HEAD requests

A quicky this time.

I needed a simple script that would make a HEAD request for a certain URL, and then make a new HEAD request if the result was a redirect, etc.

Well, this is it:

#!/usr/bin/env bash

# This script makes a HEAD request for the given URL.
# If the result has a status 301 or 302,
# a new HEAD request is made for the new URL.
# Etc.

# For more info, see
# https://www.ohreally.nl/2020/12/10/head-requests/

################################################################################

# Copyright (c) 2020 Rob La Lau 

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

################################################################################

# Dependencies.
# `ncat' is part of Nmap.
AWK=`which awk`   || exit 1
NCAT=`which ncat` || exit 1
SED=`which sed`   || exit 1

# Usage message.
usage() {
	echo "Usage: $0 "
	echo
	echo "Only http and https URLs are supported."
	exit 1
}

# First (and only) parameter is the URL.
url=$1
[ -z "${url}" ] && usage

# URL parts.
proto=${url%%://*}
uri=${url##*://}
host=${uri%%/*}
path=${uri##*/}
if [ "${host}" = "${path}" ]; then
	path="/"
else
	path="/${path}"
fi

# SSL/TLS, or not?
case ${proto} in
	http)
		param=""
		port=80
		;;
	https)
		param="--ssl"
		port=443
		;;
	*)
		usage
		;;
esac

# Make request and process result.
while read line; do
	echo ${line}
	case ${line} in
		HTTP/*)
			status=$(echo ${line} | "${AWK}" '{print $2}')
			;;
		Location:*)
			# Line ends in CRLF.
			location=$(echo ${line} | "${SED}" -E 's/^[a-z:]+ (.*)/\1/i;s/\r$//')
			;;
		*)
			# Ignore.
			;;
	esac
done < <(printf "HEAD ${path} HTTP/1.1\r\nHost: ${host}\r\n\r\n" | "${NCAT}" ${param} ${host} ${port})

# Rinse repeat.
[ ${status} -eq 301 -o ${status} -eq 302 ] && $0 ${location}

Looks good, doesn’t it…?

Note:
With a badly configured web server, this script may loop forever. If that happens, hit ^C (Ctrl-C).

This script can also be downloaded from my Github account.

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