A single-character option may be combined with the following option, if any.
This is particularly useful when invoking a script using the #! construct which
only allows one argument. Example:
- -0digits
- specifies the record separator ($/) as an octal number.
If there are no digits, the null character is the separator.
Other switches may precede or follow the digits.
For example, if you have a version of
find
which can print filenames terminated by the null character, you can say this:
find . -name '*.bak' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole since there is no
legal character with that value.
- -a
- turns on autosplit mode when used with a
-n
or
-p.
An implicit split command to the @F array
is done as the first thing inside the implicit while loop produced by
the
-n
or
-p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
- -c
- causes
perl
to check the syntax of the script and then exit without executing it.
- -d
- runs the script under the perl debugger.
See the section on Debugging.
- -Dnumber
- sets debugging flags.
To watch how it executes your script, use
-D14.
(This only works if debugging is compiled into your
perl.)
Another nice value is -D1024, which lists your compiled syntax tree.
And -D512 displays compiled regular expressions.
- -e commandline
- may be used to enter one line of script.
Multiple
-e
commands may be given to build up a multi-line script.
If
-e
is given,
perl
will not look for a script filename in the argument list.
- -iextension
- specifies that files processed by the <> construct are to be edited
in-place.
It does this by renaming the input file, opening the output file by the
same name, and selecting that output file as the default for print statements.
The extension, if supplied, is added to the name of the
old file to make a backup copy.
If no extension is supplied, no backup is made.
Saying "perl -p -i.bak -e "s/foo/bar/;" ... " is the same as using
the script:
#!/usr/bin/perl -pi.bak
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
while (<>) {
if ($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
-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 eof to locate the end of each input file, in case you want
to append to each file, or reset line numbering (see example under eof).
- -Idirectory
- may be used in conjunction with
-P
to tell the C preprocessor where to look for include files.
By default /usr/include and /usr/lib/perl are searched.
- -loctnum
- enables automatic line-ending processing. It has two effects:
first, it automatically chops the line terminator when used with
-n
or
-p ,
and second, it assigns $\ to have the value of
octnum
so that any print statements will have that line terminator added back on. If
octnum
is omitted, sets $\ to the current value of $/.
For instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
Note that the assignment $\ = $/ is done when the switch is processed,
so the input record separator can be different than the output record
separator if the
-l
switch is followed by a
-0
switch:
gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
This sets $\ to newline and then sets $/ to the null character.
- -n
- causes
perl
to assume the following loop around your script, which makes it iterate
over filename arguments somewhat like "sed -n" or awk:
while (<>) {
... # your script goes here
}
Note that the lines are not printed by default.
See
-p
to have lines printed.
Here is an efficient way to delete all files older than a week:
gfind . -mtime +7 -print | perl -nle 'unlink;'
This is faster than using the -exec switch of find because you don't have to
start a process on every filename found.
- -p
- causes
perl
to assume the following loop around your script, which makes it iterate
over filename arguments somewhat like sed:
while (<>) {
... # your script goes here
} continue {
print;
}
Note that the lines are printed automatically.
To suppress printing use the
-n
switch.
A
-p
overrides a
-n
switch.
- -P
- causes your script to be run through the C preprocessor before
compilation by
perl.
(Since both comments and cpp directives begin with the # character,
you should avoid starting comments with any words recognized
by the C preprocessor such as "if", "else" or "define".)
- -s
- enables some rudimentary switch parsing for switches on the command line
after the script name but before any filename arguments (or before a --).
Any switch found there is removed from @ARGV and sets the corresponding variable in the
perl
script.
The following script prints "true" if and only if the script is
invoked with a -xyz switch.
#!/usr/bin/perl -s
if ($xyz) { print "true\n"; }
- -S
- makes
perl
use the PATH environment variable to search for the script
(unless the name of the script starts with a slash).
Typically this is used to emulate #! startup on machines that don't
support #!, in the following manner:
#!/usr/bin/perl
eval "exec /usr/bin/perl -S $0 $*"
if $running_under_some_shell;
The system ignores the first line and feeds the script to /bin/sh,
which proceeds to try to execute the
perl
script as a shell script.
The shell executes the second line as a normal shell command, and thus
starts up the
perl
interpreter.
On some systems $0 doesn't always contain the full pathname,
so the
-S
tells
perl
to search for the script if necessary.
After
perl
locates the script, it parses the lines and ignores them because
the variable $running_under_some_shell is never true.
A better construct than $* would be ${1+"$@"}, which handles embedded spaces
and such in the filenames, but doesn't work if the script is being interpreted
by csh.
In order to start up sh rather than csh, some systems may have to replace the
#! line with a line containing just
a colon, which will be politely ignored by perl.
Other systems can't control that, and need a totally devious construct that
will work under any of csh, sh or perl, such as the following:
eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -S $0 $argv:q'
if 0;
- -u
- causes
perl
to dump core after compiling your script.
You can then take this core dump and turn it into an executable file
by using the undump program (not supplied).
This speeds startup at the expense of some disk space (which you can
minimize by stripping the executable).
(Still, a "hello world" executable comes out to about 200K on my machine.)
If you are going to run your executable as a set-id program then you
should probably compile it using taintperl rather than normal perl.
If you want to execute a portion of your script before dumping, use the
dump operator instead.
Note: availability of undump is platform specific and may not be available
for a specific port of perl.
- -U
- allows
perl
to do unsafe operations.
Currently the only "unsafe" operations are the unlinking of directories while
running as superuser, and running setuid programs with fatal taint checks
turned into warnings.
- -v
- prints the version and patchlevel of your
perl
executable.
- -w
- prints warnings about identifiers that are mentioned only once, and scalar
variables that are used before being set.
Also warns about redefined subroutines, and references to undefined
filehandles or filehandles opened readonly that you are attempting to
write on.
Also warns you if you use == on values that don't look like numbers, and if
your subroutines recurse more than 100 deep.
- -xdirectory
- tells
perl
that the script is embedded in a message.
Leading garbage will be discarded until the first line that starts
with #! and contains the string "perl".
Any meaningful switches on that line will be applied (but only one
group of switches, as with normal #! processing).
If a directory name is specified, Perl will switch to that directory
before running the script.
The
-x
switch only controls the the disposal of leading garbage.
The script must be terminated with __END__ if there is trailing garbage
to be ignored (the script can process any or all of the trailing garbage
via the DATA filehandle if desired).