core/git/git.install

#!/bin/sh

post_install() {
  # make git-shell a valid shell
  if ! grep -qe '^/usr/bin/git-shell$' etc/shells; then
    echo '/usr/bin/git-shell' >> etc/shells
  fi
}

# do not modify user settings (shell) in post-upgrade function!

post_remove() {
  sed -i -r '/^\/usr\/bin\/git-shell$/d' etc/shells
}