Question

I’m writing a small shell script that needs to reverse the lines of a text file. Is there a standard filter command to do this sort of thing?

My specific application is that I’m getting a list of Git commit identifiers, and I want to process them in reverse order:

git log --pretty=oneline work...master | grep -v DEBUG: | cut -d' ' -f1 | reverse 

The best I’ve come up with is to implement reverse like this:

... | cat -b | sort -rn | cut -f2- 

This uses cat to number every line, then sort to sort them in descending numeric order (which ends up reversing the whole file), then cut to remove the unneeded line number.

The above works for my application, but may fail in the general case because cat -b only numbers nonblank lines.

Is there a better, more general way to do this?

Answer 1

In GNU coreutils, there’s tac(1)