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=head1 NAME
perlrun - how to execute the Perl interpreter
=head1 SYNOPSIS
B<perl> S<[ B<-sTuU> ]>
S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
S<[ B<-P> ]>
S<[ B<-S> ]>
S<[ B<-x>[I<dir>] ]>
S<[ B<-i>[I<extension>] ]>
S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
=head1 DESCRIPTION
Upon startup, Perl looks for your script in one of the following
places:
=over 4
=item 1.
Specified line by line via B<-e> switches on the command line.
=item 2.
Contained in the file specified by the first filename on the command line.
(Note that systems supporting the #! notation invoke interpreters this way.)
=item 3.
Passed in implicitly via standard input. This only works if there are
no filename arguments--to pass arguments to a STDIN script you
must explicitly specify a "-" for the script name.
=back
With methods 2 and 3, Perl starts parsing the input file from the
beginning, unless you've specified a B<-x> switch, in which case it
scans for the first line starting with #! and containing the word
"perl", and starts there instead. This is useful for running a script
embedded in a larger message. (In this case you would indicate the end
of the script using the __END__ token.)
As of Perl 5, the #! line is always examined for switches as the line is
being parsed. Thus, if you're on a machine that only allows one argument
with the #! line, or worse, doesn't even recognize the #! line, you still
can get consistent switch behavior regardless of how Perl was invoked,
even if B<-x> was used to find the beginning of the script.
Because many operating systems silently chop off kernel interpretation of
the #! line after 32 characters, some switches may be passed in on the
command line, and some may not; you could even get a "-" without its
letter, if you're not careful. You probably want to make sure that all
your switches fall either before or after that 32 character boundary.
Most switches don't actually care if they're processed redundantly, but
getting a - instead of a complete switch could cause Perl to try to
execute standard input instead of your script. And a partial B<-I> switch
could also cause odd results.
Parsing of the #! switches starts wherever "perl" is mentioned in the line.
The sequences "-*" and "- " are specifically ignored so that you could,
if you were so inclined, say
#!/bin/sh -- # -*- perl -*- -p
eval 'exec perl $0 -S ${1+"$@"}'
if 0;
to let Perl see the B<-p> switch.
If the #! line does not contain the word "perl", the program named after
the #! is executed instead of the Perl interpreter. This is slightly
bizarre, but it helps people on machines that don't do #!, because they
can tell a program that their SHELL is /usr/bin/perl, and Perl will then
dispatch the program to the correct interpreter for them.
After locating your script, Perl compiles the entire script to an
internal form. If there are any compilation errors, execution of the
script is not attempted. (This is unlike the typical shell script,
which might run partway through before finding a syntax error.)
If the script is syntactically correct, it is executed. If the script
runs off the end without hitting an exit() or die() operator, an implicit
C<exit(0)> is provided to indicate successful completion.
=head2 Switches
A single-character switch may be combined with the following switch, if
any.
#!/usr/bin/perl -spi.bak # same as -s -p -i.bak
Switches include:
=over 5
=item B<-0>[I<digits>]
specifies the record separator (C<$/>) as an octal number. If there are
no digits, the null character is the separator. Other switches may
precede or follow the digits. For example, if you have a version of
B<find> which can print filenames terminated by the null character, you
can say this:
find . -name '*.bak' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole since there is no
legal character with that value.
=item B<-a>
turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
split command to the @F array is done as the first thing inside the
implicit while loop produced by the B<-n> or B<-p>.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using B<-F>.
=item B<-c>
causes Perl to check the syntax of the script and then exit without
executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
since these are considered as occurring outside the execution of
your program.
=item B<-d>
runs the script under the Perl debugger. See L<perldebug>.
=item B<-d:>I<foo>
runs the script under the control of a debugging or tracing module
installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
Devel::DProf profiler. See L<perldebug>.
=item B<-D>I<number>
=item B<-D>I<list>
sets debugging flags. To watch how it executes your script, use
B<-D14>. (This only works if debugging is compiled into your
Perl.) Another nice value is B<-D1024>, which lists your compiled
syntax tree. And B<-D512> displays compiled regular expressions. As an
alternative specify a list of letters instead of numbers (e.g. B<-D14> is
equivalent to B<-Dtls>):
1 p Tokenizing and Parsing
2 s Stack Snapshots
4 l Label Stack Processing
8 t Trace Execution
16 o Operator Node Construction
32 c String/Numeric Conversions
64 P Print Preprocessor Command for -P
128 m Memory Allocation
256 f Format Processing
512 r Regular Expression Parsing
1024 x Syntax Tree Dump
2048 u Tainting Checks
4096 L Memory Leaks (not supported anymore)
8192 H Hash Dump -- usurps values()
16384 X Scratchpad Allocation
32768 D Cleaning Up
=item B<-e> I<commandline>
may be used to enter one line of script.
If B<-e> is given, Perl
will not look for a script filename in the argument list.
Multiple B<-e> commands may
be given to build up a multi-line script.
Make sure to use semicolons where you would in a normal program.
=item B<-F>I<pattern>
specifies the pattern to split on if B<-a> is also in effect. The
pattern may be surrounded by C<//>, C<""> or C<''>, otherwise it will be
put in single quotes.
=item B<-h>
prints a summary of the options.
=item B<-i>[I<extension>]
specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
in-place. It does this by renaming the input file, opening the output
file by the original name, and selecting that output file as the default
for print() statements. The extension, if supplied, is added to the name
of the old file to make a backup copy. If no extension is supplied, no
backup is made. From the shell, saying
$ perl -p -i.bak -e "s/foo/bar/; ... "
is the same as using the script:
#!/usr/bin/perl -pi.bak
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
while (<>) {
if ($ARGV ne $oldargv) {
rename($ARGV, $ARGV . '.bak');
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
}
s/foo/bar/;
}
continue {
print; # this prints to original filename
}
select(STDOUT);
except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
know when the filename has changed. It does, however, use ARGVOUT for
the selected filehandle. Note that STDOUT is restored as the
default output filehandle after the loop.
You can use C<eof> without parenthesis to locate the end of each input file,
in case you want to append to each file, or reset line numbering (see
example in L<perlfunc/eof>).
=item B<-I>I<directory>
Directories specified by B<-I> are prepended to the search path for
modules (@INC), and also tells the C preprocessor where to search for
include files. The C preprocessor is invoked with B<-P>; by default it
searches /usr/i