>>77 Perl5

@s = split '', '213cba213cba213cba';
@i = 0..$#s;
@k = grep{$s[$_] =~ /[a-z]/} 0..$#s;
@l = sort @s[@k];
$s[$k[$_]] = $l[$_] for 0..$#k;
use feature 'say';
say @s;


$ perl 11_77.pl
213aaa213bbb213ccc