prettify_json.rb: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/prettify_json.rb - from package: rubygem-json
/usr/lib/ruby/gems/1.8/gems/json-1.4.6/bin/prettify_json.rb - from package: rubygem-json

You may install the required package with command yum install {package}

Error in other languages:
prettify_json.rb: bevel nie gevind nie
prettify_json.rb: comandă negăsită
prettify_json.rb: comando não encontrado
prettify_json.rb: commande introuvable
prettify_json.rb: command not found
prettify_json.rb: käsku ei ole
prettify_json.rb: không tìm thấy lệnh
prettify_json.rb: komanda nerasta
prettify_json.rb: Kommando nicht gefunden.
prettify_json.rb: kommandot finns inte
prettify_json.rb: komut yok
prettify_json.rb: nie znaleziono polecenia
prettify_json.rb: níor aimsíodh an t-ordú
prettify_json.rb: no se encontró la orden
prettify_json.rb: no s'ha trobat l'ordre
prettify_json.rb: opdracht niet gevonden
prettify_json.rb: parancs nem található
prettify_json.rb: perintah tidak ditemukan
prettify_json.rb: príkaz nenájdený
prettify_json.rb: příkaz nenalezen
prettify_json.rb: команда не найдена
prettify_json.rb: командата не е открита
prettify_json.rb: 命令找不到
prettify_json.rb: コマンドが見つかりません