Example for decoding a JWT Payload with your Shell (bash, zsh...)

readme.md

Setup

Add this to your .profile, .bashrc, .zshrc...

decode_base64_url() {
  local len=$((${#1} % 4))
  local result="$1"
  if [ $len -eq 2 ]; then result="$1"'=='
  elif [ $len -eq 3 ]; then result="$1"'=' 
  fi
  echo "$result" | tr '_-' '/+' | openssl enc -d -base64
}

decode_jwt(){
   decode_base64_url $(echo -n $2 | cut -d "." -f $1) | jq .
}

# Decode JWT header
alias jwth="decode_jwt 1"

# Decode JWT Payload
alias jwtp="decode_jwt 2"

Usage

jwtp eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ

Output

{
  "sub": "1234567890",
  "name": "John Doe",
  "admin": true
}

openssl enc -d -base64 doesn't work out of the box on mac (mocos mojave, LibreSSL 2.6.5 openssl version ) with base64 long lines without carriage-returns.

Handle it to be linux/mac compliant with a dummy test on the base64 command:
base64 -d on linux (or mac with linux base64 tool) and base64 -D on mac

Forked here https://gist.github.com/lounagen/bdcf3e59122e80bae6da114352d0280c

Just found this through $SEARCHENGINE

This is shorter (mapfile is bash-only):

#!/bin/bash

decode_jwt(){
     printf "%s" "$1" | base64 -d 2>/dev/null | jq .
}

mapfile jwt < <(printf "%s" "$1" | tr '.' '\n')
decode_jwt "${jwt[0]}"
echo
decode_jwt "${jwt[1]}"

Putting that into an alias would of course work too.

I created a script with full decode https://gist.github.com/stokito/f2d7ea0b300f14638a9063559384ec89

Thanks for the helpful gist
I've adjusted it a bit

• used base64 instead of openssl (so I don't have to install it on an alpine docker image)
• changed the order of arguments in the decode_jwt method, expecting the jwt first, and defaulting the second argument to 2 (as we usually need to decode the body)

_decode_base64_url() {
  local len=$((${#1} % 4))
  local result="$1"
  if [ $len -eq 2 ]; then result="$1"'=='
  elif [ $len -eq 3 ]; then result="$1"'=' 
  fi
  echo "$result" | tr '_-' '/+' | base64 -d
}

# $1 => JWT to decode
# $2 => either 1 for header or 2 for body (default is 2)
decode_jwt() { _decode_base64_url $(echo -n $1 | cut -d "." -f ${2:-2}) | jq .; }

# decodes body (default behaviour)
decode_jwt $MY_JWT
# decodes header
decode_jwt $MY_JWT 1 

Link to the fork: https://gist.github.com/a-magdy/a771f1426043ab4b66b19cc9a652908b

Using Jq

function jwt_decode(){
    jq -R 'split(".") | .[1] | @base64d | fromjson' <<< "$1"
}

Usage:

╰─ jwt_decode eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022
}

@vithalreddy Perfect cheers :)

@vithalreddy beautiful, thanks !

Solution from @vithalreddy works perfectly across platforms, thanks!

Perfect. Thanks @vithalreddy.

Awesome when people share their knowledge for free. Thanks men!

I will add your script to my jarvis assistant

https://github.com/jrichardsz/linux-commandline-assistant/tree/master/commands

Thanks, @vithalreddy and @chriswhite199 ! Your answers are better than what I came up with on my own. Combining your two answers:

function jwt_decode(){
    jq -R 'split(".") | .[1] | @base64d | fromjson |
      # you can replace the "localtime" with "gmttime" if that makes sense
      if .exp then (.expStr = (.exp | localtime | strftime("%Y-%m-%dT%H:%M:%S %Z"))) else . end |
      if .iat then (.iatStr = (.iat | localtime | strftime("%Y-%m-%dT%H:%M:%S %Z"))) else . end |
    .' <<< "$1"
}

Not as good as @vithalreddy's solution, but with minimal reliance on jq for the header and payload:

# Decode JWT header, payload and expiration time
alias jwth='cut -d "." -f 1 | tr "_-" "+/" | awk "{while (length(\$0) % 4) { \$0 = \$0 \"=\" } print}" | base64 -d | jq'
alias jwtp='cut -d "." -f 2 | tr "_-" "+/" | awk "{while (length(\$0) % 4) { \$0 = \$0 \"=\" } print}" | base64 -d | jq'
alias jwtexp='cut -d "." -f 2 | tr "_-" "+/" | awk "{while (length(\$0) % 4) { \$0 = \$0 \"=\" } print}" | base64 -d | jq -r ".exp" | xargs -I {} sh -c "echo UTC: \$(date -u -d @{}) && echo Local: \$(date -d @{})"'