forg: 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/forg - from package: forg

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

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