http://www.perlmonks.org?node_id=1227548


in reply to Isolating DNA cont.

You are missing a closing (right) curly for the while loop, as the asymmetric indentation suggests. Here's the perltidy version (Tip #10 from the Basic debugging checklist):
#!/usr/bin/perl -w use strict; use diagnostics; my $file = "$ARGV[0]"; open( DAT, $file ) || die("Can not open file!"); while (<DAT>) { my $seq = $_; if ( $seq =~ m/^[ATCG]+$/ ) { my $DNA = ''; $DNA = $seq; my $revcom = reverse($DNA); $revcom =~ tr/ACGTacgt/TGCAtgca/; print $revcom; } }

I also got rid of the trailing semicolon after your right curly.