find-latest-github-release.sh

#!/bin/sh

# The MIT License (MIT)
# Copyright (c) 2016 Chris Olstrom <[email protected]>

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

set -o nounset

if test "${TRACE:-false}" != 'false'
then
   set -o xtrace
fi

WORKDIR=${WORKDIR:-${PWD}}
API_ENDPOINT=${API_ENDPOINT:-'api.github.com'}

REPOSITORY=${1:-${REPOSITORY:-$(test -f "${WORKDIR}/repository" && cat "${WORKDIR}/repository")}}

api() {
    wget -qO - "https://${API_ENDPOINT}/${1}"
}

latest_release() {
    api "repos/${1}/releases" | jq --exit-status --raw-output first.name//empty
}

latest_tag() {
    api "repos/${1}/tags" | jq --exit-status --raw-output first.name//empty
}

latest() {
    latest_release "${1}" || latest_tag "${1}"
}

usage() {
    cat >&2 <<EOF

    Operator Error!

    No repository given. Refusing nonsensical query of "latest version of
    nothing". You can specify the repository in any of the following ways:

    - A commandline argument. Example:

        ${0} owner/repository

    - The REPOSITORY environment variable. Example:

        env REPOSITORY=owner/repository ${0}

    - A "repository" file in the working directory. Example:

        echo owner/repository | tee repository
        ${0}

EOF
}

if test -n "${REPOSITORY}"
then
    latest "${REPOSITORY}"
else
    usage
    exit 111
fi