3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-CsTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the #! notation invoke interpreters this
37 way. See L<Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with #! and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The #! line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the #! line, or worse, doesn't even recognize the #! line, you
57 still can get consistent switch behavior regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the #! line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
80 #!/bin/sh -- # -*- perl -*- -p
81 eval 'exec perl -wS $0 ${1+"$@"}'
82 if $running_under_some_shell;
84 to let Perl see the B<-p> switch.
86 A similar trick involves the B<env> program, if you have it.
90 The examples above use a relative path to the perl interpreter,
91 getting whatever version is first in the user's path. If you want
92 a specific version of Perl, say, perl5.005_57, you should place
93 that directly in the #! line's path.
95 If the #! line does not contain the word "perl", the program named after
96 the #! is executed instead of the Perl interpreter. This is slightly
97 bizarre, but it helps people on machines that don't do #!, because they
98 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
99 dispatch the program to the correct interpreter for them.
101 After locating your program, Perl compiles the entire program to an
102 internal form. If there are any compilation errors, execution of the
103 program is not attempted. (This is unlike the typical shell script,
104 which might run part-way through before finding a syntax error.)
106 If the program is syntactically correct, it is executed. If the program
107 runs off the end without hitting an exit() or die() operator, an implicit
108 C<exit(0)> is provided to indicate successful completion.
110 =head2 #! and quoting on non-Unix systems
112 Unix's #! technique can be simulated on other systems:
120 extproc perl -S -your_switches
122 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
127 Create a batch file to run your program, and codify it in
128 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
129 distribution for more information).
133 The Win95/NT installation, when using the ActiveState installer for Perl,
134 will modify the Registry to associate the F<.pl> extension with the perl
135 interpreter. If you install Perl by other means (including building from
136 the sources), you may have to modify the Registry yourself. Note that
137 this means you can no longer tell the difference between an executable
138 Perl program and a Perl library file.
142 A Macintosh perl program will have the appropriate Creator and
143 Type, so that double-clicking them will invoke the perl application.
149 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
150 $ exit++ + ++$status != 0 and $exit = $status = undef;
152 at the top of your program, where B<-mysw> are any command line switches you
153 want to pass to Perl. You can now invoke the program directly, by saying
154 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
155 via F<DCL$PATH> by just using the name of the program).
157 This incantation is a bit much to remember, but Perl will display it for
158 you if you say C<perl "-V:startperl">.
162 Command-interpreters on non-Unix systems have rather different ideas
163 on quoting than Unix shells. You'll need to learn the special
164 characters in your command-interpreter (C<*>, C<\> and C<"> are
165 common) and how to protect whitespace and these characters to run
166 one-liners (see B<-e> below).
168 On some systems, you may have to change single-quotes to double ones,
169 which you must I<not> do on Unix or Plan 9 systems. You might also
170 have to change a single % to a %%.
175 perl -e 'print "Hello world\n"'
178 perl -e "print \"Hello world\n\""
181 print "Hello world\n"
182 (then Run "Myscript" or Shift-Command-R)
185 perl -e "print ""Hello world\n"""
187 The problem is that none of this is reliable: it depends on the
188 command and it is entirely possible neither works. If B<4DOS> were
189 the command shell, this would probably work better:
191 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
193 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
194 when nobody was looking, but just try to find documentation for its
197 Under the Macintosh, it depends which environment you are using. The MacPerl
198 shell, or MPW, is much like Unix shells in its support for several
199 quoting variants, except that it makes free use of the Macintosh's non-ASCII
200 characters as control characters.
202 There is no general solution to all of this. It's just a mess.
204 =head2 Location of Perl
206 It may seem obvious to say, but Perl is useful only when users can
207 easily find it. When possible, it's good for both F</usr/bin/perl>
208 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
209 that can't be done, system administrators are strongly encouraged
210 to put (symlinks to) perl and its accompanying utilities into a
211 directory typically found along a user's PATH, or in some other
212 obvious and convenient place.
214 In this documentation, C<#!/usr/bin/perl> on the first line of the program
215 will stand in for whatever method works on your system. You are
216 advised to use a specific path if you care about a specific version.
218 #!/usr/local/bin/perl5.00554
220 or if you just want to be running at least version, place a statement
221 like this at the top of your program:
225 =head2 Command Switches
227 As with all standard commands, a single-character switch may be
228 clustered with the following switch, if any.
230 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
236 =item B<-0>[I<digits>]
238 specifies the input record separator (C<$/>) as an octal number. If there are
239 no digits, the null character is the separator. Other switches may
240 precede or follow the digits. For example, if you have a version of
241 B<find> which can print filenames terminated by the null character, you
244 find . -name '*.orig' -print0 | perl -n0e unlink
246 The special value 00 will cause Perl to slurp files in paragraph mode.
247 The value 0777 will cause Perl to slurp files whole because there is no
248 legal character with that value.
252 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
253 split command to the @F array is done as the first thing inside the
254 implicit while loop produced by the B<-n> or B<-p>.
256 perl -ane 'print pop(@F), "\n";'
265 An alternate delimiter may be specified using B<-F>.
269 enables Perl to use the Unicode APIs on the target system.
271 As of Perl 5.8.1, if C<-C> is used and the locale settings (the LC_ALL,
272 LC_CTYPE, and LANG environment variables) indicate a UTF-8 locale,
273 the STDIN is expected to be in UTF-8, the STDOUT and STDERR are
274 expected to be in UTF-8, and C<:utf8> is the default file open layer.
275 See L<perluniintro>, L<perlfunc/open>, and L<open> for more information.
276 The magic variable C<${^UTF8_LOCALE}> reflects this state,
277 see L<perlvar/"${^UTF8_LOCALE}">. (Another way of setting this
278 variable is to set the environment variable PERL_UTF8_LOCALE.)
280 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
281 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
282 This feature was practically unused, however, and the command line
283 switch was therefore "recycled".)
287 causes Perl to check the syntax of the program and then exit without
288 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
289 C<use> blocks, because these are considered as occurring outside the
290 execution of your program. C<INIT> and C<END> blocks, however, will
295 runs the program under the Perl debugger. See L<perldebug>.
297 =item B<-d:>I<foo[=bar,baz]>
299 runs the program under the control of a debugging, profiling, or
300 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
301 the program using the Devel::DProf profiler. As with the B<-M>
302 flag, options may be passed to the Devel::foo package where they
303 will be received and interpreted by the Devel::foo::import routine.
304 The comma-separated list of options must follow a C<=> character.
307 =item B<-D>I<letters>
311 sets debugging flags. To watch how it executes your program, use
312 B<-Dtls>. (This works only if debugging is compiled into your
313 Perl.) Another nice value is B<-Dx>, which lists your compiled
314 syntax tree. And B<-Dr> displays compiled regular expressions;
315 the format of the output is explained in L<perldebguts>.
317 As an alternative, specify a number instead of list of letters (e.g.,
318 B<-D14> is equivalent to B<-Dtls>):
320 1 p Tokenizing and parsing
322 with v, displays all stacks
323 4 l Context (loop) stack processing
325 16 o Method and overloading resolution
326 32 c String/numeric conversions
327 64 P Print profiling info, preprocessor command for -P, source file input state
328 128 m Memory allocation
329 256 f Format processing
330 512 r Regular expression parsing and execution
331 1024 x Syntax tree dump
332 2048 u Tainting checks
333 4096 (Obsolete, previously used for LEAKTEST)
334 8192 H Hash dump -- usurps values()
335 16384 X Scratchpad allocation
337 65536 S Thread synchronization
339 262144 R Include reference counts of dumped variables (eg when using -Ds)
340 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
341 1048576 v Verbose: use in conjunction with other flags
342 2097152 C Copy On Write
344 All these flags require B<-DDEBUGGING> when you compile the Perl
345 executable (but see L<Devel::Peek>, L<re> which may change this).
346 See the F<INSTALL> file in the Perl source distribution
347 for how to do this. This flag is automatically set if you include B<-g>
348 option when C<Configure> asks you about optimizer/debugger flags.
350 If you're just trying to get a print out of each line of Perl code
351 as it executes, the way that C<sh -x> provides for shell scripts,
352 you can't use Perl's B<-D> switch. Instead do this
354 # If you have "env" utility
355 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
357 # Bourne shell syntax
358 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
361 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
363 See L<perldebug> for details and variations.
365 =item B<-e> I<commandline>
367 may be used to enter one line of program. If B<-e> is given, Perl
368 will not look for a filename in the argument list. Multiple B<-e>
369 commands may be given to build up a multi-line script. Make sure
370 to use semicolons where you would in a normal program.
372 =item B<-F>I<pattern>
374 specifies the pattern to split on if B<-a> is also in effect. The
375 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
376 put in single quotes.
380 prints a summary of the options.
382 =item B<-i>[I<extension>]
384 specifies that files processed by the C<E<lt>E<gt>> construct are to be
385 edited in-place. It does this by renaming the input file, opening the
386 output file by the original name, and selecting that output file as the
387 default for print() statements. The extension, if supplied, is used to
388 modify the name of the old file to make a backup copy, following these
391 If no extension is supplied, no backup is made and the current file is
394 If the extension doesn't contain a C<*>, then it is appended to the
395 end of the current filename as a suffix. If the extension does
396 contain one or more C<*> characters, then each C<*> is replaced
397 with the current filename. In Perl terms, you could think of this
400 ($backup = $extension) =~ s/\*/$file_name/g;
402 This allows you to add a prefix to the backup file, instead of (or in
403 addition to) a suffix:
405 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
407 Or even to place backup copies of the original files into another
408 directory (provided the directory already exists):
410 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
412 These sets of one-liners are equivalent:
414 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
415 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
417 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
418 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
420 From the shell, saying
422 $ perl -p -i.orig -e "s/foo/bar/; ... "
424 is the same as using the program:
426 #!/usr/bin/perl -pi.orig
429 which is equivalent to
432 $extension = '.orig';
434 if ($ARGV ne $oldargv) {
435 if ($extension !~ /\*/) {
436 $backup = $ARGV . $extension;
439 ($backup = $extension) =~ s/\*/$ARGV/g;
441 rename($ARGV, $backup);
442 open(ARGVOUT, ">$ARGV");
449 print; # this prints to original filename
453 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
454 know when the filename has changed. It does, however, use ARGVOUT for
455 the selected filehandle. Note that STDOUT is restored as the default
456 output filehandle after the loop.
458 As shown above, Perl creates the backup file whether or not any output
459 is actually changed. So this is just a fancy way to copy files:
461 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
463 $ perl -p -i'.orig' -e 1 file1 file2 file3...
465 You can use C<eof> without parentheses to locate the end of each input
466 file, in case you want to append to each file, or reset line numbering
467 (see example in L<perlfunc/eof>).
469 If, for a given file, Perl is unable to create the backup file as
470 specified in the extension then it will skip that file and continue on
471 with the next one (if it exists).
473 For a discussion of issues surrounding file permissions and B<-i>,
474 see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
476 You cannot use B<-i> to create directories or to strip extensions from
479 Perl does not expand C<~> in filenames, which is good, since some
480 folks use it for their backup files:
482 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
484 Finally, the B<-i> switch does not impede execution when no
485 files are given on the command line. In this case, no backup is made
486 (the original file cannot, of course, be determined) and processing
487 proceeds from STDIN to STDOUT as might be expected.
489 =item B<-I>I<directory>
491 Directories specified by B<-I> are prepended to the search path for
492 modules (C<@INC>), and also tells the C preprocessor where to search for
493 include files. The C preprocessor is invoked with B<-P>; by default it
494 searches /usr/include and /usr/lib/perl.
496 =item B<-l>[I<octnum>]
498 enables automatic line-ending processing. It has two separate
499 effects. First, it automatically chomps C<$/> (the input record
500 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
501 (the output record separator) to have the value of I<octnum> so
502 that any print statements will have that separator added back on.
503 If I<octnum> is omitted, sets C<$\> to the current value of
504 C<$/>. For instance, to trim lines to 80 columns:
506 perl -lpe 'substr($_, 80) = ""'
508 Note that the assignment C<$\ = $/> is done when the switch is processed,
509 so the input record separator can be different than the output record
510 separator if the B<-l> switch is followed by a B<-0> switch:
512 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
514 This sets C<$\> to newline and then sets C<$/> to the null character.
516 =item B<-m>[B<->]I<module>
518 =item B<-M>[B<->]I<module>
520 =item B<-M>[B<->]I<'module ...'>
522 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
524 B<-m>I<module> executes C<use> I<module> C<();> before executing your
527 B<-M>I<module> executes C<use> I<module> C<;> before executing your
528 program. You can use quotes to add extra code after the module name,
529 e.g., C<'-Mmodule qw(foo bar)'>.
531 If the first character after the B<-M> or B<-m> is a dash (C<->)
532 then the 'use' is replaced with 'no'.
534 A little builtin syntactic sugar means you can also say
535 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
536 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
537 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
538 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
539 removes the distinction between B<-m> and B<-M>.
543 causes Perl to assume the following loop around your program, which
544 makes it iterate over filename arguments somewhat like B<sed -n> or
549 ... # your program goes here
552 Note that the lines are not printed by default. See B<-p> to have
553 lines printed. If a file named by an argument cannot be opened for
554 some reason, Perl warns you about it and moves on to the next file.
556 Here is an efficient way to delete all files older than a week:
558 find . -mtime +7 -print | perl -nle unlink
560 This is faster than using the B<-exec> switch of B<find> because you don't
561 have to start a process on every filename found. It does suffer from
562 the bug of mishandling newlines in pathnames, which you can fix if
563 you follow the example under B<-0>.
565 C<BEGIN> and C<END> blocks may be used to capture control before or after
566 the implicit program loop, just as in B<awk>.
570 causes Perl to assume the following loop around your program, which
571 makes it iterate over filename arguments somewhat like B<sed>:
576 ... # your program goes here
578 print or die "-p destination: $!\n";
581 If a file named by an argument cannot be opened for some reason, Perl
582 warns you about it, and moves on to the next file. Note that the
583 lines are printed automatically. An error occurring during printing is
584 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
585 overrides a B<-n> switch.
587 C<BEGIN> and C<END> blocks may be used to capture control before or after
588 the implicit loop, just as in B<awk>.
592 B<NOTE: Use of -P is strongly discouraged because of its inherent
593 problems, including poor portability.>
595 This option causes your program to be run through the C preprocessor before
596 compilation by Perl. Because both comments and B<cpp> directives begin
597 with the # character, you should avoid starting comments with any words
598 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
600 If you're considering using C<-P>, you might also want to look at the
601 Filter::cpp module from CPAN.
603 The problems of -P include, but are not limited to:
609 The C<#!> line is stripped, so any switches there don't apply.
613 A C<-P> on a C<#!> line doesn't work.
617 B<All> lines that begin with (whitespace and) a C<#> but
618 do not look like cpp commands, are stripped, including anything
619 inside Perl strings, regular expressions, and here-docs .
623 In some platforms the C preprocessor knows too much: it knows about
624 the C++ -style until-end-of-line comments starting with C<"//">.
625 This will cause problems with common Perl constructs like
629 because after -P this will became illegal code
633 The workaround is to use some other quoting separator than C<"/">,
634 like for example C<"!">:
642 It requires not only a working C preprocessor but also a working
643 F<sed>. If not on UNIX, you are probably out of luck on this.
647 Script line numbers are not preserved.
651 The C<-x> does not work with C<-P>.
657 enables rudimentary switch parsing for switches on the command
658 line after the program name but before any filename arguments (or before
659 an argument of B<-->). This means you can have switches with two leading
660 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
661 corresponding variable in the Perl program. The following program
662 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
663 if it is invoked with B<-xyz=abc>.
666 if ($xyz) { print "$xyz\n" }
668 Do note that B<--help> creates the variable ${-help}, which is not compliant
673 makes Perl use the PATH environment variable to search for the
674 program (unless the name of the program contains directory separators).
676 On some platforms, this also makes Perl append suffixes to the
677 filename while searching for it. For example, on Win32 platforms,
678 the ".bat" and ".cmd" suffixes are appended if a lookup for the
679 original name fails, and if the name does not already end in one
680 of those suffixes. If your Perl was compiled with DEBUGGING turned
681 on, using the -Dp switch to Perl shows how the search progresses.
683 Typically this is used to emulate #! startup on platforms that
684 don't support #!. This example works on many platforms that
685 have a shell compatible with Bourne shell:
688 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
689 if $running_under_some_shell;
691 The system ignores the first line and feeds the program to F</bin/sh>,
692 which proceeds to try to execute the Perl program as a shell script.
693 The shell executes the second line as a normal shell command, and thus
694 starts up the Perl interpreter. On some systems $0 doesn't always
695 contain the full pathname, so the B<-S> tells Perl to search for the
696 program if necessary. After Perl locates the program, it parses the
697 lines and ignores them because the variable $running_under_some_shell
698 is never true. If the program will be interpreted by csh, you will need
699 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
700 embedded spaces (and such) in the argument list. To start up sh rather
701 than csh, some systems may have to replace the #! line with a line
702 containing just a colon, which will be politely ignored by Perl. Other
703 systems can't control that, and need a totally devious construct that
704 will work under any of B<csh>, B<sh>, or Perl, such as the following:
706 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
707 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
708 if $running_under_some_shell;
710 If the filename supplied contains directory separators (i.e., is an
711 absolute or relative pathname), and if that file is not found,
712 platforms that append file extensions will do so and try to look
713 for the file with those extensions added, one by one.
715 On DOS-like platforms, if the program does not contain directory
716 separators, it will first be searched for in the current directory
717 before being searched for on the PATH. On Unix platforms, the
718 program will be searched for strictly on the PATH.
722 Like B<-T>, but taint checks will issue warnings rather than fatal
723 errors. These warnings can be controlled normally with C<no warnings
726 B<NOTE: this is not a substitute for -T.> This is meant only to be
727 used as a temporary development aid while securing legacy code:
728 for real production code and for new secure code written from scratch
729 always use the real B<-T>.
733 forces "taint" checks to be turned on so you can test them. Ordinarily
734 these checks are done only when running setuid or setgid. It's a
735 good idea to turn them on explicitly for programs that run on behalf
736 of someone else whom you might not necessarily trust, such as CGI
737 programs or any internet servers you might write in Perl. See
738 L<perlsec> for details. For security reasons, this option must be
739 seen by Perl quite early; usually this means it must appear early
740 on the command line or in the #! line for systems which support
745 This obsolete switch causes Perl to dump core after compiling your
746 program. You can then in theory take this core dump and turn it
747 into an executable file by using the B<undump> program (not supplied).
748 This speeds startup at the expense of some disk space (which you
749 can minimize by stripping the executable). (Still, a "hello world"
750 executable comes out to about 200K on my machine.) If you want to
751 execute a portion of your program before dumping, use the dump()
752 operator instead. Note: availability of B<undump> is platform
753 specific and may not be available for a specific port of Perl.
755 This switch has been superseded in favor of the new Perl code
756 generator backends to the compiler. See L<B> and L<B::Bytecode>
761 allows Perl to do unsafe operations. Currently the only "unsafe"
762 operations are the unlinking of directories while running as superuser,
763 and running setuid programs with fatal taint checks turned into
764 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
765 be used along with this option to actually I<generate> the
766 taint-check warnings.
770 prints the version and patchlevel of your perl executable.
774 prints summary of the major perl configuration values and the current
779 Prints to STDOUT the value of the named configuration variable.
784 will provide strong clues about what your MANPATH variable should
785 be set to in order to access the Perl documentation.
789 prints warnings about dubious constructs, such as variable names
790 that are mentioned only once and scalar variables that are used
791 before being set, redefined subroutines, references to undefined
792 filehandles or filehandles opened read-only that you are attempting
793 to write on, values used as a number that doesn't look like numbers,
794 using an array as though it were a scalar, if your subroutines
795 recurse more than 100 deep, and innumerable other things.
797 This switch really just enables the internal C<^$W> variable. You
798 can disable or promote into fatal errors specific warnings using
799 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
800 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
801 facility is also available if you want to manipulate entire classes
802 of warnings; see L<warnings> or L<perllexwarn>.
806 Enables all warnings regardless of C<no warnings> or C<$^W>.
811 Disables all warnings regardless of C<use warnings> or C<$^W>.
814 =item B<-x> I<directory>
816 tells Perl that the program is embedded in a larger chunk of unrelated
817 ASCII text, such as in a mail message. Leading garbage will be
818 discarded until the first line that starts with #! and contains the
819 string "perl". Any meaningful switches on that line will be applied.
820 If a directory name is specified, Perl will switch to that directory
821 before running the program. The B<-x> switch controls only the
822 disposal of leading garbage. The program must be terminated with
823 C<__END__> if there is trailing garbage to be ignored (the program
824 can process any or all of the trailing garbage via the DATA filehandle
835 Used if chdir has no argument.
839 Used if chdir has no argument and HOME is not set.
843 Used in executing subprocesses, and in finding the program if B<-S> is
848 A colon-separated list of directories in which to look for Perl library
849 files before looking in the standard library and the current
850 directory. Any architecture-specific directories under the specified
851 locations are automatically included if they exist. If PERL5LIB is not
852 defined, PERLLIB is used.
854 When running taint checks (either because the program was running setuid
855 or setgid, or the B<-T> switch was used), neither variable is used.
856 The program should instead say:
858 use lib "/my/directory";
862 Command-line options (switches). Switches in this variable are taken
863 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
864 switches are allowed. When running taint checks (because the program
865 was running setuid or setgid, or the B<-T> switch was used), this
866 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
867 enabled, and any subsequent options ignored.
871 A space (or colon) separated list of PerlIO layers. If perl is built
872 to use PerlIO system for IO (the default) these layers effect perl's IO.
874 It is conventional to start layer names with a colon e.g. C<:perlio> to
875 emphasise their similarity to variable "attributes". But the code that parses
876 layer specification strings (which is also used to decode the PERLIO
877 environment variable) treats the colon as a separator.
879 The list becomes the default for I<all> perl's IO. Consequently only built-in
880 layers can appear in this list, as external layers (such as :encoding()) need
881 IO in order to load them!. See L<"open pragma"|open> for how to add external
882 encodings as defaults.
884 The layers that it makes sense to include in the PERLIO environment
885 variable are summarised below. For more details see L<PerlIO>.
891 Turns I<off> the C<:utf8> flag for the layer below.
892 Unlikely to be useful in global PERLIO environment variable.
896 A layer that implements DOS/Windows like CRLF line endings.
897 On read converts pairs of CR,LF to a single "\n" newline character.
898 On write converts each "\n" to a CR,LF pair.
899 Based on the C<:perlio> layer.
903 A layer which implements "reading" of files by using C<mmap()> to
904 make (whole) file appear in the process's address space, and then
905 using that as PerlIO's "buffer". This I<may> be faster in certain
906 circumstances for large files, and may result in less physical memory
907 use when multiple processes are reading the same file.
909 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
910 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
911 needs extra house-keeping (to extend the file) which negates any advantage.
913 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
917 A from scratch implementation of buffering for PerlIO. Provides fast
918 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
919 and in general attempts to minimize data copying.
921 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
925 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
926 It makes the stream pass each byte as-is without any translation.
927 In particular CRLF translation, and/or :utf8 inuited from locale
930 Arranges for all accesses go straight to the lowest buffered layer provided
931 by the configration. That is it strips off any layers above that layer.
933 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
934 referred to as a "discipline") is documented as the inverse of the
935 C<:crlf> layer. That is no longer the case - other layers which would
936 alter binary nature of the stream are also disabled. If you want UNIX
937 line endings on a platform that normally does CRLF translation, but still
938 want UTF-8 or encoding defaults the appropriate thing to do is to add
939 C<:perlio> to PERLIO environment variable.
943 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
944 library calls. The layer provides both buffering and IO.
945 Note that C<:stdio> layer does I<not> do CRLF translation even if that
946 is platforms normal behaviour. You will need a C<:crlf> layer above it
951 Lowest level layer which provides basic PerlIO operations in terms of
952 UNIX/POSIX numeric file descriptor calls
953 C<open(), read(), write(), lseek(), close()>
957 Turns on a flag on the layer below to tell perl that data sent to the
958 stream should be converted to perl internal "utf8" form and that data from the
959 stream should be considered as so encoded. On ASCII based platforms the
960 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
961 May be useful in PERLIO environment variable to make UTF-8 the
962 default. (To turn off that behaviour use C<:bytes> layer.)
966 On Win32 platforms this I<experimental> layer uses native "handle" IO
967 rather than unix-like numeric file descriptor layer. Known to be
968 buggy in this release.
972 On all platforms the default set of layers should give acceptable results.
974 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
975 Configure is setup to prefer "stdio" implementation if system's library
976 provides for fast access to the buffer, otherwise it uses the "unix perlio"
979 On Win32 the default in this release is "unix crlf". Win32's "stdio"
980 has a number of bugs/mis-features for perl IO which are somewhat
981 C compiler vendor/version dependent. Using our own C<crlf> layer as
982 the buffer avoids those issues and makes things more uniform.
983 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
986 This release uses C<unix> as the bottom layer on Win32 and so still uses C
987 compiler's numeric file descriptor routines. There is an experimental native
988 C<win32> layer which is expected to be enhanced and should eventually replace
993 If set to the name of a file or device then certain operations of PerlIO
994 sub-system will be logged to that file (opened as append). Typical uses
997 PERLIO_DEBUG=/dev/tty perl script ...
999 and Win32 approximate equivalent:
1001 set PERLIO_DEBUG=CON
1007 A colon-separated list of directories in which to look for Perl library
1008 files before looking in the standard library and the current directory.
1009 If PERL5LIB is defined, PERLLIB is not used.
1013 The command used to load the debugger code. The default is:
1015 BEGIN { require 'perl5db.pl' }
1017 =item PERL5SHELL (specific to the Win32 port)
1019 May be set to an alternative shell that perl must use internally for
1020 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1021 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1022 to be space-separated. Precede any character that needs to be protected
1023 (like a space or backslash) with a backslash.
1025 Note that Perl doesn't use COMSPEC for this purpose because
1026 COMSPEC has a high degree of variability among users, leading to
1027 portability concerns. Besides, perl can use a shell that may not be
1028 fit for interactive use, and setting COMSPEC to such a shell may
1029 interfere with the proper functioning of other programs (which usually
1030 look in COMSPEC to find a shell fit for interactive use).
1032 =item PERL_DEBUG_MSTATS
1034 Relevant only if perl is compiled with the malloc included with the perl
1035 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1036 If set, this causes memory statistics to be dumped after execution. If set
1037 to an integer greater than one, also causes memory statistics to be dumped
1040 =item PERL_DESTRUCT_LEVEL
1042 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1043 this controls the behavior of global destruction of objects and other
1044 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1048 If using the C<encoding> pragma without an explicit encoding name, the
1049 PERL_ENCODING environment variable is consulted for an encoding name.
1051 =item PERL_ROOT (specific to the VMS port)
1053 A translation concealed rooted logical name that contains perl and the
1054 logical device for the @INC path on VMS only. Other logical names that
1055 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1056 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1057 L<perlvms> and in F<README.vms> in the Perl source distribution.
1059 =item SYS$LOGIN (specific to the VMS port)
1061 Used if chdir has no argument and HOME and LOGDIR are not set.
1065 Perl also has environment variables that control how Perl handles data
1066 specific to particular natural languages. See L<perllocale>.
1068 Apart from these, Perl uses no other environment variables, except
1069 to make them available to the program being executed, and to child
1070 processes. However, programs running setuid would do well to execute
1071 the following lines before doing anything else, just to keep people
1074 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1075 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1076 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};