Question

Probably this is a very basic question for shell programmers.
But suppose I have a text file A and B
and B is a subset of A.

I want to create a text file C which contains (A-B) data.

So omit all the common lines .

The line in files are numeric data: like

id , some aspect, other aspec.

Thanks.

Answer 1

Use sort and uniq

sort a b | uniq -u

If you want the lines that are the same between A and B, you can use uniq -d

sort a b | uniq -d

This assumes of course that the data in A and B are exactly the same. There cannot be any lose spaces or tabs in the datasets. If there are, you’ll have to clean up the data with sed, tr, or awk first.

Edit

As Peter. O pointed out, this will fail if there happen to be exact duplicates in file a. If that’s an issue, you can fix it by doing this:

sort <(sort -u a) b | uniq -u