bundle_ruby: 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/lib/ruby/gems/1.8/gems/bundler-1.5.2/bin/bundle_ruby - from package: rubygem-bundler

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

On Debian possible default full paths are:

/usr/bin/bundle_ruby - from package: bundler

You may install the required package with command apt-get install {package}

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