3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
12 S<[ B<-A>[I<module>][=I<assertions>] ]>
13 S<[ B<-C [I<number/list>] >]>
17 S<[ B<-i>[I<extension>] ]>
18 S<[ B<-eE> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
22 The normal way to run a Perl program is by making it directly
23 executable, or else by passing the name of the source file as an
24 argument on the command line. (An interactive Perl environment
25 is also possible--see L<perldebug> for details on how to do that.)
26 Upon startup, Perl looks for your program in one of the following
33 Specified line by line via B<-e> or B<-E> switches on the command line.
37 Contained in the file specified by the first filename on the command line.
38 (Note that systems supporting the #! notation invoke interpreters this
39 way. See L<Location of Perl>.)
43 Passed in implicitly via standard input. This works only if there are
44 no filename arguments--to pass arguments to a STDIN-read program you
45 must explicitly specify a "-" for the program name.
49 With methods 2 and 3, Perl starts parsing the input file from the
50 beginning, unless you've specified a B<-x> switch, in which case it
51 scans for the first line starting with #! and containing the word
52 "perl", and starts there instead. This is useful for running a program
53 embedded in a larger message. (In this case you would indicate the end
54 of the program using the C<__END__> token.)
56 The #! line is always examined for switches as the line is being
57 parsed. Thus, if you're on a machine that allows only one argument
58 with the #! line, or worse, doesn't even recognize the #! line, you
59 still can get consistent switch behavior regardless of how Perl was
60 invoked, even if B<-x> was used to find the beginning of the program.
62 Because historically some operating systems silently chopped off
63 kernel interpretation of the #! line after 32 characters, some
64 switches may be passed in on the command line, and some may not;
65 you could even get a "-" without its letter, if you're not careful.
66 You probably want to make sure that all your switches fall either
67 before or after that 32-character boundary. Most switches don't
68 actually care if they're processed redundantly, but getting a "-"
69 instead of a complete switch could cause Perl to try to execute
70 standard input instead of your program. And a partial B<-I> switch
71 could also cause odd results.
73 Some switches do care if they are processed twice, for instance
74 combinations of B<-l> and B<-0>. Either put all the switches after
75 the 32-character boundary (if applicable), or replace the use of
76 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
78 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
79 The sequences "-*" and "- " are specifically ignored so that you could,
80 if you were so inclined, say
82 #!/bin/sh -- # -*- perl -*- -p
83 eval 'exec perl -wS $0 ${1+"$@"}'
84 if $running_under_some_shell;
86 to let Perl see the B<-p> switch.
88 A similar trick involves the B<env> program, if you have it.
92 The examples above use a relative path to the perl interpreter,
93 getting whatever version is first in the user's path. If you want
94 a specific version of Perl, say, perl5.005_57, you should place
95 that directly in the #! line's path.
97 If the #! line does not contain the word "perl", the program named after
98 the #! is executed instead of the Perl interpreter. This is slightly
99 bizarre, but it helps people on machines that don't do #!, because they
100 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
101 dispatch the program to the correct interpreter for them.
103 After locating your program, Perl compiles the entire program to an
104 internal form. If there are any compilation errors, execution of the
105 program is not attempted. (This is unlike the typical shell script,
106 which might run part-way through before finding a syntax error.)
108 If the program is syntactically correct, it is executed. If the program
109 runs off the end without hitting an exit() or die() operator, an implicit
110 C<exit(0)> is provided to indicate successful completion.
112 =head2 #! and quoting on non-Unix systems
115 Unix's #! technique can be simulated on other systems:
123 extproc perl -S -your_switches
125 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
130 Create a batch file to run your program, and codify it in
131 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
132 distribution for more information).
136 The Win95/NT installation, when using the ActiveState installer for Perl,
137 will modify the Registry to associate the F<.pl> extension with the perl
138 interpreter. If you install Perl by other means (including building from
139 the sources), you may have to modify the Registry yourself. Note that
140 this means you can no longer tell the difference between an executable
141 Perl program and a Perl library file.
145 Under "Classic" MacOS, a perl program will have the appropriate Creator and
146 Type, so that double-clicking them will invoke the MacPerl application.
147 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
148 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
154 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
155 $ exit++ + ++$status != 0 and $exit = $status = undef;
157 at the top of your program, where B<-mysw> are any command line switches you
158 want to pass to Perl. You can now invoke the program directly, by saying
159 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
160 via F<DCL$PATH> by just using the name of the program).
162 This incantation is a bit much to remember, but Perl will display it for
163 you if you say C<perl "-V:startperl">.
167 Command-interpreters on non-Unix systems have rather different ideas
168 on quoting than Unix shells. You'll need to learn the special
169 characters in your command-interpreter (C<*>, C<\> and C<"> are
170 common) and how to protect whitespace and these characters to run
171 one-liners (see B<-e> below).
173 On some systems, you may have to change single-quotes to double ones,
174 which you must I<not> do on Unix or Plan 9 systems. You might also
175 have to change a single % to a %%.
180 perl -e 'print "Hello world\n"'
183 perl -e "print \"Hello world\n\""
186 print "Hello world\n"
187 (then Run "Myscript" or Shift-Command-R)
190 perl -e "print ""Hello world\n"""
192 The problem is that none of this is reliable: it depends on the
193 command and it is entirely possible neither works. If B<4DOS> were
194 the command shell, this would probably work better:
196 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
198 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
199 when nobody was looking, but just try to find documentation for its
202 Under the Macintosh, it depends which environment you are using. The MacPerl
203 shell, or MPW, is much like Unix shells in its support for several
204 quoting variants, except that it makes free use of the Macintosh's non-ASCII
205 characters as control characters.
207 There is no general solution to all of this. It's just a mess.
209 =head2 Location of Perl
210 X<perl, location of interpreter>
212 It may seem obvious to say, but Perl is useful only when users can
213 easily find it. When possible, it's good for both F</usr/bin/perl>
214 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
215 that can't be done, system administrators are strongly encouraged
216 to put (symlinks to) perl and its accompanying utilities into a
217 directory typically found along a user's PATH, or in some other
218 obvious and convenient place.
220 In this documentation, C<#!/usr/bin/perl> on the first line of the program
221 will stand in for whatever method works on your system. You are
222 advised to use a specific path if you care about a specific version.
224 #!/usr/local/bin/perl5.00554
226 or if you just want to be running at least version, place a statement
227 like this at the top of your program:
231 =head2 Command Switches
232 X<perl, command switches> X<command switches>
234 As with all standard commands, a single-character switch may be
235 clustered with the following switch, if any.
237 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
243 =item B<-0>[I<octal/hexadecimal>]
246 specifies the input record separator (C<$/>) as an octal or
247 hexadecimal number. If there are no digits, the null character is the
248 separator. Other switches may precede or follow the digits. For
249 example, if you have a version of B<find> which can print filenames
250 terminated by the null character, you can say this:
252 find . -name '*.orig' -print0 | perl -n0e unlink
254 The special value 00 will cause Perl to slurp files in paragraph mode.
255 The value 0777 will cause Perl to slurp files whole because there is no
256 legal byte with that value.
258 If you want to specify any Unicode character, use the hexadecimal
259 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
260 (This means that you cannot use the C<-x> with a directory name that
261 consists of hexadecimal digits.)
263 =item B<-A[I<module>][=I<assertions>]>
266 Activates the assertions given after the equal sign as a comma-separated
267 list of assertion names or regular expressions. If no assertion name
268 is given, activates all assertions.
270 The module L<assertions::activate> is used by default to activate the
271 selected assertions. An alternate module may be specified including
272 its name between the switch and the equal sign.
274 See L<assertions> and L<assertions::activate>.
279 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
280 split command to the @F array is done as the first thing inside the
281 implicit while loop produced by the B<-n> or B<-p>.
283 perl -ane 'print pop(@F), "\n";'
292 An alternate delimiter may be specified using B<-F>.
294 =item B<-C [I<number/list>]>
297 The C<-C> flag controls some Unicode of the Perl Unicode features.
299 As of 5.8.1, the C<-C> can be followed either by a number or a list
300 of option letters. The letters, their numeric values, and effects
301 are as follows; listing the letters is equal to summing the numbers.
303 I 1 STDIN is assumed to be in UTF-8
304 O 2 STDOUT will be in UTF-8
305 E 4 STDERR will be in UTF-8
307 i 8 UTF-8 is the default PerlIO layer for input streams
308 o 16 UTF-8 is the default PerlIO layer for output streams
310 A 32 the @ARGV elements are expected to be strings encoded
312 L 64 normally the "IOEioA" are unconditional,
313 the L makes them conditional on the locale environment
314 variables (the LC_ALL, LC_TYPE, and LANG, in the order
315 of decreasing precedence) -- if the variables indicate
316 UTF-8, then the selected "IOEioA" are in effect
318 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
319 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
322 The C<io> options mean that any subsequent open() (or similar I/O
323 operations) will have the C<:utf8> PerlIO layer implicitly applied
324 to them, in other words, UTF-8 is expected from any input stream,
325 and UTF-8 is produced to any output stream. This is just the default,
326 with explicit layers in open() and with binmode() one can manipulate
329 C<-C> on its own (not followed by any number or option list), or the
330 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
331 same effect as C<-CSDL>. In other words, the standard I/O handles and
332 the default C<open()> layer are UTF-8-fied B<but> only if the locale
333 environment variables indicate a UTF-8 locale. This behaviour follows
334 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
336 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
337 disable all the above Unicode features.
339 The read-only magic variable C<${^UNICODE}> reflects the numeric value
340 of this setting. This is variable is set during Perl startup and is
341 thereafter read-only. If you want runtime effects, use the three-arg
342 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
343 and the C<open> pragma (see L<open>).
345 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
346 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
347 This feature was practically unused, however, and the command line
348 switch was therefore "recycled".)
353 causes Perl to check the syntax of the program and then exit without
354 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
355 C<use> blocks, because these are considered as occurring outside the
356 execution of your program. C<INIT> and C<END> blocks, however, will
364 runs the program under the Perl debugger. See L<perldebug>.
365 If B<t> is specified, it indicates to the debugger that threads
366 will be used in the code being debugged.
368 =item B<-d:>I<foo[=bar,baz]>
371 =item B<-dt:>I<foo[=bar,baz]>
373 runs the program under the control of a debugging, profiling, or
374 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
375 the program using the Devel::DProf profiler. As with the B<-M>
376 flag, options may be passed to the Devel::foo package where they
377 will be received and interpreted by the Devel::foo::import routine.
378 The comma-separated list of options must follow a C<=> character.
379 If B<t> is specified, it indicates to the debugger that threads
380 will be used in the code being debugged.
383 =item B<-D>I<letters>
384 X<-D> X<DEBUGGING> X<-DDEBUGGING>
388 sets debugging flags. To watch how it executes your program, use
389 B<-Dtls>. (This works only if debugging is compiled into your
390 Perl.) Another nice value is B<-Dx>, which lists your compiled
391 syntax tree. And B<-Dr> displays compiled regular expressions;
392 the format of the output is explained in L<perldebguts>.
394 As an alternative, specify a number instead of list of letters (e.g.,
395 B<-D14> is equivalent to B<-Dtls>):
397 1 p Tokenizing and parsing (with v, displays parse stack)
398 2 s Stack snapshots (with v, displays all stacks)
399 4 l Context (loop) stack processing
401 16 o Method and overloading resolution
402 32 c String/numeric conversions
403 64 P Print profiling info, preprocessor command for -P, source file input state
404 128 m Memory allocation
405 256 f Format processing
406 512 r Regular expression parsing and execution
407 1024 x Syntax tree dump
408 2048 u Tainting checks
409 4096 (Obsolete, previously used for LEAKTEST)
410 8192 H Hash dump -- usurps values()
411 16384 X Scratchpad allocation
413 65536 S Thread synchronization
415 262144 R Include reference counts of dumped variables (eg when using -Ds)
416 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
417 1048576 v Verbose: use in conjunction with other flags
418 2097152 C Copy On Write
419 4194304 A Consistency checks on internal structures
420 8388608 q quiet - currently only suppresses the "EXECUTING" message
422 All these flags require B<-DDEBUGGING> when you compile the Perl
423 executable (but see L<Devel::Peek>, L<re> which may change this).
424 See the F<INSTALL> file in the Perl source distribution
425 for how to do this. This flag is automatically set if you include B<-g>
426 option when C<Configure> asks you about optimizer/debugger flags.
428 If you're just trying to get a print out of each line of Perl code
429 as it executes, the way that C<sh -x> provides for shell scripts,
430 you can't use Perl's B<-D> switch. Instead do this
432 # If you have "env" utility
433 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
435 # Bourne shell syntax
436 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
439 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
441 See L<perldebug> for details and variations.
443 =item B<-e> I<commandline>
446 may be used to enter one line of program. If B<-e> is given, Perl
447 will not look for a filename in the argument list. Multiple B<-e>
448 commands may be given to build up a multi-line script. Make sure
449 to use semicolons where you would in a normal program.
451 =item B<-E> I<commandline>
454 behaves just like B<-e>, except that it implicitly enables all
455 optional features (in the main compilation unit). See L<feature>.
460 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
462 Perl can be built so that it by default will try to execute
463 F<$Config{sitelib}/sitecustomize.pl> at startup. This is a hook that
464 allows the sysadmin to customize how perl behaves. It can for
465 instance be used to add entries to the @INC array to make perl find
466 modules in non-standard locations.
468 =item B<-F>I<pattern>
471 specifies the pattern to split on if B<-a> is also in effect. The
472 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
473 put in single quotes. You can't use literal whitespace in the pattern.
478 prints a summary of the options.
480 =item B<-i>[I<extension>]
483 specifies that files processed by the C<E<lt>E<gt>> construct are to be
484 edited in-place. It does this by renaming the input file, opening the
485 output file by the original name, and selecting that output file as the
486 default for print() statements. The extension, if supplied, is used to
487 modify the name of the old file to make a backup copy, following these
490 If no extension is supplied, no backup is made and the current file is
493 If the extension doesn't contain a C<*>, then it is appended to the
494 end of the current filename as a suffix. If the extension does
495 contain one or more C<*> characters, then each C<*> is replaced
496 with the current filename. In Perl terms, you could think of this
499 ($backup = $extension) =~ s/\*/$file_name/g;
501 This allows you to add a prefix to the backup file, instead of (or in
502 addition to) a suffix:
504 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
506 Or even to place backup copies of the original files into another
507 directory (provided the directory already exists):
509 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
511 These sets of one-liners are equivalent:
513 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
514 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
516 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
517 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
519 From the shell, saying
521 $ perl -p -i.orig -e "s/foo/bar/; ... "
523 is the same as using the program:
525 #!/usr/bin/perl -pi.orig
528 which is equivalent to
531 $extension = '.orig';
533 if ($ARGV ne $oldargv) {
534 if ($extension !~ /\*/) {
535 $backup = $ARGV . $extension;
538 ($backup = $extension) =~ s/\*/$ARGV/g;
540 rename($ARGV, $backup);
541 open(ARGVOUT, ">$ARGV");
548 print; # this prints to original filename
552 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
553 know when the filename has changed. It does, however, use ARGVOUT for
554 the selected filehandle. Note that STDOUT is restored as the default
555 output filehandle after the loop.
557 As shown above, Perl creates the backup file whether or not any output
558 is actually changed. So this is just a fancy way to copy files:
560 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
562 $ perl -p -i'.orig' -e 1 file1 file2 file3...
564 You can use C<eof> without parentheses to locate the end of each input
565 file, in case you want to append to each file, or reset line numbering
566 (see example in L<perlfunc/eof>).
568 If, for a given file, Perl is unable to create the backup file as
569 specified in the extension then it will skip that file and continue on
570 with the next one (if it exists).
572 For a discussion of issues surrounding file permissions and B<-i>,
573 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?>.
575 You cannot use B<-i> to create directories or to strip extensions from
578 Perl does not expand C<~> in filenames, which is good, since some
579 folks use it for their backup files:
581 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
583 Note that because B<-i> renames or deletes the original file before
584 creating a new file of the same name, UNIX-style soft and hard links will
587 Finally, the B<-i> switch does not impede execution when no
588 files are given on the command line. In this case, no backup is made
589 (the original file cannot, of course, be determined) and processing
590 proceeds from STDIN to STDOUT as might be expected.
592 =item B<-I>I<directory>
595 Directories specified by B<-I> are prepended to the search path for
596 modules (C<@INC>), and also tells the C preprocessor where to search for
597 include files. The C preprocessor is invoked with B<-P>; by default it
598 searches /usr/include and /usr/lib/perl.
600 =item B<-l>[I<octnum>]
603 enables automatic line-ending processing. It has two separate
604 effects. First, it automatically chomps C<$/> (the input record
605 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
606 (the output record separator) to have the value of I<octnum> so
607 that any print statements will have that separator added back on.
608 If I<octnum> is omitted, sets C<$\> to the current value of
609 C<$/>. For instance, to trim lines to 80 columns:
611 perl -lpe 'substr($_, 80) = ""'
613 Note that the assignment C<$\ = $/> is done when the switch is processed,
614 so the input record separator can be different than the output record
615 separator if the B<-l> switch is followed by a B<-0> switch:
617 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
619 This sets C<$\> to newline and then sets C<$/> to the null character.
621 =item B<-m>[B<->]I<module>
624 =item B<-M>[B<->]I<module>
626 =item B<-M>[B<->]I<'module ...'>
628 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
630 B<-m>I<module> executes C<use> I<module> C<();> before executing your
633 B<-M>I<module> executes C<use> I<module> C<;> before executing your
634 program. You can use quotes to add extra code after the module name,
635 e.g., C<'-Mmodule qw(foo bar)'>.
637 If the first character after the B<-M> or B<-m> is a dash (C<->)
638 then the 'use' is replaced with 'no'.
640 A little builtin syntactic sugar means you can also say
641 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
642 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
643 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
644 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
645 removes the distinction between B<-m> and B<-M>.
647 A consequence of this is that B<-MFoo=number> never does a version check
648 (unless C<Foo::import()> itself is set up to do a version check, which
649 could happen for example if Foo inherits from Exporter.)
654 causes Perl to assume the following loop around your program, which
655 makes it iterate over filename arguments somewhat like B<sed -n> or
660 ... # your program goes here
663 Note that the lines are not printed by default. See B<-p> to have
664 lines printed. If a file named by an argument cannot be opened for
665 some reason, Perl warns you about it and moves on to the next file.
667 Here is an efficient way to delete all files that haven't been modified for
670 find . -mtime +7 -print | perl -nle unlink
672 This is faster than using the B<-exec> switch of B<find> because you don't
673 have to start a process on every filename found. It does suffer from
674 the bug of mishandling newlines in pathnames, which you can fix if
675 you follow the example under B<-0>.
677 C<BEGIN> and C<END> blocks may be used to capture control before or after
678 the implicit program loop, just as in B<awk>.
683 causes Perl to assume the following loop around your program, which
684 makes it iterate over filename arguments somewhat like B<sed>:
689 ... # your program goes here
691 print or die "-p destination: $!\n";
694 If a file named by an argument cannot be opened for some reason, Perl
695 warns you about it, and moves on to the next file. Note that the
696 lines are printed automatically. An error occurring during printing is
697 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
698 overrides a B<-n> switch.
700 C<BEGIN> and C<END> blocks may be used to capture control before or after
701 the implicit loop, just as in B<awk>.
706 B<NOTE: Use of -P is strongly discouraged because of its inherent
707 problems, including poor portability.>
709 This option causes your program to be run through the C preprocessor before
710 compilation by Perl. Because both comments and B<cpp> directives begin
711 with the # character, you should avoid starting comments with any words
712 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
714 If you're considering using C<-P>, you might also want to look at the
715 Filter::cpp module from CPAN.
717 The problems of -P include, but are not limited to:
723 The C<#!> line is stripped, so any switches there don't apply.
727 A C<-P> on a C<#!> line doesn't work.
731 B<All> lines that begin with (whitespace and) a C<#> but
732 do not look like cpp commands, are stripped, including anything
733 inside Perl strings, regular expressions, and here-docs .
737 In some platforms the C preprocessor knows too much: it knows about
738 the C++ -style until-end-of-line comments starting with C<"//">.
739 This will cause problems with common Perl constructs like
743 because after -P this will became illegal code
747 The workaround is to use some other quoting separator than C<"/">,
748 like for example C<"!">:
756 It requires not only a working C preprocessor but also a working
757 F<sed>. If not on UNIX, you are probably out of luck on this.
761 Script line numbers are not preserved.
765 The C<-x> does not work with C<-P>.
772 enables rudimentary switch parsing for switches on the command
773 line after the program name but before any filename arguments (or before
774 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
775 corresponding variable in the Perl program. The following program
776 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
777 if it is invoked with B<-xyz=abc>.
780 if ($xyz) { print "$xyz\n" }
782 Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
783 with C<strict refs>. Also, when using this option on a script with
784 warnings enabled you may get a lot of spurious "used only once" warnings.
789 makes Perl use the PATH environment variable to search for the
790 program (unless the name of the program contains directory separators).
792 On some platforms, this also makes Perl append suffixes to the
793 filename while searching for it. For example, on Win32 platforms,
794 the ".bat" and ".cmd" suffixes are appended if a lookup for the
795 original name fails, and if the name does not already end in one
796 of those suffixes. If your Perl was compiled with DEBUGGING turned
797 on, using the -Dp switch to Perl shows how the search progresses.
799 Typically this is used to emulate #! startup on platforms that don't
800 support #!. Its also convenient when debugging a script that uses #!,
801 and is thus normally found by the shell's $PATH search mechanism.
803 This example works on many platforms that have a shell compatible with
807 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
808 if $running_under_some_shell;
810 The system ignores the first line and feeds the program to F</bin/sh>,
811 which proceeds to try to execute the Perl program as a shell script.
812 The shell executes the second line as a normal shell command, and thus
813 starts up the Perl interpreter. On some systems $0 doesn't always
814 contain the full pathname, so the B<-S> tells Perl to search for the
815 program if necessary. After Perl locates the program, it parses the
816 lines and ignores them because the variable $running_under_some_shell
817 is never true. If the program will be interpreted by csh, you will need
818 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
819 embedded spaces (and such) in the argument list. To start up sh rather
820 than csh, some systems may have to replace the #! line with a line
821 containing just a colon, which will be politely ignored by Perl. Other
822 systems can't control that, and need a totally devious construct that
823 will work under any of B<csh>, B<sh>, or Perl, such as the following:
825 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
826 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
827 if $running_under_some_shell;
829 If the filename supplied contains directory separators (i.e., is an
830 absolute or relative pathname), and if that file is not found,
831 platforms that append file extensions will do so and try to look
832 for the file with those extensions added, one by one.
834 On DOS-like platforms, if the program does not contain directory
835 separators, it will first be searched for in the current directory
836 before being searched for on the PATH. On Unix platforms, the
837 program will be searched for strictly on the PATH.
842 Like B<-T>, but taint checks will issue warnings rather than fatal
843 errors. These warnings can be controlled normally with C<no warnings
846 B<NOTE: this is not a substitute for -T.> This is meant only to be
847 used as a temporary development aid while securing legacy code:
848 for real production code and for new secure code written from scratch
849 always use the real B<-T>.
854 forces "taint" checks to be turned on so you can test them. Ordinarily
855 these checks are done only when running setuid or setgid. It's a
856 good idea to turn them on explicitly for programs that run on behalf
857 of someone else whom you might not necessarily trust, such as CGI
858 programs or any internet servers you might write in Perl. See
859 L<perlsec> for details. For security reasons, this option must be
860 seen by Perl quite early; usually this means it must appear early
861 on the command line or in the #! line for systems which support
867 This obsolete switch causes Perl to dump core after compiling your
868 program. You can then in theory take this core dump and turn it
869 into an executable file by using the B<undump> program (not supplied).
870 This speeds startup at the expense of some disk space (which you
871 can minimize by stripping the executable). (Still, a "hello world"
872 executable comes out to about 200K on my machine.) If you want to
873 execute a portion of your program before dumping, use the dump()
874 operator instead. Note: availability of B<undump> is platform
875 specific and may not be available for a specific port of Perl.
877 This switch has been superseded in favor of the new Perl code
878 generator backends to the compiler. See L<B> and L<B::Bytecode>
884 allows Perl to do unsafe operations. Currently the only "unsafe"
885 operations are attempting to unlink directories while running as
886 superuser, and running setuid programs with fatal taint checks turned
887 into warnings. Note that the B<-w> switch (or the C<$^W> variable)
888 must be used along with this option to actually I<generate> the
889 taint-check warnings.
894 prints the version and patchlevel of your perl executable.
899 prints summary of the major perl configuration values and the current
902 =item B<-V:>I<configvar>
904 Prints to STDOUT the value of the named configuration variable(s),
905 with multiples when your configvar argument looks like a regex (has
906 non-letters). For example:
909 libc='/lib/libc-2.2.4.so';
911 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
912 libc='/lib/libc-2.2.4.so';
914 libpth='/usr/local/lib /lib /usr/lib';
915 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
917 libc='/lib/libc-2.2.4.so';
921 Additionally, extra colons can be used to control formatting. A
922 trailing colon suppresses the linefeed and terminator ';', allowing
923 you to embed queries into shell commands. (mnemonic: PATH separator
926 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
927 compression-vars: zcat='' zip='zip' are here !
929 A leading colon removes the 'name=' part of the response, this allows
930 you to map to the name you need. (mnemonic: empty label)
932 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
935 Leading and trailing colons can be used together if you need
936 positional parameter values without the names. Note that in the case
937 below, the PERL_API params are returned in alphabetical order.
939 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
940 building_on 'linux' '5' '1' '9' now
945 prints warnings about dubious constructs, such as variable names
946 that are mentioned only once and scalar variables that are used
947 before being set, redefined subroutines, references to undefined
948 filehandles or filehandles opened read-only that you are attempting
949 to write on, values used as a number that don't look like numbers,
950 using an array as though it were a scalar, if your subroutines
951 recurse more than 100 deep, and innumerable other things.
953 This switch really just enables the internal C<$^W> variable. You
954 can disable or promote into fatal errors specific warnings using
955 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
956 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
957 facility is also available if you want to manipulate entire classes
958 of warnings; see L<warnings> or L<perllexwarn>.
963 Enables all warnings regardless of C<no warnings> or C<$^W>.
969 Disables all warnings regardless of C<use warnings> or C<$^W>.
975 =item B<-x> I<directory>
977 tells Perl that the program is embedded in a larger chunk of unrelated
978 ASCII text, such as in a mail message. Leading garbage will be
979 discarded until the first line that starts with #! and contains the
980 string "perl". Any meaningful switches on that line will be applied.
981 If a directory name is specified, Perl will switch to that directory
982 before running the program. The B<-x> switch controls only the
983 disposal of leading garbage. The program must be terminated with
984 C<__END__> if there is trailing garbage to be ignored (the program
985 can process any or all of the trailing garbage via the DATA filehandle
991 X<perl, environment variables>
998 Used if chdir has no argument.
1003 Used if chdir has no argument and HOME is not set.
1008 Used in executing subprocesses, and in finding the program if B<-S> is
1014 A list of directories in which to look for Perl library
1015 files before looking in the standard library and the current
1016 directory. Any architecture-specific directories under the specified
1017 locations are automatically included if they exist. If PERL5LIB is not
1018 defined, PERLLIB is used. Directories are separated (like in PATH) by
1019 a colon on unixish platforms and by a semicolon on Windows (the proper
1020 path separator being given by the command C<perl -V:path_sep>).
1022 When running taint checks (either because the program was running setuid
1023 or setgid, or the B<-T> switch was used), neither variable is used.
1024 The program should instead say:
1026 use lib "/my/directory";
1031 Command-line options (switches). Switches in this variable are taken
1032 as if they were on every Perl command line. Only the B<-[CDIMUdmtwA]>
1033 switches are allowed. When running taint checks (because the program
1034 was running setuid or setgid, or the B<-T> switch was used), this
1035 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
1036 enabled, and any subsequent options ignored.
1041 A space (or colon) separated list of PerlIO layers. If perl is built
1042 to use PerlIO system for IO (the default) these layers effect perl's IO.
1044 It is conventional to start layer names with a colon e.g. C<:perlio> to
1045 emphasise their similarity to variable "attributes". But the code that parses
1046 layer specification strings (which is also used to decode the PERLIO
1047 environment variable) treats the colon as a separator.
1049 An unset or empty PERLIO is equivalent to C<:stdio>.
1051 The list becomes the default for I<all> perl's IO. Consequently only built-in
1052 layers can appear in this list, as external layers (such as :encoding()) need
1053 IO in order to load them!. See L<"open pragma"|open> for how to add external
1054 encodings as defaults.
1056 The layers that it makes sense to include in the PERLIO environment
1057 variable are briefly summarised below. For more details see L<PerlIO>.
1064 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1065 Unlikely to be useful on its own in the global PERLIO environment variable.
1066 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1071 A layer which does CRLF to "\n" translation distinguishing "text" and
1072 "binary" files in the manner of MS-DOS and similar operating systems.
1073 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1074 as being an end-of-file marker.)
1079 A layer which implements "reading" of files by using C<mmap()> to
1080 make (whole) file appear in the process's address space, and then
1081 using that as PerlIO's "buffer".
1086 This is a re-implementation of "stdio-like" buffering written as a
1087 PerlIO "layer". As such it will call whatever layer is below it for
1088 its operations (typically C<:unix>).
1093 An experimental pseudolayer that removes the topmost layer.
1094 Use with the same care as is reserved for nitroglycerin.
1099 A pseudolayer that manipulates other layers. Applying the C<:raw>
1100 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1101 pass each byte as-is without any translation. In particular CRLF
1102 translation, and/or :utf8 intuited from locale are disabled.
1104 Unlike in the earlier versions of Perl C<:raw> is I<not>
1105 just the inverse of C<:crlf> - other layers which would affect the
1106 binary nature of the stream are also removed or disabled.
1111 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1112 library calls. The layer provides both buffering and IO.
1113 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1114 is platforms normal behaviour. You will need a C<:crlf> layer above it
1120 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1125 A pseudolayer that turns on a flag on the layer below to tell perl
1126 that output should be in utf8 and that input should be regarded as
1127 already in utf8 form. May be useful in PERLIO environment
1128 variable to make UTF-8 the default. (To turn off that behaviour
1129 use C<:bytes> layer.)
1134 On Win32 platforms this I<experimental> layer uses native "handle" IO
1135 rather than unix-like numeric file descriptor layer. Known to be
1136 buggy in this release.
1140 On all platforms the default set of layers should give acceptable results.
1142 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1143 Configure is setup to prefer "stdio" implementation if system's library
1144 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1147 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1148 has a number of bugs/mis-features for perl IO which are somewhat
1149 C compiler vendor/version dependent. Using our own C<crlf> layer as
1150 the buffer avoids those issues and makes things more uniform.
1151 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1154 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1155 compiler's numeric file descriptor routines. There is an experimental native
1156 C<win32> layer which is expected to be enhanced and should eventually be
1157 the default under Win32.
1162 If set to the name of a file or device then certain operations of PerlIO
1163 sub-system will be logged to that file (opened as append). Typical uses
1166 PERLIO_DEBUG=/dev/tty perl script ...
1168 and Win32 approximate equivalent:
1170 set PERLIO_DEBUG=CON
1173 This functionality is disabled for setuid scripts and for scripts run
1179 A list of directories in which to look for Perl library
1180 files before looking in the standard library and the current directory.
1181 If PERL5LIB is defined, PERLLIB is not used.
1186 The command used to load the debugger code. The default is:
1188 BEGIN { require 'perl5db.pl' }
1190 =item PERL5DB_THREADED
1193 If set to a true value, indicates to the debugger that the code being
1194 debugged uses threads.
1196 =item PERL5SHELL (specific to the Win32 port)
1199 May be set to an alternative shell that perl must use internally for
1200 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1201 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1202 to be space-separated. Precede any character that needs to be protected
1203 (like a space or backslash) with a backslash.
1205 Note that Perl doesn't use COMSPEC for this purpose because
1206 COMSPEC has a high degree of variability among users, leading to
1207 portability concerns. Besides, perl can use a shell that may not be
1208 fit for interactive use, and setting COMSPEC to such a shell may
1209 interfere with the proper functioning of other programs (which usually
1210 look in COMSPEC to find a shell fit for interactive use).
1212 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1213 X<PERL_ALLOW_NON_IFS_LSP>
1215 Set to 1 to allow the use of non-IFS compatible LSP's.
1216 Perl normally searches for an IFS-compatible LSP because this is required
1217 for its emulation of Windows sockets as real filehandles. However, this may
1218 cause problems if you have a firewall such as McAfee Guardian which requires
1219 all applications to use its LSP which is not IFS-compatible, because clearly
1220 Perl will normally avoid using such an LSP.
1221 Setting this environment variable to 1 means that Perl will simply use the
1222 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1223 happy (and in that particular case Perl still works too because McAfee
1224 Guardian's LSP actually plays some other games which allow applications
1225 requiring IFS compatibility to work).
1227 =item PERL_DEBUG_MSTATS
1228 X<PERL_DEBUG_MSTATS>
1230 Relevant only if perl is compiled with the malloc included with the perl
1231 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1232 If set, this causes memory statistics to be dumped after execution. If set
1233 to an integer greater than one, also causes memory statistics to be dumped
1236 =item PERL_DESTRUCT_LEVEL
1237 X<PERL_DESTRUCT_LEVEL>
1239 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1240 this controls the behavior of global destruction of objects and other
1241 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1243 =item PERL_DL_NONLAZY
1246 Set to one to have perl resolve B<all> undefined symbols when it loads
1247 a dynamic library. The default behaviour is to resolve symbols when
1248 they are used. Setting this variable is useful during testing of
1249 extensions as it ensures that you get an error on misspelled function
1250 names even if the test suite doesn't call it.
1255 If using the C<encoding> pragma without an explicit encoding name, the
1256 PERL_ENCODING environment variable is consulted for an encoding name.
1258 =item PERL_HASH_SEED
1261 (Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
1262 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1263 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1264 things, that hash keys will be ordered the same between different runs
1267 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1268 If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1269 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1271 If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1272 the pseudorandom seed supplied by the operating system and libraries.
1273 This means that each different run of Perl will have a different
1274 ordering of the results of keys(), values(), and each().
1276 B<Please note that the hash seed is sensitive information>. Hashes are
1277 randomized to protect against local and remote attacks against Perl
1278 code. By manually setting a seed this protection may be partially or
1281 See L<perlsec/"Algorithmic Complexity Attacks"> and
1282 L</PERL_HASH_SEED_DEBUG> for more information.
1284 =item PERL_HASH_SEED_DEBUG
1285 X<PERL_HASH_SEED_DEBUG>
1287 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1288 the hash seed at the beginning of execution. This, combined with
1289 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1290 behavior caused by hash randomization.
1292 B<Note that the hash seed is sensitive information>: by knowing it one
1293 can craft a denial-of-service attack against Perl code, even remotely,
1294 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1295 B<Do not disclose the hash seed> to people who don't need to know it.
1296 See also hash_seed() of L<Hash::Util>.
1298 =item PERL_ROOT (specific to the VMS port)
1301 A translation concealed rooted logical name that contains perl and the
1302 logical device for the @INC path on VMS only. Other logical names that
1303 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1304 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1305 L<perlvms> and in F<README.vms> in the Perl source distribution.
1310 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1311 signals behaviour (immediate but unsafe) is restored. If set to
1312 C<safe> the safe (or deferred) signals are used.
1313 See L<perlipc/"Deferred Signals (Safe Signals)">.
1318 Equivalent to the B<-C> command-line switch. Note that this is not
1319 a boolean variable-- setting this to C<"1"> is not the right way to
1320 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1321 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1322 your shell before starting Perl). See the description of the C<-C>
1323 switch for more information.
1325 =item SYS$LOGIN (specific to the VMS port)
1328 Used if chdir has no argument and HOME and LOGDIR are not set.
1332 Perl also has environment variables that control how Perl handles data
1333 specific to particular natural languages. See L<perllocale>.
1335 Apart from these, Perl uses no other environment variables, except
1336 to make them available to the program being executed, and to child
1337 processes. However, programs running setuid would do well to execute
1338 the following lines before doing anything else, just to keep people
1341 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1342 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1343 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};