Shell script to check for new Github releases

release-check.sh

#!/bin/bash
# Send email notification of new Github project releases

usage () {
  cat <<EOF
Usage: release-check.sh [OPTION]... PROJECT...
Check for new releases on Github PROJECTs

Options:
  -h          Print this help text
  -t ADDRESS  Send email notifications to ADDRESS
  -f ADDRESS  Optional From email ADDRESS
  -l PATH     Path to last release file
              Default: last_release
EOF
}

last_release_path="last_release"
from=""
to=""

while getopts ":ht:f:l:" opt; do
  case $opt in
    h)
      usage
      exit 0
      ;;
    t)
      to="$OPTARG"
      ;;
    f)
      from="$OPTARG"
      ;;
    l)
      last_release_path="$OPTARG"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      usage >&2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done

shift $((OPTIND-1))

if [ -z "$1" ]; then
  echo "No projects specified!" >&2
  usage >&2
  exit 1
fi

if [ ! -f "$last_release_path" ]; then
  touch "$last_release_path"
fi

for project
do
  last_release="$(grep -w "$project" "$last_release_path" | cut -f 2)"

  url="https://github.com/$project/releases.atom"
  feed="$(curl --silent --fail "$url")"
  if [ $? -ne 0 ]; then
    echo "Error fetching feed!" >&2
    continue
  fi

  latest_release="$(echo $feed | xmllint --xpath "//*[local-name()='entry'][1]/*[local-name()='title']/text()" -)"
  if [ $? -ne 0 ]; then
    echo "Error parsing feed!" >&2
    continue
  fi

  if [ "$latest_release" != "$last_release" ]; then
    echo "New release found for $project"
    echo "New release: $latest_release"
    echo "Previous release: $last_release"

    if [ -n "$last_release" ]; then
      sed -i '' "s|$project	.*|$project	$latest_release|" "$last_release_path"
    else
      printf '%s\t%s\n' "$project" "$latest_release" >> "$last_release_path"
    fi

    if [ -n "$to" ]; then
      from_arg=""
      if [ -n "$from" ]; then
        from_arg="-r $from"
      fi

      mailx -s "New release for $project" $from_arg "$to" <<EOF
There is a new release available for $project
The latest release is $latest_release
EOF

      if [ $? -ne 0 ]; then
        echo "Error sending notification email!" >&2
      fi
    fi
  else
    echo "No new releases for $project"
    echo "Current release: $last_release"
  fi
done