Automatic prune with Git fetch or pull

If someone deleted a remote branch because the work is over and I don't know, I won't do a git fetch --prune and eventually I will push back the deleted branch.

Is there a viable solution for forcing Git to use the prune mode when fetching / pulling without having to specify it every time?

Since git 1.8.5 (Q4 2013):

"git fetch" (hence "git pull" as well) learned to check "fetch.prune" and "remote.*.prune" configuration variables and to behave as if the "--prune" command line option was given.

That means that, if you set remote.origin.prune to true:

git config remote.origin.prune true

Any git fetch or git pull will automatically prune.

Note: Git 2.12 (Q1 2017) will fix a bug related to this configuration, which would make git remote rename misbehave.
See "How do I rename a git remote?".

See more at commit 737c5a9:

Without "git fetch --prune", remote-tracking branches for a branch the other side already has removed will stay forever.
Some people want to always run "git fetch --prune".

To accommodate users who want to either prune always or when fetching from a particular remote, add two new configuration variables "fetch.prune" and "remote.<name>.prune":

• "fetch.prune" allows to enable prune for all fetch operations.
• "remote.<name>.prune" allows to change the behaviour per remote.

The latter will naturally override the former, and the --[no-]prune option from the command line will override the configured default.

Since --prune is a potentially destructive operation (Git doesn't keep reflogs for deleted references yet), we don't want to prune without users consent, so this configuration will not be on by default.

git config --global fetch.prune true

To always --prune for git fetch and git pull in all your Git repositories:

git config --global fetch.prune true

This above command appends in your global Git configuration (typically ~/.gitconfig) the following lines. Use git config -e --global to view your global configuration.

[fetch]
    prune = true

git config remote.origin.prune true

To always --prune but from one single repository:

git config remote.origin.prune true
                 #^^^^^^
                 #replace with your repo name

This above command adds in your local Git configuration (typically .git/config) the below last line. Use git config -e to view your local configuration.

[remote "origin"]
    url = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    fetch = +refs/heads/*:refs/remotes/origin/*
    prune = true

You can also use --global within the second command or use instead --local within the first command.

git config --global gui.pruneDuringFetch true

If you use git gui you may also be interested by:

git config --global gui.pruneDuringFetch true

that appends:

[gui]
    pruneDuringFetch = true

References

The corresponding documentations from git help config:

--global

  For writing options: write to global ~/.gitconfig file rather than the repository .git/config, write to $XDG_CONFIG_HOME/git/config file if this file exists and the ~/.gitconfig file doesn’t.

--local

  For writing options: write to the repository .git/config file. This is the default behavior.

fetch.prune

  If true, fetch will automatically behave as if the --prune option was given on the command line. See also remote.<name>.prune.

gui.pruneDuringFetch

  "true" if git-gui should prune remote-tracking branches when performing a fetch. The default value is "false".

remote.<name>.prune

  When set to true, fetching from this remote by default will also remove any remote-tracking references that no longer exist on the remote (as if the --prune option was given on the command line). Overrides fetch.prune settings, if any.

If you want to always prune when you fetch, I can suggest to use Aliases.

Just type git config -e to open your editor and change the configuration for a specific project and add a section like

[alias]
pfetch = fetch --prune   

the when you fetch with git pfetch the prune will be done automatically.

and eventually I will push back the deleted branch

This is something that I think you should address. If you have git configured so that it pushes branches you aren't trying to push, this can be a problem. I personally prefer to set it up so that I only push a branch when I explicitly specify a branch that I want to push.

See https://stackoverflow.com/a/948397/3753318 for some guidance on how to configure the push settings in your git repository.