3 perlrun - how to execute the Perl interpreter
7 B<perl> [B<-acdhnpPsSTuUvw>] [B<-0[octal>]] [B<-D[number/list]>]
8 [B<-F regexp>] [B<-i[extension>]] [B<-I<lt>dir<gt>>]
9 [B<-l[octal]>] [B<-x[dir]>]
10 [programfile | B<-e command>] [argument ...]
14 Upon startup, Perl looks for your script in one of the following
21 Specified line by line via B<-e> switches on the command line.
25 Contained in the file specified by the first filename on the command line.
26 (Note that systems supporting the #! notation invoke interpreters this way.)
30 Passed in implicitly via standard input. This only works if there are
31 no filename arguments--to pass arguments to a STDIN script you
32 must explicitly specify a "-" for the script name.
36 With methods 2 and 3, Perl starts parsing the input file from the
37 beginning, unless you've specified a B<-x> switch, in which case it
38 scans for the first line starting with #! and containing the word
39 "perl", and starts there instead. This is useful for running a script
40 embedded in a larger message. (In this case you would indicate the end
41 of the script using the __END__ token.)
43 As of Perl 5, the #! line is always examined for switches as the line is
44 being parsed. Thus, if you're on a machine that only allows one argument
45 with the #! line, or worse, doesn't even recognize the #! line, you still
46 can get consistent switch behavior regardless of how Perl was invoked,
47 even if B<-x> was used to find the beginning of the script.
49 Because many operating systems silently chop off kernel interpretation of
50 the #! line after 32 characters, some switches may be passed in on the
51 command line, and some may not; you could even get a "-" without its
52 letter, if you're not careful. You probably want to make sure that all
53 your switches fall either before or after that 32 character boundary.
54 Most switches don't actually care if they're processed redundantly, but
55 getting a - instead of a complete switch could cause Perl to try to
56 execute standard input instead of your script. And a partial B<-I> switch
57 could also cause odd results.
59 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
60 The sequences "-*" and "- " are specifically ignored so that you could,
61 if you were so inclined, say
63 #!/bin/sh -- # -*- perl -*- -p
64 eval 'exec perl $0 -S ${1+"$@"}'
67 to let Perl see the B<-p> switch.
69 If the #! line does not contain the word "perl", the program named after
70 the #! is executed instead of the Perl interpreter. This is slightly
71 bizarre, but it helps people on machines that don't do #!, because they
72 can tell a program that their SHELL is /usr/bin/perl, and Perl will then
73 dispatch the program to the correct interpreter for them.
75 After locating your script, Perl compiles the entire script to an
76 internal form. If there are any compilation errors, execution of the
77 script is not attempted. (This is unlike the typical shell script,
78 which might run partway through before finding a syntax error.)
80 If the script is syntactically correct, it is executed. If the script
81 runs off the end without hitting an exit() or die() operator, an implicit
82 C<exit(0)> is provided to indicate successful completion.
86 A single-character switch may be combined with the following switch, if
89 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
97 specifies the record separator (C<$/>) as an octal number. If there are
98 no digits, the null character is the separator. Other switches may
99 precede or follow the digits. For example, if you have a version of
100 B<find> which can print filenames terminated by the null character, you
103 find . -name '*.bak' -print0 | perl -n0e unlink
105 The special value 00 will cause Perl to slurp files in paragraph mode.
106 The value 0777 will cause Perl to slurp files whole since there is no
107 legal character with that value.
111 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
112 split command to the @F array is done as the first thing inside the
113 implicit while loop produced by the B<-n> or B<-p>.
115 perl -ane 'print pop(@F), "\n";'
124 An alternate delimiter may be specified using B<-F>.
128 causes Perl to check the syntax of the script and then exit without
129 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
130 since these are considered as occurring outside the execution of
135 runs the script under the Perl debugger. See L<perldebug>.
139 runs the script under the control of a debugging or tracing module
140 installed as Devel::foo. E.g., -d:DProf executes the script using the
141 Devel::DProf profiler. See L<perldebug>.
147 sets debugging flags. To watch how it executes your script, use
148 B<-D14>. (This only works if debugging is compiled into your
149 Perl.) Another nice value is B<-D1024>, which lists your compiled
150 syntax tree. And B<-D512> displays compiled regular expressions. As an
151 alternative specify a list of letters instead of numbers (e.g. B<-D14> is
152 equivalent to B<-Dtls>):
154 1 p Tokenizing and Parsing
156 4 l Label Stack Processing
158 16 o Operator Node Construction
159 32 c String/Numeric Conversions
160 64 P Print Preprocessor Command for -P
161 128 m Memory Allocation
162 256 f Format Processing
163 512 r Regular Expression Parsing
164 1024 x Syntax Tree Dump
165 2048 u Tainting Checks
166 4096 L Memory Leaks (not supported anymore)
167 8192 H Hash Dump -- usurps values()
168 16384 X Scratchpad Allocation
171 =item B<-e> I<commandline>
173 may be used to enter one line of script.
174 If B<-e> is given, Perl
175 will not look for a script filename in the argument list.
176 Multiple B<-e> commands may
177 be given to build up a multi-line script.
178 Make sure to use semicolons where you would in a normal program.
182 specifies a regular expression to split on if B<-a> is also in effect.
183 If regexp has C<//> around it, the slashes will be ignored.
185 =item B<-i>I<extension>
187 specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
188 in-place. It does this by renaming the input file, opening the output
189 file by the original name, and selecting that output file as the default
190 for print() statements. The extension, if supplied, is added to the name
191 of the old file to make a backup copy. If no extension is supplied, no
192 backup is made. From the shell, saying
194 $ perl -p -i.bak -e "s/foo/bar/; ... "
196 is the same as using the script:
198 #!/usr/bin/perl -pi.bak
201 which is equivalent to
205 if ($ARGV ne $oldargv) {
206 rename($ARGV, $ARGV . '.bak');
207 open(ARGVOUT, ">$ARGV");
214 print; # this prints to original filename
218 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
219 know when the filename has changed. It does, however, use ARGVOUT for
220 the selected filehandle. Note that STDOUT is restored as the
221 default output filehandle after the loop.
223 You can use C<eof> without parenthesis to locate the end of each input file,
224 in case you want to append to each file, or reset line numbering (see
225 example in L<perlfunc/eof>).
227 =item B<-I>I<directory>
229 may be used in conjunction with B<-P> to tell the C preprocessor where
230 to look for include files. By default /usr/include and /usr/lib/perl
235 enables automatic line-ending processing. It has two effects: first,
236 it automatically chomps the line terminator when used with B<-n> or
237 B<-p>, and second, it assigns "C<$\>" to have the value of I<octnum> so that
238 any print statements will have that line terminator added back on. If
239 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
240 instance, to trim lines to 80 columns:
242 perl -lpe 'substr($_, 80) = ""'
244 Note that the assignment C<$\ = $/> is done when the switch is processed,
245 so the input record separator can be different than the output record
246 separator if the B<-l> switch is followed by a B<-0> switch:
248 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
250 This sets $\ to newline and then sets $/ to the null character.
256 C<-m>I<module> executes C<use> I<module> C<();> before executing your
259 C<-M>I<module> executes C<use> I<module> C<;> before executing your
260 script. You can use quotes to add extra code after the module name,
261 e.g., C<-M'module qw(foo bar)'>.
263 A little built-in syntactic sugar means you can also say
264 C<-mmodule=foo> or C<-Mmodule=foo> as a shortcut for
265 C<-M'module qw(foo)'>. Note that using the C<=> form
266 removes the distinction between -m and -M.
270 causes Perl to assume the following loop around your script, which
271 makes it iterate over filename arguments somewhat like B<sed -n> or
275 ... # your script goes here
278 Note that the lines are not printed by default. See B<-p> to have
279 lines printed. Here is an efficient way to delete all files older than
282 find . -mtime +7 -print | perl -nle 'unlink;'
284 This is faster than using the C<-exec> switch of B<find> because you don't
285 have to start a process on every filename found.
287 C<BEGIN> and C<END> blocks may be used to capture control before or after
288 the implicit loop, just as in B<awk>.
292 causes Perl to assume the following loop around your script, which
293 makes it iterate over filename arguments somewhat like B<sed>:
297 ... # your script goes here
302 Note that the lines are printed automatically. To suppress printing
303 use the B<-n> switch. A B<-p> overrides a B<-n> switch.
305 C<BEGIN> and C<END> blocks may be used to capture control before or after
306 the implicit loop, just as in awk.
310 causes your script to be run through the C preprocessor before
311 compilation by Perl. (Since both comments and cpp directives begin
312 with the # character, you should avoid starting comments with any words
313 recognized by the C preprocessor such as "if", "else" or "define".)
317 enables some rudimentary switch parsing for switches on the command
318 line after the script name but before any filename arguments (or before
319 a B<-->). Any switch found there is removed from @ARGV and sets the
320 corresponding variable in the Perl script. The following script
321 prints "true" if and only if the script is invoked with a B<-xyz> switch.
324 if ($xyz) { print "true\n"; }
328 makes Perl use the PATH environment variable to search for the
329 script (unless the name of the script starts with a slash). Typically
330 this is used to emulate #! startup on machines that don't support #!,
331 in the following manner:
334 eval "exec /usr/bin/perl -S $0 $*"
335 if $running_under_some_shell;
337 The system ignores the first line and feeds the script to /bin/sh,
338 which proceeds to try to execute the Perl script as a shell script.
339 The shell executes the second line as a normal shell command, and thus
340 starts up the Perl interpreter. On some systems $0 doesn't always
341 contain the full pathname, so the B<-S> tells Perl to search for the
342 script if necessary. After Perl locates the script, it parses the
343 lines and ignores them because the variable $running_under_some_shell
344 is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
345 handles embedded spaces and such in the filenames, but doesn't work if
346 the script is being interpreted by csh. In order to start up sh rather
347 than csh, some systems may have to replace the #! line with a line
348 containing just a colon, which will be politely ignored by Perl. Other
349 systems can't control that, and need a totally devious construct that
350 will work under any of csh, sh or Perl, such as the following:
352 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
353 & eval 'exec /usr/bin/perl -S $0 $argv:q'
358 forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
359 done only when running setuid or setgid. It's a good idea to turn
360 them on explicitly for programs run on another's behalf, such as CGI
361 programs. See L<perlsec>.
365 causes Perl to dump core after compiling your script. You can then
366 take this core dump and turn it into an executable file by using the
367 B<undump> program (not supplied). This speeds startup at the expense of
368 some disk space (which you can minimize by stripping the executable).
369 (Still, a "hello world" executable comes out to about 200K on my
370 machine.) If you want to execute a portion of your script before dumping,
371 use the dump() operator instead. Note: availability of B<undump> is
372 platform specific and may not be available for a specific port of
377 allows Perl to do unsafe operations. Currently the only "unsafe"
378 operations are the unlinking of directories while running as superuser,
379 and running setuid programs with fatal taint checks turned into
384 prints the version and patchlevel of your Perl executable.
388 prints summary of the major perl configuration values and the current
393 Prints to STDOUT the value of the named configuration variable.
397 prints warnings about identifiers that are mentioned only once, and
398 scalar variables that are used before being set. Also warns about
399 redefined subroutines, and references to undefined filehandles or
400 filehandles opened readonly that you are attempting to write on. Also
401 warns you if you use values as a number that doesn't look like numbers, using
402 an array as though it were a scalar, if
403 your subroutines recurse more than 100 deep, and innumerable other things.
404 See L<perldiag> and L<perltrap>.
406 =item B<-x> I<directory>
408 tells Perl that the script is embedded in a message. Leading
409 garbage will be discarded until the first line that starts with #! and
410 contains the string "perl". Any meaningful switches on that line will
411 be applied (but only one group of switches, as with normal #!
412 processing). If a directory name is specified, Perl will switch to
413 that directory before running the script. The B<-x> switch only
414 controls the the disposal of leading garbage. The script must be
415 terminated with C<__END__> if there is trailing garbage to be ignored (the
416 script can process any or all of the trailing garbage via the DATA
417 filehandle if desired).