3
perlvar - Perl predefined variables
7
=head2 Predefined Names
9
The following names have special meaning to Perl. Most
10
punctuation names have reasonable mnemonics, or analogs in the
11
shells. Nevertheless, if you wish to use long variable names,
16
at the top of your program. This will alias all the short names to the
17
long names in the current package. Some even have medium names,
18
generally borrowed from B<awk>.
20
If you don't mind the performance hit, variables that depend on the
21
currently selected filehandle may instead be set by calling an
22
appropriate object method on the IO::Handle object. (Summary lines
23
below for this contain the word HANDLE.) First you must say
27
after which you may use either
35
Each method returns the old value of the IO::Handle attribute.
36
The methods each take an optional EXPR, which if supplied specifies the
37
new value for the IO::Handle attribute in question. If not supplied,
38
most methods do nothing to the current value--except for
39
autoflush(), which will assume a 1 for you, just to be different.
40
Because loading in the IO::Handle class is an expensive operation, you should
41
learn how to use the regular built-in variables.
43
A few of these variables are considered "read-only". This means that if
44
you try to assign to this variable, either directly or indirectly through
45
a reference, you'll raise a run-time exception.
47
The following list is ordered by scalar variables first, then the
48
arrays, then the hashes.
56
The default input and pattern-searching space. The following pairs are
59
while (<>) {...} # equivalent only in while!
60
while (defined($_ = <>)) {...}
71
Here are the places where Perl will assume $_ even if you
78
Various unary functions, including functions like ord() and int(), as well
79
as the all file tests (C<-f>, C<-d>) except for C<-t>, which defaults to
84
Various list functions like print() and unlink().
88
The pattern matching operations C<m//>, C<s///>, and C<tr///> when used
89
without an C<=~> operator.
93
The default iterator variable in a C<foreach> loop if no other
98
The implicit iterator variable in the grep() and map() functions.
102
The default place to put an input record when a C<< <FH> >>
103
operation's result is tested by itself as the sole criterion of a C<while>
104
test. Outside a C<while> test, this will not happen.
108
(Mnemonic: underline is understood in certain operations.)
116
Contains the subpattern from the corresponding set of capturing
117
parentheses from the last pattern match, not counting patterns
118
matched in nested blocks that have been exited already. (Mnemonic:
119
like \digits.) These variables are all read-only and dynamically
120
scoped to the current BLOCK.
126
The string matched by the last successful pattern match (not counting
127
any matches hidden within a BLOCK or eval() enclosed by the current
128
BLOCK). (Mnemonic: like & in some editors.) This variable is read-only
129
and dynamically scoped to the current BLOCK.
131
The use of this variable anywhere in a program imposes a considerable
132
performance penalty on all regular expression matches. See L<BUGS>.
138
The string preceding whatever was matched by the last successful
139
pattern match (not counting any matches hidden within a BLOCK or eval
140
enclosed by the current BLOCK). (Mnemonic: C<`> often precedes a quoted
141
string.) This variable is read-only.
143
The use of this variable anywhere in a program imposes a considerable
144
performance penalty on all regular expression matches. See L<BUGS>.
150
The string following whatever was matched by the last successful
151
pattern match (not counting any matches hidden within a BLOCK or eval()
152
enclosed by the current BLOCK). (Mnemonic: C<'> often follows a quoted
157
print "$`:$&:$'\n"; # prints abc:def:ghi
159
This variable is read-only and dynamically scoped to the current BLOCK.
161
The use of this variable anywhere in a program imposes a considerable
162
performance penalty on all regular expression matches. See L<BUGS>.
164
=item $LAST_PAREN_MATCH
168
The last bracket matched by the last search pattern. This is useful if
169
you don't know which one of a set of alternative patterns matched. For
172
/Version: (.*)|Revision: (.*)/ && ($rev = $+);
174
(Mnemonic: be positive and forward looking.)
175
This variable is read-only and dynamically scoped to the current BLOCK.
177
=item @LAST_MATCH_END
181
This array holds the offsets of the ends of the last successful
182
submatches in the currently active dynamic scope. C<$+[0]> is
183
the offset into the string of the end of the entire match. This
184
is the same value as what the C<pos> function returns when called
185
on the variable that was matched against. The I<n>th element
186
of this array holds the offset of the I<n>th submatch, so
187
C<$+[1]> is the offset past where $1 ends, C<$+[2]> the offset
188
past where $2 ends, and so on. You can use C<$#+> to determine
189
how many subgroups were in the last successful match. See the
190
examples given for the C<@-> variable.
192
=item $MULTILINE_MATCHING
196
Set to a non-zero integer value to do multi-line matching within a
197
string, 0 (or undefined) to tell Perl that it can assume that strings
198
contain a single line, for the purpose of optimizing pattern matches.
199
Pattern matches on strings containing multiple newlines can produce
200
confusing results when C<$*> is 0 or undefined. Default is undefined.
201
(Mnemonic: * matches multiple things.) This variable influences the
202
interpretation of only C<^> and C<$>. A literal newline can be searched
203
for even when C<$* == 0>.
205
Use of C<$*> is deprecated in modern Perl, supplanted by
206
the C</s> and C</m> modifiers on pattern matching.
208
Assigning a non-numerical value to C<$*> triggers a warning (and makes
209
C<$*> act if C<$* == 0>), while assigning a numerical value to C<$*>
210
makes that an implicit C<int> is applied on the value.
212
=item input_line_number HANDLE EXPR
214
=item $INPUT_LINE_NUMBER
220
The current input record number for the last file handle from which
221
you just read() (or called a C<seek> or C<tell> on). The value
222
may be different from the actual physical line number in the file,
223
depending on what notion of "line" is in effect--see C<$/> on how
224
to change that. An explicit close on a filehandle resets the line
225
number. Because C<< <> >> never does an explicit close, line
226
numbers increase across ARGV files (but see examples in L<perlfunc/eof>).
227
Consider this variable read-only: setting it does not reposition
228
the seek pointer; you'll have to do that on your own. Localizing C<$.>
229
has the effect of also localizing Perl's notion of "the last read
230
filehandle". (Mnemonic: many programs use "." to mean the current line
233
=item input_record_separator HANDLE EXPR
235
=item $INPUT_RECORD_SEPARATOR
241
The input record separator, newline by default. This
242
influences Perl's idea of what a "line" is. Works like B<awk>'s RS
243
variable, including treating empty lines as a terminator if set to
244
the null string. (An empty line cannot contain any spaces
245
or tabs.) You may set it to a multi-character string to match a
246
multi-character terminator, or to C<undef> to read through the end
247
of file. Setting it to C<"\n\n"> means something slightly
248
different than setting to C<"">, if the file contains consecutive
249
empty lines. Setting to C<""> will treat two or more consecutive
250
empty lines as a single empty line. Setting to C<"\n\n"> will
251
blindly assume that the next input character belongs to the next
252
paragraph, even if it's a newline. (Mnemonic: / delimits
253
line boundaries when quoting poetry.)
255
undef $/; # enable "slurp" mode
256
$_ = <FH>; # whole file now here
259
Remember: the value of C<$/> is a string, not a regex. B<awk> has to be
260
better for something. :-)
262
Setting C<$/> to a reference to an integer, scalar containing an integer, or
263
scalar that's convertible to an integer will attempt to read records
264
instead of lines, with the maximum record size being the referenced
267
$/ = \32768; # or \"32768", or \$var_containing_32768
271
will read a record of no more than 32768 bytes from FILE. If you're
272
not reading from a record-oriented file (or your OS doesn't have
273
record-oriented files), then you'll likely get a full chunk of data
274
with every read. If a record is larger than the record size you've
275
set, you'll get the record back in pieces.
277
On VMS, record reads are done with the equivalent of C<sysread>,
278
so it's best not to mix record and non-record reads on the same
279
file. (This is unlikely to be a problem, because any file you'd
280
want to read in record mode is probably unusable in line mode.)
281
Non-VMS systems do normal I/O, so it's safe to mix record and
282
non-record reads of a file.
284
See also L<perlport/"Newlines">. Also see C<$.>.
286
=item autoflush HANDLE EXPR
288
=item $OUTPUT_AUTOFLUSH
292
If set to nonzero, forces a flush right away and after every write
293
or print on the currently selected output channel. Default is 0
294
(regardless of whether the channel is really buffered by the
295
system or not; C<$|> tells you only whether you've asked Perl
296
explicitly to flush after each write). STDOUT will
297
typically be line buffered if output is to the terminal and block
298
buffered otherwise. Setting this variable is useful primarily when
299
you are outputting to a pipe or socket, such as when you are running
300
a Perl program under B<rsh> and want to see the output as it's
301
happening. This has no effect on input buffering. See L<perlfunc/getc>
302
for that. (Mnemonic: when you want your pipes to be piping hot.)
304
=item output_field_separator HANDLE EXPR
306
=item $OUTPUT_FIELD_SEPARATOR
312
The output field separator for the print operator. Ordinarily the
313
print operator simply prints out its arguments without further
314
adornment. To get behavior more like B<awk>, set this variable as
315
you would set B<awk>'s OFS variable to specify what is printed
316
between fields. (Mnemonic: what is printed when there is a "," in
317
your print statement.)
319
=item output_record_separator HANDLE EXPR
321
=item $OUTPUT_RECORD_SEPARATOR
327
The output record separator for the print operator. Ordinarily the
328
print operator simply prints out its arguments as is, with no
329
trailing newline or other end-of-record string added. To get
330
behavior more like B<awk>, set this variable as you would set
331
B<awk>'s ORS variable to specify what is printed at the end of the
332
print. (Mnemonic: you set C<$\> instead of adding "\n" at the
333
end of the print. Also, it's just like C<$/>, but it's what you
334
get "back" from Perl.)
336
=item $LIST_SEPARATOR
340
This is like C<$,> except that it applies to array and slice values
341
interpolated into a double-quoted string (or similar interpreted
342
string). Default is a space. (Mnemonic: obvious, I think.)
344
=item $SUBSCRIPT_SEPARATOR
350
The subscript separator for multidimensional array emulation. If you
351
refer to a hash element as
357
$foo{join($;, $a, $b, $c)}
361
@foo{$a,$b,$c} # a slice--note the @
365
($foo{$a},$foo{$b},$foo{$c})
367
Default is "\034", the same as SUBSEP in B<awk>. If your
368
keys contain binary data there might not be any safe value for C<$;>.
369
(Mnemonic: comma (the syntactic subscript separator) is a
370
semi-semicolon. Yeah, I know, it's pretty lame, but C<$,> is already
371
taken for something more important.)
373
Consider using "real" multidimensional arrays as described
380
The output format for printed numbers. This variable is a half-hearted
381
attempt to emulate B<awk>'s OFMT variable. There are times, however,
382
when B<awk> and Perl have differing notions of what counts as
383
numeric. The initial value is "%.I<n>g", where I<n> is the value
384
of the macro DBL_DIG from your system's F<float.h>. This is different from
385
B<awk>'s default OFMT setting of "%.6g", so you need to set C<$#>
386
explicitly to get B<awk>'s value. (Mnemonic: # is the number sign.)
388
Use of C<$#> is deprecated.
390
=item format_page_number HANDLE EXPR
392
=item $FORMAT_PAGE_NUMBER
396
The current page number of the currently selected output channel.
398
(Mnemonic: % is page number in B<nroff>.)
400
=item format_lines_per_page HANDLE EXPR
402
=item $FORMAT_LINES_PER_PAGE
406
The current page length (printable lines) of the currently selected
407
output channel. Default is 60.
409
(Mnemonic: = has horizontal lines.)
411
=item format_lines_left HANDLE EXPR
413
=item $FORMAT_LINES_LEFT
417
The number of lines left on the page of the currently selected output
420
(Mnemonic: lines_on_page - lines_printed.)
422
=item @LAST_MATCH_START
426
$-[0] is the offset of the start of the last successful match.
427
C<$-[>I<n>C<]> is the offset of the start of the substring matched by
428
I<n>-th subpattern, or undef if the subpattern did not match.
430
Thus after a match against $_, $& coincides with C<substr $_, $-[0],
431
$+[0] - $-[0]>. Similarly, C<$>I<n> coincides with C<substr $_, $-[>I<n>C<],
432
$+[>I<n>C<] - $-[>I<n>C<]> if C<$-[>I<n>C<]> is defined, and $+ coincides with
433
C<substr $_, $-[$#-], $+[$#-]>. One can use C<$#-> to find the last
434
matched subgroup in the last successful match. Contrast with
435
C<$#+>, the number of subgroups in the regular expression. Compare
438
This array holds the offsets of the beginnings of the last
439
successful submatches in the currently active dynamic scope.
440
C<$-[0]> is the offset into the string of the beginning of the
441
entire match. The I<n>th element of this array holds the offset
442
of the I<n>th submatch, so C<$+[1]> is the offset where $1
443
begins, C<$+[2]> the offset where $2 begins, and so on.
444
You can use C<$#-> to determine how many subgroups were in the
445
last successful match. Compare with the C<@+> variable.
447
After a match against some variable $var:
451
=item C<$`> is the same as C<substr($var, 0, $-[0])>
453
=item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
455
=item C<$'> is the same as C<substr($var, $+[0])>
457
=item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
459
=item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
461
=item C<$3> is the same as C<substr $var, $-[3], $+[3] - $-[3])>
465
=item format_name HANDLE EXPR
471
The name of the current report format for the currently selected output
472
channel. Default is the name of the filehandle. (Mnemonic: brother to
475
=item format_top_name HANDLE EXPR
477
=item $FORMAT_TOP_NAME
481
The name of the current top-of-page format for the currently selected
482
output channel. Default is the name of the filehandle with _TOP
483
appended. (Mnemonic: points to top of page.)
485
=item format_line_break_characters HANDLE EXPR
487
=item $FORMAT_LINE_BREAK_CHARACTERS
491
The current set of characters after which a string may be broken to
492
fill continuation fields (starting with ^) in a format. Default is
493
S<" \n-">, to break on whitespace or hyphens. (Mnemonic: a "colon" in
494
poetry is a part of a line.)
496
=item format_formfeed HANDLE EXPR
498
=item $FORMAT_FORMFEED
502
What formats output as a form feed. Default is \f.
508
The current value of the write() accumulator for format() lines. A format
509
contains formline() calls that put their result into C<$^A>. After
510
calling its format, write() prints out the contents of C<$^A> and empties.
511
So you never really see the contents of C<$^A> unless you call
512
formline() yourself and then look at it. See L<perlform> and
513
L<perlfunc/formline()>.
519
The status returned by the last pipe close, backtick (C<``>) command,
520
successful call to wait() or waitpid(), or from the system()
521
operator. This is just the 16-bit status word returned by the
522
wait() system call (or else is made up to look like it). Thus, the
523
exit value of the subprocess is really (C<<< $? >> 8 >>>), and
524
C<$? & 127> gives which signal, if any, the process died from, and
525
C<$? & 128> reports whether there was a core dump. (Mnemonic:
526
similar to B<sh> and B<ksh>.)
528
Additionally, if the C<h_errno> variable is supported in C, its value
529
is returned via $? if any C<gethost*()> function fails.
531
If you have installed a signal handler for C<SIGCHLD>, the
532
value of C<$?> will usually be wrong outside that handler.
534
Inside an C<END> subroutine C<$?> contains the value that is going to be
535
given to C<exit()>. You can modify C<$?> in an C<END> subroutine to
536
change the exit status of your program. For example:
539
$? = 1 if $? == 255; # die would make it 255
542
Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
543
actual VMS exit status, instead of the default emulation of POSIX
546
Also see L<Error Indicators>.
554
If used numerically, yields the current value of the C C<errno>
555
variable, with all the usual caveats. (This means that you shouldn't
556
depend on the value of C<$!> to be anything in particular unless
557
you've gotten a specific error return indicating a system error.)
558
If used an a string, yields the corresponding system error string.
559
You can assign a number to C<$!> to set I<errno> if, for instance,
560
you want C<"$!"> to return the string for error I<n>, or you want
561
to set the exit value for the die() operator. (Mnemonic: What just
564
Also see L<Error Indicators>.
566
=item $EXTENDED_OS_ERROR
570
Error information specific to the current operating system. At
571
the moment, this differs from C<$!> under only VMS, OS/2, and Win32
572
(and for MacPerl). On all other platforms, C<$^E> is always just
575
Under VMS, C<$^E> provides the VMS status value from the last
576
system error. This is more specific information about the last
577
system error than that provided by C<$!>. This is particularly
578
important when C<$!> is set to B<EVMSERR>.
580
Under OS/2, C<$^E> is set to the error code of the last call to
581
OS/2 API either via CRT, or directly from perl.
583
Under Win32, C<$^E> always returns the last error information
584
reported by the Win32 call C<GetLastError()> which describes
585
the last error from within the Win32 API. Most Win32-specific
586
code will report errors via C<$^E>. ANSI C and Unix-like calls
587
set C<errno> and so most portable Perl code will report errors
590
Caveats mentioned in the description of C<$!> generally apply to
591
C<$^E>, also. (Mnemonic: Extra error explanation.)
593
Also see L<Error Indicators>.
599
The Perl syntax error message from the last eval() operator. If null, the
600
last eval() parsed and executed correctly (although the operations you
601
invoked may have failed in the normal fashion). (Mnemonic: Where was
602
the syntax error "at"?)
604
Warning messages are not collected in this variable. You can,
605
however, set up a routine to process warnings by setting C<$SIG{__WARN__}>
608
Also see L<Error Indicators>.
616
The process number of the Perl running this script. You should
617
consider this variable read-only, although it will be altered
618
across fork() calls. (Mnemonic: same as shells.)
626
The real uid of this process. (Mnemonic: it's the uid you came I<from>,
627
if you're running setuid.)
629
=item $EFFECTIVE_USER_ID
635
The effective uid of this process. Example:
637
$< = $>; # set real to effective uid
638
($<,$>) = ($>,$<); # swap real and effective uid
640
(Mnemonic: it's the uid you went I<to>, if you're running setuid.)
641
C<< $< >> and C<< $> >> can be swapped only on machines
642
supporting setreuid().
650
The real gid of this process. If you are on a machine that supports
651
membership in multiple groups simultaneously, gives a space separated
652
list of groups you are in. The first number is the one returned by
653
getgid(), and the subsequent ones by getgroups(), one of which may be
654
the same as the first number.
656
However, a value assigned to C<$(> must be a single number used to
657
set the real gid. So the value given by C<$(> should I<not> be assigned
658
back to C<$(> without being forced numeric, such as by adding zero.
660
(Mnemonic: parentheses are used to I<group> things. The real gid is the
661
group you I<left>, if you're running setgid.)
663
=item $EFFECTIVE_GROUP_ID
669
The effective gid of this process. If you are on a machine that
670
supports membership in multiple groups simultaneously, gives a space
671
separated list of groups you are in. The first number is the one
672
returned by getegid(), and the subsequent ones by getgroups(), one of
673
which may be the same as the first number.
675
Similarly, a value assigned to C<$)> must also be a space-separated
676
list of numbers. The first number sets the effective gid, and
677
the rest (if any) are passed to setgroups(). To get the effect of an
678
empty list for setgroups(), just repeat the new effective gid; that is,
679
to force an effective gid of 5 and an effectively empty setgroups()
680
list, say C< $) = "5 5" >.
682
(Mnemonic: parentheses are used to I<group> things. The effective gid
683
is the group that's I<right> for you, if you're running setgid.)
685
C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on
686
machines that support the corresponding I<set[re][ug]id()> routine. C<$(>
687
and C<$)> can be swapped only on machines supporting setregid().
693
Contains the name of the program being executed. On some operating
694
systems assigning to C<$0> modifies the argument area that the B<ps>
695
program sees. This is more useful as a way of indicating the current
696
program state than it is for hiding the program you're running.
697
(Mnemonic: same as B<sh> and B<ksh>.)
699
Note for BSD users: setting C<$0> does not completely remove "perl"
700
from the ps(1) output. For example, setting C<$0> to C<"foobar"> will
701
result in C<"perl: foobar (perl)">. This is an operating system
706
The index of the first element in an array, and of the first character
707
in a substring. Default is 0, but you could theoretically set it
708
to 1 to make Perl behave more like B<awk> (or Fortran) when
709
subscripting and when evaluating the index() and substr() functions.
710
(Mnemonic: [ begins subscripts.)
712
As of release 5 of Perl, assignment to C<$[> is treated as a compiler
713
directive, and cannot influence the behavior of any other file.
714
Its use is highly discouraged.
718
The version + patchlevel / 1000 of the Perl interpreter. This variable
719
can be used to determine whether the Perl interpreter executing a
720
script is in the right range of versions. (Mnemonic: Is this version
721
of perl in the right bracket?) Example:
723
warn "No checksumming!\n" if $] < 3.019;
725
See also the documentation of C<use VERSION> and C<require VERSION>
726
for a convenient way to fail if the running Perl interpreter is too old.
728
The use of this variable is deprecated. The floating point representation
729
can sometimes lead to inaccurate numeric comparisons. See C<$^V> for a
730
more modern representation of the Perl version that allows accurate string
737
The current value of the flag associated with the B<-c> switch.
738
Mainly of use with B<-MO=...> to allow code to alter its behavior
739
when being compiled, such as for example to AUTOLOAD at compile
740
time rather than normal, deferred loading. See L<perlcc>. Setting
741
C<$^C = 1> is similar to calling C<B::minus_c>.
747
The current value of the debugging flags. (Mnemonic: value of B<-D>
754
The maximum system file descriptor, ordinarily 2. System file
755
descriptors are passed to exec()ed processes, while higher file
756
descriptors are not. Also, during an open(), system file descriptors are
757
preserved even if the open() fails. (Ordinary file descriptors are
758
closed before the open() is attempted.) The close-on-exec
759
status of a file descriptor will be decided according to the value of
760
C<$^F> when the corresponding file, pipe, or socket was opened, not the
765
WARNING: This variable is strictly for internal use only. Its availability,
766
behavior, and contents are subject to change without notice.
768
This variable contains compile-time hints for the Perl interpreter. At the
769
end of compilation of a BLOCK the value of this variable is restored to the
770
value when the interpreter started to compile the BLOCK.
772
When perl begins to parse any block construct that provides a lexical scope
773
(e.g., eval body, required file, subroutine body, loop body, or conditional
774
block), the existing value of $^H is saved, but its value is left unchanged.
775
When the compilation of the block is completed, it regains the saved value.
776
Between the points where its value is saved and restored, code that
777
executes within BEGIN blocks is free to change the value of $^H.
779
This behavior provides the semantic of lexical scoping, and is used in,
780
for instance, the C<use strict> pragma.
782
The contents should be an integer; different bits of it are used for
783
different pragmatic flags. Here's an example:
785
sub add_100 { $^H |= 0x100 }
792
Consider what happens during execution of the BEGIN block. At this point
793
the BEGIN block has already been compiled, but the body of foo() is still
794
being compiled. The new value of $^H will therefore be visible only while
795
the body of foo() is being compiled.
797
Substitution of the above BEGIN block with:
799
BEGIN { require strict; strict->import('vars') }
801
demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
802
version of the same lexical pragma:
804
BEGIN { require strict; strict->import('vars') if $condition }
808
WARNING: This variable is strictly for internal use only. Its availability,
809
behavior, and contents are subject to change without notice.
811
The %^H hash provides the same scoping semantic as $^H. This makes it
812
useful for implementation of lexically scoped pragmas.
818
The current value of the inplace-edit extension. Use C<undef> to disable
819
inplace editing. (Mnemonic: value of B<-i> switch.)
823
By default, running out of memory is an untrappable, fatal error.
824
However, if suitably built, Perl can use the contents of C<$^M>
825
as an emergency memory pool after die()ing. Suppose that your Perl
826
were compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc.
829
$^M = 'a' x (1 << 16);
831
would allocate a 64K buffer for use in an emergency. See the
832
F<INSTALL> file in the Perl distribution for information on how to
833
enable this option. To discourage casual use of this advanced
834
feature, there is no L<English|English> long name for this variable.
840
The name of the operating system under which this copy of Perl was
841
built, as determined during the configuration process. The value
842
is identical to C<$Config{'osname'}>. See also L<Config> and the
843
B<-V> command-line switch documented in L<perlrun>.
849
The internal variable for debugging support. The meanings of the
850
various bits are subject to change, but currently indicate:
856
Debug subroutine enter/exit.
860
Line-by-line debugging.
864
Switch off optimizations.
868
Preserve more data for future interactive inspections.
872
Keep info about source lines on which a subroutine is defined.
876
Start with single-step on.
880
Use subroutine address instead of name when reporting.
884
Report C<goto &subroutine> as well.
888
Provide informative "file" names for evals based on the place they were compiled.
892
Provide informative names to anonymous subroutines based on the place they
897
Some bits may be relevant at compile-time only, some at
898
run-time only. This is a new mechanism and the details may change.
900
=item $LAST_REGEXP_CODE_RESULT
904
The result of evaluation of the last successful C<(?{ code })>
905
regular expression assertion (see L<perlre>). May be written to.
907
=item $EXCEPTIONS_BEING_CAUGHT
911
Current state of the interpreter. Undefined if parsing of the current
912
module/eval is not finished (may happen in $SIG{__DIE__} and
913
$SIG{__WARN__} handlers). True if inside an eval(), otherwise false.
919
The time at which the program began running, in seconds since the
920
epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
921
and B<-C> filetests are based on this value.
927
The revision, version, and subversion of the Perl interpreter, represented
928
as a string composed of characters with those ordinals. Thus in Perl v5.6.0
929
it equals C<chr(5) . chr(6) . chr(0)> and will return true for
930
C<$^V eq v5.6.0>. Note that the characters in this string value can
931
potentially be in Unicode range.
933
This can be used to determine whether the Perl interpreter executing a
934
script is in the right range of versions. (Mnemonic: use ^V for Version
937
warn "No \"our\" declarations!\n" if $^V and $^V lt v5.6.0;
939
See the documentation of C<use VERSION> and C<require VERSION>
940
for a convenient way to fail if the running Perl interpreter is too old.
942
See also C<$]> for an older representation of the Perl version.
948
The current value of the warning switch, initially true if B<-w>
949
was used, false otherwise, but directly modifiable. (Mnemonic:
950
related to the B<-w> switch.) See also L<warnings>.
952
=item ${^WARNING_BITS}
954
The current set of warning checks enabled by the C<use warnings> pragma.
955
See the documentation of C<warnings> for more details.
957
=item ${^WIDE_SYSTEM_CALLS}
959
Global flag that enables system calls made by Perl to use wide character
960
APIs native to the system, if available. This is currently only implemented
961
on the Windows platform.
963
This can also be enabled from the command line using the C<-C> switch.
965
The initial value is typically C<0> for compatibility with Perl versions
966
earlier than 5.6, but may be automatically set to C<1> by Perl if the system
967
provides a user-settable default (e.g., C<$ENV{LC_CTYPE}>).
969
The C<bytes> pragma always overrides the effect of this flag in the current
970
lexical scope. See L<bytes>.
972
=item $EXECUTABLE_NAME
976
The name that the Perl binary itself was executed as, from C's C<argv[0]>.
977
This may not be a full pathname, nor even necessarily in your path.
981
contains the name of the current file when reading from <>.
985
The array @ARGV contains the command-line arguments intended for
986
the script. C<$#ARGV> is generally the number of arguments minus
987
one, because C<$ARGV[0]> is the first argument, I<not> the program's
988
command name itself. See C<$0> for the command name.
992
The array @INC contains the list of places that the C<do EXPR>,
993
C<require>, or C<use> constructs look for their library files. It
994
initially consists of the arguments to any B<-I> command-line
995
switches, followed by the default Perl library, probably
996
F</usr/local/lib/perl>, followed by ".", to represent the current
997
directory. If you need to modify this at runtime, you should use
998
the C<use lib> pragma to get the machine-dependent library properly
1001
use lib '/mypath/libdir/';
1006
Within a subroutine the array @_ contains the parameters passed to that
1007
subroutine. See L<perlsub>.
1011
The hash %INC contains entries for each filename included via the
1012
C<do>, C<require>, or C<use> operators. The key is the filename
1013
you specified (with module names converted to pathnames), and the
1014
value is the location of the file found. The C<require>
1015
operator uses this hash to determine whether a particular file has
1016
already been included.
1022
The hash %ENV contains your current environment. Setting a
1023
value in C<ENV> changes the environment for any child processes
1024
you subsequently fork() off.
1030
The hash %SIG contains signal handlers for signals. For example:
1032
sub handler { # 1st argument is signal name
1034
print "Caught a SIG$sig--shutting down\n";
1039
$SIG{'INT'} = \&handler;
1040
$SIG{'QUIT'} = \&handler;
1042
$SIG{'INT'} = 'DEFAULT'; # restore default action
1043
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
1045
Using a value of C<'IGNORE'> usually has the effect of ignoring the
1046
signal, except for the C<CHLD> signal. See L<perlipc> for more about
1049
Here are some other examples:
1051
$SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not recommended)
1052
$SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber
1053
$SIG{"PIPE"} = *Plumber; # somewhat esoteric
1054
$SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return??
1056
Be sure not to use a bareword as the name of a signal handler,
1057
lest you inadvertently call it.
1059
If your system has the sigaction() function then signal handlers are
1060
installed using it. This means you get reliable signal handling. If
1061
your system has the SA_RESTART flag it is used when signals handlers are
1062
installed. This means that system calls for which restarting is supported
1063
continue rather than returning when a signal arrives. If you want your
1064
system calls to be interrupted by signal delivery then do something like
1067
use POSIX ':signal_h';
1070
sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 }
1071
or die "Error setting SIGALRM handler: $!\n";
1075
Certain internal hooks can be also set using the %SIG hash. The
1076
routine indicated by C<$SIG{__WARN__}> is called when a warning message is
1077
about to be printed. The warning message is passed as the first
1078
argument. The presence of a __WARN__ hook causes the ordinary printing
1079
of warnings to STDERR to be suppressed. You can use this to save warnings
1080
in a variable, or turn warnings into fatal errors, like this:
1082
local $SIG{__WARN__} = sub { die $_[0] };
1085
The routine indicated by C<$SIG{__DIE__}> is called when a fatal exception
1086
is about to be thrown. The error message is passed as the first
1087
argument. When a __DIE__ hook routine returns, the exception
1088
processing continues as it would have in the absence of the hook,
1089
unless the hook routine itself exits via a C<goto>, a loop exit, or a die().
1090
The C<__DIE__> handler is explicitly disabled during the call, so that you
1091
can die from a C<__DIE__> handler. Similarly for C<__WARN__>.
1093
Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called
1094
even inside an eval(). Do not use this to rewrite a pending exception
1095
in C<$@>, or as a bizarre substitute for overriding CORE::GLOBAL::die().
1096
This strange action at a distance may be fixed in a future release
1097
so that C<$SIG{__DIE__}> is only called if your program is about
1098
to exit, as was the original intent. Any other use is deprecated.
1100
C<__DIE__>/C<__WARN__> handlers are very special in one respect:
1101
they may be called to report (probable) errors found by the parser.
1102
In such a case the parser may be in inconsistent state, so any
1103
attempt to evaluate Perl code from such a handler will probably
1104
result in a segfault. This means that warnings or errors that
1105
result from parsing Perl should be used with extreme caution, like
1108
require Carp if defined $^S;
1109
Carp::confess("Something wrong") if defined &Carp::confess;
1110
die "Something wrong, but could not load Carp to give backtrace...
1111
To see backtrace try starting Perl with -MCarp switch";
1113
Here the first line will load Carp I<unless> it is the parser who
1114
called the handler. The second line will print backtrace and die if
1115
Carp was available. The third line will be executed only if Carp was
1118
See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
1119
L<warnings> for additional information.
1123
=head2 Error Indicators
1125
The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information
1126
about different types of error conditions that may appear during
1127
execution of a Perl program. The variables are shown ordered by
1128
the "distance" between the subsystem which reported the error and
1129
the Perl process. They correspond to errors detected by the Perl
1130
interpreter, C library, operating system, or an external program,
1133
To illustrate the differences between these variables, consider the
1134
following Perl expression, which uses a single-quoted string:
1137
open PIPE, "/cdrom/install |";
1139
close PIPE or die "bad pipe: $?, $!";
1142
After execution of this statement all 4 variables may have been set.
1144
C<$@> is set if the string to be C<eval>-ed did not compile (this
1145
may happen if C<open> or C<close> were imported with bad prototypes),
1146
or if Perl code executed during evaluation die()d . In these cases
1147
the value of $@ is the compile error, or the argument to C<die>
1148
(which will interpolate C<$!> and C<$?>!). (See also L<Fatal>,
1151
When the eval() expression above is executed, open(), C<< <PIPE> >>,
1152
and C<close> are translated to calls in the C run-time library and
1153
thence to the operating system kernel. C<$!> is set to the C library's
1154
C<errno> if one of these calls fails.
1156
Under a few operating systems, C<$^E> may contain a more verbose
1157
error indicator, such as in this case, "CDROM tray not closed."
1158
Systems that do not support extended error messages leave C<$^E>
1161
Finally, C<$?> may be set to non-0 value if the external program
1162
F</cdrom/install> fails. The upper eight bits reflect specific
1163
error conditions encountered by the program (the program's exit()
1164
value). The lower eight bits reflect mode of failure, like signal
1165
death and core dump information See wait(2) for details. In
1166
contrast to C<$!> and C<$^E>, which are set only if error condition
1167
is detected, the variable C<$?> is set on each C<wait> or pipe
1168
C<close>, overwriting the old value. This is more like C<$@>, which
1169
on every eval() is always set on failure and cleared on success.
1171
For more details, see the individual descriptions at C<$@>, C<$!>, C<$^E>,
1174
=head2 Technical Note on the Syntax of Variable Names
1176
Variable names in Perl can have several formats. Usually, they
1177
must begin with a letter or underscore, in which case they can be
1178
arbitrarily long (up to an internal limit of 251 characters) and
1179
may contain letters, digits, underscores, or the special sequence
1180
C<::> or C<'>. In this case, the part before the last C<::> or
1181
C<'> is taken to be a I<package qualifier>; see L<perlmod>.
1183
Perl variable names may also be a sequence of digits or a single
1184
punctuation or control character. These names are all reserved for
1185
special uses by Perl; for example, the all-digits names are used
1186
to hold data captured by backreferences after a regular expression
1187
match. Perl has a special syntax for the single-control-character
1188
names: It understands C<^X> (caret C<X>) to mean the control-C<X>
1189
character. For example, the notation C<$^W> (dollar-sign caret
1190
C<W>) is the scalar variable whose name is the single character
1191
control-C<W>. This is better than typing a literal control-C<W>
1194
Finally, new in Perl 5.6, Perl variable names may be alphanumeric
1195
strings that begin with control characters (or better yet, a caret).
1196
These variables must be written in the form C<${^Foo}>; the braces
1197
are not optional. C<${^Foo}> denotes the scalar variable whose
1198
name is a control-C<F> followed by two C<o>'s. These variables are
1199
reserved for future special uses by Perl, except for the ones that
1200
begin with C<^_> (control-underscore or caret-underscore). No
1201
control-character name that begins with C<^_> will acquire a special
1202
meaning in any future version of Perl; such names may therefore be
1203
used safely in programs. C<$^_> itself, however, I<is> reserved.
1205
Perl identifiers that begin with digits, control characters, or
1206
punctuation characters are exempt from the effects of the C<package>
1207
declaration and are always forced to be in package C<main>. A few
1208
other names are also exempt:
1216
In particular, the new special C<${^_XYZ}> variables are always taken
1217
to be in package C<main>, regardless of any C<package> declarations
1222
Due to an unfortunate accident of Perl's implementation, C<use
1223
English> imposes a considerable performance penalty on all regular
1224
expression matches in a program, regardless of whether they occur
1225
in the scope of C<use English>. For that reason, saying C<use
1226
English> in libraries is strongly discouraged. See the
1227
Devel::SawAmpersand module documentation from CPAN
1228
(http://www.perl.com/CPAN/modules/by-module/Devel/)
1229
for more information.
1231
Having to even think about the C<$^S> variable in your exception
1232
handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented
1233
invites grievous and difficult to track down errors. Avoid it
1234
and use an C<END{}> or CORE::GLOBAL::die override instead.
added
removed
0CPAN/Pod-Simple-3.03/t/test_old_perlvar.pod
