Pure Bash urlencode function.

urlencode.sh

#!/bin/bash

function URLEncode {

	local dataLength="${#1}"
	local index

	for ((index = 0;index < dataLength;index++)); do
		local char="${1:index:1}"
		case $char in
			[a-zA-Z0-9.~_-])
				printf "$char"
				;;
			*)
				printf "%%%02X" "'$char"
				;;
		esac
	done
}

encoded=$(URLEncode "my\value\will!be&encoded")
echo "$encoded"