little cubes

Moving a branch pointer in Git

My struggles with a seemingly simple task

Branches are just pointersSection titled: Branches are just pointers

Before reading this article (article may be a generous term for my ramblings), you should understand that in Git, a branch is nothing more than a pointer to a certain commit. There is very little difference between the name of a branch, and the commit hash that it points to.

* c5c2d07 (HEAD) Try different meta tags
* f3dfc69 (facebook) Add meta tags for facebook
* 04268d7 Allow opening of jeopardy category tile on mobile
* 8de6814 Add Jeopardy unanswered state

In the above commits, facebook, f3dfc69, and head^ are all equivalent to Git in most circumstances.

Why I want to move themSection titled: Why I want to move them

Often you’ll get into a situation where a remote branch gets updated, and then you have to move your local version. You could use pull, but pull has the potential to unintentionally merge, so I avoid it like the plague. Instead, I would like to so something like git move master origin/master to update my local master branch to point to the same commit that origin/master currently points to.

Writing a custom git commandSection titled: Writing a custom git command

# If there are 0 or 1 arguments
if [ $# -eq 0 ] || [ $# -eq 1 ]
echo "Usage: git move <BRANCH-NAME> <BRANCH-POINTER>"
exit 1
git branch -D $1
git branch $1 $2
echo ""
echo "Branch $1 moved to $2"

This solution worked fine for me for a long time, but there was always one problem that I didn’t even realize was coming from this script. When you delete a branch and create a new one of the same name, your new branch no longer tracks the remote branch that is used to.

Ok, no deletingSection titled: Ok, no deleting

So I needed to figure out a way to do it without deleting the branch. The obvious solution seemed to be reset --hard, so I gave that a whirl.

Terminal window
parseBranchName = !git branch | grep '*' | sed 's/* //' # Get the current branch name
master = !git parseBranchName > b.txt && git checkout master && git reset --hard up/master && sed 's/ //' b.txt | xargs git checkout && rm b.txt # Move local master to point to up/master

I shied away from a bash script because looking up its odd syntax had proven to be a pain for me last time. But that left me with the limitation of writing a typical git alias. The largest problem here is that I wanted to keep the current branch checked out and not end up with master checked out after each time that command is run. Because of that I needed to first parse the current branch name, then pass that data along to the end of the script in order to re-checkout that branch.

The only way I could come up with to do that over several commands was to write it to a file, and then read and delete that file. That was annoying because sometimes when the command would fail for one reason or another, I would end up with a random b.txt file sitting in my repo. Also, even though the current branch was checked out in the end, I did checkout a different branch for a few microseconds, which was enough to trigger Visual Studio to think that it should reload.

How that monstrosity worksSection titled: How that monstrosity works

parseBranchName parses the output of git branch to fet the name of the current cranch you’re on (it looks for the branch name with a * in front of it). This branch name is then written out to a text file b.txt. This is all done to store your current branch so that you don’t end up on a different branch when the command is finished.

We then do the actual moving with checking out the master branch and resetting it to point to the same commit as up/master. We then read back in b.txt, use xargs to pass the stored branch name as an argument to git checkout, and finally delete the b.txt file.

Whew, that was a lot of work. When this script failed for some reason, you are left with a random b.txt file hanging around…which I may have committed more than once.

FinallySection titled: Finally

Finally, after going through all of this, I learned that git already has a built-in way of doing this (naturally).

Terminal window
move = branch -f
master = !git move master up/master

Git branch has a -f flag that will force the branch to be “created” even if the branch already exists, effectively moving it, keeping the remote tracking in tact. I learned a lot about it Git by going through this adventure, but the lesson in the end is clearly “google it before reinventing the wheel”.