You can chomp <DATA> straight away before passing it to the sort routine. [...]
[...]
sort part_sort chomp <DATA>;

<DATA> is immutable, so you cannot chomp it (chomp actually tries to modify what it gets - it returns the number of removed characters, not a list of chomped strings).

#!/usr/bin/perl
print chomp <DATA>;

__DATA__
This piece of code will trigger the following compilation error:

Can't modify <HANDLE> in chomp at - line 2, near "<DATA>;"
Execution of test aborted due to compilation errors.
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2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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