You might want to have a look at map which you could use here. Again, you need to pass out the chomped string, not the return value of chomp.

knoppix@Microknoppix:~$ cat xxxx
line 4
line 2
line 5
line 1
line 6
line 3
knoppix@Microknoppix:~$ cat xxxx | perl -E '
> say for sort map { chomp; $_ } <>;'
line 1
line 2
line 3
line 4
line 5
line 6
knoppix@Microknoppix:~$
[download]

I hope this is helpful.