Unless I'm missing something here, both of those last two solutions give the letters in the wrong order. The order requested is divider, after, before - not before, divider, after. The following should work:

use strict;
use warnings;

my $str = 'AFNMIWEBFASBPMLASIFBYRW';
my $mid = 'I';
my @sorting;

push @{$sorting[($_ cmp $mid) + 1]}, $_ for split '', $str;
$str = join '', @{$sorting[1]}, (sort @{$sorting[2]}), (sort @{$sortin
+g[0]});

print $str;
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