Thanks for the lesson repson. I see the wisdom of your changes:

• replaced multiple print statements with here docs
• eliminated useless scalar use
• replaced the hash with string concatenation via assignment op
• one while instead of for loops, sorting and subroutine
• more elegant flow eliminates need for multiple exits

But the final print statement:

print ($good_lines+$bad_lines) . "lines read from $infile\n",
            "$bad_lines comment lines detected in $infile\n",
            "$good_lines lines written to $outfile\n";
[download]

Failed on 5.00503 with the warning:

print (...) interpreted as function at unc_rep.pl line 40.
[download]

So /me sweeps up around the monastery:

my$lines=($good_lines+$bad_lines);
print "$lines lines read from $infile\n",
      "$bad_lines comment lines detected in $infile\n",
      "$good_lines lines written to $outfile\n";
[download]

ps - fixed omission of the 2nd $0 in the original.