Refspec

A refspec maps remote branches to local references. It defines the branches and tags which will be fetched from the remote repository into the agent workspace.

A refspec defines the remote references that will be retrieved and how they map to local references. If left blank, it will default to the normal git fetch behavior and will retrieve all branches. This default behavior is sufficient for most cases.

The default refspec is +refs/heads/*:refs/remotes/REPOSITORYNAME/ where REPOSITORYNAME is the value you specify in the above repository “Name” field. The default refspec retrieves all branches. If a checkout only needs one branch, then a more restrictive refspec can reduce the data transfer from the remote repository to the agent workspace. For example, +refs/heads/master:refs/remotes/origin/master will retrieve only the master branch and nothing else.

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Multiple refspecs can be entered by separating them with a space character. The refspec value +refs/heads/master:refs/remotes/origin/master +refs/heads/develop:refs/remotes/origin/develop retrieves the master branch and the develop branch and nothing else.

Refer to the git refspec documentation for more refspec details.

Source