Problem Statement

Provide a function or mechanism to convert a provided string into URL encoding representation. In URL encoding, special characters, control characters and extended characters are converted into a percent symbol followed by a two digit hexadecimal code, So a space character encodes into %20 within the string. For the purposes of this task, every character except 0-9, A-Z and a-z requires conversion, so the following characters all require conversion by default:

The string "http://foo bar/" would be encoded as "http%3A%2F%2Ffoo%20bar%2F".

It is permissible to use an exception string (containing a set of symbols that do not need to be converted). However, this is an optional feature and is not a requirement of this task.

Let's start with the solution:

urlencode() {
    local LC_ALL=C # support unicode: loop bytes, not characters
    local c i n=${#1}
    for (( i=0; i<n; i++ )); do
        c="${1:i:1}"
        case "$c" in
            #' ') printf '+' ;; # HTML5 variant
            [[:alnum:].~_-]) printf '%s' "$c" ;;
            *) printf '%%%02x' "'$c" ;;
        esac
    done
}

urlencode "http://foo bar/"