You say you "tried the search and replace function" (I can only assume you mean a substitution regex), but don't show your work. It's a whole lot easier for us to help fix your code if you show us your code. Read How (Not) To Ask A Question.

Assuming your input has not been mangled by lack of <code> tags (Markup in the Monastery), you can iterate over the set with a while loop and a regular expression. It might look something like:

#!/usr/bin/perl
use strict;
use warnings;

$_ = '2 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2';
while (/(\d) (\d)/g) {
    my ($first, $second) = ($1, $2);
    # insert logic for output
}
[download]

See Global matching in perlretut.