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>[: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> ]...>
17 S<[ B<-C [I<number/list>] >]> ]>
21 The normal way to run a Perl program is by making it directly
22 executable, or else by passing the name of the source file as an
23 argument on the command line. (An interactive Perl environment
24 is also possible--see L<perldebug> for details on how to do that.)
25 Upon startup, Perl looks for your program in one of the following
32 Specified line by line via B<-e> switches on the command line.
36 Contained in the file specified by the first filename on the command line.
37 (Note that systems supporting the #! notation invoke interpreters this
38 way. See L<Location of Perl>.)
42 Passed in implicitly via standard input. This works only if there are
43 no filename arguments--to pass arguments to a STDIN-read program you
44 must explicitly specify a "-" for the program name.
48 With methods 2 and 3, Perl starts parsing the input file from the
49 beginning, unless you've specified a B<-x> switch, in which case it
50 scans for the first line starting with #! and containing the word
51 "perl", and starts there instead. This is useful for running a program
52 embedded in a larger message. (In this case you would indicate the end
53 of the program using the C<__END__> token.)
55 The #! line is always examined for switches as the line is being
56 parsed. Thus, if you're on a machine that allows only one argument
57 with the #! line, or worse, doesn't even recognize the #! line, you
58 still can get consistent switch behavior regardless of how Perl was
59 invoked, even if B<-x> was used to find the beginning of the program.
61 Because historically some operating systems silently chopped off
62 kernel interpretation of the #! line after 32 characters, some
63 switches may be passed in on the command line, and some may not;
64 you could even get a "-" without its letter, if you're not careful.
65 You probably want to make sure that all your switches fall either
66 before or after that 32-character boundary. Most switches don't
67 actually care if they're processed redundantly, but getting a "-"
68 instead of a complete switch could cause Perl to try to execute
69 standard input instead of your program. And a partial B<-I> switch
70 could also cause odd results.
72 Some switches do care if they are processed twice, for instance
73 combinations of B<-l> and B<-0>. Either put all the switches after
74 the 32-character boundary (if applicable), or replace the use of
75 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
77 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
78 The sequences "-*" and "- " are specifically ignored so that you could,
79 if you were so inclined, say
81 #!/bin/sh -- # -*- perl -*- -p
82 eval 'exec perl -wS $0 ${1+"$@"}'
83 if $running_under_some_shell;
85 to let Perl see the B<-p> switch.
87 A similar trick involves the B<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.005_57, you should place
94 that directly in the #! line's path.
96 If the #! line does not contain the word "perl", the program named after
97 the #! is executed instead of the Perl interpreter. This is slightly
98 bizarre, but it helps people on machines that don't do #!, because they
99 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
100 dispatch the program to the correct interpreter for them.
102 After locating your program, Perl compiles the entire program to an
103 internal form. If there are any compilation errors, execution of the
104 program is not attempted. (This is unlike the typical shell script,
105 which might run part-way through before finding a syntax error.)
107 If the program is syntactically correct, it is executed. If the program
108 runs off the end without hitting an exit() or die() operator, an implicit
109 C<exit(0)> is provided to indicate successful completion.
111 =head2 #! and quoting on non-Unix systems
113 Unix's #! technique can be simulated on other systems:
121 extproc perl -S -your_switches
123 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
128 Create a batch file to run your program, and codify it in
129 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
130 distribution for more information).
134 The Win95/NT installation, when using the ActiveState installer for Perl,
135 will modify the Registry to associate the F<.pl> extension with the perl
136 interpreter. If you install Perl by other means (including building from
137 the sources), you may have to modify the Registry yourself. Note that
138 this means you can no longer tell the difference between an executable
139 Perl program and a Perl library file.
143 A Macintosh perl program will have the appropriate Creator and
144 Type, so that double-clicking them will invoke the perl application.
150 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
151 $ exit++ + ++$status != 0 and $exit = $status = undef;
153 at the top of your program, where B<-mysw> are any command line switches you
154 want to pass to Perl. You can now invoke the program directly, by saying
155 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
156 via F<DCL$PATH> by just using the name of the program).
158 This incantation is a bit much to remember, but Perl will display it for
159 you if you say C<perl "-V:startperl">.
163 Command-interpreters on non-Unix systems have rather different ideas
164 on quoting than Unix shells. You'll need to learn the special
165 characters in your command-interpreter (C<*>, C<\> and C<"> are
166 common) and how to protect whitespace and these characters to run
167 one-liners (see B<-e> below).
169 On some systems, you may have to change single-quotes to double ones,
170 which you must I<not> do on Unix or Plan 9 systems. You might also
171 have to change a single % to a %%.
176 perl -e 'print "Hello world\n"'
179 perl -e "print \"Hello world\n\""
182 print "Hello world\n"
183 (then Run "Myscript" or Shift-Command-R)
186 perl -e "print ""Hello world\n"""
188 The problem is that none of this is reliable: it depends on the
189 command and it is entirely possible neither works. If B<4DOS> were
190 the command shell, this would probably work better:
192 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
194 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
195 when nobody was looking, but just try to find documentation for its
198 Under the Macintosh, it depends which environment you are using. The MacPerl
199 shell, or MPW, is much like Unix shells in its support for several
200 quoting variants, except that it makes free use of the Macintosh's non-ASCII
201 characters as control characters.
203 There is no general solution to all of this. It's just a mess.
205 =head2 Location of Perl
207 It may seem obvious to say, but Perl is useful only when users can
208 easily find it. When possible, it's good for both F</usr/bin/perl>
209 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
210 that can't be done, system administrators are strongly encouraged
211 to put (symlinks to) perl and its accompanying utilities into a
212 directory typically found along a user's PATH, or in some other
213 obvious and convenient place.
215 In this documentation, C<#!/usr/bin/perl> on the first line of the program
216 will stand in for whatever method works on your system. You are
217 advised to use a specific path if you care about a specific version.
219 #!/usr/local/bin/perl5.00554
221 or if you just want to be running at least version, place a statement
222 like this at the top of your program:
226 =head2 Command Switches
228 As with all standard commands, a single-character switch may be
229 clustered with the following switch, if any.
231 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
237 =item B<-0>[I<digits>]
239 specifies the input record separator (C<$/>) as an octal number. If there are
240 no digits, the null character is the separator. Other switches may
241 precede or follow the digits. For example, if you have a version of
242 B<find> which can print filenames terminated by the null character, you
245 find . -name '*.orig' -print0 | perl -n0e unlink
247 The special value 00 will cause Perl to slurp files in paragraph mode.
248 The value 0777 will cause Perl to slurp files whole because there is no
249 legal character with that value.
253 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
254 split command to the @F array is done as the first thing inside the
255 implicit while loop produced by the B<-n> or B<-p>.
257 perl -ane 'print pop(@F), "\n";'
266 An alternate delimiter may be specified using B<-F>.
268 =item B<-C [I<number/list>]>
270 The C<-C> flag controls some Unicode of the Perl Unicode features.
272 As of 5.8.1, the C<-C> can be followed either by a number or a list
273 of option letters. The letters and their numeric values are as follows;
274 listing the letters is equal to summing the numbers.
276 I 1 STDIN is assumed to be in UTF-8
277 O 2 STDOUT will be in UTF-8
278 E 4 STDERR will be in UTF-8
280 i 8 the default input layer expects UTF-8
281 o 16 the default output layer enforces UTF-8
283 A 32 the @ARGV elements are supposed to be in UTF-8
284 L 64 normally the "IOEioA" are unconditional,
285 the L makes them conditional on the locale environment
286 variables (the LC_ALL, LC_TYPE, and LANG, in the order
287 of decreasing precedence) -- if the variables indicate
288 UTF-8, then the selected "IOEioA" are in effect
290 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
291 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
294 The C<-C> on its own (not followed by any number or option list),
295 or an empty string as the C<$ENV{PERL_UNICODE}), has the same effect
296 as <-CSDL>. In other words, the standard I/O handles and the default
297 C<open()> layer are UTF-8-fied B<but> only if the locale environment
298 variables indicate a UTF-8 locale. This behavior follows the I<implicit>
299 UTF-8 behaviour of Perl 5.8.0.
301 You can use C<-C0> to explicitly disable all the above Unicode features.
303 See L<perluniintro>, L<perlfunc/open>, and L<open> for more information.
305 The read-only magic variable C<${^UNICODE}> reflects the state of this
306 setting, see L<perlvar/"${^UNICODE}">. (Another way of setting this
307 variable is to set the environment variable PERL_UNICODE.)
309 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
310 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
311 This feature was practically unused, however, and the command line
312 switch was therefore "recycled".)
316 causes Perl to check the syntax of the program and then exit without
317 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
318 C<use> blocks, because these are considered as occurring outside the
319 execution of your program. C<INIT> and C<END> blocks, however, will
324 runs the program under the Perl debugger. See L<perldebug>.
326 =item B<-d:>I<foo[=bar,baz]>
328 runs the program under the control of a debugging, profiling, or
329 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
330 the program using the Devel::DProf profiler. As with the B<-M>
331 flag, options may be passed to the Devel::foo package where they
332 will be received and interpreted by the Devel::foo::import routine.
333 The comma-separated list of options must follow a C<=> character.
336 =item B<-D>I<letters>
340 sets debugging flags. To watch how it executes your program, use
341 B<-Dtls>. (This works only if debugging is compiled into your
342 Perl.) Another nice value is B<-Dx>, which lists your compiled
343 syntax tree. And B<-Dr> displays compiled regular expressions;
344 the format of the output is explained in L<perldebguts>.
346 As an alternative, specify a number instead of list of letters (e.g.,
347 B<-D14> is equivalent to B<-Dtls>):
349 1 p Tokenizing and parsing
351 with v, displays all stacks
352 4 l Context (loop) stack processing
354 16 o Method and overloading resolution
355 32 c String/numeric conversions
356 64 P Print profiling info, preprocessor command for -P, source file input state
357 128 m Memory allocation
358 256 f Format processing
359 512 r Regular expression parsing and execution
360 1024 x Syntax tree dump
361 2048 u Tainting checks
362 4096 (Obsolete, previously used for LEAKTEST)
363 8192 H Hash dump -- usurps values()
364 16384 X Scratchpad allocation
366 65536 S Thread synchronization
368 262144 R Include reference counts of dumped variables (eg when using -Ds)
369 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
370 1048576 v Verbose: use in conjunction with other flags
371 2097152 C Copy On Write
373 All these flags require B<-DDEBUGGING> when you compile the Perl
374 executable (but see L<Devel::Peek>, L<re> which may change this).
375 See the F<INSTALL> file in the Perl source distribution
376 for how to do this. This flag is automatically set if you include B<-g>
377 option when C<Configure> asks you about optimizer/debugger flags.
379 If you're just trying to get a print out of each line of Perl code
380 as it executes, the way that C<sh -x> provides for shell scripts,
381 you can't use Perl's B<-D> switch. Instead do this
383 # If you have "env" utility
384 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
386 # Bourne shell syntax
387 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
390 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
392 See L<perldebug> for details and variations.
394 =item B<-e> I<commandline>
396 may be used to enter one line of program. If B<-e> is given, Perl
397 will not look for a filename in the argument list. Multiple B<-e>
398 commands may be given to build up a multi-line script. Make sure
399 to use semicolons where you would in a normal program.
401 =item B<-F>I<pattern>
403 specifies the pattern to split on if B<-a> is also in effect. The
404 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
405 put in single quotes.
409 prints a summary of the options.
411 =item B<-i>[I<extension>]
413 specifies that files processed by the C<E<lt>E<gt>> construct are to be
414 edited in-place. It does this by renaming the input file, opening the
415 output file by the original name, and selecting that output file as the
416 default for print() statements. The extension, if supplied, is used to
417 modify the name of the old file to make a backup copy, following these
420 If no extension is supplied, no backup is made and the current file is
423 If the extension doesn't contain a C<*>, then it is appended to the
424 end of the current filename as a suffix. If the extension does
425 contain one or more C<*> characters, then each C<*> is replaced
426 with the current filename. In Perl terms, you could think of this
429 ($backup = $extension) =~ s/\*/$file_name/g;
431 This allows you to add a prefix to the backup file, instead of (or in
432 addition to) a suffix:
434 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
436 Or even to place backup copies of the original files into another
437 directory (provided the directory already exists):
439 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
441 These sets of one-liners are equivalent:
443 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
444 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
446 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
447 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
449 From the shell, saying
451 $ perl -p -i.orig -e "s/foo/bar/; ... "
453 is the same as using the program:
455 #!/usr/bin/perl -pi.orig
458 which is equivalent to
461 $extension = '.orig';
463 if ($ARGV ne $oldargv) {
464 if ($extension !~ /\*/) {
465 $backup = $ARGV . $extension;
468 ($backup = $extension) =~ s/\*/$ARGV/g;
470 rename($ARGV, $backup);
471 open(ARGVOUT, ">$ARGV");
478 print; # this prints to original filename
482 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
483 know when the filename has changed. It does, however, use ARGVOUT for
484 the selected filehandle. Note that STDOUT is restored as the default
485 output filehandle after the loop.
487 As shown above, Perl creates the backup file whether or not any output
488 is actually changed. So this is just a fancy way to copy files:
490 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
492 $ perl -p -i'.orig' -e 1 file1 file2 file3...
494 You can use C<eof> without parentheses to locate the end of each input
495 file, in case you want to append to each file, or reset line numbering
496 (see example in L<perlfunc/eof>).
498 If, for a given file, Perl is unable to create the backup file as
499 specified in the extension then it will skip that file and continue on
500 with the next one (if it exists).
502 For a discussion of issues surrounding file permissions and B<-i>,
503 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?>.
505 You cannot use B<-i> to create directories or to strip extensions from
508 Perl does not expand C<~> in filenames, which is good, since some
509 folks use it for their backup files:
511 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
513 Finally, the B<-i> switch does not impede execution when no
514 files are given on the command line. In this case, no backup is made
515 (the original file cannot, of course, be determined) and processing
516 proceeds from STDIN to STDOUT as might be expected.
518 =item B<-I>I<directory>
520 Directories specified by B<-I> are prepended to the search path for
521 modules (C<@INC>), and also tells the C preprocessor where to search for
522 include files. The C preprocessor is invoked with B<-P>; by default it
523 searches /usr/include and /usr/lib/perl.
525 =item B<-l>[I<octnum>]
527 enables automatic line-ending processing. It has two separate
528 effects. First, it automatically chomps C<$/> (the input record
529 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
530 (the output record separator) to have the value of I<octnum> so
531 that any print statements will have that separator added back on.
532 If I<octnum> is omitted, sets C<$\> to the current value of
533 C<$/>. For instance, to trim lines to 80 columns:
535 perl -lpe 'substr($_, 80) = ""'
537 Note that the assignment C<$\ = $/> is done when the switch is processed,
538 so the input record separator can be different than the output record
539 separator if the B<-l> switch is followed by a B<-0> switch:
541 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
543 This sets C<$\> to newline and then sets C<$/> to the null character.
545 =item B<-m>[B<->]I<module>
547 =item B<-M>[B<->]I<module>
549 =item B<-M>[B<->]I<'module ...'>
551 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
553 B<-m>I<module> executes C<use> I<module> C<();> before executing your
556 B<-M>I<module> executes C<use> I<module> C<;> before executing your
557 program. You can use quotes to add extra code after the module name,
558 e.g., C<'-Mmodule qw(foo bar)'>.
560 If the first character after the B<-M> or B<-m> is a dash (C<->)
561 then the 'use' is replaced with 'no'.
563 A little builtin syntactic sugar means you can also say
564 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
565 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
566 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
567 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
568 removes the distinction between B<-m> and B<-M>.
572 causes Perl to assume the following loop around your program, which
573 makes it iterate over filename arguments somewhat like B<sed -n> or
578 ... # your program goes here
581 Note that the lines are not printed by default. See B<-p> to have
582 lines printed. If a file named by an argument cannot be opened for
583 some reason, Perl warns you about it and moves on to the next file.
585 Here is an efficient way to delete all files older than a week:
587 find . -mtime +7 -print | perl -nle unlink
589 This is faster than using the B<-exec> switch of B<find> because you don't
590 have to start a process on every filename found. It does suffer from
591 the bug of mishandling newlines in pathnames, which you can fix if
592 you follow the example under B<-0>.
594 C<BEGIN> and C<END> blocks may be used to capture control before or after
595 the implicit program loop, just as in B<awk>.
599 causes Perl to assume the following loop around your program, which
600 makes it iterate over filename arguments somewhat like B<sed>:
605 ... # your program goes here
607 print or die "-p destination: $!\n";
610 If a file named by an argument cannot be opened for some reason, Perl
611 warns you about it, and moves on to the next file. Note that the
612 lines are printed automatically. An error occurring during printing is
613 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
614 overrides a B<-n> switch.
616 C<BEGIN> and C<END> blocks may be used to capture control before or after
617 the implicit loop, just as in B<awk>.
621 B<NOTE: Use of -P is strongly discouraged because of its inherent
622 problems, including poor portability.>
624 This option causes your program to be run through the C preprocessor before
625 compilation by Perl. Because both comments and B<cpp> directives begin
626 with the # character, you should avoid starting comments with any words
627 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
629 If you're considering using C<-P>, you might also want to look at the
630 Filter::cpp module from CPAN.
632 The problems of -P include, but are not limited to:
638 The C<#!> line is stripped, so any switches there don't apply.
642 A C<-P> on a C<#!> line doesn't work.
646 B<All> lines that begin with (whitespace and) a C<#> but
647 do not look like cpp commands, are stripped, including anything
648 inside Perl strings, regular expressions, and here-docs .
652 In some platforms the C preprocessor knows too much: it knows about
653 the C++ -style until-end-of-line comments starting with C<"//">.
654 This will cause problems with common Perl constructs like
658 because after -P this will became illegal code
662 The workaround is to use some other quoting separator than C<"/">,
663 like for example C<"!">:
671 It requires not only a working C preprocessor but also a working
672 F<sed>. If not on UNIX, you are probably out of luck on this.
676 Script line numbers are not preserved.
680 The C<-x> does not work with C<-P>.
686 enables rudimentary switch parsing for switches on the command
687 line after the program name but before any filename arguments (or before
688 an argument of B<-->). This means you can have switches with two leading
689 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
690 corresponding variable in the Perl program. The following program
691 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
692 if it is invoked with B<-xyz=abc>.
695 if ($xyz) { print "$xyz\n" }
697 Do note that B<--help> creates the variable ${-help}, which is not compliant
702 makes Perl use the PATH environment variable to search for the
703 program (unless the name of the program contains directory separators).
705 On some platforms, this also makes Perl append suffixes to the
706 filename while searching for it. For example, on Win32 platforms,
707 the ".bat" and ".cmd" suffixes are appended if a lookup for the
708 original name fails, and if the name does not already end in one
709 of those suffixes. If your Perl was compiled with DEBUGGING turned
710 on, using the -Dp switch to Perl shows how the search progresses.
712 Typically this is used to emulate #! startup on platforms that
713 don't support #!. This example works on many platforms that
714 have a shell compatible with Bourne shell:
717 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
718 if $running_under_some_shell;
720 The system ignores the first line and feeds the program to F</bin/sh>,
721 which proceeds to try to execute the Perl program as a shell script.
722 The shell executes the second line as a normal shell command, and thus
723 starts up the Perl interpreter. On some systems $0 doesn't always
724 contain the full pathname, so the B<-S> tells Perl to search for the
725 program if necessary. After Perl locates the program, it parses the
726 lines and ignores them because the variable $running_under_some_shell
727 is never true. If the program will be interpreted by csh, you will need
728 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
729 embedded spaces (and such) in the argument list. To start up sh rather
730 than csh, some systems may have to replace the #! line with a line
731 containing just a colon, which will be politely ignored by Perl. Other
732 systems can't control that, and need a totally devious construct that
733 will work under any of B<csh>, B<sh>, or Perl, such as the following:
735 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
736 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
737 if $running_under_some_shell;
739 If the filename supplied contains directory separators (i.e., is an
740 absolute or relative pathname), and if that file is not found,
741 platforms that append file extensions will do so and try to look
742 for the file with those extensions added, one by one.
744 On DOS-like platforms, if the program does not contain directory
745 separators, it will first be searched for in the current directory
746 before being searched for on the PATH. On Unix platforms, the
747 program will be searched for strictly on the PATH.
751 Like B<-T>, but taint checks will issue warnings rather than fatal
752 errors. These warnings can be controlled normally with C<no warnings
755 B<NOTE: this is not a substitute for -T.> This is meant only to be
756 used as a temporary development aid while securing legacy code:
757 for real production code and for new secure code written from scratch
758 always use the real B<-T>.
762 forces "taint" checks to be turned on so you can test them. Ordinarily
763 these checks are done only when running setuid or setgid. It's a
764 good idea to turn them on explicitly for programs that run on behalf
765 of someone else whom you might not necessarily trust, such as CGI
766 programs or any internet servers you might write in Perl. See
767 L<perlsec> for details. For security reasons, this option must be
768 seen by Perl quite early; usually this means it must appear early
769 on the command line or in the #! line for systems which support
774 This obsolete switch causes Perl to dump core after compiling your
775 program. You can then in theory take this core dump and turn it
776 into an executable file by using the B<undump> program (not supplied).
777 This speeds startup at the expense of some disk space (which you
778 can minimize by stripping the executable). (Still, a "hello world"
779 executable comes out to about 200K on my machine.) If you want to
780 execute a portion of your program before dumping, use the dump()
781 operator instead. Note: availability of B<undump> is platform
782 specific and may not be available for a specific port of Perl.
784 This switch has been superseded in favor of the new Perl code
785 generator backends to the compiler. See L<B> and L<B::Bytecode>
790 allows Perl to do unsafe operations. Currently the only "unsafe"
791 operations are the unlinking of directories while running as superuser,
792 and running setuid programs with fatal taint checks turned into
793 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
794 be used along with this option to actually I<generate> the
795 taint-check warnings.
799 prints the version and patchlevel of your perl executable.
803 prints summary of the major perl configuration values and the current
808 Prints to STDOUT the value of the named configuration variable.
813 will provide strong clues about what your MANPATH variable should
814 be set to in order to access the Perl documentation.
818 prints warnings about dubious constructs, such as variable names
819 that are mentioned only once and scalar variables that are used
820 before being set, redefined subroutines, references to undefined
821 filehandles or filehandles opened read-only that you are attempting
822 to write on, values used as a number that doesn't look like numbers,
823 using an array as though it were a scalar, if your subroutines
824 recurse more than 100 deep, and innumerable other things.
826 This switch really just enables the internal C<$^W> variable. You
827 can disable or promote into fatal errors specific warnings using
828 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
829 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
830 facility is also available if you want to manipulate entire classes
831 of warnings; see L<warnings> or L<perllexwarn>.
835 Enables all warnings regardless of C<no warnings> or C<$^W>.
840 Disables all warnings regardless of C<use warnings> or C<$^W>.
843 =item B<-x> I<directory>
845 tells Perl that the program is embedded in a larger chunk of unrelated
846 ASCII text, such as in a mail message. Leading garbage will be
847 discarded until the first line that starts with #! and contains the
848 string "perl". Any meaningful switches on that line will be applied.
849 If a directory name is specified, Perl will switch to that directory
850 before running the program. The B<-x> switch controls only the
851 disposal of leading garbage. The program must be terminated with
852 C<__END__> if there is trailing garbage to be ignored (the program
853 can process any or all of the trailing garbage via the DATA filehandle
864 Used if chdir has no argument.
868 Used if chdir has no argument and HOME is not set.
872 Used in executing subprocesses, and in finding the program if B<-S> is
877 A colon-separated list of directories in which to look for Perl library
878 files before looking in the standard library and the current
879 directory. Any architecture-specific directories under the specified
880 locations are automatically included if they exist. If PERL5LIB is not
881 defined, PERLLIB is used.
883 When running taint checks (either because the program was running setuid
884 or setgid, or the B<-T> switch was used), neither variable is used.
885 The program should instead say:
887 use lib "/my/directory";
891 Command-line options (switches). Switches in this variable are taken
892 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
893 switches are allowed. When running taint checks (because the program
894 was running setuid or setgid, or the B<-T> switch was used), this
895 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
896 enabled, and any subsequent options ignored.
900 A space (or colon) separated list of PerlIO layers. If perl is built
901 to use PerlIO system for IO (the default) these layers effect perl's IO.
903 It is conventional to start layer names with a colon e.g. C<:perlio> to
904 emphasise their similarity to variable "attributes". But the code that parses
905 layer specification strings (which is also used to decode the PERLIO
906 environment variable) treats the colon as a separator.
908 The list becomes the default for I<all> perl's IO. Consequently only built-in
909 layers can appear in this list, as external layers (such as :encoding()) need
910 IO in order to load them!. See L<"open pragma"|open> for how to add external
911 encodings as defaults.
913 The layers that it makes sense to include in the PERLIO environment
914 variable are summarised below. For more details see L<PerlIO>.
920 Turns I<off> the C<:utf8> flag for the layer below.
921 Unlikely to be useful in global PERLIO environment variable.
925 A layer that implements DOS/Windows like CRLF line endings.
926 On read converts pairs of CR,LF to a single "\n" newline character.
927 On write converts each "\n" to a CR,LF pair.
928 Based on the C<:perlio> layer.
932 A layer which implements "reading" of files by using C<mmap()> to
933 make (whole) file appear in the process's address space, and then
934 using that as PerlIO's "buffer". This I<may> be faster in certain
935 circumstances for large files, and may result in less physical memory
936 use when multiple processes are reading the same file.
938 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
939 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
940 needs extra house-keeping (to extend the file) which negates any advantage.
942 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
946 A from scratch implementation of buffering for PerlIO. Provides fast
947 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
948 and in general attempts to minimize data copying.
950 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
954 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
955 It makes the stream pass each byte as-is without any translation.
956 In particular CRLF translation, and/or :utf8 inuited from locale
959 Arranges for all accesses go straight to the lowest buffered layer provided
960 by the configration. That is it strips off any layers above that layer.
962 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
963 referred to as a "discipline") is documented as the inverse of the
964 C<:crlf> layer. That is no longer the case - other layers which would
965 alter binary nature of the stream are also disabled. If you want UNIX
966 line endings on a platform that normally does CRLF translation, but still
967 want UTF-8 or encoding defaults the appropriate thing to do is to add
968 C<:perlio> to PERLIO environment variable.
972 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
973 library calls. The layer provides both buffering and IO.
974 Note that C<:stdio> layer does I<not> do CRLF translation even if that
975 is platforms normal behaviour. You will need a C<:crlf> layer above it
980 Lowest level layer which provides basic PerlIO operations in terms of
981 UNIX/POSIX numeric file descriptor calls
982 C<open(), read(), write(), lseek(), close()>
986 Turns on a flag on the layer below to tell perl that data sent to the
987 stream should be converted to perl internal "utf8" form and that data from the
988 stream should be considered as so encoded. On ASCII based platforms the
989 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
990 May be useful in PERLIO environment variable to make UTF-8 the
991 default. (To turn off that behaviour use C<:bytes> layer.)
995 On Win32 platforms this I<experimental> layer uses native "handle" IO
996 rather than unix-like numeric file descriptor layer. Known to be
997 buggy in this release.
1001 On all platforms the default set of layers should give acceptable results.
1003 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1004 Configure is setup to prefer "stdio" implementation if system's library
1005 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1008 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1009 has a number of bugs/mis-features for perl IO which are somewhat
1010 C compiler vendor/version dependent. Using our own C<crlf> layer as
1011 the buffer avoids those issues and makes things more uniform.
1012 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1015 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1016 compiler's numeric file descriptor routines. There is an experimental native
1017 C<win32> layer which is expected to be enhanced and should eventually replace
1022 If set to the name of a file or device then certain operations of PerlIO
1023 sub-system will be logged to that file (opened as append). Typical uses
1026 PERLIO_DEBUG=/dev/tty perl script ...
1028 and Win32 approximate equivalent:
1030 set PERLIO_DEBUG=CON
1036 A colon-separated list of directories in which to look for Perl library
1037 files before looking in the standard library and the current directory.
1038 If PERL5LIB is defined, PERLLIB is not used.
1042 The command used to load the debugger code. The default is:
1044 BEGIN { require 'perl5db.pl' }
1046 =item PERL5SHELL (specific to the Win32 port)
1048 May be set to an alternative shell that perl must use internally for
1049 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1050 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1051 to be space-separated. Precede any character that needs to be protected
1052 (like a space or backslash) with a backslash.
1054 Note that Perl doesn't use COMSPEC for this purpose because
1055 COMSPEC has a high degree of variability among users, leading to
1056 portability concerns. Besides, perl can use a shell that may not be
1057 fit for interactive use, and setting COMSPEC to such a shell may
1058 interfere with the proper functioning of other programs (which usually
1059 look in COMSPEC to find a shell fit for interactive use).
1061 =item PERL_DEBUG_MSTATS
1063 Relevant only if perl is compiled with the malloc included with the perl
1064 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1065 If set, this causes memory statistics to be dumped after execution. If set
1066 to an integer greater than one, also causes memory statistics to be dumped
1069 =item PERL_DESTRUCT_LEVEL
1071 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1072 this controls the behavior of global destruction of objects and other
1073 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1077 If using the C<encoding> pragma without an explicit encoding name, the
1078 PERL_ENCODING environment variable is consulted for an encoding name.
1080 =item PERL_ROOT (specific to the VMS port)
1082 A translation concealed rooted logical name that contains perl and the
1083 logical device for the @INC path on VMS only. Other logical names that
1084 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1085 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1086 L<perlvms> and in F<README.vms> in the Perl source distribution.
1090 Equivalent to the B<-C> command-line switch.
1092 =item SYS$LOGIN (specific to the VMS port)
1094 Used if chdir has no argument and HOME and LOGDIR are not set.
1098 Perl also has environment variables that control how Perl handles data
1099 specific to particular natural languages. See L<perllocale>.
1101 Apart from these, Perl uses no other environment variables, except
1102 to make them available to the program being executed, and to child
1103 processes. However, programs running setuid would do well to execute
1104 the following lines before doing anything else, just to keep people
1107 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1108 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1109 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};