In brief
git format-patch prepares files for transferring changes, including commit messages and metadata. Creating them does not automatically send email.
Useful to know
git format-patch prepares files for transferring changes, including commit messages and metadata. Creating them does not automatically send email. [1]
Specify the base and sequence when exchanging patches. A patch against another revision can need adaptation. Recipients should inspect the contents and choose how to apply them rather than treating every external file as an already approved change.
Sources
For further detail and to check the information: