sh url_decode

url_decode.inc.sh

url_decode() {
    local arg ;
    if [ $# -gt 0 ]; then
        for arg; do
            printf -- '%s\n' "${arg}" ;
        done | url_decode ;
    else
        check_printf ;
        printf -- '%b\n' "$(sed -E -e 's/\+/ /g' -e 's/%([0-9a-fA-F]{2})/\\x\1/g')" ;
    fi ;
    unset -v arg ;
}

# busybox sh and bash both worked
# dash has a printf built-in that must be avoided
# fallback to the printf program when a built-in failed
check_printf() {
    if [ 'Z' != "$(command printf -- '%b\n' '\x5a')" ]; then 
        printf() { /usr/bin/env printf "$@" ; } ;
    fi ;
}