What is a tracking branch, and what is the `-u` flag for when pushing?

A tracking branch is a local branch linked to a remote branch, its upstream. That link lets you use git push and git pull without typing the remote and the branch every time. The -u flag (or --set-upstream) creates that link the first time you push a branch.

When your local branch knows which remote branch it corresponds to, Git can do several things for you:

• git push with no arguments knows where to upload.
• git pull with no arguments knows where to download from.
• git status tells you "you're 2 commits ahead / 1 behind origin/main".

That link is called the upstream. It's set the first time with git push -u origin nombre-rama. The -u is a shortcut for --set-upstream: "remember that this local branch follows this remote branch". After that, you no longer need to repeat the remote or the branch.

# First time you push a new branch: create the link with -u
git switch -c mi-feature
git push -u origin mi-feature
# Now local mi-feature follows origin/mi-feature

# From here, this is all you need:
git push          # knows it goes to origin/mi-feature
git pull          # knows where to fetch from

# See which upstream each branch has
git branch -vv
# * mi-feature 1a2b3c4 [origin/mi-feature] Agrega login
#   main       5d6e7f8 [origin/main] Version inicial

# Set the upstream of an already existing branch
git branch --set-upstream-to=origin/mi-feature

Forgetting the -u the first time and having Git respond with an error like "fatal: The current branch has no upstream branch", without knowing why. The fix is to run git push -u origin nombre-rama the first time. Another mistake is thinking you need to add -u on every push: you only need it once, to create the link.

"A tracking branch is a local branch linked to a remote branch, its upstream. That link makes git push and git pull know where to go without me typing the remote and the branch every time, and makes git status tell me how many commits I'm ahead or behind. The link is created the first time with git push -u origin nombre-rama; the -u is --set-upstream. After that I just run plain git push or git pull."