gambas3: 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/gambas3 - from package: gambas3-ide

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

Error in other languages:
gambas3: bevel nie gevind nie
gambas3: comandă negăsită
gambas3: comando não encontrado
gambas3: commande introuvable
gambas3: command not found
gambas3: käsku ei ole
gambas3: không tìm thấy lệnh
gambas3: komanda nerasta
gambas3: Kommando nicht gefunden.
gambas3: kommandot finns inte
gambas3: komut yok
gambas3: nie znaleziono polecenia
gambas3: níor aimsíodh an t-ordú
gambas3: no se encontró la orden
gambas3: no s'ha trobat l'ordre
gambas3: opdracht niet gevonden
gambas3: parancs nem található
gambas3: perintah tidak ditemukan
gambas3: príkaz nenájdený
gambas3: příkaz nenalezen
gambas3: команда не найдена
gambas3: командата не е открита
gambas3: 命令找不到
gambas3: コマンドが見つかりません