Git add lines to index by grep/regex

Question

I have a giant patch that I would like to break into multiple logical git commits. A large number of the changes are simply changing variable names or function calls, such that they could easily be located with a grep. If I could add to the index any changes that match a regex then clean up in git gui, it would save me a lot of manual work. Is there a good way to update the index on a line-by-line basis using a regex within git or from some output of grep (e.g. line numbers)?

I found a similar question, but I'm not sure how to build the temporary file from a regex-type search.

Answer 1

patchutils has a command grepdiff that can be use to achieve this.

# check that the regex search correctly matches the changes you want.
git diff -U0 | grepdiff 'regex search' --output-matching=hunk  

# then apply the changes to the index
git diff -U0 | grepdiff 'regex search' --output-matching=hunk | git apply --cached --unidiff-zero 

I use -U0 on the diff to avoid getting unrelated changes. You might want to adjust this value to suite your situation.