git-rel

#!/usr/bin/env sh
# Taken from https://github.com/ahmedelgabri/dotfiles/blob/master/extra/bin/git-rel
# Usage: git-rel [<ref>]
# Shows the relationship between the current branch and <ref>. With no <ref>,
# the current branch's remote tracking branch is used.
#
# Examples:
#
#   $ git-rel
#     15 ahead
#     11 behind
#
#   $ git-rel v1.1
#     230 ahead

strip_prefix() {
  echo "$@" |
    sed 's@refs/heads/@@'
}

current_branch() {
  git symbolic-ref -q HEAD |
    sed 's@refs/heads/@@'
}

tracking_branch() {
  remote=$(git config --get branch."$(current_branch)".remote)
  merge=$(git config --get branch."$(current_branch)".merge)
  echo "$remote/$(strip_prefix "$merge")"
}

ref="${1:-$(tracking_branch)}"

git rev-list --left-right --abbrev-commit --abbrev "$ref"...HEAD |
  cut -c1 |
  sort |
  uniq -c |
  tr '\n' ',' |
  sed "
  s/>/ahead/
  s/</behind/
  s/,$//g
  s/,/, /g
"