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, their numeric values, and effects
274 are as follows; 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 UTF-8 is the default PerlIO layer for input streams
281 o 16 UTF-8 is the default PerlIO layer for output streams
283 A 32 the @ARGV elements are expected to be strings encoded 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<io> options mean that any subsequent open() (or similar I/O
295 operations) will have the C<:utf8> PerlIO layer implicitly applied
296 to them, in other words, UTF-8 is expected from any input stream,
297 and UTF-8 is produced to any output stream. This is just the default,
298 with explicit layers in open() and with binmode() one can manipulate
301 C<-C> on its own (not followed by any number or option list), or the
302 empty string C<""> for the C<$ENV{PERL_UNICODE}, has the same effect
303 as <-CSDL>. In other words, the standard I/O handles and the default
304 C<open()> layer are UTF-8-fied B<but> only if the locale environment
305 variables indicate a UTF-8 locale. This behaviour follows the
306 I<implicit> UTF-8 behaviour of Perl 5.8.0.
308 You can use C<-C0> to explicitly disable all the above Unicode features.
310 See L<perlfunc/open>, and L<open> for more information.
312 The read-only magic variable C<${^UNICODE}> reflects the numeric value
313 of this setting, see L<perlvar/"${^UNICODE}">.
315 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
316 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
317 This feature was practically unused, however, and the command line
318 switch was therefore "recycled".)
322 causes Perl to check the syntax of the program and then exit without
323 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
324 C<use> blocks, because these are considered as occurring outside the
325 execution of your program. C<INIT> and C<END> blocks, however, will
330 runs the program under the Perl debugger. See L<perldebug>.
332 =item B<-d:>I<foo[=bar,baz]>
334 runs the program under the control of a debugging, profiling, or
335 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
336 the program using the Devel::DProf profiler. As with the B<-M>
337 flag, options may be passed to the Devel::foo package where they
338 will be received and interpreted by the Devel::foo::import routine.
339 The comma-separated list of options must follow a C<=> character.
342 =item B<-D>I<letters>
346 sets debugging flags. To watch how it executes your program, use
347 B<-Dtls>. (This works only if debugging is compiled into your
348 Perl.) Another nice value is B<-Dx>, which lists your compiled
349 syntax tree. And B<-Dr> displays compiled regular expressions;
350 the format of the output is explained in L<perldebguts>.
352 As an alternative, specify a number instead of list of letters (e.g.,
353 B<-D14> is equivalent to B<-Dtls>):
355 1 p Tokenizing and parsing
357 with v, displays all stacks
358 4 l Context (loop) stack processing
360 16 o Method and overloading resolution
361 32 c String/numeric conversions
362 64 P Print profiling info, preprocessor command for -P, source file input state
363 128 m Memory allocation
364 256 f Format processing
365 512 r Regular expression parsing and execution
366 1024 x Syntax tree dump
367 2048 u Tainting checks
368 4096 (Obsolete, previously used for LEAKTEST)
369 8192 H Hash dump -- usurps values()
370 16384 X Scratchpad allocation
372 65536 S Thread synchronization
374 262144 R Include reference counts of dumped variables (eg when using -Ds)
375 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
376 1048576 v Verbose: use in conjunction with other flags
377 2097152 C Copy On Write
379 All these flags require B<-DDEBUGGING> when you compile the Perl
380 executable (but see L<Devel::Peek>, L<re> which may change this).
381 See the F<INSTALL> file in the Perl source distribution
382 for how to do this. This flag is automatically set if you include B<-g>
383 option when C<Configure> asks you about optimizer/debugger flags.
385 If you're just trying to get a print out of each line of Perl code
386 as it executes, the way that C<sh -x> provides for shell scripts,
387 you can't use Perl's B<-D> switch. Instead do this
389 # If you have "env" utility
390 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
392 # Bourne shell syntax
393 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
396 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
398 See L<perldebug> for details and variations.
400 =item B<-e> I<commandline>
402 may be used to enter one line of program. If B<-e> is given, Perl
403 will not look for a filename in the argument list. Multiple B<-e>
404 commands may be given to build up a multi-line script. Make sure
405 to use semicolons where you would in a normal program.
407 =item B<-F>I<pattern>
409 specifies the pattern to split on if B<-a> is also in effect. The
410 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
411 put in single quotes.
415 prints a summary of the options.
417 =item B<-i>[I<extension>]
419 specifies that files processed by the C<E<lt>E<gt>> construct are to be
420 edited in-place. It does this by renaming the input file, opening the
421 output file by the original name, and selecting that output file as the
422 default for print() statements. The extension, if supplied, is used to
423 modify the name of the old file to make a backup copy, following these
426 If no extension is supplied, no backup is made and the current file is
429 If the extension doesn't contain a C<*>, then it is appended to the
430 end of the current filename as a suffix. If the extension does
431 contain one or more C<*> characters, then each C<*> is replaced
432 with the current filename. In Perl terms, you could think of this
435 ($backup = $extension) =~ s/\*/$file_name/g;
437 This allows you to add a prefix to the backup file, instead of (or in
438 addition to) a suffix:
440 $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
442 Or even to place backup copies of the original files into another
443 directory (provided the directory already exists):
445 $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
447 These sets of one-liners are equivalent:
449 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
450 $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
452 $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
453 $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
455 From the shell, saying
457 $ perl -p -i.orig -e "s/foo/bar/; ... "
459 is the same as using the program:
461 #!/usr/bin/perl -pi.orig
464 which is equivalent to
467 $extension = '.orig';
469 if ($ARGV ne $oldargv) {
470 if ($extension !~ /\*/) {
471 $backup = $ARGV . $extension;
474 ($backup = $extension) =~ s/\*/$ARGV/g;
476 rename($ARGV, $backup);
477 open(ARGVOUT, ">$ARGV");
484 print; # this prints to original filename
488 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
489 know when the filename has changed. It does, however, use ARGVOUT for
490 the selected filehandle. Note that STDOUT is restored as the default
491 output filehandle after the loop.
493 As shown above, Perl creates the backup file whether or not any output
494 is actually changed. So this is just a fancy way to copy files:
496 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
498 $ perl -p -i'.orig' -e 1 file1 file2 file3...
500 You can use C<eof> without parentheses to locate the end of each input
501 file, in case you want to append to each file, or reset line numbering
502 (see example in L<perlfunc/eof>).
504 If, for a given file, Perl is unable to create the backup file as
505 specified in the extension then it will skip that file and continue on
506 with the next one (if it exists).
508 For a discussion of issues surrounding file permissions and B<-i>,
509 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?>.
511 You cannot use B<-i> to create directories or to strip extensions from
514 Perl does not expand C<~> in filenames, which is good, since some
515 folks use it for their backup files:
517 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
519 Finally, the B<-i> switch does not impede execution when no
520 files are given on the command line. In this case, no backup is made
521 (the original file cannot, of course, be determined) and processing
522 proceeds from STDIN to STDOUT as might be expected.
524 =item B<-I>I<directory>
526 Directories specified by B<-I> are prepended to the search path for
527 modules (C<@INC>), and also tells the C preprocessor where to search for
528 include files. The C preprocessor is invoked with B<-P>; by default it
529 searches /usr/include and /usr/lib/perl.
531 =item B<-l>[I<octnum>]
533 enables automatic line-ending processing. It has two separate
534 effects. First, it automatically chomps C<$/> (the input record
535 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
536 (the output record separator) to have the value of I<octnum> so
537 that any print statements will have that separator added back on.
538 If I<octnum> is omitted, sets C<$\> to the current value of
539 C<$/>. For instance, to trim lines to 80 columns:
541 perl -lpe 'substr($_, 80) = ""'
543 Note that the assignment C<$\ = $/> is done when the switch is processed,
544 so the input record separator can be different than the output record
545 separator if the B<-l> switch is followed by a B<-0> switch:
547 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
549 This sets C<$\> to newline and then sets C<$/> to the null character.
551 =item B<-m>[B<->]I<module>
553 =item B<-M>[B<->]I<module>
555 =item B<-M>[B<->]I<'module ...'>
557 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
559 B<-m>I<module> executes C<use> I<module> C<();> before executing your
562 B<-M>I<module> executes C<use> I<module> C<;> before executing your
563 program. You can use quotes to add extra code after the module name,
564 e.g., C<'-Mmodule qw(foo bar)'>.
566 If the first character after the B<-M> or B<-m> is a dash (C<->)
567 then the 'use' is replaced with 'no'.
569 A little builtin syntactic sugar means you can also say
570 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
571 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
572 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
573 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
574 removes the distinction between B<-m> and B<-M>.
578 causes Perl to assume the following loop around your program, which
579 makes it iterate over filename arguments somewhat like B<sed -n> or
584 ... # your program goes here
587 Note that the lines are not printed by default. See B<-p> to have
588 lines printed. If a file named by an argument cannot be opened for
589 some reason, Perl warns you about it and moves on to the next file.
591 Here is an efficient way to delete all files older than a week:
593 find . -mtime +7 -print | perl -nle unlink
595 This is faster than using the B<-exec> switch of B<find> because you don't
596 have to start a process on every filename found. It does suffer from
597 the bug of mishandling newlines in pathnames, which you can fix if
598 you follow the example under B<-0>.
600 C<BEGIN> and C<END> blocks may be used to capture control before or after
601 the implicit program loop, just as in B<awk>.
605 causes Perl to assume the following loop around your program, which
606 makes it iterate over filename arguments somewhat like B<sed>:
611 ... # your program goes here
613 print or die "-p destination: $!\n";
616 If a file named by an argument cannot be opened for some reason, Perl
617 warns you about it, and moves on to the next file. Note that the
618 lines are printed automatically. An error occurring during printing is
619 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
620 overrides a B<-n> switch.
622 C<BEGIN> and C<END> blocks may be used to capture control before or after
623 the implicit loop, just as in B<awk>.
627 B<NOTE: Use of -P is strongly discouraged because of its inherent
628 problems, including poor portability.>
630 This option causes your program to be run through the C preprocessor before
631 compilation by Perl. Because both comments and B<cpp> directives begin
632 with the # character, you should avoid starting comments with any words
633 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
635 If you're considering using C<-P>, you might also want to look at the
636 Filter::cpp module from CPAN.
638 The problems of -P include, but are not limited to:
644 The C<#!> line is stripped, so any switches there don't apply.
648 A C<-P> on a C<#!> line doesn't work.
652 B<All> lines that begin with (whitespace and) a C<#> but
653 do not look like cpp commands, are stripped, including anything
654 inside Perl strings, regular expressions, and here-docs .
658 In some platforms the C preprocessor knows too much: it knows about
659 the C++ -style until-end-of-line comments starting with C<"//">.
660 This will cause problems with common Perl constructs like
664 because after -P this will became illegal code
668 The workaround is to use some other quoting separator than C<"/">,
669 like for example C<"!">:
677 It requires not only a working C preprocessor but also a working
678 F<sed>. If not on UNIX, you are probably out of luck on this.
682 Script line numbers are not preserved.
686 The C<-x> does not work with C<-P>.
692 enables rudimentary switch parsing for switches on the command
693 line after the program name but before any filename arguments (or before
694 an argument of B<-->). This means you can have switches with two leading
695 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
696 corresponding variable in the Perl program. The following program
697 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
698 if it is invoked with B<-xyz=abc>.
701 if ($xyz) { print "$xyz\n" }
703 Do note that B<--help> creates the variable ${-help}, which is not compliant
708 makes Perl use the PATH environment variable to search for the
709 program (unless the name of the program contains directory separators).
711 On some platforms, this also makes Perl append suffixes to the
712 filename while searching for it. For example, on Win32 platforms,
713 the ".bat" and ".cmd" suffixes are appended if a lookup for the
714 original name fails, and if the name does not already end in one
715 of those suffixes. If your Perl was compiled with DEBUGGING turned
716 on, using the -Dp switch to Perl shows how the search progresses.
718 Typically this is used to emulate #! startup on platforms that
719 don't support #!. This example works on many platforms that
720 have a shell compatible with Bourne shell:
723 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
724 if $running_under_some_shell;
726 The system ignores the first line and feeds the program to F</bin/sh>,
727 which proceeds to try to execute the Perl program as a shell script.
728 The shell executes the second line as a normal shell command, and thus
729 starts up the Perl interpreter. On some systems $0 doesn't always
730 contain the full pathname, so the B<-S> tells Perl to search for the
731 program if necessary. After Perl locates the program, it parses the
732 lines and ignores them because the variable $running_under_some_shell
733 is never true. If the program will be interpreted by csh, you will need
734 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
735 embedded spaces (and such) in the argument list. To start up sh rather
736 than csh, some systems may have to replace the #! line with a line
737 containing just a colon, which will be politely ignored by Perl. Other
738 systems can't control that, and need a totally devious construct that
739 will work under any of B<csh>, B<sh>, or Perl, such as the following:
741 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
742 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
743 if $running_under_some_shell;
745 If the filename supplied contains directory separators (i.e., is an
746 absolute or relative pathname), and if that file is not found,
747 platforms that append file extensions will do so and try to look
748 for the file with those extensions added, one by one.
750 On DOS-like platforms, if the program does not contain directory
751 separators, it will first be searched for in the current directory
752 before being searched for on the PATH. On Unix platforms, the
753 program will be searched for strictly on the PATH.
757 Like B<-T>, but taint checks will issue warnings rather than fatal
758 errors. These warnings can be controlled normally with C<no warnings
761 B<NOTE: this is not a substitute for -T.> This is meant only to be
762 used as a temporary development aid while securing legacy code:
763 for real production code and for new secure code written from scratch
764 always use the real B<-T>.
768 forces "taint" checks to be turned on so you can test them. Ordinarily
769 these checks are done only when running setuid or setgid. It's a
770 good idea to turn them on explicitly for programs that run on behalf
771 of someone else whom you might not necessarily trust, such as CGI
772 programs or any internet servers you might write in Perl. See
773 L<perlsec> for details. For security reasons, this option must be
774 seen by Perl quite early; usually this means it must appear early
775 on the command line or in the #! line for systems which support
780 This obsolete switch causes Perl to dump core after compiling your
781 program. You can then in theory take this core dump and turn it
782 into an executable file by using the B<undump> program (not supplied).
783 This speeds startup at the expense of some disk space (which you
784 can minimize by stripping the executable). (Still, a "hello world"
785 executable comes out to about 200K on my machine.) If you want to
786 execute a portion of your program before dumping, use the dump()
787 operator instead. Note: availability of B<undump> is platform
788 specific and may not be available for a specific port of Perl.
790 This switch has been superseded in favor of the new Perl code
791 generator backends to the compiler. See L<B> and L<B::Bytecode>
796 allows Perl to do unsafe operations. Currently the only "unsafe"
797 operations are the unlinking of directories while running as superuser,
798 and running setuid programs with fatal taint checks turned into
799 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
800 be used along with this option to actually I<generate> the
801 taint-check warnings.
805 prints the version and patchlevel of your perl executable.
809 prints summary of the major perl configuration values and the current
814 Prints to STDOUT the value of the named configuration variable.
819 will provide strong clues about what your MANPATH variable should
820 be set to in order to access the Perl documentation.
824 prints warnings about dubious constructs, such as variable names
825 that are mentioned only once and scalar variables that are used
826 before being set, redefined subroutines, references to undefined
827 filehandles or filehandles opened read-only that you are attempting
828 to write on, values used as a number that doesn't look like numbers,
829 using an array as though it were a scalar, if your subroutines
830 recurse more than 100 deep, and innumerable other things.
832 This switch really just enables the internal C<$^W> variable. You
833 can disable or promote into fatal errors specific warnings using
834 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
835 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
836 facility is also available if you want to manipulate entire classes
837 of warnings; see L<warnings> or L<perllexwarn>.
841 Enables all warnings regardless of C<no warnings> or C<$^W>.
846 Disables all warnings regardless of C<use warnings> or C<$^W>.
849 =item B<-x> I<directory>
851 tells Perl that the program is embedded in a larger chunk of unrelated
852 ASCII text, such as in a mail message. Leading garbage will be
853 discarded until the first line that starts with #! and contains the
854 string "perl". Any meaningful switches on that line will be applied.
855 If a directory name is specified, Perl will switch to that directory
856 before running the program. The B<-x> switch controls only the
857 disposal of leading garbage. The program must be terminated with
858 C<__END__> if there is trailing garbage to be ignored (the program
859 can process any or all of the trailing garbage via the DATA filehandle
870 Used if chdir has no argument.
874 Used if chdir has no argument and HOME is not set.
878 Used in executing subprocesses, and in finding the program if B<-S> is
883 A colon-separated list of directories in which to look for Perl library
884 files before looking in the standard library and the current
885 directory. Any architecture-specific directories under the specified
886 locations are automatically included if they exist. If PERL5LIB is not
887 defined, PERLLIB is used.
889 When running taint checks (either because the program was running setuid
890 or setgid, or the B<-T> switch was used), neither variable is used.
891 The program should instead say:
893 use lib "/my/directory";
897 Command-line options (switches). Switches in this variable are taken
898 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
899 switches are allowed. When running taint checks (because the program
900 was running setuid or setgid, or the B<-T> switch was used), this
901 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
902 enabled, and any subsequent options ignored.
906 A space (or colon) separated list of PerlIO layers. If perl is built
907 to use PerlIO system for IO (the default) these layers effect perl's IO.
909 It is conventional to start layer names with a colon e.g. C<:perlio> to
910 emphasise their similarity to variable "attributes". But the code that parses
911 layer specification strings (which is also used to decode the PERLIO
912 environment variable) treats the colon as a separator.
914 The list becomes the default for I<all> perl's IO. Consequently only built-in
915 layers can appear in this list, as external layers (such as :encoding()) need
916 IO in order to load them!. See L<"open pragma"|open> for how to add external
917 encodings as defaults.
919 The layers that it makes sense to include in the PERLIO environment
920 variable are summarised below. For more details see L<PerlIO>.
926 Turns I<off> the C<:utf8> flag for the layer below.
927 Unlikely to be useful in global PERLIO environment variable.
931 A layer that implements DOS/Windows like CRLF line endings.
932 On read converts pairs of CR,LF to a single "\n" newline character.
933 On write converts each "\n" to a CR,LF pair.
934 Based on the C<:perlio> layer.
938 A layer which implements "reading" of files by using C<mmap()> to
939 make (whole) file appear in the process's address space, and then
940 using that as PerlIO's "buffer". This I<may> be faster in certain
941 circumstances for large files, and may result in less physical memory
942 use when multiple processes are reading the same file.
944 Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
945 layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
946 needs extra house-keeping (to extend the file) which negates any advantage.
948 The C<:mmap> layer will not exist if platform does not support C<mmap()>.
952 A from scratch implementation of buffering for PerlIO. Provides fast
953 access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
954 and in general attempts to minimize data copying.
956 C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
960 Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
961 It makes the stream pass each byte as-is without any translation.
962 In particular CRLF translation, and/or :utf8 inuited from locale
965 Arranges for all accesses go straight to the lowest buffered layer provided
966 by the configration. That is it strips off any layers above that layer.
968 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
969 referred to as a "discipline") is documented as the inverse of the
970 C<:crlf> layer. That is no longer the case - other layers which would
971 alter binary nature of the stream are also disabled. If you want UNIX
972 line endings on a platform that normally does CRLF translation, but still
973 want UTF-8 or encoding defaults the appropriate thing to do is to add
974 C<:perlio> to PERLIO environment variable.
978 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
979 library calls. The layer provides both buffering and IO.
980 Note that C<:stdio> layer does I<not> do CRLF translation even if that
981 is platforms normal behaviour. You will need a C<:crlf> layer above it
986 Lowest level layer which provides basic PerlIO operations in terms of
987 UNIX/POSIX numeric file descriptor calls
988 C<open(), read(), write(), lseek(), close()>
992 Turns on a flag on the layer below to tell perl that data sent to the
993 stream should be converted to perl internal "utf8" form and that data from the
994 stream should be considered as so encoded. On ASCII based platforms the
995 encoding is UTF-8 and on EBCDIC platforms UTF-EBCDIC.
996 May be useful in PERLIO environment variable to make UTF-8 the
997 default. (To turn off that behaviour use C<:bytes> layer.)
1001 On Win32 platforms this I<experimental> layer uses native "handle" IO
1002 rather than unix-like numeric file descriptor layer. Known to be
1003 buggy in this release.
1007 On all platforms the default set of layers should give acceptable results.
1009 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1010 Configure is setup to prefer "stdio" implementation if system's library
1011 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1014 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1015 has a number of bugs/mis-features for perl IO which are somewhat
1016 C compiler vendor/version dependent. Using our own C<crlf> layer as
1017 the buffer avoids those issues and makes things more uniform.
1018 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1021 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1022 compiler's numeric file descriptor routines. There is an experimental native
1023 C<win32> layer which is expected to be enhanced and should eventually replace
1028 If set to the name of a file or device then certain operations of PerlIO
1029 sub-system will be logged to that file (opened as append). Typical uses
1032 PERLIO_DEBUG=/dev/tty perl script ...
1034 and Win32 approximate equivalent:
1036 set PERLIO_DEBUG=CON
1042 A colon-separated list of directories in which to look for Perl library
1043 files before looking in the standard library and the current directory.
1044 If PERL5LIB is defined, PERLLIB is not used.
1048 The command used to load the debugger code. The default is:
1050 BEGIN { require 'perl5db.pl' }
1052 =item PERL5SHELL (specific to the Win32 port)
1054 May be set to an alternative shell that perl must use internally for
1055 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
1056 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1057 to be space-separated. Precede any character that needs to be protected
1058 (like a space or backslash) with a backslash.
1060 Note that Perl doesn't use COMSPEC for this purpose because
1061 COMSPEC has a high degree of variability among users, leading to
1062 portability concerns. Besides, perl can use a shell that may not be
1063 fit for interactive use, and setting COMSPEC to such a shell may
1064 interfere with the proper functioning of other programs (which usually
1065 look in COMSPEC to find a shell fit for interactive use).
1067 =item PERL_DEBUG_MSTATS
1069 Relevant only if perl is compiled with the malloc included with the perl
1070 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1071 If set, this causes memory statistics to be dumped after execution. If set
1072 to an integer greater than one, also causes memory statistics to be dumped
1075 =item PERL_DESTRUCT_LEVEL
1077 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1078 this controls the behavior of global destruction of objects and other
1079 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1083 If using the C<encoding> pragma without an explicit encoding name, the
1084 PERL_ENCODING environment variable is consulted for an encoding name.
1086 =item PERL_ROOT (specific to the VMS port)
1088 A translation concealed rooted logical name that contains perl and the
1089 logical device for the @INC path on VMS only. Other logical names that
1090 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1091 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1092 L<perlvms> and in F<README.vms> in the Perl source distribution.
1096 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1097 signals behaviour (immediate but unsafe) is restored. If set to
1098 C<safe> the safe signals are used.
1102 Equivalent to the B<-C> command-line switch.
1104 =item SYS$LOGIN (specific to the VMS port)
1106 Used if chdir has no argument and HOME and LOGDIR are not set.
1110 Perl also has environment variables that control how Perl handles data
1111 specific to particular natural languages. See L<perllocale>.
1113 Apart from these, Perl uses no other environment variables, except
1114 to make them available to the program being executed, and to child
1115 processes. However, programs running setuid would do well to execute
1116 the following lines before doing anything else, just to keep people
1119 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1120 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1121 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};