$ab  = "AABABAABABABAB";;

$abmatch = "AABABAABABABAB";;
print +(( $abc & $abmatch ) eq $abmatch) ? 'yes' : 'no';;
yes

$abnomatch = "ABBABAABABABAB";;
print +(( $abc & $abnomatch ) eq $abmatch) ? 'yes' : 'no';;
no