You cannot (should not) write to the open file while you are still reading from it. Open a new tempfile, write to that, then once the whole file has been read and written, close both and rename the tempfile as the original file (taking a backup first to be prudent). The alternative is to read the whole file in first, store the results in RAM and then write them all out in one go. HTH.

In reply to Re: Inserting new column by hippo
in thread Inserting new column by Avi_Perl_Beginner

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