Source filtering is a nice feature of newer versions of Perl (5.6 and later) because it allows the programmer to write extensions to the Perl language without tampering with the Perl source code itself. That is, you can create a macro language out of Perl.
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 "; }
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. "; =pod You will fear the wrath of Pod! Fear my wrath! =cut
This prints:
Flocks of Red SoX cause shocks to the BronX.
3.137.172.115