So what have you tried so far?

My idea: read the first file, build a regex from all lines (by joining the lines with |), then read the second file, and prepend a # to all lines which match the regex.

(It's easier if you first produce the correct output instead of editing the file in-place).

In reply to Re: how to comment the lines if found a match by moritz
in thread how to comment the lines if found a match by kavitha

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