note philiprbrenan <code> use feature ":5.14"; use warnings FATAL => qw(all); use strict; use Data::Dump qw(dump pp); my @positions; for(split /\n/, <<'END') 1 ACAC 2 AGAC 3 AGTC 4 ACCA END {push @positions, [split/ /] unless /[GT]/; } say "With bases: ", dump(@positions); $_ = $_->[0] for @positions; say "Without bases: ", dump(@positions); </code> <p>Produces</p> <code> With bases: ([1, "ACAC"], [4, "ACAC"]) Without bases: (1, 4) </code> 991184 991184