while ( <FH> ) {
    next if $_ eq 'foo'; # Where foo can only appear once in the file
    print;
}

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

do_something(5);

sub do_something {
    my $target = shift;
    my $block;
    my $block2 = sub {
        print "No need to check $_ against $target anymore\n";
    };
    my $block1 = sub {
        if ( $_ == $target ) {
            print "Skipping $target\n";
            $block = $block2;
        }
        else {
            print "$_ is not $target\n";
        }
    };
    $block = $block1;
    for ( 1 .. 9 ) {
        $block->();
    }
}