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:
| Usage: perl -0digits |
This 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.
|
| Usage: perl -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";
}
|
| Usage: perl -c |
Causes perl to check the syntax of the script and then
exit without executing it.
|
| Usage: perl -d |
Runs the script under the perl debugger. See the section on
debugging.
|
| Usage: perl -D |
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.
|
| Usage: perl -ecommandline |
This 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.
|
| Usage: perl -iextension |
This 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. For example
perl -p -i.bak -e "s/foo/bar/;" ...
This 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
|
| Usage: perl -Idirectory |
This switch 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.
|
| Usage: perl -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 $/ to the null character.
|
| Usage: perl -n |
This causes perl to assume the following loop around your script,
which makes it iterate over filename arguments somewhat like
"sed -n" or awk:
while (<>) {
... # your script goes here
}
Note that the lines are not printed by default. See -p
to have lines printed. Here is an efficient way to delete all
files older than a week:
gfind . -mtime +7 -print | perl -nle 'unlink;'
This is faster than using the -exec switch of find because you
don't have to start a process on every filename found.
|
| Usage: perl -p |
Causes perl to assume the following loop around your script,
which makes it iterate over filename arguments somewhat like sed:
while (<>) {
... # your script goes here
} continue {
print;
}
Note that the lines are printed automatically. To suppress
printing use the -n switch. A -p overrides a
-n switch.
|
| Usage: perl -P |
Causes your script to be run through the C preprocessor
before compilation by perl. (Since both comments and cpp
directives begin with the # character, you should avoid starting
comments with any words recognized by the C preprocessor
such as "if", "else" or "define".)
|
| Usage: perl -s |
Enables some rudimentary switch parsing for switches on
the command line after the script name but before any filename
arguments (or before a --). Any switch found there is removed
from @ARGV and sets the corresponding variable in the perl script.
The following script prints "true" if and only if the script is
invoked with a -xyz switch.
#!/usr/bin/perl -s
if ($xyz){
print "true\n";
}
|
| Usage: perl -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;
|
| Usage: perl -u |
This 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 (which is not supplied with our system).
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 (your own) 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.
|
| Usage: perl -U |
This 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.
|
| Usage: perl -v |
Prints the version and patchlevel of your perl executable.
|
| Usage: perl -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.
|
| Usage: perl -x |
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.
Note that the script can process any or all of the trailing garbage via the
DATA filehandle if desired.
|
