Filter::Simple is based on Filter:Util::Call, but simplifies the means by which you can begin doing your own source filtering with Perl. Filter::Simple ships with the Perl 5.8 source kit.

Using Filter::Simple is, well, easy. Basically, Filter::Simple implements FILTER { ... }, which you can use to handle many of your simple source-filtering needs. Let's say that you want a good glass of ale, and you decide that you don't want Perl to print, but pint instead. You can implement something like the following with Filter::Simple. First, create a module called Print_to_Pint:

package Print_to_Pint;
 
use Filter::Simple;
FILTER { s/pint/print/g; }
 
# true
1;

Now, use Print_to_Pint to do something with pint:

#!/usr/local/bin/perl -w
 
use Print_to_Pint;
 
my $bottles = 99;
my $last = 1;
 
foreach my $bottle (reverse($last .. $bottles)) {
    pint "$bottle -> burp\n";
}

By default, Filter::Simple ignores no behavior, i.e., it stops filtering after a no Module is encountered. You can alter this behavior by passing another argument to use Filter::Simple or to FILTER { ... }. For example:

package Print_to_Pint;
use Filter::Simple;
    FILTER {
        s/pint/print/g;
}
"";

Filter::Simple also supports FILTER_ONLY, which allows you to support multiple filters to handle different parts of your source code. FILTER_ONLY takes several subroutines as options: code, executable, string, regex, quotelike, and all. code or executable filters all Perl code, except Pod or _ _DATA_ _ types. quotelike filters other Perl quotelike stuff, including here documents. string filters all string-related parts. regex filters all pattern-literal parts of quotelike.

For example, the following module will skip all incidences of Pod in the PodSucks module:

package PodSucks;
 
use Filter::Simple;
 
FILTER_ONLY
	executable => sub { s/x/X/g },
	executable => sub { print }
 
# True. True.
1;

The above code might not make that much sense, but take a look at the test program now, and it should become clear:

#!/usr/local/bin/perl -w

use PodSucks;

print "Flocks of Red Sox cause shocks to the Bronx.\n";
 
=pod
You will fear the wrath of Pod! Fear my wrath!
=cut

This prints:

Flocks of Red SoX cause shocks to the BronX.

8.112. FileHandle		8.114. Filter::Util::Call