Bash script to download an asset from the latest GitHub release of a private repo

download_private_latest_github_release_asset.sh

#!/bin/bash

set -e

OWNER=""
REPO=""
FILE_PATTERN="" # example: "build-*.zip"
TOKEN="" # personal access token with permissions to read "Content"
# INCLUDE_PRERELEASE="true" # whether to include prereleases - remove the # to enable

echo "Fetching releases for ${OWNER}/${REPO}..."

if [ "$INCLUDE_PRERELEASE" = "true" ]; then
    echo "Including prereleases..."
    # get all releases and find the latest one (including prereleases)
    RELEASE_JSON=$(curl -s -H "Authorization: token ${TOKEN}" \
        "https://api.github.com/repos/${OWNER}/${REPO}/releases" | \
        jq '.[0]' 2>/dev/null || echo "[]")

    # fallback if jq is not available
    if [ "$RELEASE_JSON" = "[]" ] || [ -z "$RELEASE_JSON" ]; then
        RELEASE_JSON=$(curl -s -H "Authorization: token ${TOKEN}" \
            "https://api.github.com/repos/${OWNER}/${REPO}/releases" | \
            sed -n '2,/^  }/p' | sed '$d')
    fi
else
    # get latest stable release
    RELEASE_JSON=$(curl -s -H "Authorization: token ${TOKEN}" \
        "https://api.github.com/repos/${OWNER}/${REPO}/releases/latest")
fi

if echo "$RELEASE_JSON" | grep -q "Not Found"; then
    echo "Error: Repository not found or no access. Check your token and repository path."
    exit 1
fi

if [ "$RELEASE_JSON" = "[]" ] || [ -z "$RELEASE_JSON" ]; then
    echo "Error: No releases found."
    exit 1
fi

# extract release tag and prerelease status
TAG=$(echo "$RELEASE_JSON" | grep '"tag_name":' | head -1 | sed -E 's/.*"tag_name": "([^"]+)".*/\1/')
IS_PRERELEASE=$(echo "$RELEASE_JSON" | grep '"prerelease":' | head -1 | sed -E 's/.*"prerelease": ([^,]+).*/\1/')

echo "Latest release: $TAG"
if [ "$IS_PRERELEASE" = "true" ]; then
    echo "Note: This is a prerelease"
fi

matches_pattern() {
    local filename="$1"
    local pattern="$2"

    regex_pattern=$(echo "$pattern" | sed 's/\./\\./g' | sed 's/\*/.*/'g)
    echo "$filename" | grep -E "^${regex_pattern}$" > /dev/null
}

# extract assets section and get name/url pairs
ASSETS_SECTION=$(echo "$RELEASE_JSON" | sed -n '/"assets": \[/,/\]/p')

# find matching files based on pattern
DOWNLOAD_URL=""
FILENAME=""
FOUND_MATCH=0

TEMP_NAMES=$(mktemp)
TEMP_URLS=$(mktemp)

# extract all asset names and URLs
echo "$ASSETS_SECTION" | grep '"name":' | sed -E 's/.*"name": "([^"]+)".*/\1/' > "$TEMP_NAMES"
echo "$ASSETS_SECTION" | grep '"url":' | sed -E 's/.*"url": "([^"]+)".*/\1/' > "$TEMP_URLS"

# find matching file
line_num=1
while IFS= read -r current_name; do
    if matches_pattern "$current_name" "$FILE_PATTERN"; then
        FILENAME="$current_name"
        DOWNLOAD_URL=$(sed -n "${line_num}p" "$TEMP_URLS")
        FOUND_MATCH=1
        break
    fi
    line_num=$((line_num + 1))
done < "$TEMP_NAMES"

rm "$TEMP_NAMES" "$TEMP_URLS"

if [ $FOUND_MATCH -eq 0 ]; then
    echo "Error: No file matching pattern '$FILE_PATTERN' found in latest release."
    echo "Available files:"
    echo "$ASSETS_SECTION" | grep '"name":' | sed -E 's/.*"name": "([^"]+)".*/  - \1/'
    exit 1
fi

echo "Downloading: $FILENAME"
echo "From: $DOWNLOAD_URL"

curl -L -H "Authorization: token ${TOKEN}" \
     -H "Accept: application/octet-stream" \
     -o "$FILENAME" \
     "$DOWNLOAD_URL"

echo "Download successful: $FILENAME"