3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTuU> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 Upon startup, Perl looks for your script in one of the following
27 Specified line by line via B<-e> switches on the command line.
31 Contained in the file specified by the first filename on the command line.
32 (Note that systems supporting the #! notation invoke interpreters this way.)
36 Passed in implicitly via standard input. This works only if there are
37 no filename arguments--to pass arguments to a STDIN script you
38 must explicitly specify a "-" for the script name.
42 With methods 2 and 3, Perl starts parsing the input file from the
43 beginning, unless you've specified a B<-x> switch, in which case it
44 scans for the first line starting with #! and containing the word
45 "perl", and starts there instead. This is useful for running a script
46 embedded in a larger message. (In this case you would indicate the end
47 of the script using the C<__END__> token.)
49 The #! line is always examined for switches as the line is being
50 parsed. Thus, if you're on a machine that allows only one argument
51 with the #! line, or worse, doesn't even recognize the #! line, you
52 still can get consistent switch behavior regardless of how Perl was
53 invoked, even if B<-x> was used to find the beginning of the script.
55 Because many operating systems silently chop off kernel interpretation of
56 the #! line after 32 characters, some switches may be passed in on the
57 command line, and some may not; you could even get a "-" without its
58 letter, if you're not careful. You probably want to make sure that all
59 your switches fall either before or after that 32 character boundary.
60 Most switches don't actually care if they're processed redundantly, but
61 getting a - instead of a complete switch could cause Perl to try to
62 execute standard input instead of your script. And a partial B<-I> switch
63 could also cause odd results.
65 Some switches do care if they are processed twice, for instance combinations
66 of B<-l> and B<-0>. Either put all the switches after the 32 character
67 boundary (if applicable), or replace the use of B<-0>I<digits> by
68 C<BEGIN{ $/ = "\0digits"; }>.
70 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
71 The sequences "-*" and "- " are specifically ignored so that you could,
72 if you were so inclined, say
74 #!/bin/sh -- # -*- perl -*- -p
75 eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
76 if $running_under_some_shell;
78 to let Perl see the B<-p> switch.
80 If the #! line does not contain the word "perl", the program named after
81 the #! is executed instead of the Perl interpreter. This is slightly
82 bizarre, but it helps people on machines that don't do #!, because they
83 can tell a program that their SHELL is /usr/bin/perl, and Perl will then
84 dispatch the program to the correct interpreter for them.
86 After locating your script, Perl compiles the entire script to an
87 internal form. If there are any compilation errors, execution of the
88 script is not attempted. (This is unlike the typical shell script,
89 which might run part-way through before finding a syntax error.)
91 If the script is syntactically correct, it is executed. If the script
92 runs off the end without hitting an exit() or die() operator, an implicit
93 C<exit(0)> is provided to indicate successful completion.
95 =head2 #! and quoting on non-Unix systems
97 Unix's #! technique can be simulated on other systems:
105 extproc perl -S -your_switches
107 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
112 Create a batch file to run your script, and codify it in
113 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
114 distribution for more information).
118 The Win95/NT installation, when using the Activeware port of Perl,
119 will modify the Registry to associate the .pl extension with the perl
120 interpreter. If you install another port of Perl, including the one
121 in the Win32 directory of the Perl distribution, then you'll have to
122 modify the Registry yourself.
126 Macintosh perl scripts will have the appropriate Creator and
127 Type, so that double-clicking them will invoke the perl application.
131 Command-interpreters on non-Unix systems have rather different ideas
132 on quoting than Unix shells. You'll need to learn the special
133 characters in your command-interpreter (C<*>, C<\> and C<"> are
134 common) and how to protect whitespace and these characters to run
135 one-liners (see C<-e> below).
137 On some systems, you may have to change single-quotes to double ones,
138 which you must I<NOT> do on Unix or Plan9 systems. You might also
139 have to change a single % to a %%.
144 perl -e 'print "Hello world\n"'
147 perl -e "print \"Hello world\n\""
150 print "Hello world\n"
151 (then Run "Myscript" or Shift-Command-R)
154 perl -e "print ""Hello world\n"""
156 The problem is that none of this is reliable: it depends on the command
157 and it is entirely possible neither works. If 4DOS was the command shell, this would
158 probably work better:
160 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
162 CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
163 when nobody was looking, but just try to find documentation for its
166 Under the Macintosh, it depends which environment you are using. The MacPerl
167 shell, or MPW, is much like Unix shells in its support for several
168 quoting variants, except that it makes free use of the Macintosh's non-ASCII
169 characters as control characters.
171 There is no general solution to all of this. It's just a mess.
175 A single-character switch may be combined with the following switch, if
178 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
184 =item B<-0>[I<digits>]
186 specifies the input record separator (C<$/>) as an octal number. If there are
187 no digits, the null character is the separator. Other switches may
188 precede or follow the digits. For example, if you have a version of
189 B<find> which can print filenames terminated by the null character, you
192 find . -name '*.bak' -print0 | perl -n0e unlink
194 The special value 00 will cause Perl to slurp files in paragraph mode.
195 The value 0777 will cause Perl to slurp files whole because there is no
196 legal character with that value.
200 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
201 split command to the @F array is done as the first thing inside the
202 implicit while loop produced by the B<-n> or B<-p>.
204 perl -ane 'print pop(@F), "\n";'
213 An alternate delimiter may be specified using B<-F>.
217 causes Perl to check the syntax of the script and then exit without
218 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
219 because these are considered as occurring outside the execution of
224 runs the script under the Perl debugger. See L<perldebug>.
228 runs the script under the control of a debugging or tracing module
229 installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
230 Devel::DProf profiler. See L<perldebug>.
232 =item B<-D>I<letters>
236 sets debugging flags. To watch how it executes your script, use
237 B<-Dtls>. (This works only if debugging is compiled into your
238 Perl.) Another nice value is B<-Dx>, which lists your compiled
239 syntax tree. And B<-Dr> displays compiled regular expressions. As an
240 alternative, specify a number instead of list of letters (e.g., B<-D14> is
241 equivalent to B<-Dtls>):
243 1 p Tokenizing and parsing
245 4 l Context (loop) stack processing
247 16 o Method and overloading resolution
248 32 c String/numeric conversions
249 64 P Print preprocessor command for -P
250 128 m Memory allocation
251 256 f Format processing
252 512 r Regular expression parsing and execution
253 1024 x Syntax tree dump
254 2048 u Tainting checks
255 4096 L Memory leaks (needs C<-DLEAKTEST> when compiling Perl)
256 8192 H Hash dump -- usurps values()
257 16384 X Scratchpad allocation
260 All these flags require C<-DDEBUGGING> when you compile the Perl
261 executable. This flag is automatically set if you include C<-g>
262 option when C<Configure> asks you about optimizer/debugger flags.
264 =item B<-e> I<commandline>
266 may be used to enter one line of script.
267 If B<-e> is given, Perl
268 will not look for a script filename in the argument list.
269 Multiple B<-e> commands may
270 be given to build up a multi-line script.
271 Make sure to use semicolons where you would in a normal program.
273 =item B<-F>I<pattern>
275 specifies the pattern to split on if B<-a> is also in effect. The
276 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
277 put in single quotes.
281 prints a summary of the options.
283 =item B<-i>[I<extension>]
285 specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
286 in-place. It does this by renaming the input file, opening the output
287 file by the original name, and selecting that output file as the default
288 for print() statements. The extension, if supplied, is added to the name
289 of the old file to make a backup copy. If no extension is supplied, no
290 backup is made. From the shell, saying
292 $ perl -p -i.bak -e "s/foo/bar/; ... "
294 is the same as using the script:
296 #!/usr/bin/perl -pi.bak
299 which is equivalent to
303 if ($ARGV ne $oldargv) {
304 rename($ARGV, $ARGV . '.bak');
305 open(ARGVOUT, ">$ARGV");
312 print; # this prints to original filename
316 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
317 know when the filename has changed. It does, however, use ARGVOUT for
318 the selected filehandle. Note that STDOUT is restored as the
319 default output filehandle after the loop.
321 You can use C<eof> without parenthesis to locate the end of each input file,
322 in case you want to append to each file, or reset line numbering (see
323 example in L<perlfunc/eof>).
325 =item B<-I>I<directory>
327 Directories specified by B<-I> are prepended to the search path for
328 modules (C<@INC>), and also tells the C preprocessor where to search for
329 include files. The C preprocessor is invoked with B<-P>; by default it
330 searches /usr/include and /usr/lib/perl.
332 =item B<-l>[I<octnum>]
334 enables automatic line-ending processing. It has two effects: first,
335 it automatically chomps "C<$/>" (the input record separator) when used
336 with B<-n> or B<-p>, and second, it assigns "C<$\>"
337 (the output record separator) to have the value of I<octnum> so that
338 any print statements will have that separator added back on. If
339 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
340 instance, to trim lines to 80 columns:
342 perl -lpe 'substr($_, 80) = ""'
344 Note that the assignment C<$\ = $/> is done when the switch is processed,
345 so the input record separator can be different than the output record
346 separator if the B<-l> switch is followed by a B<-0> switch:
348 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
350 This sets C<$\> to newline and then sets C<$/> to the null character.
352 =item B<-m>[B<->]I<module>
354 =item B<-M>[B<->]I<module>
356 =item B<-M>[B<->]I<'module ...'>
358 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
360 C<-m>I<module> executes C<use> I<module> C<();> before executing your
363 C<-M>I<module> executes C<use> I<module> C<;> before executing your
364 script. You can use quotes to add extra code after the module name,
365 e.g., C<-M'module qw(foo bar)'>.
367 If the first character after the C<-M> or C<-m> is a dash (C<->)
368 then the 'use' is replaced with 'no'.
370 A little builtin syntactic sugar means you can also say
371 C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
372 C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
373 importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
374 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
375 removes the distinction between C<-m> and C<-M>.
379 causes Perl to assume the following loop around your script, which
380 makes it iterate over filename arguments somewhat like B<sed -n> or
384 ... # your script goes here
387 Note that the lines are not printed by default. See B<-p> to have
388 lines printed. If a file named by an argument cannot be opened for
389 some reason, Perl warns you about it, and moves on to the next file.
391 Here is an efficient way to delete all files older than a week:
393 find . -mtime +7 -print | perl -nle 'unlink;'
395 This is faster than using the C<-exec> switch of B<find> because you don't
396 have to start a process on every filename found.
398 C<BEGIN> and C<END> blocks may be used to capture control before or after
399 the implicit loop, just as in B<awk>.
403 causes Perl to assume the following loop around your script, which
404 makes it iterate over filename arguments somewhat like B<sed>:
408 ... # your script goes here
410 print or die "-p destination: $!\n";
413 If a file named by an argument cannot be opened for some reason, Perl
414 warns you about it, and moves on to the next file. Note that the
415 lines are printed automatically. An error occuring during printing is
416 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
417 overrides a B<-n> switch.
419 C<BEGIN> and C<END> blocks may be used to capture control before or after
420 the implicit loop, just as in awk.
424 causes your script to be run through the C preprocessor before
425 compilation by Perl. (Because both comments and cpp directives begin
426 with the # character, you should avoid starting comments with any words
427 recognized by the C preprocessor such as "if", "else", or "define".)
431 enables some rudimentary switch parsing for switches on the command
432 line after the script name but before any filename arguments (or before
433 a B<-->). Any switch found there is removed from @ARGV and sets the
434 corresponding variable in the Perl script. The following script
435 prints "true" if and only if the script is invoked with a B<-xyz> switch.
438 if ($xyz) { print "true\n"; }
442 makes Perl use the PATH environment variable to search for the
443 script (unless the name of the script contains directory separators).
444 On some platforms, this also makes Perl append suffixes to the
445 filename while searching for it. For example, on Win32 platforms,
446 the ".bat" and ".cmd" suffixes are appended if a lookup for the
447 original name fails, and if the name does not already end in one
448 of those suffixes. If your Perl was compiled with DEBUGGING turned
449 on, using the -Dp switch to Perl shows how the search progresses.
451 If the file supplied contains directory separators (i.e. it is an
452 absolute or relative pathname), and if the file is not found,
453 platforms that append file extensions will do so and try to look
454 for the file with those extensions added, one by one.
456 On DOS-like platforms, if the script does not contain directory
457 separators, it will first be searched for in the current directory
458 before being searched for on the PATH. On Unix platforms, the
459 script will be searched for strictly on the PATH.
461 Typically this is used to emulate #! startup on platforms that
462 don't support #!. This example works on many platforms that
463 have a shell compatible with Bourne shell:
466 eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
467 if $running_under_some_shell;
469 The system ignores the first line and feeds the script to /bin/sh,
470 which proceeds to try to execute the Perl script as a shell script.
471 The shell executes the second line as a normal shell command, and thus
472 starts up the Perl interpreter. On some systems $0 doesn't always
473 contain the full pathname, so the B<-S> tells Perl to search for the
474 script if necessary. After Perl locates the script, it parses the
475 lines and ignores them because the variable $running_under_some_shell
476 is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
477 handles embedded spaces and such in the filenames, but doesn't work if
478 the script is being interpreted by csh. To start up sh rather
479 than csh, some systems may have to replace the #! line with a line
480 containing just a colon, which will be politely ignored by Perl. Other
481 systems can't control that, and need a totally devious construct that
482 will work under any of csh, sh, or Perl, such as the following:
484 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
485 & eval 'exec /usr/bin/perl -S $0 $argv:q'
486 if $running_under_some_shell;
490 forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
491 done only when running setuid or setgid. It's a good idea to turn
492 them on explicitly for programs run on another's behalf, such as CGI
493 programs. See L<perlsec>.
497 causes Perl to dump core after compiling your script. You can then
498 take this core dump and turn it into an executable file by using the
499 B<undump> program (not supplied). This speeds startup at the expense of
500 some disk space (which you can minimize by stripping the executable).
501 (Still, a "hello world" executable comes out to about 200K on my
502 machine.) If you want to execute a portion of your script before dumping,
503 use the dump() operator instead. Note: availability of B<undump> is
504 platform specific and may not be available for a specific port of
509 allows Perl to do unsafe operations. Currently the only "unsafe"
510 operations are the unlinking of directories while running as superuser,
511 and running setuid programs with fatal taint checks turned into
512 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
513 be used along with this option to actually B<generate> the
514 taint-check warnings.
518 prints the version and patchlevel of your Perl executable.
522 prints summary of the major perl configuration values and the current
527 Prints to STDOUT the value of the named configuration variable.
531 prints warnings about variable names that are mentioned only once, and
532 scalar variables that are used before being set. Also warns about
533 redefined subroutines, and references to undefined filehandles or
534 filehandles opened read-only that you are attempting to write on. Also
535 warns you if you use values as a number that doesn't look like numbers,
536 using an array as though it were a scalar, if your subroutines recurse
537 more than 100 deep, and innumerable other things.
539 You can disable specific warnings using C<__WARN__> hooks, as described
540 in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
542 =item B<-x> I<directory>
544 tells Perl that the script is embedded in a message. Leading
545 garbage will be discarded until the first line that starts with #! and
546 contains the string "perl". Any meaningful switches on that line will
547 be applied. If a directory name is specified, Perl will switch to
548 that directory before running the script. The B<-x> switch controls
549 only the disposal of leading garbage. The script must be
550 terminated with C<__END__> if there is trailing garbage to be ignored (the
551 script can process any or all of the trailing garbage via the DATA
552 filehandle if desired).
562 Used if chdir has no argument.
566 Used if chdir has no argument and HOME is not set.
570 Used in executing subprocesses, and in finding the script if B<-S> is
575 A colon-separated list of directories in which to look for Perl library
576 files before looking in the standard library and the current
577 directory. If PERL5LIB is not defined, PERLLIB is used. When running
578 taint checks (because the script was running setuid or setgid, or the
579 B<-T> switch was used), neither variable is used. The script should
582 use lib "/my/directory";
586 Command-line options (switches). Switches in this variable are taken
587 as if they were on every Perl command line. Only the B<-[DIMUdmw]>
588 switches are allowed. When running taint checks (because the script
589 was running setuid or setgid, or the B<-T> switch was used), this
594 A colon-separated list of directories in which to look for Perl library
595 files before looking in the standard library and the current directory.
596 If PERL5LIB is defined, PERLLIB is not used.
600 The command used to load the debugger code. The default is:
602 BEGIN { require 'perl5db.pl' }
604 =item PERL5SHELL (specific to WIN32 port)
606 May be set to an alternative shell that perl must use internally for
607 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
608 on WindowsNT and C<command.com /c> on Windows95. The value is considered
609 to be space delimited. Precede any character that needs to be protected
610 (like a space or backslash) with a backslash.
612 Note that Perl doesn't use COMSPEC for this purpose because
613 COMSPEC has a high degree of variability among users, leading to
614 portability concerns. Besides, perl can use a shell that may not be
615 fit for interactive use, and setting COMSPEC to such a shell may
616 interfere with the proper functioning of other programs (which usually
617 look in COMSPEC to find a shell fit for interactive use).
619 =item PERL_DEBUG_MSTATS
621 Relevant only if perl is compiled with the malloc included with the perl
622 distribution (that is, if C<perl -V:d_mymalloc> is 'define'),
623 if set, this causes memory statistics to be dumped after execution. If set
624 to an integer greater than one, also causes memory statistics to be dumped
627 =item PERL_DESTRUCT_LEVEL
629 Relevant only if your perl executable was built with B<-DDEBUGGING>,
630 this controls the behavior of global destruction of objects and other
635 Perl also has environment variables that control how Perl handles data
636 specific to particular natural languages. See L<perllocale>.
638 Apart from these, Perl uses no other environment variables, except
639 to make them available to the script being executed, and to child
640 processes. However, scripts running setuid would do well to execute
641 the following lines before doing anything else, just to keep people
644 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
645 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
646 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};