438 | 1928 | =back |
7f315d2e | 1929 | |
1fa81471 DR |
1930 | =head2 Variables related to the interpreter state |
1931 | ||
1932 | These variables provide information about the current interpreter state. | |
1933 | ||
1934 | =over 8 | |
1935 | ||
1936 | =item $COMPILING | |
1937 | ||
1938 | =item $^C | |
1939 | X<$^C> X<$COMPILING> | |
1940 | ||
1941 | The current value of the flag associated with the B<-c> switch. | |
1942 | Mainly of use with B<-MO=...> to allow code to alter its behavior | |
1943 | when being compiled, such as for example to C<AUTOLOAD> at compile | |
241a59d9 | 1944 | time rather than normal, deferred loading. Setting |
1fa81471 DR |
1945 | C<$^C = 1> is similar to calling C<B::minus_c>. |
1946 | ||
60cf4914 | 1947 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
1948 | |
1949 | =item $DEBUGGING | |
1950 | ||
1951 | =item $^D | |
1952 | X<$^D> X<$DEBUGGING> | |
1953 | ||
241a59d9 | 1954 | The current value of the debugging flags. May be read or set. Like its |
a975eeba | 1955 | L<command-line equivalent|perlrun/B<-D>I<letters>>, you can use numeric |
8af589bf KW |
1956 | or symbolic values, e.g. C<$^D = 10> or C<$^D = "st">. See |
1957 | L<perlrun/B<-D>I<number>>. The contents of this variable also affects the | |
1958 | debugger operation. See L<perldebguts/Debugger Internals>. | |
1fa81471 DR |
1959 | |
1960 | Mnemonic: value of B<-D> switch. | |
1961 | ||
1962 | =item ${^ENCODING} | |
1963 | X<${^ENCODING}> | |
1964 | ||
981b911e | 1965 | This variable is no longer supported. |
a3ee04ba | 1966 | |
981b911e FC |
1967 | It used to hold the I<object reference> to the C<Encode> object that was |
1968 | used to convert the source code to Unicode. | |
a3ee04ba | 1969 | |
981b911e FC |
1970 | Its purpose was to allow your non-ASCII Perl |
1971 | scripts not to have to be written in UTF-8; this was | |
a3ee04ba | 1972 | useful before editors that worked on UTF-8 encoded text were common, but |
981b911e FC |
1973 | that was long ago. It caused problems, such as affecting the operation |
1974 | of other modules that weren't expecting it, causing general mayhem. | |
a3ee04ba | 1975 | |
981b911e FC |
1976 | If you need something like this functionality, it is recommended that use |
1977 | you a simple source filter, such as L<Filter::Encoding>. | |
a3ee04ba KW |
1978 | |
1979 | If you are coming here because code of yours is being adversely affected | |
1980 | by someone's use of this variable, you can usually work around it by | |
1981 | doing this: | |
1982 | ||
1983 | local ${^ENCODING}; | |
1984 | ||
1985 | near the beginning of the functions that are getting broken. This | |
1986 | undefines the variable during the scope of execution of the including | |
1987 | function. | |
1fa81471 | 1988 | |
981b911e | 1989 | This variable was added in Perl 5.8.2 and removed in 5.26.0. |
1fa81471 DR |
1990 | |
1991 | =item ${^GLOBAL_PHASE} | |
1992 | X<${^GLOBAL_PHASE}> | |
1993 | ||
1994 | The current phase of the perl interpreter. | |
1995 | ||
1996 | Possible values are: | |
1997 | ||
1998 | =over 8 | |
1999 | ||
2000 | =item CONSTRUCT | |
2001 | ||
241a59d9 | 2002 | The C<PerlInterpreter*> is being constructed via C<perl_construct>. This |
1fa81471 | 2003 | value is mostly there for completeness and for use via the |
241a59d9 | 2004 | underlying C variable C<PL_phase>. It's not really possible for Perl |
1fa81471 DR |
2005 | code to be executed unless construction of the interpreter is |
2006 | finished. | |
2007 | ||
2008 | =item START | |
2009 | ||
241a59d9 | 2010 | This is the global compile-time. That includes, basically, every |
1fa81471 DR |
2011 | C<BEGIN> block executed directly or indirectly from during the |
2012 | compile-time of the top-level program. | |
2013 | ||
2014 | This phase is not called "BEGIN" to avoid confusion with | |
2015 | C<BEGIN>-blocks, as those are executed during compile-time of any | |
241a59d9 | 2016 | compilation unit, not just the top-level program. A new, localised |
1fa81471 DR |
2017 | compile-time entered at run-time, for example by constructs as |
2018 | C<eval "use SomeModule"> are not global interpreter phases, and | |
2019 | therefore aren't reflected by C<${^GLOBAL_PHASE}>. | |
2020 | ||
2021 | =item CHECK | |
2022 | ||
2023 | Execution of any C<CHECK> blocks. | |
2024 | ||
2025 | =item INIT | |
2026 | ||
2027 | Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks. | |
2028 | ||
2029 | =item RUN | |
2030 | ||
2031 | The main run-time, i.e. the execution of C<PL_main_root>. | |
2032 | ||
2033 | =item END | |
2034 | ||
2035 | Execution of any C<END> blocks. | |
2036 | ||
2037 | =item DESTRUCT | |
2038 | ||
2039 | Global destruction. | |
2040 | ||
2041 | =back | |
2042 | ||
241a59d9 | 2043 | Also note that there's no value for UNITCHECK-blocks. That's because |
1fa81471 DR |
2044 | those are run for each compilation unit individually, and therefore is |
2045 | not a global interpreter phase. | |
2046 | ||
2047 | Not every program has to go through each of the possible phases, but | |
2048 | transition from one phase to another can only happen in the order | |
2049 | described in the above list. | |
2050 | ||
2051 | An example of all of the phases Perl code can see: | |
2052 | ||
2053 | BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" } | |
2054 | ||
2055 | INIT { print "init-time: ${^GLOBAL_PHASE}\n" } | |
2056 | ||
2057 | CHECK { print "check-time: ${^GLOBAL_PHASE}\n" } | |
2058 | ||
2059 | { | |
2060 | package Print::Phase; | |
2061 | ||
2062 | sub new { | |
2063 | my ($class, $time) = @_; | |
2064 | return bless \$time, $class; | |
2065 | } | |
2066 | ||
2067 | sub DESTROY { | |
2068 | my $self = shift; | |
2069 | print "$$self: ${^GLOBAL_PHASE}\n"; | |
2070 | } | |
2071 | } | |
2072 | ||
2073 | print "run-time: ${^GLOBAL_PHASE}\n"; | |
2074 | ||
2075 | my $runtime = Print::Phase->new( | |
2076 | "lexical variables are garbage collected before END" | |
2077 | ); | |
2078 | ||
2079 | END { print "end-time: ${^GLOBAL_PHASE}\n" } | |
2080 | ||
2081 | our $destruct = Print::Phase->new( | |
2082 | "package variables are garbage collected after END" | |
2083 | ); | |
2084 | ||
2085 | This will print out | |
2086 | ||
2087 | compile-time: START | |
2088 | check-time: CHECK | |
2089 | init-time: INIT | |
2090 | run-time: RUN | |
2091 | lexical variables are garbage collected before END: RUN | |
2092 | end-time: END | |
2093 | package variables are garbage collected after END: DESTRUCT | |
2094 | ||
2095 | This variable was added in Perl 5.14.0. | |
2096 | ||
2097 | =item $^H | |
2098 | X<$^H> | |
2099 | ||
241a59d9 FC |
2100 | WARNING: This variable is strictly for |
2101 | internal use only. Its availability, | |
1fa81471 DR |
2102 | behavior, and contents are subject to change without notice. |
2103 | ||
241a59d9 | 2104 | This variable contains compile-time hints for the Perl interpreter. At the |
1fa81471 DR |
2105 | end of compilation of a BLOCK the value of this variable is restored to the |
2106 | value when the interpreter started to compile the BLOCK. | |
2107 | ||
2108 | When perl begins to parse any block construct that provides a lexical scope | |
2109 | (e.g., eval body, required file, subroutine body, loop body, or conditional | |
2110 | block), the existing value of C<$^H> is saved, but its value is left unchanged. | |
2111 | When the compilation of the block is completed, it regains the saved value. | |
2112 | Between the points where its value is saved and restored, code that | |
2113 | executes within BEGIN blocks is free to change the value of C<$^H>. | |
2114 | ||
2115 | This behavior provides the semantic of lexical scoping, and is used in, | |
2116 | for instance, the C<use strict> pragma. | |
2117 | ||
2118 | The contents should be an integer; different bits of it are used for | |
241a59d9 | 2119 | different pragmatic flags. Here's an example: |
1fa81471 | 2120 | |
9548c15c | 2121 | sub add_100 { $^H |= 0x100 } |
1fa81471 | 2122 | |
9548c15c FC |
2123 | sub foo { |
2124 | BEGIN { add_100() } | |
2125 | bar->baz($boon); | |
2126 | } | |
1fa81471 | 2127 | |
241a59d9 | 2128 | Consider what happens during execution of the BEGIN block. At this point |
1fa81471 | 2129 | the BEGIN block has already been compiled, but the body of C<foo()> is still |
241a59d9 FC |
2130 | being compiled. The new value of C<$^H> |
2131 | will therefore be visible only while | |
1fa81471 DR |
2132 | the body of C<foo()> is being compiled. |
2133 | ||
2134 | Substitution of C<BEGIN { add_100() }> block with: | |
2135 | ||
9548c15c | 2136 | BEGIN { require strict; strict->import('vars') } |
1fa81471 | 2137 | |
241a59d9 | 2138 | demonstrates how C<use strict 'vars'> is implemented. Here's a conditional |
1fa81471 DR |
2139 | version of the same lexical pragma: |
2140 | ||
9548c15c FC |
2141 | BEGIN { |
2142 | require strict; strict->import('vars') if $condition | |
2143 | } | |
1fa81471 DR |
2144 | |
2145 | This variable was added in Perl 5.003. | |
2146 | ||
2147 | =item %^H | |
2148 | X<%^H> | |
2149 | ||
241a59d9 FC |
2150 | The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes |
2151 | it useful for implementation of lexically scoped pragmas. See | |
112284f4 KW |
2152 | L<perlpragma>. All the entries are stringified when accessed at |
2153 | runtime, so only simple values can be accommodated. This means no | |
2154 | pointers to objects, for example. | |
1fa81471 DR |
2155 | |
2156 | When putting items into C<%^H>, in order to avoid conflicting with other | |
2157 | users of the hash there is a convention regarding which keys to use. | |
2158 | A module should use only keys that begin with the module's name (the | |
2159 | name of its main package) and a "/" character. For example, a module | |
2160 | C<Foo::Bar> should use keys such as C<Foo::Bar/baz>. | |
2161 | ||
60cf4914 | 2162 | This variable was added in Perl v5.6.0. |
1fa81471 DR |
2163 | |
2164 | =item ${^OPEN} | |
2165 | X<${^OPEN}> | |
2166 | ||
241a59d9 | 2167 | An internal variable used by PerlIO. A string in two parts, separated |
1fa81471 DR |
2168 | by a C<\0> byte, the first part describes the input layers, the second |
2169 | part describes the output layers. | |
2170 | ||
60cf4914 | 2171 | This variable was added in Perl v5.8.0. |
1fa81471 DR |
2172 | |
2173 | =item $PERLDB | |
2174 | ||
2175 | =item $^P | |
2176 | X<$^P> X<$PERLDB> | |
2177 | ||
241a59d9 | 2178 | The internal variable for debugging support. The meanings of the |
1fa81471 DR |
2179 | various bits are subject to change, but currently indicate: |
2180 | ||
2181 | =over 6 | |
2182 | ||
2183 | =item 0x01 | |
2184 | ||
2185 | Debug subroutine enter/exit. | |
2186 | ||
2187 | =item 0x02 | |
2188 | ||
241a59d9 FC |
2189 | Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for |
2190 | each statement executed. Also causes saving source code lines (like | |
2191 | 0x400). | |
1fa81471 DR |
2192 | |
2193 | =item 0x04 | |
2194 | ||
2195 | Switch off optimizations. | |
2196 | ||
2197 | =item 0x08 | |
2198 | ||
2199 | Preserve more data for future interactive inspections. | |
2200 | ||
2201 | =item 0x10 | |
2202 | ||
2203 | Keep info about source lines on which a subroutine is defined. | |
2204 | ||
2205 | =item 0x20 | |
2206 | ||
2207 | Start with single-step on. | |
2208 | ||
2209 | =item 0x40 | |
2210 | ||
2211 | Use subroutine address instead of name when reporting. | |
2212 | ||
2213 | =item 0x80 | |
2214 | ||
2215 | Report C<goto &subroutine> as well. | |
2216 | ||
2217 | =item 0x100 | |
2218 | ||
2219 | Provide informative "file" names for evals based on the place they were compiled. | |
2220 | ||
2221 | =item 0x200 | |
2222 | ||
2223 | Provide informative names to anonymous subroutines based on the place they | |
2224 | were compiled. | |
2225 | ||
2226 | =item 0x400 | |
2227 | ||
2228 | Save source code lines into C<@{"_<$filename"}>. | |
2229 | ||
aab47982 RS |
2230 | =item 0x800 |
2231 | ||
2232 | When saving source, include evals that generate no subroutines. | |
2233 | ||
2234 | =item 0x1000 | |
2235 | ||
2236 | When saving source, include source that did not compile. | |
2237 | ||
1fa81471 DR |
2238 | =back |
2239 | ||
2240 | Some bits may be relevant at compile-time only, some at | |
241a59d9 | 2241 | run-time only. This is a new mechanism and the details may change. |
1fa81471 DR |
2242 | See also L<perldebguts>. |
2243 | ||
2244 | =item ${^TAINT} | |
2245 | X<${^TAINT}> | |
2246 | ||
241a59d9 | 2247 | Reflects if taint mode is on or off. 1 for on (the program was run with |
1fa81471 DR |
2248 | B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with |
2249 | B<-t> or B<-TU>). | |
2250 | ||
2251 | This variable is read-only. | |
2252 | ||
60cf4914 | 2253 | This variable was added in Perl v5.8.0. |
1fa81471 DR |
2254 | |
2255 | =item ${^UNICODE} | |
2256 | X<${^UNICODE}> | |
2257 | ||
241a59d9 | 2258 | Reflects certain Unicode settings of Perl. See L<perlrun> |
1fa81471 DR |
2259 | documentation for the C<-C> switch for more information about |
2260 | the possible values. | |
2261 | ||
2262 | This variable is set during Perl startup and is thereafter read-only. | |
2263 | ||
60cf4914 | 2264 | This variable was added in Perl v5.8.2. |
1fa81471 DR |
2265 | |
2266 | =item ${^UTF8CACHE} | |
2267 | X<${^UTF8CACHE}> | |
2268 | ||
2269 | This variable controls the state of the internal UTF-8 offset caching code. | |
2270 | 1 for on (the default), 0 for off, -1 to debug the caching code by checking | |
2271 | all its results against linear scans, and panicking on any discrepancy. | |
2272 | ||
94df5432 KW |
2273 | This variable was added in Perl v5.8.9. It is subject to change or |
2274 | removal without notice, but is currently used to avoid recalculating the | |
2275 | boundaries of multi-byte UTF-8-encoded characters. | |
1fa81471 DR |
2276 | |
2277 | =item ${^UTF8LOCALE} | |
2278 | X<${^UTF8LOCALE}> | |
2279 | ||
2280 | This variable indicates whether a UTF-8 locale was detected by perl at | |
241a59d9 | 2281 | startup. This information is used by perl when it's in |
1fa81471 DR |
2282 | adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line |
2283 | switch); see L<perlrun> for more info on this. | |
2284 | ||
60cf4914 | 2285 | This variable was added in Perl v5.8.8. |
1fa81471 DR |
2286 | |
2287 | =back | |
2288 | ||
b0c22438 | 2289 | =head2 Deprecated and removed variables |
7f315d2e | 2290 | |
0b9346e6 | 2291 | Deprecating a variable announces the intent of the perl maintainers to |
241a59d9 FC |
2292 | eventually remove the variable from the language. It may still be |
2293 | available despite its status. Using a deprecated variable triggers | |
b0c22438 | 2294 | a warning. |
7f315d2e | 2295 | |
84dabc03 | 2296 | Once a variable is removed, its use triggers an error telling you |
b0c22438 | 2297 | the variable is unsupported. |
7f315d2e | 2298 | |
84dabc03 | 2299 | See L<perldiag> for details about error messages. |
7f315d2e | 2300 | |
b0c22438 | 2301 | =over 8 |
7f315d2e | 2302 | |
84dabc03 | 2303 | =item $# |
b7a15f05 | 2304 | X<$#> |
84dabc03 | 2305 | |
38e5787b | 2306 | C<$#> was a variable that could be used to format printed numbers. |
60cf4914 | 2307 | After a deprecation cycle, its magic was removed in Perl v5.10.0 and |
84dabc03 | 2308 | using it now triggers a warning: C<$# is no longer supported>. |
2309 | ||
2310 | This is not the sigil you use in front of an array name to get the | |
241a59d9 FC |
2311 | last index, like C<$#array>. That's still how you get the last index |
2312 | of an array in Perl. The two have nothing to do with each other. | |
84dabc03 | 2313 | |
2314 | Deprecated in Perl 5. | |
2315 | ||
60cf4914 | 2316 | Removed in Perl v5.10.0. |
84dabc03 | 2317 | |
7f315d2e CO |
2318 | =item $* |
2319 | X<$*> | |
2320 | ||
84dabc03 | 2321 | C<$*> was a variable that you could use to enable multiline matching. |
60cf4914 | 2322 | After a deprecation cycle, its magic was removed in Perl v5.10.0. |
7f315d2e | 2323 | Using it now triggers a warning: C<$* is no longer supported>. |
84dabc03 | 2324 | You should use the C</s> and C</m> regexp modifiers instead. |
7f315d2e | 2325 | |
b0c22438 | 2326 | Deprecated in Perl 5. |
7f315d2e | 2327 | |
60cf4914 | 2328 | Removed in Perl v5.10.0. |
7f315d2e | 2329 | |
84dabc03 | 2330 | =item $[ |
b7a15f05 | 2331 | X<$[> |
84dabc03 | 2332 | |
b82b06b8 FC |
2333 | This variable stores the index of the first element in an array, and |
2334 | of the first character in a substring. The default is 0, but you could | |
2335 | theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran) | |
2336 | when subscripting and when evaluating the index() and substr() functions. | |
84dabc03 | 2337 | |
b82b06b8 FC |
2338 | As of release 5 of Perl, assignment to C<$[> is treated as a compiler |
2339 | directive, and cannot influence the behavior of any other file. | |
2340 | (That's why you can only assign compile-time constants to it.) | |
2341 | Its use is highly discouraged. | |
2342 | ||
60cf4914 | 2343 | Prior to Perl v5.10.0, assignment to C<$[> could be seen from outer lexical |
b82b06b8 FC |
2344 | scopes in the same file, unlike other compile-time directives (such as |
2345 | L<strict>). Using local() on it would bind its value strictly to a lexical | |
2346 | block. Now it is always lexically scoped. | |
2347 | ||
60cf4914 | 2348 | As of Perl v5.16.0, it is implemented by the L<arybase> module. See |
b82b06b8 | 2349 | L<arybase> for more details on its behaviour. |
84dabc03 | 2350 | |
6b54f8ab FC |
2351 | Under C<use v5.16>, or C<no feature "array_base">, C<$[> no longer has any |
2352 | effect, and always contains 0. Assigning 0 to it is permitted, but any | |
2353 | other value will produce an error. | |
2354 | ||
b82b06b8 FC |
2355 | Mnemonic: [ begins subscripts. |
2356 | ||
60cf4914 | 2357 | Deprecated in Perl v5.12.0. |
e1dccc0d | 2358 | |
b0c22438 | 2359 | =back |
2b92dfce | 2360 | |
0b9346e6 | 2361 | =cut |