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8.113. Filter::Simple
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\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.
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| 8.112. FileHandle |  | 8.114. Filter::Util::Call |
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