Two completely different subs, the first is much faster, the second is much more flexible. You need to replace @ary with your actual data :)

#!/usr/bin/perl

use warnings;
use strict;

my @ary = (0..5);

print map { "@$_\n" } pairs(@ary);
print "\nCHOOSE:\n";
print map { "@$_\n" } choose(2, @ary);

# hard-coded return of pairs
sub pairs {
    my @result;
    foreach my $i (0..$#_-1) {
        foreach my $j ($i+1..$#_) {
            push @result, [$_[$i], $_[$j]];
        }
    }
    return @result;
}

#more general solution: choose any combinations of k elms from @_:

sub choose {
    no warnings 'recursion';
    my $k = shift;
    my @ary = @_;
    my $n = scalar @ary;
    
    return if ($k > $n) || ($k < 1);
    if ($k == 1) {
        return map { [$_] } @ary;
    }

    my @AoA;
    foreach my $i (0..($n-$k)) {
        push @AoA, map { [$ary[$i], @{$_}] } choose($k-1, @ary[ $i+1..
+$#ary ]);
    }
    return @AoA;
}
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