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use v5.14;
use warnings;
...
while (my ($c,$r) = splice @matches,0,2) {
  say "$c - $r";
}

INPUT: 11 12 13 14 15 16 17 18 19
11 - 12
13 - 14
15 - 16
17 - 18

use v5.14;
use warnings;
...
  say "$c $r";
  die unless $stop--;
}

INPUT: 1 2 3 4 5 6 7 8 9
1 2