A bash script to fork all repositories from one organisation to other. If repo already exists in destination org, then it creates a PR for the default branch to sync the changes if any.

fork-or-sync-all-repos-between-2-orgs.sh

#!/usr/bin/env bash

# Ask for user input
read -p "Enter the source organization: " source_org
read -p "Enter the destination organization: " dest_org
read -p "Enter the GitHub token: " gh_token
read -p "Enter the repositories to exclude (comma-separated): " excluded_repos_input

# Convert comma-separated excluded repositories to an array
IFS=',' read -r -a excluded_repos <<< "$excluded_repos_input"

per_page=1000

echo "Forking repos from $source_org to $dest_org"

repos=$(hub api -H "Authorization: token $gh_token" "/orgs/$source_org/repos?per_page=$per_page" | jq -r '.[] | .name')
dest_repos=$(hub api -H "Authorization: token $gh_token" "/orgs/$dest_org/repos?per_page=$per_page" | jq -r '.[] | .name')

for repo in $repos; do
    if [[ " ${excluded_repos[@]} " =~ " ${repo} " ]]; then
        echo "Skipping $repo (excluded)"
        continue
    fi
    if echo "${dest_repos[@]}" | grep -qw "$repo"; then
        echo "Checking for new changes in $repo"
        temp_dir=$(mktemp -d)
        git clone "https://github.com/$dest_org/$repo.git" "$temp_dir/$repo"
        cd "$temp_dir/$repo"
        git remote add upstream "https://github.com/$source_org/$repo.git"
        git fetch upstream
        default_branch=$(hub api -H "Authorization: token $gh_token" "/repos/$source_org/$repo" | jq -r '.default_branch')
        if git rev-list HEAD...upstream/$default_branch --count | grep -q '^[1-9][0-9]*$'; then
            echo "Creating PR to sync $repo (new changes found)"
            git checkout -b sync-upstream
            git merge upstream/$default_branch
            git push origin sync-upstream
            hub pull-request -m "Sync with upstream $source_org/$repo" -b $dest_org:main -h $dest_org:sync-upstream
        else
            echo "No new changes in $repo"
        fi
        cd -
        rm -rf "$temp_dir"
        continue
    fi
    echo "Forking $repo"
    hub api -X POST -H "Authorization: token $gh_token" "/repos/$source_org/$repo/forks" \
            -F "organization=$dest_org" -F "default_branch_only=false" -F "name=$repo" | jq .
    sleep 1
done

Pre-requisites

1. Install jq (https://jqlang.github.io/jq/)
2. Install hub (https://hub.github.com)
3. Create a PAT with access to both organisation's repos, see create a fork endpoint on GH docs (https://docs.github.com/en/rest/repos/forks#create-a-fork)