git-find-fork

#!/bin/sh

# git-find-fork:  finds a fork of a GitHub repository, or returns the upstream
#   repository if the fork does not exist.
# Usage:  git-find-fork ORG UPSTREAM_ORG REPONAME
# Prints the first one of these that exists:
#   https://github.com/${ORG}/${REPO}.git
#   https://github.com/${UPSTREAM_ORG}/${REPO}.git

# Often, you can use the `git-clone-related` script instead of this one.

if [ "$#" -ne 3 ]; then
  SCRIPT_NAME=$(basename -- "$0")
  >&2 echo "Error: ${SCRIPT_NAME} requires 3 arguments, got $#"
  >&2 echo "Usage: ${SCRIPT_NAME} ORG UPSTREAM_ORG REPONAME"
  exit 1
fi

ORG=$1
UPSTREAM_ORG=$2
REPONAME=$3

# Problem with "git ls-remote": it may ask for GitHub credentials.
# (It also downloads more information than `wget` or `curl` does.)
# export GITEXISTS="git ls-remote"
if command -v wget > /dev/null; then
  export GITEXISTS="wget -q --spider"
elif command -v curl > /dev/null; then
  export GITEXISTS="curl --output /dev/null --silent --head --fail --location"
else
  echo "git-find-fork: Neither wget nor curl is installed" >&2
  exit 2
fi

if (${GITEXISTS} "https://github.com/${ORG}/${REPONAME}.git" > /dev/null); then
  OWNER="${ORG}"
else
  OWNER="${UPSTREAM_ORG}"
fi
echo "https://github.com/${OWNER}/${REPONAME}.git"