I needed to add a read-only collaborator to many repositories, and doing it via the website was really tedious

add-collaborator.sh

#!/bin/bash
GITHUB_TOKEN=$(git config --global github.token) # I've defined an API token in my git config -- ymmv
GITHUB_USER=""    # the collaborator
REPO_OWNER=""     # the owner of the repos
REPOS=""          # space-delimited list of repositories
PERMISSION="pull" # may be one of "admin", "push" (i.e., read/write -- default), or "pull" (i.e., read-only)
for REPO in ${REPOS} ; do
	curl -X PUT -i -d '{ "permission": "'${PERMISSION}'" }' \
		-H 'Accept: application/vnd.github.ironman-preview+json' \
		-H "Authorization: token ${GITHUB_TOKEN}" \
		https://api.github.com/repos/${REPO_OWNER}/${REPO}/collaborators/${GITHUB_USER}
done