Did you do something wrong? I got what you expected: 
#!/your/perl/here

use strict;
use warnings;

my @list = qw(apple1 apple apple20);

my @sorted = @list[
    map { unpack "N", substr($_,-4) }
    sort
    map {
        my $key = $list[$_];
        $key =~ s[(\d+)][ pack "N", $1 ]ge;
        $key . pack "N", $_
    } 0..$#list
];

print "@sorted\n";

[download]
gives: 
apple apple1 apple20

[download]
Post your code and let's check it.

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to Re^2: [ Natural Sort ]: Sorting a string with numbers by QM
in thread [ Natural Sort ]: Sorting a string with numbers by zzspectrez

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