(Gnome 3) Gnome Extension Downloader: A script that takes an extension's ID # or URL and downloads a .zip containing the latest version of that extension

gnome-dlext.sh

#!/usr/bin/env bash

#
# gnome-dlext - a gnome extension download tool
#
#   instructions:
#     1. find the url of the extension you wish to download on extensions.gnome.org
#     2. run this script with either the extension url, or the id number contained in it
#     3. if there are no errors, your extension should then be downloaded!
#
#   note: other extension servers can be used by editing GNOME_EXTENSIONS_DOMAIN below
#
# written by: Kevin MacMartin <[email protected]>
# released under the MIT license (http://opensource.org/licenses/MIT)
#

# set this to the domain (no http:// or trailing slash) of the extension server
GNOME_EXTENSIONS_DOMAIN='extensions.gnome.org'

# Simple function to display an error and quit
function error_quit() {
    echo "Error: $1"
    exit 1
}

[[ ! $(type -P wget) ]] && error_quit "wget must be installed to run this script"
[[ ! $(type -P gnome-shell) ]] && error_quit "gnome-shell must be installed to run this script"

# Extract the gnome shell version from the output of 'gnome-shell --version'
GNOME_SHELL_VERSION=$(gnome-shell --version | sed 's|^.* ||' | grep -o -e '^[0-9][0-9]*\.[0-9][0-9]*')

# Display usage information if not input is received
[[ -z "$1" ]] \
    && echo "Usage: $(grep -o -e "[^\/]*$" <<< "$0") [extension-id|extension-url] : download the requested extension" \
    && exit 0

# Parse the argument provided by the user for the extension id
EXTENSION_ID=$(grep -o -e '[0-9]*' <<< "$1" | head -n 1)
# Fail if an extension id couldn't be parsed
[[ -z "$EXTENSION_ID" ]] \
    && error_quit "$1 is not a valid extension id or url"

# Use the extension id to query the extension server for the download URL
DOWNLOAD_URL=$(wget -T 1 -t 1 -qO- 'https://'$GNOME_EXTENSIONS_DOMAIN'/extension-info/?pk='$EXTENSION_ID'&shell_version='$GNOME_SHELL_VERSION \
    | grep -o -e '"download_url": "[^"]*"' \
    | sed 's|"download_url": "|https://'$GNOME_EXTENSIONS_DOMAIN'|;s|"$||')
# Fail if a download URL couldn't be parsed
[[ -z "$DOWNLOAD_URL" ]] \
    && error_quit  "no response from server\n"

# Parse the download URL for the filename of the download
DOWNLOAD_FILENAME=$(sed 's|^.*/||;s|\.zip.*$|\.zip|' <<< "$DOWNLOAD_URL")
# Fail if the file already exists
[[ -f "$DOWNLOAD_FILENAME" ]] \
    && error_quit "$DOWNLOAD_FILENAME already exists"

# Download the url we grabbed and save it as the filename we parsed
wget "$DOWNLOAD_URL" -O "$DOWNLOAD_FILENAME"