encode.sh

#!/usr/bin/env bash

encode()
{

    local string=$1
    local strlen=${#string}

    for (( pos=0 ; pos<strlen ; pos++ )); do
        c=${string:$pos:1}
        case "$c" in [-_.~a-zA-Z0-9] ) o="${c}" ;;
            *) printf -v o '%%%02x' "'$c"
        esac
        encoded+="${o}"
    done
    echo $encoded
}

echo $(encode $1)