raven: 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/raven - from package: php-Raven
/usr/bin/raven - from package: python-raven

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

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