fetch

#!/bin/bash

function usage {
	cat <<EOF
Usage
-----

	$0 <url> <output-file> <sha256-checksum>


EOF
}

function main {
	if [ $# -ne 3 ]; then
		usage
		return 1
	fi

	local URL=$1
	local OUTFILE=$2
	local CHECKSUM=$3

	local TMPFILE=$(mktemp fetch.tmp.XXXXXX)
	if [ $? -ne 0 ]; then
		echo "Error creating temporary file."
		return 1
	fi

	echo "[+] Fetching '$URL' into '$TMPFILE'..."
	wget -O "$TMPFILE" "$URL"
	if [ $? -ne 0 ]; then
		echo "Error downloading '$URL'."
		rm -f "$TMPFILE"
		return 1
	fi
	echo "[+] Done."
	echo "[+] Checking checksum of '$TMPFILE' ($CHECKSUM)..."
	local SUM=$(openssl dgst -sha256 -r < "$TMPFILE" | awk '{print $1}')
	if [ $? -ne 0 ]; then
		echo "Error computing checksum for '$URL'."
		rm -f "$TMPFILE"
		return 1
	fi
	if [ "$SUM" != "$CHECKSUM" ]; then
		echo "Checksum mismatch for '$URL': got '$SUM' / expecting '$CHECKSUM'."
		rm -f "$TMPFILE"
		return 1
	fi
	echo "[+] Done."
	echo "[+] Renaming '$TMPFILE' to '$OUTFILE'..."
	mv "$TMPFILE" "$OUTFILE"
	if [ $? -ne 0 ]; then
		echo "Error renaming '$TMPFILE' to '$OUTFILE'."
		rm -f "$TMPFILE"
		return 1
	fi
	echo "[+] Done."
	return 0
}

main "$@"