ysh: 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/ysh - from package: libyaml-shell-perl

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

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