url friendly base64 encoder and decoder

base64url.sh

#!/usr/bin/env bash

encode() {
  local input="$1"
  if [ -z "$input" ]; then
    input=$(cat)
  fi
  echo -n "$input" | base64 -w0 | tr '+/' '-_' | tr -d '='
}

decode() {
  local input="$1"
  if [ -z "$input" ]; then
    input=$(cat)
  fi
  local len=$(( ${#input} % 4 ))
  if [ $len -eq 2 ]; then input="${input}=="
  elif [ $len -eq 3 ]; then input="${input}="
  fi
  echo -n "$input" | tr '_-' '/+' | base64 -d
}

if [ "$1" == "-d" ]; then
  if [ -n "$2" ]; then
    decode "$2"
  else
    decode
  fi
else
  if [ -n "$1" ]; then
    encode "$1"
  else
    encode
  fi
fi