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1=head1 NAME
2
3perlvar - Perl predefined variables
4
5=head1 DESCRIPTION
6
7=head2 Predefined Names
8
b0c18621 9The following names have special meaning to Perl. Most
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10punctuation names have reasonable mnemonics, or analogs in the
11shells. Nevertheless, if you wish to use long variable names,
12you need only say
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13
14 use English;
15
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16at the top of your program. This aliases all the short names to the long
17names in the current package. Some even have medium names, generally
18borrowed from B<awk>. In general, it's best to use the
a0d0e21e 19
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20 use English '-no_match_vars';
21
22invocation if you don't need $PREMATCH, $MATCH, or $POSTMATCH, as it avoids
23a certain performance hit with the use of regular expressions. See
24L<English>.
25
26Variables that depend on the currently selected filehandle may be set by
27calling an appropriate object method on the IO::Handle object, although
28this is less efficient than using the regular built-in variables. (Summary
29lines below for this contain the word HANDLE.) First you must say
a0d0e21e 30
19799a22 31 use IO::Handle;
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32
33after which you may use either
34
35 method HANDLE EXPR
36
5a964f20 37or more safely,
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38
39 HANDLE->method(EXPR)
40
14218588 41Each method returns the old value of the IO::Handle attribute.
a1ce9542 42The methods each take an optional EXPR, which, if supplied, specifies the
19799a22 43new value for the IO::Handle attribute in question. If not supplied,
14218588 44most methods do nothing to the current value--except for
a0d0e21e 45autoflush(), which will assume a 1 for you, just to be different.
a1ce9542 46
14218588 47Because loading in the IO::Handle class is an expensive operation, you should
19799a22 48learn how to use the regular built-in variables.
a0d0e21e 49
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50A few of these variables are considered "read-only". This means that if
51you try to assign to this variable, either directly or indirectly through
52a reference, you'll raise a run-time exception.
a0d0e21e 53
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54You should be very careful when modifying the default values of most
55special variables described in this document. In most cases you want
56to localize these variables before changing them, since if you don't,
57the change may affect other modules which rely on the default values
58of the special variables that you have changed. This is one of the
59correct ways to read the whole file at once:
60
b0169937 61 open my $fh, "<", "foo" or die $!;
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62 local $/; # enable localized slurp mode
63 my $content = <$fh>;
64 close $fh;
65
66But the following code is quite bad:
67
b0169937 68 open my $fh, "<", "foo" or die $!;
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69 undef $/; # enable slurp mode
70 my $content = <$fh>;
71 close $fh;
72
73since some other module, may want to read data from some file in the
74default "line mode", so if the code we have just presented has been
75executed, the global value of C<$/> is now changed for any other code
76running inside the same Perl interpreter.
77
78Usually when a variable is localized you want to make sure that this
79change affects the shortest scope possible. So unless you are already
80inside some short C<{}> block, you should create one yourself. For
81example:
82
83 my $content = '';
b0169937 84 open my $fh, "<", "foo" or die $!;
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85 {
86 local $/;
87 $content = <$fh>;
88 }
89 close $fh;
90
91Here is an example of how your own code can go broken:
92
93 for (1..5){
94 nasty_break();
95 print "$_ ";
96 }
97 sub nasty_break {
98 $_ = 5;
99 # do something with $_
100 }
101
102You probably expect this code to print:
103
104 1 2 3 4 5
105
106but instead you get:
107
108 5 5 5 5 5
109
110Why? Because nasty_break() modifies C<$_> without localizing it
111first. The fix is to add local():
112
113 local $_ = 5;
114
115It's easy to notice the problem in such a short example, but in more
116complicated code you are looking for trouble if you don't localize
117changes to the special variables.
118
fb73857a 119The following list is ordered by scalar variables first, then the
87275199 120arrays, then the hashes.
fb73857a 121
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122=over 8
123
124=item $ARG
125
126=item $_
a054c801 127X<$_> X<$ARG>
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128
129The default input and pattern-searching space. The following pairs are
130equivalent:
131
19799a22 132 while (<>) {...} # equivalent only in while!
54310121 133 while (defined($_ = <>)) {...}
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134
135 /^Subject:/
136 $_ =~ /^Subject:/
137
138 tr/a-z/A-Z/
139 $_ =~ tr/a-z/A-Z/
140
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141 chomp
142 chomp($_)
a0d0e21e 143
54310121 144Here are the places where Perl will assume $_ even if you
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145don't use it:
146
147=over 3
148
149=item *
150
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151The following functions:
152
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153abs, alarm, chomp, chop, chr, chroot, cos, defined, eval, exp, glob,
154hex, int, lc, lcfirst, length, log, lstat, mkdir, oct, ord, pos, print,
155quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only),
b0c18621 156rmdir, sin, split (on its second argument), sqrt, stat, study, uc, ucfirst,
b0169937 157unlink, unpack.
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158
159=item *
160
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161All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN.
162See L<perlfunc/-X>
163
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164
165=item *
166
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167The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>)
168when used without an C<=~> operator.
cb1a09d0 169
54310121 170=item *
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171
172The default iterator variable in a C<foreach> loop if no other
173variable is supplied.
174
54310121 175=item *
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176
177The implicit iterator variable in the grep() and map() functions.
178
54310121 179=item *
cb1a09d0 180
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181The implicit variable of given().
182
183=item *
184
c47ff5f1 185The default place to put an input record when a C<< <FH> >>
cb1a09d0 186operation's result is tested by itself as the sole criterion of a C<while>
14218588 187test. Outside a C<while> test, this will not happen.
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188
189=back
190
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191As C<$_> is a global variable, this may lead in some cases to unwanted
192side-effects. As of perl 5.9.1, you can now use a lexical version of
193C<$_> by declaring it in a file or in a block with C<my>. Moreover,
4fd88bf8 194declaring C<our $_> restores the global C<$_> in the current scope.
59f00321 195
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196(Mnemonic: underline is understood in certain operations.)
197
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198=back
199
200=over 8
201
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202=item $a
203
204=item $b
a054c801 205X<$a> X<$b>
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206
207Special package variables when using sort(), see L<perlfunc/sort>.
208Because of this specialness $a and $b don't need to be declared
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209(using use vars, or our()) even when using the C<strict 'vars'> pragma.
210Don't lexicalize them with C<my $a> or C<my $b> if you want to be
211able to use them in the sort() comparison block or function.
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212
213=back
214
215=over 8
216
8491f48b 217=item $<I<digits>> ($1, $2, ...)
a054c801 218X<$1> X<$2> X<$3>
a0d0e21e 219
19799a22 220Contains the subpattern from the corresponding set of capturing
8491f48b 221parentheses from the last successful pattern match, not counting patterns
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222matched in nested blocks that have been exited already. (Mnemonic:
223like \digits.) These variables are all read-only and dynamically
224scoped to the current BLOCK.
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225
226=item $MATCH
227
228=item $&
a054c801 229X<$&> X<$MATCH>
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230
231The string matched by the last successful pattern match (not counting
232any matches hidden within a BLOCK or eval() enclosed by the current
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233BLOCK). (Mnemonic: like & in some editors.) This variable is read-only
234and dynamically scoped to the current BLOCK.
a0d0e21e 235
19ddd453 236The use of this variable anywhere in a program imposes a considerable
667e1aea 237performance penalty on all regular expression matches. See L</BUGS>.
19ddd453 238
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239See L</@-> for a replacement.
240
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241=item ${^MATCH}
242X<${^MATCH}>
243
6210e03f 244This is similar to C<$&> (C<$MATCH>) except that it does not incur the
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245performance penalty associated with that variable, and is only guaranteed
246to return a defined value when the pattern was compiled or executed with
87e95b7f 247the C</p> modifier.
cde0cee5 248
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249=item $PREMATCH
250
251=item $`
a054c801 252X<$`> X<$PREMATCH>
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253
254The string preceding whatever was matched by the last successful
255pattern match (not counting any matches hidden within a BLOCK or eval
a8f8344d 256enclosed by the current BLOCK). (Mnemonic: C<`> often precedes a quoted
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257string.) This variable is read-only.
258
19ddd453 259The use of this variable anywhere in a program imposes a considerable
667e1aea 260performance penalty on all regular expression matches. See L</BUGS>.
19ddd453 261
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262See L</@-> for a replacement.
263
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264=item ${^PREMATCH}
265X<${^PREMATCH}>
266
267This is similar to C<$`> ($PREMATCH) except that it does not incur the
268performance penalty associated with that variable, and is only guaranteed
269to return a defined value when the pattern was compiled or executed with
87e95b7f 270the C</p> modifier.
cde0cee5 271
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272=item $POSTMATCH
273
274=item $'
a054c801 275X<$'> X<$POSTMATCH>
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276
277The string following whatever was matched by the last successful
278pattern match (not counting any matches hidden within a BLOCK or eval()
a8f8344d 279enclosed by the current BLOCK). (Mnemonic: C<'> often follows a quoted
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280string.) Example:
281
22d0716c 282 local $_ = 'abcdefghi';
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283 /def/;
284 print "$`:$&:$'\n"; # prints abc:def:ghi
285
19799a22 286This variable is read-only and dynamically scoped to the current BLOCK.
a0d0e21e 287
19ddd453 288The use of this variable anywhere in a program imposes a considerable
667e1aea 289performance penalty on all regular expression matches. See L</BUGS>.
19ddd453 290
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291See L</@-> for a replacement.
292
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293=item ${^POSTMATCH}
294X<${^POSTMATCH}>
295
296This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the
297performance penalty associated with that variable, and is only guaranteed
298to return a defined value when the pattern was compiled or executed with
87e95b7f 299the C</p> modifier.
cde0cee5 300
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301=item $LAST_PAREN_MATCH
302
303=item $+
a054c801 304X<$+> X<$LAST_PAREN_MATCH>
a0d0e21e 305
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306The text matched by the last bracket of the last successful search pattern.
307This is useful if you don't know which one of a set of alternative patterns
308matched. For example:
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309
310 /Version: (.*)|Revision: (.*)/ && ($rev = $+);
311
312(Mnemonic: be positive and forward looking.)
19799a22 313This variable is read-only and dynamically scoped to the current BLOCK.
a0d0e21e 314
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315=item $LAST_SUBMATCH_RESULT
316
a01268b5 317=item $^N
a054c801 318X<$^N>
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319
320The text matched by the used group most-recently closed (i.e. the group
321with the rightmost closing parenthesis) of the last successful search
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322pattern. (Mnemonic: the (possibly) Nested parenthesis that most
323recently closed.)
324
210b36aa 325This is primarily used inside C<(?{...})> blocks for examining text
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326recently matched. For example, to effectively capture text to a variable
327(in addition to C<$1>, C<$2>, etc.), replace C<(...)> with
328
329 (?:(...)(?{ $var = $^N }))
330
331By setting and then using C<$var> in this way relieves you from having to
332worry about exactly which numbered set of parentheses they are.
333
334This variable is dynamically scoped to the current BLOCK.
335
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336=item @LAST_MATCH_END
337
6cef1e77 338=item @+
a054c801 339X<@+> X<@LAST_MATCH_END>
6cef1e77 340
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341This array holds the offsets of the ends of the last successful
342submatches in the currently active dynamic scope. C<$+[0]> is
343the offset into the string of the end of the entire match. This
344is the same value as what the C<pos> function returns when called
345on the variable that was matched against. The I<n>th element
346of this array holds the offset of the I<n>th submatch, so
347C<$+[1]> is the offset past where $1 ends, C<$+[2]> the offset
348past where $2 ends, and so on. You can use C<$#+> to determine
349how many subgroups were in the last successful match. See the
350examples given for the C<@-> variable.
6cef1e77 351
43239f90 352=item %LAST_PAREN_MATCH
8e08999f 353
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354=item %+
355X<%+>
356
357Similar to C<@+>, the C<%+> hash allows access to the named capture
358buffers, should they exist, in the last successful match in the
359currently active dynamic scope.
360
3195cf34 361For example, C<$+{foo}> is equivalent to C<$1> after the following match:
81714fb9 362
3195cf34 363 'foo' =~ /(?<foo>foo)/;
81714fb9 364
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365The keys of the C<%+> hash list only the names of buffers that have
366captured (and that are thus associated to defined values).
44a2ac75 367
3195cf34 368The underlying behaviour of C<%+> is provided by the
80305961 369L<Tie::Hash::NamedCapture> module.
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370
371B<Note:> C<%-> and C<%+> are tied views into a common internal hash
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372associated with the last successful regular expression. Therefore mixing
373iterative access to them via C<each> may have unpredictable results.
3195cf34 374Likewise, if the last successful match changes, then the results may be
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375surprising.
376
fcc7d916 377=item HANDLE->input_line_number(EXPR)
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378
379=item $INPUT_LINE_NUMBER
380
381=item $NR
382
383=item $.
a054c801 384X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number>
a0d0e21e 385
81714fb9 386Current line number for the last filehandle accessed.
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387
388Each filehandle in Perl counts the number of lines that have been read
389from it. (Depending on the value of C<$/>, Perl's idea of what
390constitutes a line may not match yours.) When a line is read from a
391filehandle (via readline() or C<< <> >>), or when tell() or seek() is
392called on it, C<$.> becomes an alias to the line counter for that
393filehandle.
394
395You can adjust the counter by assigning to C<$.>, but this will not
396actually move the seek pointer. I<Localizing C<$.> will not localize
397the filehandle's line count>. Instead, it will localize perl's notion
398of which filehandle C<$.> is currently aliased to.
399
400C<$.> is reset when the filehandle is closed, but B<not> when an open
401filehandle is reopened without an intervening close(). For more
e48df184 402details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does
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403an explicit close, line numbers increase across ARGV files (but see
404examples in L<perlfunc/eof>).
405
406You can also use C<< HANDLE->input_line_number(EXPR) >> to access the
407line counter for a given filehandle without having to worry about
408which handle you last accessed.
409
410(Mnemonic: many programs use "." to mean the current line number.)
411
412=item IO::Handle->input_record_separator(EXPR)
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413
414=item $INPUT_RECORD_SEPARATOR
415
416=item $RS
417
418=item $/
a054c801 419X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR>
a0d0e21e 420
b0c18621 421The input record separator, newline by default. This
14218588 422influences Perl's idea of what a "line" is. Works like B<awk>'s RS
19799a22 423variable, including treating empty lines as a terminator if set to
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424the null string. (An empty line cannot contain any spaces
425or tabs.) You may set it to a multi-character string to match a
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426multi-character terminator, or to C<undef> to read through the end
427of file. Setting it to C<"\n\n"> means something slightly
428different than setting to C<"">, if the file contains consecutive
429empty lines. Setting to C<""> will treat two or more consecutive
430empty lines as a single empty line. Setting to C<"\n\n"> will
431blindly assume that the next input character belongs to the next
14218588 432paragraph, even if it's a newline. (Mnemonic: / delimits
19799a22 433line boundaries when quoting poetry.)
a0d0e21e 434
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435 local $/; # enable "slurp" mode
436 local $_ = <FH>; # whole file now here
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437 s/\n[ \t]+/ /g;
438
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439Remember: the value of C<$/> is a string, not a regex. B<awk> has to be
440better for something. :-)
68dc0745 441
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442Setting C<$/> to a reference to an integer, scalar containing an integer, or
443scalar that's convertible to an integer will attempt to read records
5b2b9c68 444instead of lines, with the maximum record size being the referenced
19799a22 445integer. So this:
5b2b9c68 446
22d0716c 447 local $/ = \32768; # or \"32768", or \$var_containing_32768
b0169937 448 open my $fh, "<", $myfile or die $!;
22d0716c 449 local $_ = <$fh>;
5b2b9c68 450
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451will read a record of no more than 32768 bytes from FILE. If you're
452not reading from a record-oriented file (or your OS doesn't have
453record-oriented files), then you'll likely get a full chunk of data
454with every read. If a record is larger than the record size you've
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455set, you'll get the record back in pieces. Trying to set the record
456size to zero or less will cause reading in the (rest of the) whole file.
5b2b9c68 457
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458On VMS, record reads are done with the equivalent of C<sysread>,
459so it's best not to mix record and non-record reads on the same
460file. (This is unlikely to be a problem, because any file you'd
83763826 461want to read in record mode is probably unusable in line mode.)
14218588 462Non-VMS systems do normal I/O, so it's safe to mix record and
19799a22 463non-record reads of a file.
5b2b9c68 464
14218588 465See also L<perlport/"Newlines">. Also see C<$.>.
883faa13 466
fcc7d916 467=item HANDLE->autoflush(EXPR)
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468
469=item $OUTPUT_AUTOFLUSH
470
471=item $|
a054c801 472X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH>
a0d0e21e 473
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474If set to nonzero, forces a flush right away and after every write
475or print on the currently selected output channel. Default is 0
14218588 476(regardless of whether the channel is really buffered by the
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477system or not; C<$|> tells you only whether you've asked Perl
478explicitly to flush after each write). STDOUT will
479typically be line buffered if output is to the terminal and block
480buffered otherwise. Setting this variable is useful primarily when
481you are outputting to a pipe or socket, such as when you are running
482a Perl program under B<rsh> and want to see the output as it's
483happening. This has no effect on input buffering. See L<perlfunc/getc>
b0c18621 484for that. See L<perldoc/select> on how to select the output channel.
b0169937 485See also L<IO::Handle>. (Mnemonic: when you want your pipes to be piping hot.)
a0d0e21e 486
46550894 487=item IO::Handle->output_field_separator EXPR
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488
489=item $OUTPUT_FIELD_SEPARATOR
490
491=item $OFS
492
493=item $,
a054c801 494X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR>
a0d0e21e 495
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496The output field separator for the print operator. If defined, this
497value is printed between each of print's arguments. Default is C<undef>.
498(Mnemonic: what is printed when there is a "," in your print statement.)
a0d0e21e 499
46550894 500=item IO::Handle->output_record_separator EXPR
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501
502=item $OUTPUT_RECORD_SEPARATOR
503
504=item $ORS
505
506=item $\
a054c801 507X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR>
a0d0e21e 508
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509The output record separator for the print operator. If defined, this
510value is printed after the last of print's arguments. Default is C<undef>.
511(Mnemonic: you set C<$\> instead of adding "\n" at the end of the print.
512Also, it's just like C<$/>, but it's what you get "back" from Perl.)
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513
514=item $LIST_SEPARATOR
515
516=item $"
a054c801 517X<$"> X<$LIST_SEPARATOR>
a0d0e21e 518
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519This is like C<$,> except that it applies to array and slice values
520interpolated into a double-quoted string (or similar interpreted
521string). Default is a space. (Mnemonic: obvious, I think.)
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522
523=item $SUBSCRIPT_SEPARATOR
524
525=item $SUBSEP
526
527=item $;
a054c801 528X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR>
a0d0e21e 529
54310121 530The subscript separator for multidimensional array emulation. If you
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531refer to a hash element as
532
533 $foo{$a,$b,$c}
534
535it really means
536
537 $foo{join($;, $a, $b, $c)}
538
539But don't put
540
541 @foo{$a,$b,$c} # a slice--note the @
542
543which means
544
545 ($foo{$a},$foo{$b},$foo{$c})
546
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547Default is "\034", the same as SUBSEP in B<awk>. If your
548keys contain binary data there might not be any safe value for C<$;>.
a0d0e21e 549(Mnemonic: comma (the syntactic subscript separator) is a
19799a22 550semi-semicolon. Yeah, I know, it's pretty lame, but C<$,> is already
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551taken for something more important.)
552
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553Consider using "real" multidimensional arrays as described
554in L<perllol>.
a0d0e21e 555
fcc7d916 556=item HANDLE->format_page_number(EXPR)
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557
558=item $FORMAT_PAGE_NUMBER
559
560=item $%
a054c801 561X<$%> X<$FORMAT_PAGE_NUMBER>
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562
563The current page number of the currently selected output channel.
19799a22 564Used with formats.
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565(Mnemonic: % is page number in B<nroff>.)
566
fcc7d916 567=item HANDLE->format_lines_per_page(EXPR)
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568
569=item $FORMAT_LINES_PER_PAGE
570
571=item $=
a054c801 572X<$=> X<$FORMAT_LINES_PER_PAGE>
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573
574The current page length (printable lines) of the currently selected
b0c18621 575output channel. Default is 60.
19799a22
GS
576Used with formats.
577(Mnemonic: = has horizontal lines.)
a0d0e21e 578
fcc7d916 579=item HANDLE->format_lines_left(EXPR)
a0d0e21e
LW
580
581=item $FORMAT_LINES_LEFT
582
583=item $-
a054c801 584X<$-> X<$FORMAT_LINES_LEFT>
a0d0e21e
LW
585
586The number of lines left on the page of the currently selected output
b0c18621 587channel.
19799a22
GS
588Used with formats.
589(Mnemonic: lines_on_page - lines_printed.)
a0d0e21e 590
fe307981
GS
591=item @LAST_MATCH_START
592
6cef1e77 593=item @-
a054c801 594X<@-> X<@LAST_MATCH_START>
6cef1e77 595
19799a22 596$-[0] is the offset of the start of the last successful match.
6cef1e77 597C<$-[>I<n>C<]> is the offset of the start of the substring matched by
8f580fb8 598I<n>-th subpattern, or undef if the subpattern did not match.
6cef1e77
IZ
599
600Thus after a match against $_, $& coincides with C<substr $_, $-[0],
5060ef7b
RGS
601$+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n],
602$+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with
603C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the last
14218588
GS
604matched subgroup in the last successful match. Contrast with
605C<$#+>, the number of subgroups in the regular expression. Compare
19799a22 606with C<@+>.
6cef1e77 607
4ba05bdc
GS
608This array holds the offsets of the beginnings of the last
609successful submatches in the currently active dynamic scope.
610C<$-[0]> is the offset into the string of the beginning of the
611entire match. The I<n>th element of this array holds the offset
0926d669
JP
612of the I<n>th submatch, so C<$-[1]> is the offset where $1
613begins, C<$-[2]> the offset where $2 begins, and so on.
4ba05bdc
GS
614
615After a match against some variable $var:
616
617=over 5
618
4375e838 619=item C<$`> is the same as C<substr($var, 0, $-[0])>
4ba05bdc 620
4375e838 621=item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
4ba05bdc 622
4375e838 623=item C<$'> is the same as C<substr($var, $+[0])>
4ba05bdc 624
b0c18621 625=item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
4ba05bdc
GS
626
627=item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
628
80dc6883 629=item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
4ba05bdc
GS
630
631=back
632
44a2ac75
YO
633=item %-
634X<%->
635
c27a5cfe 636Similar to C<%+>, this variable allows access to the named capture groups
3195cf34 637in the last successful match in the currently active dynamic scope. To
c27a5cfe 638each capture group name found in the regular expression, it associates a
3195cf34
RGS
639reference to an array containing the list of values captured by all
640buffers with that name (should there be several of them), in the order
641where they appear.
642
643Here's an example:
44a2ac75 644
3195cf34
RGS
645 if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) {
646 foreach my $bufname (sort keys %-) {
647 my $ary = $-{$bufname};
44a2ac75 648 foreach my $idx (0..$#$ary) {
3195cf34 649 print "\$-{$bufname}[$idx] : ",
44a2ac75
YO
650 (defined($ary->[$idx]) ? "'$ary->[$idx]'" : "undef"),
651 "\n";
652 }
653 }
654 }
655
656would print out:
657
658 $-{A}[0] : '1'
659 $-{A}[1] : '3'
660 $-{B}[0] : '2'
661 $-{B}[1] : '4'
662
3195cf34
RGS
663The keys of the C<%-> hash correspond to all buffer names found in
664the regular expression.
665
666The behaviour of C<%-> is implemented via the
80305961 667L<Tie::Hash::NamedCapture> module.
44a2ac75 668
3195cf34 669B<Note:> C<%-> and C<%+> are tied views into a common internal hash
44a2ac75
YO
670associated with the last successful regular expression. Therefore mixing
671iterative access to them via C<each> may have unpredictable results.
3195cf34 672Likewise, if the last successful match changes, then the results may be
44a2ac75
YO
673surprising.
674
fcc7d916 675=item HANDLE->format_name(EXPR)
a0d0e21e
LW
676
677=item $FORMAT_NAME
678
679=item $~
a054c801 680X<$~> X<$FORMAT_NAME>
a0d0e21e
LW
681
682The name of the current report format for the currently selected output
14218588 683channel. Default is the name of the filehandle. (Mnemonic: brother to
19799a22 684C<$^>.)
a0d0e21e 685
fcc7d916 686=item HANDLE->format_top_name(EXPR)
a0d0e21e
LW
687
688=item $FORMAT_TOP_NAME
689
690=item $^
a054c801 691X<$^> X<$FORMAT_TOP_NAME>
a0d0e21e
LW
692
693The name of the current top-of-page format for the currently selected
14218588 694output channel. Default is the name of the filehandle with _TOP
a0d0e21e
LW
695appended. (Mnemonic: points to top of page.)
696
46550894 697=item IO::Handle->format_line_break_characters EXPR
a0d0e21e
LW
698
699=item $FORMAT_LINE_BREAK_CHARACTERS
700
701=item $:
a054c801 702X<$:> X<FORMAT_LINE_BREAK_CHARACTERS>
a0d0e21e
LW
703
704The current set of characters after which a string may be broken to
54310121 705fill continuation fields (starting with ^) in a format. Default is
a0d0e21e
LW
706S<" \n-">, to break on whitespace or hyphens. (Mnemonic: a "colon" in
707poetry is a part of a line.)
708
46550894 709=item IO::Handle->format_formfeed EXPR
a0d0e21e
LW
710
711=item $FORMAT_FORMFEED
712
713=item $^L
a054c801 714X<$^L> X<$FORMAT_FORMFEED>
a0d0e21e 715
14218588 716What formats output as a form feed. Default is \f.
a0d0e21e
LW
717
718=item $ACCUMULATOR
719
720=item $^A
a054c801 721X<$^A> X<$ACCUMULATOR>
a0d0e21e
LW
722
723The current value of the write() accumulator for format() lines. A format
19799a22 724contains formline() calls that put their result into C<$^A>. After
a0d0e21e 725calling its format, write() prints out the contents of C<$^A> and empties.
14218588 726So you never really see the contents of C<$^A> unless you call
a0d0e21e
LW
727formline() yourself and then look at it. See L<perlform> and
728L<perlfunc/formline()>.
729
730=item $CHILD_ERROR
731
732=item $?
a054c801 733X<$?> X<$CHILD_ERROR>
a0d0e21e 734
54310121 735The status returned by the last pipe close, backtick (C<``>) command,
19799a22
GS
736successful call to wait() or waitpid(), or from the system()
737operator. This is just the 16-bit status word returned by the
e5218da5 738traditional Unix wait() system call (or else is made up to look like it). Thus, the
c47ff5f1 739exit value of the subprocess is really (C<<< $? >> 8 >>>), and
19799a22
GS
740C<$? & 127> gives which signal, if any, the process died from, and
741C<$? & 128> reports whether there was a core dump. (Mnemonic:
742similar to B<sh> and B<ksh>.)
a0d0e21e 743
7b8d334a 744Additionally, if the C<h_errno> variable is supported in C, its value
14218588 745is returned via $? if any C<gethost*()> function fails.
7b8d334a 746
19799a22 747If you have installed a signal handler for C<SIGCHLD>, the
aa689395
PP
748value of C<$?> will usually be wrong outside that handler.
749
a8f8344d
PP
750Inside an C<END> subroutine C<$?> contains the value that is going to be
751given to C<exit()>. You can modify C<$?> in an C<END> subroutine to
19799a22
GS
752change the exit status of your program. For example:
753
754 END {
755 $? = 1 if $? == 255; # die would make it 255
b0c18621 756 }
a8f8344d 757
aa689395 758Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
ff0cee69 759actual VMS exit status, instead of the default emulation of POSIX
9bc98430 760status; see L<perlvms/$?> for details.
f86702cc 761
55602bd2
IZ
762Also see L<Error Indicators>.
763
e5218da5 764=item ${^CHILD_ERROR_NATIVE}
a054c801 765X<$^CHILD_ERROR_NATIVE>
e5218da5
GA
766
767The native status returned by the last pipe close, backtick (C<``>)
768command, successful call to wait() or waitpid(), or from the system()
769operator. On POSIX-like systems this value can be decoded with the
770WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, WSTOPSIG
771and WIFCONTINUED functions provided by the L<POSIX> module.
772
773Under VMS this reflects the actual VMS exit status; i.e. it is the same
774as $? when the pragma C<use vmsish 'status'> is in effect.
775
0a378802 776=item ${^ENCODING}
a054c801 777X<$^ENCODING>
0a378802 778
740bd165
PN
779The I<object reference> to the Encode object that is used to convert
780the source code to Unicode. Thanks to this variable your perl script
781does not have to be written in UTF-8. Default is I<undef>. The direct
749e08de 782manipulation of this variable is highly discouraged.
0a378802 783
a0d0e21e
LW
784=item $OS_ERROR
785
786=item $ERRNO
787
788=item $!
a054c801 789X<$!> X<$ERRNO> X<$OS_ERROR>
a0d0e21e 790
19799a22 791If used numerically, yields the current value of the C C<errno>
6ab308ee
JH
792variable, or in other words, if a system or library call fails, it
793sets this variable. This means that the value of C<$!> is meaningful
794only I<immediately> after a B<failure>:
795
b0169937 796 if (open my $fh, "<", $filename) {
6ab308ee
JH
797 # Here $! is meaningless.
798 ...
799 } else {
800 # ONLY here is $! meaningful.
801 ...
802 # Already here $! might be meaningless.
803 }
804 # Since here we might have either success or failure,
805 # here $! is meaningless.
806
807In the above I<meaningless> stands for anything: zero, non-zero,
808C<undef>. A successful system or library call does B<not> set
809the variable to zero.
810
271df126 811If used as a string, yields the corresponding system error string.
19799a22
GS
812You can assign a number to C<$!> to set I<errno> if, for instance,
813you want C<"$!"> to return the string for error I<n>, or you want
814to set the exit value for the die() operator. (Mnemonic: What just
815went bang?)
a0d0e21e 816
55602bd2
IZ
817Also see L<Error Indicators>.
818
daaddde1
MS
819=item %OS_ERROR
820
821=item %ERRNO
822
4c5cef9b 823=item %!
a054c801 824X<%!>
4c5cef9b
MJD
825
826Each element of C<%!> has a true value only if C<$!> is set to that
827value. For example, C<$!{ENOENT}> is true if and only if the current
3be065a1
JH
828value of C<$!> is C<ENOENT>; that is, if the most recent error was
829"No such file or directory" (or its moral equivalent: not all operating
830systems give that exact error, and certainly not all languages).
831To check if a particular key is meaningful on your system, use
832C<exists $!{the_key}>; for a list of legal keys, use C<keys %!>.
833See L<Errno> for more information, and also see above for the
834validity of C<$!>.
4c5cef9b 835
5c055ba3
PP
836=item $EXTENDED_OS_ERROR
837
838=item $^E
a054c801 839X<$^E> X<$EXTENDED_OS_ERROR>
5c055ba3 840
22fae026
TM
841Error information specific to the current operating system. At
842the moment, this differs from C<$!> under only VMS, OS/2, and Win32
843(and for MacPerl). On all other platforms, C<$^E> is always just
844the same as C<$!>.
845
846Under VMS, C<$^E> provides the VMS status value from the last
847system error. This is more specific information about the last
848system error than that provided by C<$!>. This is particularly
d516a115 849important when C<$!> is set to B<EVMSERR>.
22fae026 850
1c1c7f20
GS
851Under OS/2, C<$^E> is set to the error code of the last call to
852OS/2 API either via CRT, or directly from perl.
22fae026
TM
853
854Under Win32, C<$^E> always returns the last error information
855reported by the Win32 call C<GetLastError()> which describes
856the last error from within the Win32 API. Most Win32-specific
19799a22 857code will report errors via C<$^E>. ANSI C and Unix-like calls
22fae026 858set C<errno> and so most portable Perl code will report errors
b0c18621 859via C<$!>.
22fae026
TM
860
861Caveats mentioned in the description of C<$!> generally apply to
862C<$^E>, also. (Mnemonic: Extra error explanation.)
5c055ba3 863
55602bd2
IZ
864Also see L<Error Indicators>.
865
a0d0e21e
LW
866=item $EVAL_ERROR
867
868=item $@
a054c801 869X<$@> X<$EVAL_ERROR>
a0d0e21e 870
4a280ebe
JG
871The Perl syntax error message from the last eval() operator.
872If $@ is the null string, the last eval() parsed and executed
873correctly (although the operations you invoked may have failed in the
874normal fashion). (Mnemonic: Where was the syntax error "at"?)
a0d0e21e 875
19799a22 876Warning messages are not collected in this variable. You can,
a8f8344d 877however, set up a routine to process warnings by setting C<$SIG{__WARN__}>
54310121 878as described below.
748a9306 879
55602bd2
IZ
880Also see L<Error Indicators>.
881
a0d0e21e
LW
882=item $PROCESS_ID
883
884=item $PID
885
886=item $$
a054c801 887X<$$> X<$PID> X<$PROCESS_ID>
a0d0e21e 888
19799a22
GS
889The process number of the Perl running this script. You should
890consider this variable read-only, although it will be altered
891across fork() calls. (Mnemonic: same as shells.)
a0d0e21e 892
4d76a344
RGS
893Note for Linux users: on Linux, the C functions C<getpid()> and
894C<getppid()> return different values from different threads. In order to
895be portable, this behavior is not reflected by C<$$>, whose value remains
896consistent across threads. If you want to call the underlying C<getpid()>,
e3256f86 897you may use the CPAN module C<Linux::Pid>.
4d76a344 898
a0d0e21e
LW
899=item $REAL_USER_ID
900
901=item $UID
902
903=item $<
a054c801 904X<< $< >> X<$UID> X<$REAL_USER_ID>
a0d0e21e 905
19799a22 906The real uid of this process. (Mnemonic: it's the uid you came I<from>,
a043a685 907if you're running setuid.) You can change both the real uid and
a537debe 908the effective uid at the same time by using POSIX::setuid(). Since
b0c18621 909changes to $< require a system call, check $! after a change attempt to
a537debe 910detect any possible errors.
a0d0e21e
LW
911
912=item $EFFECTIVE_USER_ID
913
914=item $EUID
915
916=item $>
a054c801 917X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>
a0d0e21e
LW
918
919The effective uid of this process. Example:
920
921 $< = $>; # set real to effective uid
922 ($<,$>) = ($>,$<); # swap real and effective uid
923
a043a685 924You can change both the effective uid and the real uid at the same
a537debe 925time by using POSIX::setuid(). Changes to $> require a check to $!
b0c18621 926to detect any possible errors after an attempted change.
a043a685 927
19799a22 928(Mnemonic: it's the uid you went I<to>, if you're running setuid.)
c47ff5f1 929C<< $< >> and C<< $> >> can be swapped only on machines
8cc95fdb 930supporting setreuid().
a0d0e21e
LW
931
932=item $REAL_GROUP_ID
933
934=item $GID
935
936=item $(
a054c801 937X<$(> X<$GID> X<$REAL_GROUP_ID>
a0d0e21e
LW
938
939The real gid of this process. If you are on a machine that supports
940membership in multiple groups simultaneously, gives a space separated
941list of groups you are in. The first number is the one returned by
942getgid(), and the subsequent ones by getgroups(), one of which may be
8cc95fdb
PP
943the same as the first number.
944
19799a22
GS
945However, a value assigned to C<$(> must be a single number used to
946set the real gid. So the value given by C<$(> should I<not> be assigned
2bc0d022
DL
947back to C<$(> without being forced numeric, such as by adding zero. Note
948that this is different to the effective gid (C<$)>) which does take a
949list.
8cc95fdb 950
a043a685 951You can change both the real gid and the effective gid at the same
a537debe
SP
952time by using POSIX::setgid(). Changes to $( require a check to $!
953to detect any possible errors after an attempted change.
a043a685 954
19799a22
GS
955(Mnemonic: parentheses are used to I<group> things. The real gid is the
956group you I<left>, if you're running setgid.)
a0d0e21e
LW
957
958=item $EFFECTIVE_GROUP_ID
959
960=item $EGID
961
962=item $)
a054c801 963X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID>
a0d0e21e
LW
964
965The effective gid of this process. If you are on a machine that
966supports membership in multiple groups simultaneously, gives a space
967separated list of groups you are in. The first number is the one
968returned by getegid(), and the subsequent ones by getgroups(), one of
8cc95fdb
PP
969which may be the same as the first number.
970
19799a22 971Similarly, a value assigned to C<$)> must also be a space-separated
14218588 972list of numbers. The first number sets the effective gid, and
8cc95fdb
PP
973the rest (if any) are passed to setgroups(). To get the effect of an
974empty list for setgroups(), just repeat the new effective gid; that is,
975to force an effective gid of 5 and an effectively empty setgroups()
976list, say C< $) = "5 5" >.
977
a043a685
GW
978You can change both the effective gid and the real gid at the same
979time by using POSIX::setgid() (use only a single numeric argument).
a537debe
SP
980Changes to $) require a check to $! to detect any possible errors
981after an attempted change.
a043a685 982
19799a22
GS
983(Mnemonic: parentheses are used to I<group> things. The effective gid
984is the group that's I<right> for you, if you're running setgid.)
a0d0e21e 985
c47ff5f1 986C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on
19799a22
GS
987machines that support the corresponding I<set[re][ug]id()> routine. C<$(>
988and C<$)> can be swapped only on machines supporting setregid().
a0d0e21e
LW
989
990=item $PROGRAM_NAME
991
992=item $0
a054c801 993X<$0> X<$PROGRAM_NAME>
a0d0e21e 994
80bca1b4
JH
995Contains the name of the program being executed.
996
997On some (read: not all) operating systems assigning to C<$0> modifies
998the argument area that the C<ps> program sees. On some platforms you
999may have to use special C<ps> options or a different C<ps> to see the
1000changes. Modifying the $0 is more useful as a way of indicating the
1001current program state than it is for hiding the program you're
1002running. (Mnemonic: same as B<sh> and B<ksh>.)
f9cbb277 1003
cf525c36 1004Note that there are platform specific limitations on the maximum
f9cbb277
JH
1005length of C<$0>. In the most extreme case it may be limited to the
1006space occupied by the original C<$0>.
a0d0e21e 1007
80bca1b4
JH
1008In some platforms there may be arbitrary amount of padding, for
1009example space characters, after the modified name as shown by C<ps>.
dda345b7 1010In some platforms this padding may extend all the way to the original
c80e2480
JH
1011length of the argument area, no matter what you do (this is the case
1012for example with Linux 2.2).
80bca1b4 1013
4bc88a62 1014Note for BSD users: setting C<$0> does not completely remove "perl"
6a4647a3
JH
1015from the ps(1) output. For example, setting C<$0> to C<"foobar"> may
1016result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix
1017and the " (perl)" suffix are shown depends on your exact BSD variant
1018and version). This is an operating system feature, Perl cannot help it.
4bc88a62 1019
e2975953
JH
1020In multithreaded scripts Perl coordinates the threads so that any
1021thread may modify its copy of the C<$0> and the change becomes visible
cf525c36 1022to ps(1) (assuming the operating system plays along). Note that
80bca1b4
JH
1023the view of C<$0> the other threads have will not change since they
1024have their own copies of it.
e2975953 1025
52c447a8
RGS
1026If the program has been given to perl via the switches C<-e> or C<-E>,
1027C<$0> will contain the string C<"-e">.
1028
7636ea95
AB
1029On Linux as of perl 5.14 the legacy process name will be set with
1030L<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as
1031perl has done since version 4.000. Now system utilities that read the
1032legacy process name such as ps, top and killall will recognize the
1033name you set when assigning to C<$0>. The string you supply will be
1034cut off at 16 bytes, this is a limitation imposed by Linux.
1035
a0d0e21e 1036=item $[
a054c801 1037X<$[>
a0d0e21e
LW
1038
1039The index of the first element in an array, and of the first character
19799a22
GS
1040in a substring. Default is 0, but you could theoretically set it
1041to 1 to make Perl behave more like B<awk> (or Fortran) when
1042subscripting and when evaluating the index() and substr() functions.
1043(Mnemonic: [ begins subscripts.)
a0d0e21e 1044
19799a22
GS
1045As of release 5 of Perl, assignment to C<$[> is treated as a compiler
1046directive, and cannot influence the behavior of any other file.
55b67815 1047(That's why you can only assign compile-time constants to it.) Its
d1d15184 1048use is deprecated, and by default will trigger a warning.
a0d0e21e 1049
f83ed198 1050Note that, unlike other compile-time directives (such as L<strict>),
af7a0647
RGS
1051assignment to C<$[> can be seen from outer lexical scopes in the same file.
1052However, you can use local() on it to strictly bind its value to a
f83ed198
RGS
1053lexical block.
1054
a0d0e21e 1055=item $]
a054c801 1056X<$]>
a0d0e21e 1057
54310121
PP
1058The version + patchlevel / 1000 of the Perl interpreter. This variable
1059can be used to determine whether the Perl interpreter executing a
1060script is in the right range of versions. (Mnemonic: Is this version
1061of perl in the right bracket?) Example:
a0d0e21e
LW
1062
1063 warn "No checksumming!\n" if $] < 3.019;
1064
54310121 1065See also the documentation of C<use VERSION> and C<require VERSION>
19799a22 1066for a convenient way to fail if the running Perl interpreter is too old.
a0d0e21e 1067
0c8d858b
MS
1068The floating point representation can sometimes lead to inaccurate
1069numeric comparisons. See C<$^V> for a more modern representation of
1070the Perl version that allows accurate string comparisons.
16070b82 1071
305aace0
NIS
1072=item $COMPILING
1073
1074=item $^C
a054c801 1075X<$^C> X<$COMPILING>
305aace0 1076
19799a22
GS
1077The current value of the flag associated with the B<-c> switch.
1078Mainly of use with B<-MO=...> to allow code to alter its behavior
1079when being compiled, such as for example to AUTOLOAD at compile
59f521f4 1080time rather than normal, deferred loading. Setting
19799a22 1081C<$^C = 1> is similar to calling C<B::minus_c>.
305aace0 1082
a0d0e21e
LW
1083=item $DEBUGGING
1084
1085=item $^D
a054c801 1086X<$^D> X<$DEBUGGING>
a0d0e21e
LW
1087
1088The current value of the debugging flags. (Mnemonic: value of B<-D>
b4ab917c
DM
1089switch.) May be read or set. Like its command-line equivalent, you can use
1090numeric or symbolic values, eg C<$^D = 10> or C<$^D = "st">.
a0d0e21e 1091
a3621e74
YO
1092=item ${^RE_DEBUG_FLAGS}
1093
1094The current value of the regex debugging flags. Set to 0 for no debug output
1095even when the re 'debug' module is loaded. See L<re> for details.
1096
0111c4fd 1097=item ${^RE_TRIE_MAXBUF}
a3621e74
YO
1098
1099Controls how certain regex optimisations are applied and how much memory they
1100utilize. This value by default is 65536 which corresponds to a 512kB temporary
1101cache. Set this to a higher value to trade memory for speed when matching
1102large alternations. Set it to a lower value if you want the optimisations to
1103be as conservative of memory as possible but still occur, and set it to a
1104negative value to prevent the optimisation and conserve the most memory.
1105Under normal situations this variable should be of no interest to you.
1106
a0d0e21e
LW
1107=item $SYSTEM_FD_MAX
1108
1109=item $^F
a054c801 1110X<$^F> X<$SYSTEM_FD_MAX>
a0d0e21e
LW
1111
1112The maximum system file descriptor, ordinarily 2. System file
1113descriptors are passed to exec()ed processes, while higher file
1114descriptors are not. Also, during an open(), system file descriptors are
1115preserved even if the open() fails. (Ordinary file descriptors are
19799a22 1116closed before the open() is attempted.) The close-on-exec
a0d0e21e 1117status of a file descriptor will be decided according to the value of
8d2a6795
GS
1118C<$^F> when the corresponding file, pipe, or socket was opened, not the
1119time of the exec().
a0d0e21e 1120
6e2995f4
PP
1121=item $^H
1122
0462a1ab
GS
1123WARNING: This variable is strictly for internal use only. Its availability,
1124behavior, and contents are subject to change without notice.
1125
1126This variable contains compile-time hints for the Perl interpreter. At the
1127end of compilation of a BLOCK the value of this variable is restored to the
1128value when the interpreter started to compile the BLOCK.
1129
1130When perl begins to parse any block construct that provides a lexical scope
1131(e.g., eval body, required file, subroutine body, loop body, or conditional
1132block), the existing value of $^H is saved, but its value is left unchanged.
1133When the compilation of the block is completed, it regains the saved value.
1134Between the points where its value is saved and restored, code that
1135executes within BEGIN blocks is free to change the value of $^H.
1136
1137This behavior provides the semantic of lexical scoping, and is used in,
1138for instance, the C<use strict> pragma.
1139
1140The contents should be an integer; different bits of it are used for
1141different pragmatic flags. Here's an example:
1142
1143 sub add_100 { $^H |= 0x100 }
1144
1145 sub foo {
1146 BEGIN { add_100() }
1147 bar->baz($boon);
1148 }
1149
1150Consider what happens during execution of the BEGIN block. At this point
1151the BEGIN block has already been compiled, but the body of foo() is still
1152being compiled. The new value of $^H will therefore be visible only while
1153the body of foo() is being compiled.
1154
1155Substitution of the above BEGIN block with:
1156
1157 BEGIN { require strict; strict->import('vars') }
1158
1159demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
1160version of the same lexical pragma:
1161
1162 BEGIN { require strict; strict->import('vars') if $condition }
1163
1164=item %^H
1165
0462a1ab 1166The %^H hash provides the same scoping semantic as $^H. This makes it
46e5f5f4 1167useful for implementation of lexically scoped pragmas. See L<perlpragma>.
6e2995f4 1168
a0d0e21e
LW
1169=item $INPLACE_EDIT
1170
1171=item $^I
a054c801 1172X<$^I> X<$INPLACE_EDIT>
a0d0e21e
LW
1173
1174The current value of the inplace-edit extension. Use C<undef> to disable
1175inplace editing. (Mnemonic: value of B<-i> switch.)
1176
fb73857a 1177=item $^M
a054c801 1178X<$^M>
fb73857a 1179
19799a22
GS
1180By default, running out of memory is an untrappable, fatal error.
1181However, if suitably built, Perl can use the contents of C<$^M>
1182as an emergency memory pool after die()ing. Suppose that your Perl
0acca065 1183were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc.
19799a22 1184Then
fb73857a 1185
19799a22 1186 $^M = 'a' x (1 << 16);
fb73857a 1187
51ee6500 1188would allocate a 64K buffer for use in an emergency. See the
19799a22 1189F<INSTALL> file in the Perl distribution for information on how to
0acca065
RGS
1190add custom C compilation flags when compiling perl. To discourage casual
1191use of this advanced feature, there is no L<English|English> long name for
1192this variable.
fb73857a 1193
5c055ba3 1194=item $OSNAME
6e2995f4 1195
5c055ba3 1196=item $^O
a054c801 1197X<$^O> X<$OSNAME>
5c055ba3
PP
1198
1199The name of the operating system under which this copy of Perl was
9bf22702
AB
1200built, as determined during the configuration process. For examples
1201see L<perlport/PLATFORMS>.
1202
1203The value is identical to C<$Config{'osname'}>. See also L<Config>
1204and the B<-V> command-line switch documented in L<perlrun>.
5c055ba3 1205
443f6d01 1206In Windows platforms, $^O is not very helpful: since it is always
7f510801
GS
1207C<MSWin32>, it doesn't tell the difference between
120895/98/ME/NT/2000/XP/CE/.NET. Use Win32::GetOSName() or
1209Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish
1210between the variants.
916d64a3 1211
e2e27056
JH
1212=item ${^OPEN}
1213
1214An internal variable used by PerlIO. A string in two parts, separated
fae2c0fb
RGS
1215by a C<\0> byte, the first part describes the input layers, the second
1216part describes the output layers.
e2e27056 1217
a0d0e21e
LW
1218=item $PERLDB
1219
1220=item $^P
a054c801 1221X<$^P> X<$PERLDB>
a0d0e21e 1222
19799a22
GS
1223The internal variable for debugging support. The meanings of the
1224various bits are subject to change, but currently indicate:
84902520
TB
1225
1226=over 6
1227
1228=item 0x01
1229
1230Debug subroutine enter/exit.
1231
1232=item 0x02
1233
4c85b59c
TB
1234Line-by-line debugging. Causes DB::DB() subroutine to be called for each
1235statement executed. Also causes saving source code lines (like 0x400).
84902520
TB
1236
1237=item 0x04
1238
1239Switch off optimizations.
1240
1241=item 0x08
1242
1243Preserve more data for future interactive inspections.
1244
1245=item 0x10
1246
1247Keep info about source lines on which a subroutine is defined.
1248
1249=item 0x20
1250
1251Start with single-step on.
1252
83ee9e09
GS
1253=item 0x40
1254
1255Use subroutine address instead of name when reporting.
1256
1257=item 0x80
1258
1259Report C<goto &subroutine> as well.
1260
1261=item 0x100
1262
1263Provide informative "file" names for evals based on the place they were compiled.
1264
1265=item 0x200
1266
1267Provide informative names to anonymous subroutines based on the place they
1268were compiled.
1269
7619c85e
RG
1270=item 0x400
1271
4c85b59c 1272Save source code lines into C<@{"_<$filename"}>.
7619c85e 1273
84902520
TB
1274=back
1275
19799a22
GS
1276Some bits may be relevant at compile-time only, some at
1277run-time only. This is a new mechanism and the details may change.
4c85b59c 1278See also L<perldebguts>.
a0d0e21e 1279
66558a10
GS
1280=item $LAST_REGEXP_CODE_RESULT
1281
b9ac3b5b 1282=item $^R
a054c801 1283X<$^R> X<$LAST_REGEXP_CODE_RESULT>
b9ac3b5b 1284
19799a22
GS
1285The result of evaluation of the last successful C<(?{ code })>
1286regular expression assertion (see L<perlre>). May be written to.
b9ac3b5b 1287
66558a10
GS
1288=item $EXCEPTIONS_BEING_CAUGHT
1289
fb73857a 1290=item $^S
a054c801 1291X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
fb73857a 1292
fa05a9fd
IST
1293Current state of the interpreter.
1294
1295 $^S State
1296 --------- -------------------
1297 undef Parsing module/eval
1298 true (1) Executing an eval
1299 false (0) Otherwise
1300
1301The first state may happen in $SIG{__DIE__} and $SIG{__WARN__} handlers.
fb73857a 1302
a0d0e21e
LW
1303=item $BASETIME
1304
1305=item $^T
a054c801 1306X<$^T> X<$BASETIME>
a0d0e21e 1307
19799a22 1308The time at which the program began running, in seconds since the
5f05dabc 1309epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
19799a22 1310and B<-C> filetests are based on this value.
a0d0e21e 1311
7c36658b
MS
1312=item ${^TAINT}
1313
9aa05f58
RGS
1314Reflects if taint mode is on or off. 1 for on (the program was run with
1315B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with
18e8c5b0 1316B<-t> or B<-TU>). This variable is read-only.
7c36658b 1317
a05d7ebb
JH
1318=item ${^UNICODE}
1319
ab9e1bb7
JH
1320Reflects certain Unicode settings of Perl. See L<perlrun>
1321documentation for the C<-C> switch for more information about
1322the possible values. This variable is set during Perl startup
1323and is thereafter read-only.
fde18df1 1324
e07ea26a
NC
1325=item ${^UTF8CACHE}
1326
1327This variable controls the state of the internal UTF-8 offset caching code.
16d9fe92
NC
13281 for on (the default), 0 for off, -1 to debug the caching code by checking
1329all its results against linear scans, and panicking on any discrepancy.
e07ea26a 1330
ea8eae40
RGS
1331=item ${^UTF8LOCALE}
1332
a69635b7 1333This variable indicates whether a UTF-8 locale was detected by perl at
ea8eae40
RGS
1334startup. This information is used by perl when it's in
1335adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line
1336switch); see L<perlrun> for more info on this.
1337
44dcb63b 1338=item $PERL_VERSION
b459063d 1339
16070b82 1340=item $^V
a054c801 1341X<$^V> X<$PERL_VERSION>
16070b82
GS
1342
1343The revision, version, and subversion of the Perl interpreter, represented
a32521b7 1344as a C<version> object.
16070b82 1345
7d2b1222 1346This variable first appeared in perl 5.6.0; earlier versions of perl will
a32521b7 1347see an undefined value. Before perl 5.10.0 $^V was represented as a v-string.
7d2b1222 1348
a32521b7 1349$^V can be used to determine whether the Perl interpreter executing a
16070b82 1350script is in the right range of versions. (Mnemonic: use ^V for Version
44dcb63b 1351Control.) Example:
16070b82 1352
7d2b1222 1353 warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1
16070b82 1354
aa2f2a36
AMS
1355To convert C<$^V> into its string representation use sprintf()'s
1356C<"%vd"> conversion:
1357
1358 printf "version is v%vd\n", $^V; # Perl's version
1359
44dcb63b 1360See the documentation of C<use VERSION> and C<require VERSION>
16070b82
GS
1361for a convenient way to fail if the running Perl interpreter is too old.
1362
1363See also C<$]> for an older representation of the Perl version.
1364
a0d0e21e
LW
1365=item $WARNING
1366
1367=item $^W
a054c801 1368X<$^W> X<$WARNING>
a0d0e21e 1369
19799a22
GS
1370The current value of the warning switch, initially true if B<-w>
1371was used, false otherwise, but directly modifiable. (Mnemonic:
4438c4b7
JH
1372related to the B<-w> switch.) See also L<warnings>.
1373
6a818117 1374=item ${^WARNING_BITS}
4438c4b7
JH
1375
1376The current set of warning checks enabled by the C<use warnings> pragma.
1377See the documentation of C<warnings> for more details.
a0d0e21e 1378
2a8c8378 1379=item ${^WIN32_SLOPPY_STAT}
174299ac 1380X<sitecustomize> X<sitecustomize.pl>
2a8c8378
JD
1381
1382If this variable is set to a true value, then stat() on Windows will
1383not try to open the file. This means that the link count cannot be
1384determined and file attributes may be out of date if additional
1385hardlinks to the file exist. On the other hand, not opening the file
1386is considerably faster, especially for files on network drives.
1387
1388This variable could be set in the F<sitecustomize.pl> file to
1389configure the local Perl installation to use "sloppy" stat() by
ee811f5e
AB
1390default. See the documentation for B<-f> in
1391L<perlrun|perlrun/"Command Switches"> for more information about site
2a8c8378
JD
1392customization.
1393
a0d0e21e
LW
1394=item $EXECUTABLE_NAME
1395
1396=item $^X
a054c801 1397X<$^X> X<$EXECUTABLE_NAME>
a0d0e21e 1398
e71940de 1399The name used to execute the current copy of Perl, from C's
21c1191d 1400C<argv[0]> or (where supported) F</proc/self/exe>.
38e4f4ae 1401
e71940de
PG
1402Depending on the host operating system, the value of $^X may be
1403a relative or absolute pathname of the perl program file, or may
1404be the string used to invoke perl but not the pathname of the
1405perl program file. Also, most operating systems permit invoking
1406programs that are not in the PATH environment variable, so there
a10d74f3
PG
1407is no guarantee that the value of $^X is in PATH. For VMS, the
1408value may or may not include a version number.
38e4f4ae 1409
e71940de
PG
1410You usually can use the value of $^X to re-invoke an independent
1411copy of the same perl that is currently running, e.g.,
1412
1413 @first_run = `$^X -le "print int rand 100 for 1..100"`;
1414
1415But recall that not all operating systems support forking or
1416capturing of the output of commands, so this complex statement
1417may not be portable.
38e4f4ae 1418
e71940de
PG
1419It is not safe to use the value of $^X as a path name of a file,
1420as some operating systems that have a mandatory suffix on
1421executable files do not require use of the suffix when invoking
1422a command. To convert the value of $^X to a path name, use the
1423following statements:
1424
304dea91 1425 # Build up a set of file names (not command names).
e71940de 1426 use Config;
68fb0eb7
PG
1427 $this_perl = $^X;
1428 if ($^O ne 'VMS')
1429 {$this_perl .= $Config{_exe}
1430 unless $this_perl =~ m/$Config{_exe}$/i;}
e71940de
PG
1431
1432Because many operating systems permit anyone with read access to
1433the Perl program file to make a copy of it, patch the copy, and
1434then execute the copy, the security-conscious Perl programmer
1435should take care to invoke the installed copy of perl, not the
1436copy referenced by $^X. The following statements accomplish
1437this goal, and produce a pathname that can be invoked as a
1438command or referenced as a file.
38e4f4ae
SB
1439
1440 use Config;
68fb0eb7
PG
1441 $secure_perl_path = $Config{perlpath};
1442 if ($^O ne 'VMS')
1443 {$secure_perl_path .= $Config{_exe}
1444 unless $secure_perl_path =~ m/$Config{_exe}$/i;}
a0d0e21e 1445
2d84a16a 1446=item ARGV
a054c801 1447X<ARGV>
2d84a16a
DM
1448
1449The special filehandle that iterates over command-line filenames in
1450C<@ARGV>. Usually written as the null filehandle in the angle operator
1451C<< <> >>. Note that currently C<ARGV> only has its magical effect
1452within the C<< <> >> operator; elsewhere it is just a plain filehandle
1453corresponding to the last file opened by C<< <> >>. In particular,
1454passing C<\*ARGV> as a parameter to a function that expects a filehandle
1455may not cause your function to automatically read the contents of all the
1456files in C<@ARGV>.
1457
a0d0e21e 1458=item $ARGV
a054c801 1459X<$ARGV>
a0d0e21e 1460
c47ff5f1 1461contains the name of the current file when reading from <>.
a0d0e21e
LW
1462
1463=item @ARGV
a054c801 1464X<@ARGV>
a0d0e21e 1465
19799a22 1466The array @ARGV contains the command-line arguments intended for
14218588 1467the script. C<$#ARGV> is generally the number of arguments minus
19799a22
GS
1468one, because C<$ARGV[0]> is the first argument, I<not> the program's
1469command name itself. See C<$0> for the command name.
a0d0e21e 1470
5ccee41e 1471=item ARGVOUT
a054c801 1472X<ARGVOUT>
5ccee41e
JA
1473
1474The special filehandle that points to the currently open output file
1475when doing edit-in-place processing with B<-i>. Useful when you have
1476to do a lot of inserting and don't want to keep modifying $_. See
1477L<perlrun> for the B<-i> switch.
1478
9b0e6e7a 1479=item @F
a054c801 1480X<@F>
9b0e6e7a
JP
1481
1482The array @F contains the fields of each line read in when autosplit
1483mode is turned on. See L<perlrun> for the B<-a> switch. This array
1484is package-specific, and must be declared or given a full package name
1485if not in package main when running under C<strict 'vars'>.
1486
a0d0e21e 1487=item @INC
a054c801 1488X<@INC>
a0d0e21e 1489
19799a22
GS
1490The array @INC contains the list of places that the C<do EXPR>,
1491C<require>, or C<use> constructs look for their library files. It
1492initially consists of the arguments to any B<-I> command-line
1493switches, followed by the default Perl library, probably
1494F</usr/local/lib/perl>, followed by ".", to represent the current
e48df184
RGS
1495directory. ("." will not be appended if taint checks are enabled, either by
1496C<-T> or by C<-t>.) If you need to modify this at runtime, you should use
19799a22
GS
1497the C<use lib> pragma to get the machine-dependent library properly
1498loaded also:
a0d0e21e 1499
cb1a09d0
AD
1500 use lib '/mypath/libdir/';
1501 use SomeMod;
303f2f76 1502
d54b56d5
RGS
1503You can also insert hooks into the file inclusion system by putting Perl
1504code directly into @INC. Those hooks may be subroutine references, array
1505references or blessed objects. See L<perlfunc/require> for details.
1506
314d39ce
MG
1507=item @ARG
1508
fb73857a 1509=item @_
a054c801 1510X<@_> X<@ARG>
fb73857a
PP
1511
1512Within a subroutine the array @_ contains the parameters passed to that
19799a22 1513subroutine. See L<perlsub>.
fb73857a 1514
a0d0e21e 1515=item %INC
a054c801 1516X<%INC>
a0d0e21e 1517
19799a22
GS
1518The hash %INC contains entries for each filename included via the
1519C<do>, C<require>, or C<use> operators. The key is the filename
1520you specified (with module names converted to pathnames), and the
14218588 1521value is the location of the file found. The C<require>
87275199 1522operator uses this hash to determine whether a particular file has
19799a22 1523already been included.
a0d0e21e 1524
89ccab8c
RGS
1525If the file was loaded via a hook (e.g. a subroutine reference, see
1526L<perlfunc/require> for a description of these hooks), this hook is
9ae8cd5b
RGS
1527by default inserted into %INC in place of a filename. Note, however,
1528that the hook may have set the %INC entry by itself to provide some more
1529specific info.
44f0be63 1530
b687b08b
TC
1531=item %ENV
1532
1533=item $ENV{expr}
a054c801 1534X<%ENV>
a0d0e21e
LW
1535
1536The hash %ENV contains your current environment. Setting a
19799a22
GS
1537value in C<ENV> changes the environment for any child processes
1538you subsequently fork() off.
a0d0e21e 1539
b687b08b
TC
1540=item %SIG
1541
1542=item $SIG{expr}
a054c801 1543X<%SIG>
a0d0e21e 1544
efbd929d 1545The hash C<%SIG> contains signal handlers for signals. For example:
a0d0e21e
LW
1546
1547 sub handler { # 1st argument is signal name
fb73857a 1548 my($sig) = @_;
a0d0e21e
LW
1549 print "Caught a SIG$sig--shutting down\n";
1550 close(LOG);
1551 exit(0);
1552 }
1553
fb73857a
PP
1554 $SIG{'INT'} = \&handler;
1555 $SIG{'QUIT'} = \&handler;
a0d0e21e 1556 ...
19799a22 1557 $SIG{'INT'} = 'DEFAULT'; # restore default action
a0d0e21e
LW
1558 $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
1559
f648820c
GS
1560Using a value of C<'IGNORE'> usually has the effect of ignoring the
1561signal, except for the C<CHLD> signal. See L<perlipc> for more about
1562this special case.
1563
19799a22 1564Here are some other examples:
a0d0e21e 1565
fb73857a 1566 $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not recommended)
a0d0e21e 1567 $SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber
19799a22 1568 $SIG{"PIPE"} = *Plumber; # somewhat esoteric
a0d0e21e
LW
1569 $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return??
1570
19799a22 1571Be sure not to use a bareword as the name of a signal handler,
b0c18621 1572lest you inadvertently call it.
748a9306 1573
44a8e56a 1574If your system has the sigaction() function then signal handlers are
9ce5b4ad 1575installed using it. This means you get reliable signal handling.
44a8e56a 1576
b0c18621
DG
1577The default delivery policy of signals changed in Perl 5.8.0 from
1578immediate (also known as "unsafe") to deferred, also known as
9ce5b4ad 1579"safe signals". See L<perlipc> for more information.
45c0772f 1580
748a9306 1581Certain internal hooks can be also set using the %SIG hash. The
a8f8344d 1582routine indicated by C<$SIG{__WARN__}> is called when a warning message is
748a9306 1583about to be printed. The warning message is passed as the first
efbd929d
AT
1584argument. The presence of a C<__WARN__> hook causes the ordinary printing
1585of warnings to C<STDERR> to be suppressed. You can use this to save warnings
748a9306
LW
1586in a variable, or turn warnings into fatal errors, like this:
1587
1588 local $SIG{__WARN__} = sub { die $_[0] };
1589 eval $proggie;
1590
efbd929d
AT
1591As the C<'IGNORE'> hook is not supported by C<__WARN__>, you can
1592disable warnings using the empty subroutine:
1593
1594 local $SIG{__WARN__} = sub {};
1595
a8f8344d 1596The routine indicated by C<$SIG{__DIE__}> is called when a fatal exception
748a9306 1597is about to be thrown. The error message is passed as the first
efbd929d 1598argument. When a C<__DIE__> hook routine returns, the exception
748a9306 1599processing continues as it would have in the absence of the hook,
efbd929d 1600unless the hook routine itself exits via a C<goto>, a loop exit, or a C<die()>.
774d564b 1601The C<__DIE__> handler is explicitly disabled during the call, so that you
fb73857a
PP
1602can die from a C<__DIE__> handler. Similarly for C<__WARN__>.
1603
19799a22
GS
1604Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called
1605even inside an eval(). Do not use this to rewrite a pending exception
efbd929d 1606in C<$@>, or as a bizarre substitute for overriding C<CORE::GLOBAL::die()>.
19799a22
GS
1607This strange action at a distance may be fixed in a future release
1608so that C<$SIG{__DIE__}> is only called if your program is about
1609to exit, as was the original intent. Any other use is deprecated.
1610
1611C<__DIE__>/C<__WARN__> handlers are very special in one respect:
1612they may be called to report (probable) errors found by the parser.
1613In such a case the parser may be in inconsistent state, so any
1614attempt to evaluate Perl code from such a handler will probably
1615result in a segfault. This means that warnings or errors that
1616result from parsing Perl should be used with extreme caution, like
1617this:
fb73857a
PP
1618
1619 require Carp if defined $^S;
1620 Carp::confess("Something wrong") if defined &Carp::confess;
1621 die "Something wrong, but could not load Carp to give backtrace...
1622 To see backtrace try starting Perl with -MCarp switch";
1623
1624Here the first line will load Carp I<unless> it is the parser who
1625called the handler. The second line will print backtrace and die if
1626Carp was available. The third line will be executed only if Carp was
1627not available.
1628
19799a22 1629See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
4438c4b7 1630L<warnings> for additional information.
68dc0745 1631
a0d0e21e 1632=back
55602bd2 1633
7f315d2e
CO
1634=head2 Names that are no longer special
1635
1636These variables had special meaning in prior versions of Perl but now
1637have no effect and will cause warnings if used. They are included
1638here for historical reference.
1639
1640=over 8
1641
1642=item $#
1643X<$#>
1644
1645C<$#> used to be a variable that could be used to format printed numbers.
1646After a deprecation cycle, its magic was removed in Perl 5.10 and using it
1647now triggers a warning: C<$# is no longer supported>.
1648
1649C<$#> is also used as sigil, which, when prepended on the name of an
1650array, gives the index of the last element in that array.
1651
1652 my @array = ("a", "b", "c");
1653 my $last_index = $#array; # $last_index is 2
1654
1655 for my $i (0 .. $#array) {
1656 print "The value of index $i is $array[$i]\n";
1657 }
1658
1659Also see L<perldata>.
1660
1661=item $*
1662X<$*>
1663
1664C<$*> used to be a variable that enabled multiline matching.
1665After a deprecation cycle, its magic was removed in Perl 5.10.
1666Using it now triggers a warning: C<$* is no longer supported>.
1667Use the C</s> and C</m> regexp modifiers instead.
1668
1669Also see L<perlre>.
1670
1671=back
1672
55602bd2 1673=head2 Error Indicators
a054c801 1674X<error> X<exception>
55602bd2 1675
19799a22
GS
1676The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information
1677about different types of error conditions that may appear during
1678execution of a Perl program. The variables are shown ordered by
1679the "distance" between the subsystem which reported the error and
1680the Perl process. They correspond to errors detected by the Perl
1681interpreter, C library, operating system, or an external program,
1682respectively.
55602bd2 1683
b0c18621 1684To illustrate the differences between these variables, consider the
19799a22 1685following Perl expression, which uses a single-quoted string:
55602bd2 1686
19799a22 1687 eval q{
22d0716c
SB
1688 open my $pipe, "/cdrom/install |" or die $!;
1689 my @res = <$pipe>;
1690 close $pipe or die "bad pipe: $?, $!";
19799a22 1691 };
55602bd2 1692
b0c18621 1693After execution of this statement all 4 variables may have been set.
55602bd2 1694
19799a22
GS
1695C<$@> is set if the string to be C<eval>-ed did not compile (this
1696may happen if C<open> or C<close> were imported with bad prototypes),
1697or if Perl code executed during evaluation die()d . In these cases
1698the value of $@ is the compile error, or the argument to C<die>
4cb1c523 1699(which will interpolate C<$!> and C<$?>). (See also L<Fatal>,
19799a22
GS
1700though.)
1701
c47ff5f1 1702When the eval() expression above is executed, open(), C<< <PIPE> >>,
19799a22
GS
1703and C<close> are translated to calls in the C run-time library and
1704thence to the operating system kernel. C<$!> is set to the C library's
b0c18621 1705C<errno> if one of these calls fails.
19799a22
GS
1706
1707Under a few operating systems, C<$^E> may contain a more verbose
1708error indicator, such as in this case, "CDROM tray not closed."
14218588 1709Systems that do not support extended error messages leave C<$^E>
19799a22
GS
1710the same as C<$!>.
1711
1712Finally, C<$?> may be set to non-0 value if the external program
1713F</cdrom/install> fails. The upper eight bits reflect specific
1714error conditions encountered by the program (the program's exit()
1715value). The lower eight bits reflect mode of failure, like signal
1716death and core dump information See wait(2) for details. In
1717contrast to C<$!> and C<$^E>, which are set only if error condition
1718is detected, the variable C<$?> is set on each C<wait> or pipe
1719C<close>, overwriting the old value. This is more like C<$@>, which
1720on every eval() is always set on failure and cleared on success.
2b92dfce 1721
19799a22
GS
1722For more details, see the individual descriptions at C<$@>, C<$!>, C<$^E>,
1723and C<$?>.
2b92dfce
GS
1724
1725=head2 Technical Note on the Syntax of Variable Names
1726
19799a22
GS
1727Variable names in Perl can have several formats. Usually, they
1728must begin with a letter or underscore, in which case they can be
1729arbitrarily long (up to an internal limit of 251 characters) and
1730may contain letters, digits, underscores, or the special sequence
1731C<::> or C<'>. In this case, the part before the last C<::> or
1732C<'> is taken to be a I<package qualifier>; see L<perlmod>.
2b92dfce
GS
1733
1734Perl variable names may also be a sequence of digits or a single
1735punctuation or control character. These names are all reserved for
19799a22
GS
1736special uses by Perl; for example, the all-digits names are used
1737to hold data captured by backreferences after a regular expression
1738match. Perl has a special syntax for the single-control-character
1739names: It understands C<^X> (caret C<X>) to mean the control-C<X>
1740character. For example, the notation C<$^W> (dollar-sign caret
1741C<W>) is the scalar variable whose name is the single character
1742control-C<W>. This is better than typing a literal control-C<W>
1743into your program.
2b92dfce 1744
87275199 1745Finally, new in Perl 5.6, Perl variable names may be alphanumeric
19799a22
GS
1746strings that begin with control characters (or better yet, a caret).
1747These variables must be written in the form C<${^Foo}>; the braces
1748are not optional. C<${^Foo}> denotes the scalar variable whose
1749name is a control-C<F> followed by two C<o>'s. These variables are
1750reserved for future special uses by Perl, except for the ones that
1751begin with C<^_> (control-underscore or caret-underscore). No
1752control-character name that begins with C<^_> will acquire a special
1753meaning in any future version of Perl; such names may therefore be
1754used safely in programs. C<$^_> itself, however, I<is> reserved.
1755
1fcb18de
RGS
1756Perl identifiers that begin with digits, control characters, or
1757punctuation characters are exempt from the effects of the C<package>
1758declaration and are always forced to be in package C<main>; they are
1759also exempt from C<strict 'vars'> errors. A few other names are also
1760exempt in these ways:
2b92dfce
GS
1761
1762 ENV STDIN
1763 INC STDOUT
1764 ARGV STDERR
5b88253b 1765 ARGVOUT _
2b92dfce
GS
1766 SIG
1767
1768In particular, the new special C<${^_XYZ}> variables are always taken
19799a22 1769to be in package C<main>, regardless of any C<package> declarations
b0c18621 1770presently in scope.
2b92dfce 1771
19799a22
GS
1772=head1 BUGS
1773
1774Due to an unfortunate accident of Perl's implementation, C<use
1775English> imposes a considerable performance penalty on all regular
1776expression matches in a program, regardless of whether they occur
1777in the scope of C<use English>. For that reason, saying C<use
1778English> in libraries is strongly discouraged. See the
1779Devel::SawAmpersand module documentation from CPAN
1577cd80 1780( http://www.cpan.org/modules/by-module/Devel/ )
a054c801
GS
1781for more information. Writing C<use English '-no_match_vars';>
1782avoids the performance penalty.
2b92dfce 1783
19799a22
GS
1784Having to even think about the C<$^S> variable in your exception
1785handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented
1786invites grievous and difficult to track down errors. Avoid it
1787and use an C<END{}> or CORE::GLOBAL::die override instead.