Like grep says: use strict; use warnings;

That won't catch your problem though. You're adding a space with @list1[$nk] = "$item1 \n";. Try dropping the space before the newline.

Other concerns:

• @list1[$nk] is better written as $list1[$nk] ; Though just until Perl 6
• You currently read the file
  Then sort (though it's not shown)
  write the file
  read it
  and then display it
• Try reading it
  sorting it
  displaying it and writing it at the same time
• IIRC, $#list1 notation is being dropped. Just go ahead and use @list1 for # of elements. scalar @list1 is you need to.
• Another version of your code is in my pad
  I'll leave that there for your review for now

Update: boo has an excellent point. I just glossed by that point.

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