my $s = "bla bla (parenthesis) somestring";
if  ($s =~ /.*(\(parenthesis\))\s*somestring/) {
        print "matched $1\n"; #this prints "(parenthesis)"
        $s =~ s/$1//;
        # $s now looks "bla bla () somestring" rather than the desired "bla bla somestring"
}