I don't quite see how the @part array is dealt with when you are looking at the entire file. However, the code that picks a random line is:

rand($.) < 1 && ($line = $_) while <FILE>;
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You could easilly change this to loop over the file, doing something with each line along the way:

while (<FILE>) {
   my $line = $_;
   chomp($line);    # note, 'chomp' is a safer version of 'chop': see 
+perldoc -f chomp;
   # do something with $line...
}
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Hope this helps.

-Blake