sub revdnacomp { # my $dna = @_; # the above means $dna gets the number of # arguments in @_, since it's a scalar context! my $dna = shift; # or my $dna = shift @_; # ah, scalar context of scalar gives expected results. # my ($dna) = @_; # would work, too my $revcomp = reverse($dna); $revcomp =~ tr/ACGTacgt/TGCAtgca/; return $revcomp; }