chomp doesn't return the chomped lines, they're modified "in place". It does, however, return the number of characters removed — which is what you're passing to the sort function in the second case, while you're discarding that value in the first case.

my @due=sort chomp (my @lines=<STDIN>);
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my @anon = chomp (my @lines=<STDIN>);
my @due=sort @anon;
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chomp (my @lines=<STDIN>);
my @due=sort @lines;
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In the first snippet you posted, you are sorting @lines. In the second, you are sorting the result of chomp. These are very different, as described in chomp's documentation.

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; $_ } <>;'
line 1
line 2
line 3
line 4
line 5
line 6
knoppix@Microknoppix:~$
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I hope this is helpful.

I think this number is the quantity of lines chomped

You can easily find out, in a number of different ways:

• From the command line, type perldoc -f chomp
• Googling for perldoc chomp usually takes you to perldoc.perl.org
• You can use the wonderful perldoc.perl.org website
• You may have HTML documentation installed depending on which Perl you're using

• my $snap = "a$/";
  warn unpack 'H*', $snap;
  warn unpack 'H*', chomp ( my $crackle = $snap );
  warn unpack 'H*', $crackle;
  warn unpack 'H*', $/;
  __END__
  610a at - line 2.
  31 at - line 3.
  61 at - line 4.
  0a at - line 5.
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  chomp, perlvar, Tutorials
• subject , not your status , goes in Title field (your question in one sentance )

I'm a bit baffled by the question - it's not that you assume chomp leaves its arguments untouched and returns the the chopped lines - then you would have written the first fragment as

my @lines = chomp(<STDIN>);
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