To modify a commit that is farther back in your history, you must move
to more complex tools. Git doesn’t have a modify-history tool,
but you can use the rebase tool to rebase a series of commits onto the
HEAD that they were originally based on instead of moving them to
another one. With the interactive rebase tool, you can then stop
after each commit you want to modify and change the message, add files,
or do whatever you wish. You can run rebase interactively by adding
the -i option to git rebase. You must indicate how far back you want to
rewrite commits by telling the command which commit to rebase onto.
For example, if you want to change the last three commit messages,
or any of the commit messages in that group, you supply as an argument
to git rebase -i the parent of the last commit you want to edit,
which is HEAD~2^ or HEAD~3. It may be easier to remember the ~3
because you’re trying to edit the last three commits, but keep in
mind that you’re actually designating four commits ago, the parent
of the last commit you want to edit:
$ git rebase -i HEAD~3
Remember again that this is a rebasing command — every commit in the
range HEAD~3..HEAD with a changed message and all of its descendants
will be rewritten. Don’t include any commit you’ve already pushed to
a central server — doing so will confuse other developers by providing
an alternate version of the same change.
Running this command gives you a list of commits in your text editor
that looks something like this:
```
pick f7f3f6d Change my name a bit
pick 310154e Update README formatting and add blame
pick a5f4a0d Add cat-file
```
If, instead of “pick” or “edit”, you specify “squash”, Git applies
both that change and the change directly before it and makes you
merge the commit messages together. So, if you want to make a single
commit from these three commits, you make the script look like this:
```
pick f7f3f6d Change my name a bit
squash 310154e Update README formatting and add blame
squash a5f4a0d Add cat-file
```
When you save and exit the editor, Git applies all three changes and
then puts you back into the editor to merge the three commit messages:
```
# This is a combination of 3 commits.
# The first commit's message is:
Change my name a bit
# This is the 2nd commit message:
Update README formatting and add blame
# This is the 3rd commit message:
Add cat-file
```
When you save that, you have a single commit that introduces the changes
of all three previous commits.