AABCBAABCCCCAB
AABABAABABABAB
AAB BAAB    AB  ## I don't care what's in string 2 where there is a C in string 1.

##</code><code>##

$ab  = "AABABAABABABAB";;

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

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