1: die 'insufficient arguments' unless @ARGV == 1;
   2: open(IN, $ARGV[0]) or die "unable to open '$ARGV[0]'";
   3: while (my $line = <IN>) {
   4:     my $prefix = sprintf '%4d', $.;
   5:     print "$prefix: $line";
   6: }
   7: close IN;
   8: 


or

   1: die 'insufficient arguments' unless @ARGV == 1;
   2: open(IN, $ARGV[0]) or die "unable to open '$ARGV[0]'";
   3: while (my $line = <IN>) {
   4:     my $prefix = sprintf '%4d: ', $.;
   5:     print $prefix . $line;
   6: }
   7: close IN;
   8: