Shell Programming and Scripting

As long as no line in either of your input files is a substring of a line in the other input file AND there is at least one line in 1.txt that is not present in 2.txt, you will get away with using the 3 grep commands above to do what you are trying to do.

If any of the conditions listed above are violated, you will not get the correct results with the above code. But, the changes I suggested in post #6 for the 1st two grep commands:

Code:

(grep -Fxvf 2.txt 1.txt; grep -Fxvf 1.txt 2.txt) > 3.txt

would give you correct results.

But, unless there are duplicated lines in one or both of your input files, the single awk script RavinderSingh13 suggested will be faster (only needing 1 process instead of 3 and only reading the 17,500 lines of input from your two files once instead of three times). If what you're saying is that want an output file named 3.txt instead of dissimilar_ones.txt, I would assume that you understand that you can change the string "dissimilar_ones.txt" in Ravinder's awk script in two places to change the name of that output file.

If there are duplicated lines in your input files that need to be preserved, Ravinder's suggested awk script could be modified slightly to handle that case (which was not mentioned in your requirements and input samples) and still the get speed improvements afforded by executing fewer processes and only needing to read your input files once.

Of course, as always, if you're using a Solaris/SunOS system, you'd need to change awk in Ravinder's script to /usr/xpg4/bin/awk or nawk.