It depends how large exactly a "very large file" is.

The typical way to do this type of work is to read your tab delimited text file and to store words you're looking for in a hash, and then to look for the word in the hash. The reason this is the good way to do that is that hash lookup is extremely fast (and does not depend on the size of the hash). Now, of course, this works only if the hash does not grow too large to fit in memory. So please provide more information about the size of your files and what you would need to store in addition to the key.

It would be good if you could provide a small extract of both files, showing cases matching your searches.

In reply to Re: Comparing a list to a tab delimited text file by Laurent_R
in thread Comparing a list to a tab delimited text file by Azaghal

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