node_exporter_functions.sh

#! /bin/sh
github_auth=${GITHUB_TOKEN:+--header="Authorization: Bearer $GITHUB_TOKEN"}
verbosity="--quiet"

github_releases() {
	{
		wget  "$verbosity" -O - "$github_auth" https://api.github.com/repos/prometheus/node_exporter/releases || {
			echo "Cannot download the list of releases from github.com" >&2; exit 2;
		}
	} | tee .cached
}

fetch_releases() {
	cat .cached 2>/dev/null || github_releases
}

assets() {
	awk -F'": "' '
		/published_at/ { PUBLISHED_DATE=$2 } 
                /browser_download_url/ {
			print PUBLISHED_DATE, $2
		}
	' | sort -k 1 | sed -e 's/"$//'
}

strip_timestamp() {
	sed -e 's/.*, //'
}

list_versions() {
	sed -e 's,https://.*/releases/download/v,,;s,/.*,,' | strip_timestamp | uniq
}

checksum_latest() {
	grep "sha256sums.txt" | tail -1 | strip_timestamp
}

checksum_version() {
	grep "/v${1?need version}/" | grep "sha256sums.txt" | strip_timestamp
}

select_arch_latest() {
	grep "linux-${1?need arch}" | tail -1 | strip_timestamp
}

select_arch_version() {
	grep "/v${2?need version}/" | grep "linux-${1?need arch}" | strip_timestamp
}

download_url() {
	while read URL
	do
		wget "$verbosity" -O "$(basename "${URL}")" "$github_auth" "${URL}" || {
			echo "Cannot download \"${URL}\"" >&2; exit 3;
		}
	done
}

fetch_releases | assets | list_versions
fetch_releases | assets | select_arch_version amd64 1.10.0 | download_url
fetch_releases | assets | checksum_version notexisting | download_url
fetch_releases | assets | checksum_version 1.10.0 | download_url
sha256sum -c --ignore-missing sha256sums.txt
fetch_releases | assets | select_arch_latest amd64
fetch_releases | assets | select_arch_latest amd64 | download_url
fetch_releases | assets | checksum_latest | download_url
sha256sum -c --ignore-missing sha256sums.txt