yash: 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/yash - from package: yash

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

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