Script to fixup/squash commits given on a cmd line - can be used as a Custom Action in SourceTree

git-fixup.sh

#!/bin/bash

lastCommit=""
editorCmd="sed -i ''"
for commit in $@; do
  lastCommit=${commit:0:7}
  editorCmd="$editorCmd -e 's/pick ${lastCommit}/fixup ${lastCommit}/'"
done

GIT_SEQUENCE_EDITOR=$editorCmd git rebase -i ${lastCommit}~2

Can be used like this:

git-fixup.sh af363a0ead31 7574fdbb9382ac3 118de7faa1e0a0

This will squash each of the given commits into its parent - useful to clean up bug-fix/syntax/reformatting/etc commits

To setup as a Custom Action in SourceTree, go to Preferences->Custom Actions:

1. Click Add
2. Menu Caption: fixup
3. Script to run: [path to git-fixup.sh]
4. Parameters: $SHA

You can then select a range of commits, right-click and choose Custom Actions->fixup to squash all of the given commits with their parents

Excellent! Now if only Source Tree would allow you to pass a new commit message to apply to the squashed commit.