excuse me for butting in here, or dont :P
But wouldnt a simple for not present:

if ( $string !~ /search patter here/ ) {
    print ( "didnt find match" );
};
[download]

for if present:

if ( $string =~ /search pattern here/ ) {
    print ( "found string" );
    } else {
    print ( "didnt find string" );
};
[download]

please keep in mind i am new at perl but i think this would work for finding or not finding patterns in strings :)
Edit: seems i just reposted some code from above lol.