#!/usr/bin/perl -w
use strict;

if ( scalar(@ARGV) < 2 ) {
    print "Usage:\n\t$0 file1 file2\n\n";
    die;
}

my @filename = ( $ARGV[0], $ARGV[1] );
my (@content);

foreach my $i ( 0, 1 ) {
    open( DF, $filename[$i] )
      or die("Can't open $filename[$i] for input: $!\n");
    while (<DF>) {
        chomp;
        push( @{ $content[$i]{$_} }, $. );
    }
    close(DF);
}

my @keycount = (
    scalar( keys( %{ $content[0] } ) ),
    scalar( keys( %{ $content[1] } ) )
);
if ( $keycount[0] != $keycount[1] ) {
    my @differential = @filename;
    if ( $keycount[0] > $keycount[1] ) {
        @differential = reverse(@filename);
    }
    print "Fewer values detected in ", $differential[0],
      " than ", $differential[1], "\n";
}
foreach my $k ( sort( keys( %{ $content[0] } ) ) ) {
    if ( defined( $content[1]{$k} ) ) {
        print $k, "\n";
        foreach ( 0, 1 ) {
            print "\tFound in ", $filename[$_], " at line(s): ",
              join( ', ', @{ $content[$_]{$k} } ), "\n";
            delete( $content[$_]{$k} );
        }
    }
}
@keycount = (
    scalar( keys( %{ $content[0] } ) ),
    scalar( keys( %{ $content[1] } ) )
);
if ( $keycount[0] or $keycount[1] ) {
    foreach ( 0, 1 ) {
        if ( $keycount[$_] ) {
            print "Found in ", $filename[$_], " but not in ",
              $filename[ ( $_ + 1 ) % 2 ], ":\n";
            foreach my $k ( sort( keys( %{ $content[$_] } ) ) ) {
                print "\t'", $k, "' at line(s): ",
                  join( ', ', @{ $content[$_]{$k} } ), "\n";
                delete( $content[$_]{$k} );
            }
        }
    }
}

##</code><code>##

$ cat file1.txt
qwerty
snakegod
ebrine
tarot
$ cat file2.txt
snakegod
ordo rosae moriatur
tarot
wrath of hibernia
$ cat file3.txt
qwerty
snakegod
ebrine
tarot
qwerty
$ cat file4.txt
qwerty

##</code><code>##

$ perl cdiff.pl file1.txt file1.txt
ebrine
        Found in file1.txt at line(s): 3
        Found in file1.txt at line(s): 3
qwerty
        Found in file1.txt at line(s): 1
        Found in file1.txt at line(s): 1
snakegod
        Found in file1.txt at line(s): 2
        Found in file1.txt at line(s): 2
tarot
        Found in file1.txt at line(s): 4
        Found in file1.txt at line(s): 4
$ perl cdiff.pl file1.txt file3.txt
ebrine
        Found in file1.txt at line(s): 3
        Found in file3.txt at line(s): 3
qwerty
        Found in file1.txt at line(s): 1
        Found in file3.txt at line(s): 1, 5
snakegod
        Found in file1.txt at line(s): 2
        Found in file3.txt at line(s): 2
tarot
        Found in file1.txt at line(s): 4
        Found in file3.txt at line(s): 4
$ perl cdiff.pl file1.txt file2.txt
snakegod
        Found in file1.txt at line(s): 2
        Found in file2.txt at line(s): 1
tarot
        Found in file1.txt at line(s): 4
        Found in file2.txt at line(s): 3
Found in file1.txt but not in file2.txt:
        'ebrine' at line(s): 3
        'qwerty' at line(s): 1
Found in file2.txt but not in file1.txt:
        'ordo rosae moriatur' at line(s): 2
        'wrath of hibernia' at line(s): 4
$ perl cdiff.pl file1.txt file4.txt
Fewer values detected in file4.txt than file1.txt
qwerty
        Found in file1.txt at line(s): 1
        Found in file4.txt at line(s): 1
Found in file1.txt but not in file4.txt:
        'ebrine' at line(s): 3
        'snakegod' at line(s): 2
        'tarot' at line(s): 4