Download specific asset using GitHub API, `curl` and `jq`

download_asset.sh

#!/bin/bash

# This script downloads specific asset that may be not included in the latest release
# but could be found in some other tag (version).
# You can set DEBUG=true ./download_asset.sh comnmand to enable debug messages.
# Requires curl, jq and head installed.
# You can set GitHub Personal Access token in $GITHUB_TOKEN to avoid API rate limiting. Look below.

# Constants (replace with your repo details)
OWNER="repo-owner-account"        # GitHub username or organization
REPO="repo-name"                  # Repository name
ASSET_NAME="themes.zip"           # Exact asset name in Releases page
GITHUB_TOKEN=""                   # Look at https://github.com/settings/tokens if you need to set GitHub PAT

# GitHub API URL
GITHUB_API_URL="https://api.github.com"

# Enable debug mode if DEBUG is set
DEBUG=${DEBUG:-false}

# Debug log function
log_debug() {
    if [ "$DEBUG" = true ]; then
        echo "[DEBUG] $1"
    fi
}

# Error log function
log_error() {
    echo "[ERROR] $1"
}

# Info log function
log_info() {
    echo "[INFO] $1"
}

# Fetch release information
log_info "Fetching release information for $OWNER/$REPO..."
if [ -n "$GITHUB_TOKEN" ]; then
    response=$(curl -s -H "Authorization: token $GITHUB_TOKEN" \
                     -H "Accept: application/vnd.github.v3+json" \
                     "$GITHUB_API_URL/repos/$OWNER/$REPO/releases")
else
    response=$(curl -s -H "Accept: application/vnd.github.v3+json" \
                     "$GITHUB_API_URL/repos/$OWNER/$REPO/releases")
fi

if [[ $? -ne 0 ]]; then
    log_error "Failed to fetch release information from GitHub API."
    exit 1
fi

if [[ -z "$response" ]]; then
    log_error "Empty response from GitHub API."
    exit 1
fi

# Write raw API response to a file for debugging
if [ "$DEBUG" = true ]; then
    echo "$response" > api_response_debug.json
    log_debug "API response saved to 'api_response_debug.json' for debugging."
fi

# Parse the JSON response to find the asset URL for the specified asset name
log_debug "Parsing JSON response to find asset URL..."
asset_url=$(echo "$response" | jq -r \
    --arg ASSET_NAME "$ASSET_NAME" \
    '.[] | .assets[]? | select(.name == $ASSET_NAME) | .browser_download_url' | head -n 1)

if [[ -z "$asset_url" || "$asset_url" == "null" ]]; then
    log_error "Asset '$ASSET_NAME' not found in any release for $OWNER/$REPO."
    log_debug "Inspect the API response in 'api_response_debug.json' for more details."
    exit 1
fi

log_info "Found asset URL: $asset_url"

# Download the asset
log_info "Downloading asset..."
curl -L -H "Authorization: token $GITHUB_TOKEN" \
     -H "Accept: application/octet-stream" \
     -o "$ASSET_NAME" "$asset_url"

if [[ $? -ne 0 ]]; then
    log_error "Failed to download the asset."
    exit 1
fi

log_info "Asset '$ASSET_NAME' downloaded successfully."

exit 0