my $file = "$ARGV[0]";

    # Better:  (my $file = $ARGV[0]) or die "Syntax error ...\n";

##</code><code>##

    open(INFILE,"$ARGV[0]") or die "Can't open $ARGV[0]: $!";

    # Better:  open(INFILE, $file) or die "Can't open '$file': $!\n";