Run git fetch after any cd command

Question

I need to run git fetch after any cd command in the background and only if I'm in a git directory.

Answer 1

There are three parts to this:

1. Run some code on changing the current directory. In zsh, you put this code in the chpwd function, or a function with a different name in the chpwd_functions array (example). See Execute bash scripts on entering a directory for a bash implementation.
2. Detect git working copies. Since you're only interested in git, you can run git rev-parse --show-toplevel. There are more advanced frameworks to detect version control if you're interested in other version control systems.
3. Run git fetch.

Here's a chpwd implementation that runs git fetch when changing into a git repository.

chpwd () {
  set -- "$(git rev-parse --show-toplevel 2>/dev/null)"
  # If cd'ing into a git working copy and not within the same working copy
  if [ -n "$1" ] && [ "$1" != "$vc_root" ]; then
    vc_root="$1"
    git fetch
  fi
}
chpwd

This code goes in your shell startup script: .zshrc for zsh, .bashrc for bash (in bash you also need the wrappers to call chpwd on a directory change).

Answer 2

You can use a function:

function cd() {
    builtin cd "$@"
    if [[ -d .git ]]; then
        git fetch &
    fi
}

Add this to your shell's startup file.

There are a couple things that are going on here:

1. First we use function cd() { to override the builtin cd behavior with our own custom code.
2. Obviously we still want to change the directory, so we do that first - we prefix it with builtin* so that the shell uses the builtin cd instead of recursively calling our custom cd() function, and we provide it with $@ as the arguments, which gets expanded by the shell to all arguments provided to the function.
3. We test if we're in a git repository^ by testing if the .git directory exists, and if it does we run git fetch, telling the shell to put it in the background by appending &.

Note that the output of git fetch will still be sent to the terminal. If you wish to discard it you can use this instead:

git fetch & 2>&1 >/dev/null

This redirects stderr into stdout, then sends stdout to /dev/null.

[*]: Note that builtin isn't in POSIX and therefore this solution isn't portable across all shells

[^]: This fails if the git repository is bare, but you almost certainly aren't going to have a bare repository on your drive, so who cares

Answer 3

make a function in your .bashrc or .zshrc file that is in your home directory.

Add the following to the bottom of the file:

cd_fetch() {
    command cd "$@"
    if [ -d .git ]; then
        git fetch & 
    fi
}
alias cdg=cd_fetch

Now close and re-open your terminal or run source ~/.zshrc and now you can change directory with the command cdg that you just aliased.

Also if you don't want to use cdg and want to use just cd change the alias definition to alias cd=cd_fetch.

This approach will still output all that git fetch normally do, to silence it replace the git fetch & line for git fetch 2>&1 >/dev/null &.