use strict;
use warnings;

my @aChapters=("ch1","ch11","ch2","ch5","ch55","ch16");
my @aSorted = sort {
  my ($sA, $iA) = ($a =~ /(^[^\d]+)(\d+)/);
  my ($sB, $iB) = ($b =~ /(^[^\d]+)(\d+)/);
  my $x = $sA cmp $sB;
  ($x = $iA <=> $iB) unless $x;
  $x;
} @aChapters;

local $"="\n";
print "@aSorted";