Switch on another branch (create if not exists), without checking if already exists?

Update Q3 2019 (Git 2.23): there now actually is a git switch command!

git switch -c aBranch 

You would need a similar alias though:

switchoc = "!f() { git switch $1 2>/dev/null || git switch -c $1; }; f"

Note the name of the alias: switchoc (for "switch or create").
As jar pointed out in the comments:

Anyone trying this in 2021, note that you cannot shadow existing git commands with aliases.
Since git switch is a git command, this alias (named "switch") won't work. You must create your unique name for the alias, like "switchit" or something.

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bgusach's alias mentioned below in the comment is safer (based on Jiří Pavelka 's answer):

switch = "!f() { git checkout $1 2>/dev/null || git checkout -b $1; }; f"

git switch abranch

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Original answer (2014) You can try:

git checkout -B foo

From git checkout man page:

If -B is given, <new_branch> is created if it doesn’t exist; otherwise, it is reset. This is the transactional equivalent of

$ git branch -f <branch> [<start point>]
$ git checkout <branch>

As mentioned below, use it with caution as it does reset the branch, which is not always desirable.
If you did reset the branch by mistake with this command, you can easily revert to its previous state with:

git reset HEAD@{1}

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Agreed with ssmith. Had the same problem and -B does not solve it, coz of reset. His solution works, however my solution looks simpler:

git checkout foo || git checkout -b foo

That works for me :)

EDIT

Without error output iff foo not exists

git checkout foo 2>/dev/null || git checkout -b foo

Note the rather important fact that -B will reset an existing branch before checking it out, which I don't believe @Ionica wants according to his question.

I certainly didn't, so the best one-liner I could come up with is this:

git checkout $(git show-ref --verify --quiet refs/heads/<branch> || echo '-b') <branch>

This can be made into a handy alias like so:

[alias]
  # git cob <branch>
  cob = "!f() { git checkout $(git show-ref --verify --quiet refs/heads/\"$1\" || echo '-b') \"$1\"; }; f"