Getting an asset from a Github Release in Bash

A few years ago, I wrote an Ansible role to download the latest version of a file from a Github release. Around the same point, I also wrote a bash script to do the same thing. For some reason, I never released either of them (or if I did, I can’t find them), so here’s the Bash one, as I needed to reuse it today :)

#!/bin/bash

AGENT=""
TRY_WGET=1
TRY_CURL=1
if [ "$TRY_WGET" == "1" ] && command -v wget >/dev/null 2>&1
then 
    AGENT=wget
elif [ "$TRY_CURL" == "1" ] && command -v curl >/dev/null 2>&1
then
    AGENT=curl
fi

if [ -z "$AGENT" ]
then
    echo "Error: No HTTP agent (curl and wget tested)" >&2
    exit 1
fi

DEBUG() {
    echo "$@" >&2
}

GET() {
    URL="$1"
    TARGET="${2:-}"
    if [ "$AGENT" == "curl" ]
    then
        if [ -z "$TARGET" ]
        then
            DEBUG curl --silent "$URL"
            curl --silent "$URL"
        elif [ "$TARGET" == "ORIGIN" ]
        then
            DEBUG curl --silent -LO "$URL"
            curl --silent -LO "$URL"
        else
            DEBUG curl --output "$TARGET" --silent "$URL"
            curl --output "$TARGET" --silent "$URL"
        fi
    else
        if [ -z "$TARGET" ]
        then
            DEBUG wget -qO- "$URL"
            wget -qO- "$URL"
        elif [ "$TARGET" == "ORIGIN" ]
        then
            DEBUG wget -q "$URL"
            wget -q "$URL"
        else
            DEBUG wget -q -O "$TARGET" "$URL"
            wget -q -O "$TARGET" "$URL"
        fi
    fi
}

REPO="${1:-}"
ASSET="${2:-}"
VERSION="${3:-latest}"

[ "$VERSION" != "latest" ] && VERSION="tags/$3"

RELEASE_JSON=$(GET "https://api.github.com/repos/$REPO/releases/$VERSION")
ASSET_URL=$(echo "$RELEASE_JSON" | grep -oP "(?<=browser_download_url\": \")[^\"]*${ASSET}" | head -n 1)

if [ -n "$ASSET_URL" ]
then
    GET "$ASSET_URL" "${OUTPUT:-ORIGIN}"
else
    echo "Asset not found" >&2
    exit 2
fi

This is also available as a gist on github.

Featured image is “Yes!” by “storebukkebruse” on Flickr and is released under a CC-BY license.