Downloads the latest VanillaMC jarfile (requires jq)

latest_vanilla.sh

#!/usr/bin/env bash

# -h or --help CLI helptext
if [[ "$1" =~ ^-{1,2}h(elp)?$ ]] ; then
    echo "Usage:"
    echo "  ./latest_vanilla.sh [branch] [asset] [output]"
    echo
    echo "Positional Arguments:"
    echo "  [branch] is \"release\" or \"snapshot\""
    echo "  [asset] is \"client\", \"client_mappings\", \"server\", or \"server_mappings\""
    echo "  [output] is a file name"
    exit
fi

# entrypoint URL
VERSION_MANIFEST="https://launchermeta.mojang.com/mc/game/version_manifest.json"

# naming CLI inputs
branch=$1
: ${branch:=release}
if ! [[ "$branch" =~ ^(release|snapshot)$ ]] ; then
    echo "Unrecognized branch \"$branch\". Expected \"release\" or \"snapshot\"."
    exit 1
fi


asset=$2
: ${asset:=server}
if ! [[ "$asset" =~ ^(client|client_mappings|server|server_mappings)$ ]] ; then
    echo "Unrecognized asset \"$asset\". Expected \"client\", \"client_mappings\", \"server\", or \"server_mappings\"."
    exit 1
fi

output=$3

# base version manifest JSON
json_versions=$(curl -s "$VERSION_MANIFEST")
latest_version=$(echo $json_versions | jq -r ".latest.$branch")
latest_url=$(echo $json_versions | jq -r ".versions | map(select(.id = "\"$latest_version\"")) | .[0].url")

# version-specific JSON
json_branch=$(curl -s "$latest_url")
latest_asset=$(echo "$json_branch" | jq -r ".downloads.$asset.url")
latest_hash=$(echo "$json_branch" | jq -r ".downloads.$asset.sha1")
latest_filename=$(echo "$latest_asset" | sed -r 's/^.*\/([^\/]+)$/\1/')
: ${output:=$latest_filename}

# download output file
if [ -f "$output" ] ; then
    echo "Checking existing file \"$output\"."
    existing_hash=$(sha1sum "$output" | sed -r 's/^([0-9a-f]{40})\b.*$/\1/')
    if [ "$latest_hash" == "$existing_hash" ] ; then
        echo "Existing file hash matches, skipping download."
        exit
    fi
fi

echo "Downloading latest $asset on the $branch branch to \"$output\"."
curl -s --output "$output" "$latest_asset"

# verify output file
output_hash=$(sha1sum "$output" | sed -r 's/^([0-9a-f]{40})\b.*$/\1/')
if [ "$latest_hash" != "$output_hash" ] ; then
    echo "Downloaded file hash $output_hash did not match expected hash $latest_hash."
    exit 1
else
    echo "Downloaded file hash $output_hash was verified correctly."
fi

Very well documented and useful script. Will definitely try to incorporate in my project! Nice job!