Merging changes from master into my branch

Answering my own question but to pull changes from upstream's master into my custom branch I did this:

git pull [URL TO UPSTREAM'S REPO] master

git checkout custom_branch && git rebase master

This will update custom_branch with changes from master branch.

Don't forget to make sure master is up to date first. git pull

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This is also possible with git checkout custom_branch && git merge master

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For an explanation on why the first one is (probably) what you should be using: When do you use git rebase instead of git merge?

git merge master will update your current branch with the changes from your local master branch, the state of which will be that of when you last pulled while on that branch.

I think this is what you are looking for: git merge origin master