#!/bin/bash
    
    # Put this into your .bashrc, or whatever.
    function git-add-regex {
      git diff -U0 | grepdiff -E "$1" --output-matching=hunk | git apply --cached --unidiff-zero
    }

git add . -N

And then review the text itself as part of the git add -p workflow

Also, you can use -p for stash push

PS: Majutsu provides this too (a magit-like tool for jj)

After switching to jujutsu, I assure you I don't miss this feature.

jj takes the opposite approach. It keeps staging things, and you use split whenever you want to separate things out.

(And yes, it stores the staged changes as revisions, so you can always back out to a previous staged state).