rivescript: 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 Debian possible default full paths are:

/usr/bin/rivescript - from package: librivescript-perl

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

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