This is a FAQ. Please type perldoc -q intersection or see perlfaq4, "How do I compute the difference of two arrays".

Hi, read the two files names in two different arrays and compare the array using List::Compare module. It will give the presence of extra names in both the files as below.

use strict;
use warnings;
use List::Compare;
my @file1 = qw(name1 name2 name3 name4 name5 name6 name7 name8 name9 n
+ame10);
my @file2 = qw(name1 name2 name3 name4 name5 name6 name7 name8 name9 n
+ame10 name11);

my $lcma = List::Compare->new(\@file1, \@file2);
print $lcma->get_complement; # extra present in file2
print $lcma->get_unique;     # extra present in file1
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use strict;
use Tie::File;

# read first file
open my $fh, '<', 'FILE1'
    or die "can't open FILE1\n";
chomp(my @file1 = <$fh>);
close $fh;

# remove from second file
tie my @file2, 'Tie::File', 'FILE2' 
    or die "can't open FILE2\n";

foreach my $x (@file1) {
    @file2 = grep {!/^$x$/} @file2;
}

untie @file2;
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HTH,
Mickey

Tough not to mention a un*x golf solution ;)

$ comm -12 <(sort FILE1) <(sort FILE2) > OUT # comm gives 3 cols
                            # 1: lines only in first file
                            # 2: lines only in second file
                            # 3: common lines 
                            # flag -# suppresses col#
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magic <(...) is to save a temporary file. If your shell does not support it just do 'sort FILE1 -o FILE1.s' comm needs sorted files for its magic.