If you want to dump lines that begin with a specific string, this approach works nicely. Instead of slurping the file (with the $/ technique), apply a quick regex on each line:

# open file, don't do the local $/ trick
while (<FILE>) {
    next if /^\s*print/;
    next if /^\s*#/;
    push @lines, $_;
}
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You could, of course, append $_ to a variable called $line if you wished. Feel free to add more small regexes, or modify the existing ones. Sometimes a line-by-line transformation is easier.