#!/usr/bin/perl
use strict;

#command line info
my $usage = "$0 -file [file name]";
die "Usage: $usage \n"; if ((@ARGV == 0) || ((scalar @ARGV)%2 != 0));
my %CommandLine = @ARGV;
my $file = $CommandLine(-file) || die "Usage: $Usage \n";
#end command line info

print "Status: numbering each line in file \"$file\".\n";

&number;

print "\nStatus: done numbering each line in file \"$file\".\n";

## SUBROUTINE

sub number {
     my $count;
open(FILE, "$file") || die "Can't locate file \"$file\": $!";
          my @file = <FILE>; # store contents of file into @file
     close FILE;
     open(FILE, ">>$file") || die "Can't locate file \"$file\": $!";
          foreach my $line (@file) {
               (undef) = <FILE>; # stores number of lines into $.
               $count++;
               print FILE, "$count. ";
               if ($count == $.) {
                    last;
               }
          }
          close FILE;
}