download

#!/usr/bin/env bash
#
# @license Apache-2.0
#
# Copyright (c) 2017 The Stdlib Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Download a remote resource.
#
# Usage: download <url> [output_filepath]
#
# Arguments:
#
#   url                 Remote resource.
#   output_filepath     Output filepath.
#

# VARIABLES #

# Set the url:
url="$1"

# Find a program for downloading a resource:
CURL=$(command -v curl 2>/dev/null)
WGET=$(command -v wget 2>/dev/null)
FETCH=$(command -v fetch 2>/dev/null)

# Define a timeout (in seconds):
timeout=30

# Define command options:
curl_opts="-fkL --connect-timeout ${timeout} -y ${timeout}"
wget_opts="--no-check-certificate --tries=1 --timeout=${timeout}"
fetch_opts="-T ${timeout}"


# FUNCTIONS #

# Prints usage information.
usage() {
	echo '' >&2
	echo 'Usage: download <url> [output_filepath]' >&2
	echo '' >&2
}


# MAIN #

# Handle arguments...
if [[ "$#" -eq 0 ]]; then
	usage
	exit 0
elif [[ "$#" -eq 1 ]]; then
	curl_opts="${curl_opts} -O"
elif [[ "$#" -eq 2 ]]; then
	curl_opts="${curl_opts} -o $2"
	wget_opts="${wget_opts} -O $2"
	fetch_opts="${fetch_opts} -o $2"
else
	echo 'ERROR: unrecognized arguments. Must provide a URL and, optionally, an output filepath.' >&2
	exit 1
fi

# Determine the command for downloading a resource...
if [[ -x "${CURL}" ]] && "${CURL}" -V >/dev/null; then
	get="${CURL}"
	opts="${curl_opts}"
elif [[ -x "${WGET}" ]] && "${WGET}" -V >/dev/null; then
	get="${WGET}"
	opts="${wget_opts}"
elif [[ -x "${FETCH}" ]]; then
	get="${FETCH}"
	opts="${fetch_opts}"
else
	echo 'ERROR: missing dependency. Please download either curl, wget, or fetch. Once installed, run the command again.' >&2
	exit 1
fi

# Download the resource:
eval "${get} ${opts} ${url}"