Github workflow to update submodules

update_submodules.yml

name: update submodules

# requires sudmodules URL to be "https..." (no ssh)
#
# requires submodule to be specified to follow a specific branch (stored in .gitmodules)
#
# clone them with:
#
#   git submodule add -b branch_to_follow https://github.com/... submodule_path
#
# or specify it with:
#
#   git config -f .gitmodules submodule.submodule_path.branch branch_to_follow
#

  # Uses the cron schedule for github actions
  #
  # https://docs.github.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows#scheduled-events
  #
  #          ┌───────────── minute (0 - 59)
  #          │ ┌───────────── hour (0 - 23)
  #          │ │ ┌───────────── day of the month (1 - 31)
  #          │ │ │ ┌───────────── month (1 - 12 or JAN-DEC)
  #          │ │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
  #          │ │ │ │ │
  #          │ │ │ │ │
  #          │ │ │ │ │
  #          * * * * *

on:
  push:
    branches:
      - main
      - master
      - dev
  schedule:
    - cron: "* * * * *"

  # to trigger update manually from the Action tab in github
  workflow_dispatch:
    inputs:
      log:
        description: "Log"
        required: false

env:
  # to update all submodules
  # SUBMOD_TO_UPDATE: "*"
  # otherwise use a space separated list of the relative paths of each submodule to update
  SUBMOD_TO_UPDATE: "lib/sub_3 lib/sub_1" 

defaults:
  run:
    shell: bash

jobs:
  update_submodules:
    # only trigger update on upstream repo
    if: github.repository_owner == 'Remi-Gau'

    runs-on: ubuntu-latest

    steps:

      - name: Clone repo
        uses: actions/checkout@v3
        with:
          submodules: true

      # check out the correct branch for each submodule and pull them all
      # https://stackoverflow.com/questions/5828324/update-git-submodule-to-latest-commit-on-origin
      - name: Update submodules
        run: |
              start_dir=$PWD
              if [ "${SUBMOD_TO_UPDATE}" = "*" ]; then
                  submodules=$(git submodule | awk '{print $2}')
              else
                  submodules=$(echo -e ${SUBMOD_TO_UPDATE} | sed "s/ /\n/g")
              fi
              nb_submod=$(echo "${submodules}" | wc -l)
              echo -e "\nUPDATING ${nb_submod} SUBMODULES"
              echo -e "${submodules}"
              for i in $(seq 1 ${nb_submod}); do
                  path=$(echo -e ${submodules} | awk -v i=${i} '{print $i}')
                  branch=$(git config --get --file .gitmodules submodule.${path}.branch)
                  echo -e "\nswitching submodule ${path} to ${branch}"
                  cd "${path}" || exit
                  git checkout ${branch}
                  cd "${start_dir}"
              done
              git submodule update --remote --merge

      # if there have been changes,
      # a PR is created using the checkout branch for this workflow
      # https://github.com/peter-evans/create-pull-request
      - name: Create Pull-Request
        uses: peter-evans/create-pull-request@v3
        with:
          commit-message: Update submodules
          delete-branch: true

When trying to update submodule that tracks something else that the default branch, things don't always got smoothly:

Run start_dir=$PWD
  start_dir=$PWD
  if [ "${SUBMOD_TO_UPDATE}" = "*" ]; then
      submodules=$(git submodule | awk '{print $2}')
  else
      submodules=$(echo -e ${SUBMOD_TO_UPDATE} | sed "s/ /\n/g")
  fi
  nb_submod=$(echo "${submodules}" | wc -l)
  echo -e "\nUPDATING ${nb_submod} SUBMODULES"
  echo -e "${submodules}"
  for i in $(seq 1 ${nb_submod}); do
      path=$(echo -e ${submodules} | awk -v i=${i} '{print $i}')
      branch=$(git config --get --file .gitmodules submodule.${path}.branch)
      echo -e "\nswitching submodule ${path} to ${branch}"
      cd "${path}" || exit
      git checkout ${branch}
      cd "${start_dir}"
  done
  git submodule update --remote --merge
  shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
  env:
    SUBMOD_TO_UPDATE: *

UPDATING 2 SUBMODULES
lib/CPP_BIDS
lib/CPP_PTB

switching submodule lib/CPP_BIDS to dev
error: pathspec 'dev' did not match any file(s) known to git
Error: Process completed with exit code 1.