foreach my $FH (@files) {
    open my $FILE, '<', $FH or die("Cannot read $FH: $!");
    my $data = join('', <$FILE>); # slurp file!

    # split on lines containing only 'GO' (and optionally, whitespace)
    foreach my $batch ( split /\n\s*go\s*\n/i, $data ) {
        # if you need the 'go', you'll need to do $batch.="\nGO"; here
        $dbh->do($batch);
        # error handling here
    }
}