deploy_ssh_authorized_keys_with_github.sh

#!/usr/bin/env bash

set -euo pipefail

authorized_keys_file=${HOME}/.ssh/authorized_keys
tmp_authorized_keys_file=$(mktemp)
github_username='yakkun'

# Fetch authorized_keys from GitHub
curl -fsSL https://github.com/${github_username}.keys -o ${tmp_authorized_keys_file}

# Whether diff is available?
set +e
diff -q ${authorized_keys_file} ${tmp_authorized_keys_file} >/dev/null
if [ $? -ne 1 ]; then
  echo 'No diffs, no deploy.'
  exit 0
fi
set -e

# Validate contents if not empty
if [ -s ${tmp_authorized_keys_file} ]; then
  if [ $(head -c 4 ${tmp_authorized_keys_file}) -ne 'ssh-' ]; then
    echo 'Seems like not ssh authorized_key file, aborted.' >&2
    exit 1
  fi
fi

# Deploy
set +e
diff -u ${authorized_keys_file} ${tmp_authorized_keys_file}
set -e
cat ${tmp_authorized_keys_file} >${authorized_keys_file}
echo 'Deployed with diffs above.'

rm ${tmp_authorized_keys_file}