website/content/blog/ahead-behind-git.md

title	date	draft	tags	math	medium_enabled
Figuring out which git repositories are ahead or behind	2023-11-09T21:05:34-05:00	false	Git	false	false

More often than I care to admit, I would pick up to do work on a device only to realize that I'm working with an older version of the codebase. I could use the git status command, but the output is verbose and stale if you haven't git fetch/pull'd.

I keep the majority of my git repositories in the folder ~/repo/ on all my devices. Inspired by a recent blog post by Clayton Errington, I wanted a way to quickly check within a folder which repositories need updating. Their blog post has a script written in PowerShell. I decided to write my own bash implementation, and also ignore the bit about modified files since I mostly care about the state of my commits with respect to the origin remote.

Before writing a recursive implementation, let's first discuss how to check the ahead/behind status for a single repository.

First things first, you need to make sure that we have all the references from the remote.

git remote update

To print out how many commits the local main branch is ahead of the one located on the origin remote we can use:

git rev-list --count origin/main..main

Similarly for checking how many commits the local main branch is behind we can use:

git rev-list --count main..origin/main

Instead of looking at the main branch, maybe we can to check whichever branch we're currently at.

branch=$(git rev-parse --abbrev-ref HEAD)

We can wrap all of this into a nice bash function. We'll additionally check if there is a .git in the current folder as none of the git commands will work without it.

check_remote() {
  if [ -d .git ]; then
    git remote update > /dev/null 2> /dev/null
    branch=$(git rev-parse --abbrev-ref HEAD)
    ahead=$(git rev-list --count origin/$branch..$branch)
    behind=$(git rev-list --count $branch..origin/$branch)
    echo "$ahead commits ahead, $behind commits behind"
  fi
}

I currently have 15 repositories in my ~/repo folder. Now I can cd into each of them and run this bash function. Or, I can have bash do it for me :)

Let's write a function called process that does just that. We'll pass in a folder as an argument stored in $1

process() {
  if [ -d "$1/.git" ]; then
    pushd "$PWD" > /dev/null
    cd "$1"
    echo -n "$1 "
    check_remote
    popd > /dev/null
  fi
}

The pushd command will keep track of the folder that we're currently in. Then we cd into the directory that has .git folder. Print the name of the folder so we can associate the ahead/behind counts, and then run the check_remote function. Lastly we popd back to the folder we started from.

All that's left is to get the list of folders to process:

find . -type d -print0

Feed it into a while read loop passing in each folder into the process function.

find . -type d -print0 | while read -d $'\0' folder
do
  process $folder
done

All together the script will look like:

#!/bin/bash

set -o errexit
set -o nounset
set -o pipefail

show_usage() {
  echo "Usage: git-remote-status [-R]"
  exit 1
}

check_remote() {
  if [ -d .git ]; then
    git remote update > /dev/null 2> /dev/null
    branch=$(git rev-parse --abbrev-ref HEAD)
    ahead=$(git rev-list --count origin/$branch..$branch)
    behind=$(git rev-list --count $branch..origin/$branch)
    echo "$ahead commits ahead, $behind commits behind"
  fi
}

if [ "$#" -eq 0 ]; then
  check_remote
  exit 0
fi

if [ "$1" != "-R" ]; then 
  show_usage
  exit 1
fi


process() {
  if [ -d "$1/.git" ]; then
    pushd "$PWD" > /dev/null
    cd "$1"
    echo -n "$1 "
    check_remote
    popd > /dev/null
  fi
}
export -f process

find . -type d -print0 | while read -d $'\0' folder
do
  process $folder
done

This gives us two options. If we pass in no flags, then it'll print out the ahead/behind status for the current folder. If we pass in -R, then we recursively check all the subfolders as well.

Example Output of git-remote-status -R:

./project1 0 commits ahead, 3 commits behind
./project2 1 commits ahead, 0 commits behind
./project3 1 commits ahead, 2 commits behind
./project4 0 commits ahead, 0 commits behind
./project5 0 commits ahead, 0 commits behind