If you are doing this a lot with large files, computing a cryptographic hash is the way to go. If, on the other hand you are:

1) Working on Windows
2) Working over network shares
3) Not doing too much

This little snippet I threw together the other day to compare the contents of two shares might help:

my $share = '\\\\someserver\\someshare\\"'
foreach my $file (@file_list)
{
    my $file2 = $share . $file;
    if (-e $file2)
    {
        my @cmp = `fc $file $file2 | findstr /c:"FC:"`;
        if ($cmp[0])
        {
            unless ($cmp[0] =~ /no differences/)
            {
                print "$file:  $cmp[0]";
            }
        }
        else
        {
            print "$file:\n"
        }
    }
    else
    {
        print "$file is missing from $share\n";
    }
}
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