I downvoted this post because it's wrong. Please test your advice if you're not sure:

#!/usr/bin/perl -w

use strict;
sub foo { print "foo\n" }

my $f = 'foo';
&$f;
[download]

I generally prefer a dispatch table:

my %ops = (
    one => \&one,
    two => \&two,
);

my $op = $q->param( 'op' );
die "Invalid operation '$op'\n" unless exists $ops{ $op };
$subs{ $op }->();
[download]

You can also mess with can, though it's less secure -- with the ops hash you can control exactly which subs can ever be called.

my $op = $q->param( 'op' );

my $sub = __PACKAGE__->can( $op );
die "Invalid op '$op'\n" unless $sub;

$sub->();
[download]