http://ask.metafilter.com/167995/Help-me-do-my-job-with-minimal-effort

program.pl

#!/usr/bin/perl -CSDAL
#
# Usage: PROGNAME big_list.txt small_list.txt > output.txt
# -CSDAL for unicode.
use strict;
use warnings;

# should maybe have this
use locale;

# Read the big/small list file names
my $bigfile = shift @ARGV;
my $smallfile = shift @ARGV;

# Read the small list file, map to UPPER CASE, remove line ending
my @small = do { local @ARGV = $smallfile; <> };
@small = map { uc $_ } @small;
chomp @small;
my %small;
$small{$_} = undef for @small;

# Read through the big list file
@ARGV = $bigfile;
while (<>) {
    chomp;            # Get rid of line ending
    print;            # print without any number following and no line ending

    my $big = uc $_;  # make it UPPER CASE
    #if (grep { $big eq $_ } @small) {     # if it is in small list
    if (exists $small{$big}) {     # if it is in small list
      print " 2";                         # add a " 2" to the end.
    }
    print "$/";       # print the line ending
}

$ cat one 
One
Two
Three
Four

$ cat two 
three
one

$ ./program.pl one two
One 2
Two
Three 2
Four