Script that compares two files of IDs, that are on separate lines

compare_list.pl

#!/usr/bin/env perl
#
# Script that compares two files of IDs, that are on separate lines
# See http://stackoverflow.com/questions/2933347/comparing-two-arrays-using-perl
#

use strict;
use warnings;
use Array::Utils qw(:all);

my $usage = "Usage: <infile.txt> <infile2.txt>\n";
my $infile = shift or die $usage;
my $infile2 = shift or die $usage;

my @a = read_into_array($infile);
my @b = read_into_array($infile2);

# intersect
my @isect = intersect(@a, @b);
print "These ", scalar(@isect), " items/s are in both:\n\n@isect\n\n";

# symmetric difference
my @diff = array_diff(@a, @b);

if (scalar(@diff) == 0){
   print "The lists are the same\n";
} else {
   print "These ", scalar(@diff), " item/s are different:\n\n@diff\n\n";
   my @a_not_b = array_minus(@a, @b);
   my @b_not_a = array_minus(@b, @a);
   if (scalar(@a_not_b) > 0){
      print "These ", scalar(@a_not_b), " item/s are in $infile but not in $infile2:\n\n@a_not_b\n\n";
   }
   if (scalar(@b_not_a) > 0){
      print "These ", scalar(@b_not_a), " item/s are in $infile2 but not in $infile:\n\n@b_not_a\n\n";
   }
}

sub read_into_array {
   my ($infile) = @_;
   my @a = ();
   open(IN,'<',$infile) || die "Could not open $infile: $!\n";
   while(<IN>){
      chomp;
      push(@a, $_);
   }
   close(IN);
   return(@a);
}

exit(0);