version control - Git: How to squash all commits on branch

Question

I make new branch from master with:

git checkout -b testbranch

I make 20 commits into it.

Now I want to squash those 20 commits. I do that with:

git rebase -i HEAD~20

What about if I don't know how many commits? Is there any way to do something like:

git rebase -i all on this branch

Answer 1

Another way to squash all your commits is to reset the index to master:

 git checkout yourBranch
 git reset $(git merge-base master $(git branch --show-current))
 git add -A
 git commit -m "one commit on yourBranch"

This isn't perfect as it implies you know from which branch "yourBranch" is coming from.
Note: finding that origin branch isn't easy/possible with Git (the visual way is often the easiest, as seen here).

Note: git branch --show-current has been introduced with Git 2.22 (Q1 20219).

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EDIT: you will need to use git push --force

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Karlotcha Hoa adds in the comments:

For the reset, you can do

git reset $(git merge-base master $(git rev-parse --abbrev-ref HEAD)) 

[That] automatically uses the branch you are currently on.
And if you use that, you can also use an alias, as the command doesn't rely on the branch name.