The Perl Cookbook has a section on working with pairs of arrays to find intersections, differences, etc.

The following is one piece of code it contains - using a temporary hash:

@a = (1, 3, 5, 6, 7, 8);
@b = (2, 3, 5, 7, 9);

@union = @isect = ();
%union = %isect = ();
%count = ();

foreach $e (@a, @b) { $union{$e}++ && $isect{$e}++ }

@union = keys %union;
@isect = keys %isect;
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That is a nice, slick/quick method -- but it will produce false positives for intersections if either array happens to contain multiple elements with the same value (e.g. in your example, if @a contained two elements with a value of 6).

In unix two files can be compared in a quick and dirty manner with the comm program. In perl, you probably want to read perldoc -q intersection

true. comm is also a good way to do that. Looping through the text file gives the added advantage of being able to discriminately direct the text based on matches, which would otherwise need multiple incantations of comm. Thanks for pointing me to the readme, I think those methods ought to do it for me.

Algorithm::HowSimilar is probably the fastest solution but only because it uses the excellent Algorithm::Diff module.

use Algorithm::HowSimilar 'compare';
my (     $av_similarity,
         $sim_ary1_to_ary2,
         $sim_ary2_to_ary1,
         $ref_ary_matches,
         $ref_ary_in_ary1_but_not_ary2,
         $ref_ary_in_ary2_but_not_ary1
       ) = compare( \@ary1, \@ary2 );
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cheers

tachyon

This is something I wrote a while back to compare two files line by line. It reports the line number and prints that line in both files, or prints no difference found. It might be useful to you...

#!/usr/bin/perl -w
use strict;
use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
use CGI ':standard';


my $txt1 = "/path/public_html/test/txt1.txt";
my $txt2 = "/path/public_html/test/txt2.txt";
my $count;
my $item;
open FH, "$txt1" or die $!;
my @all = <FH>;
close FH;

print "Content-type: text/html\n\n";

open PAGE, "$txt2" or die $!;

foreach my $line (<PAGE>)  {
    $count++;
    $item = shift (@all);
    if ($line ne $item) {
        print "line no:  $count<br>
        $line<br>
        $item<br>";
        }    else {
        print "No differences found<br>";    
    }    
}
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Very slick DrHyde! Adding to the TMTOWTDI, you could also use the module Array::Compare.

Or Data::Compare!