My problem is that I need to positively match the files containing _only_ the "99","END"
So if I understand correctly, the files you want to match have only one line in them, namely "99","END"\r\n, with the \n presumably being used as the record separator for reading the lines, this being linux. You also can examine the lines only on a line-by-line basis.

The (untested) string '\A(?!"99","END"\r\n\z)' compiled to a regex will only match a line other than '"99","END"\r\n', so if the count of this regex in the hash is greater than zero, you know the file contained a line or lines other than '"99","END"\r\n' and so is not a file of interest.

Update: Added back some "s on END that somehow got dropped in a couple of places.

In reply to Re: using a regex to determine if a string is the start of the FILE by AnomalousMonk
in thread using a regex to determine if a string is the start of the FILE by ftumsh

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