myvi: 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/share/doc/mh-book/examples/mh/bin/myvi - from package: mh-book

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

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