Git diff and merge with p4merge (macOS)

.gitconfig

[merge]
  keepBackup = false
	tool = p4merge
[mergetool "p4merge"]
	cmd = /Applications/p4merge.app/Contents/Resources/launchp4merge "\"$PWD/$BASE\"" "\"$PWD/$REMOTE\"" "\"$PWD/$LOCAL\"" "\"$PWD/$MERGED\""
	keepTemporaries = false
	trustExitCode = false
	keepBackup = false
[diff]
    tool = p4merge
[difftool "p4merge"]
	cmd = /Applications/p4merge.app/Contents/Resources/launchp4merge "\"$LOCAL\"" "\"$REMOTE\""

1. Install p4merge
   -- either from perforce.com
   -- or if you have homebrew, install it with: brew cask install p4merge
2. copy and paste the above snippet into your ~/.gitconfig file (at the bottom)
   -- if you don't think you have that file, run ls -al ~ to verify
   -- if you don't, then run touch ~/.gitconfig
3. Then you can do git mergetool and git difftool to use p4merge
4. Note that git diff will still just use the default inline diff viewer