secure `curl <url> | sh`

curlsh

#! /bin/bash
# secure the use of `curl <url> | sh`
#
# @see http://blog.classicalcode.com/2012/11/curl-pipe-sh-exploit-proof-of-concept/ 
# @see http://www.djm.org.uk/protect-yourself-from-non-obvious-dangers-curl-url-pipe-sh/
# @see https://github.com/djm/pipe-to-sh-poc
#

# define a variable content using heredoc
function define()
{
    IFS=$''
    read -d '' ${1} || true; 
}

# Help message
define Usage << "HELP"

Usage: curlsh [OPTIONS] FILE [ARGUMENTS]
Options:
    -h          display this message
    -d          temporary working directory (default: /tmp)
    -e          text editor
    -q          quiet mode, disable the secure mode (!!! WARNING !!!)
HELP

# print the help message
function usage()
{
    echo -e "$Usage"
}

# if no given parameters, abort
if [ $# -eq 0 ]
then
    usage
    exit 1
fi

# default command line options
OPTIONS=":hd:e:q"

# default temporary working directory
TMPDIR="/tmp"

# default temporary file name
TMPFILE="curlsh.XXXXXXXX"

# quiet mode default value
QUIETMODE=0

# default editor
EDITOR="cat"

# get command line options
while getopts $OPTIONS option
do
    case $option in
        d) [[ -d "${OPTARG}" ]] && TMPDIR=${OPTARG};;
        e) [[ -e "$(which ${OPTARG})" ]] && EDITOR=$(which ${OPTARG});;
        q) QUIETMODE=1;;
        h | *) usage && exit 0 || exit 1;;
    esac
done
shift $(($OPTIND - 1 ))

# yes/no menu choice
function yesno()
{
    local def=${2:-n}
    while ! [[ "$choice" =~ [yYnN] ]]
    do
        read -s -p  "$1 ? [$def]" choice
        choice=${choice:-$def}
        echo ''
    done
    [[ "$choice" =~ [yY] ]] && return 0 || return 1
}

# curlsh function
function curlsh {
    file=$(mktemp $TMPDIR/$TMPFILE) || { echo "Failed creating file"; return; }
    curl -s "$1" > $file || { echo "Failed to curl file"; return; }
    if [[ $QUIETMODE -eq 0 ]]
    then
        echo ""
        echo "**** BEGIN FILE CONTENT ****"
        $EDITOR $file || { echo "Editor quit with error code"; return; }
        echo "**** END FILE CONTENT ****"
        echo ""
        if ! yesno 'Would you want to execute this script' 'N'
        then
            echo 'Abort.'
            rm $file
            exit 1
        fi
    fi
    shift
    sh $file $@
    rm $file
}

curlsh $@

exit 0