gopen: 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 CentOS possible default full paths are:

/usr/bin/gopen - from package: gnustep-gui

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/gopen - from package: gnustep-gui-runtime

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

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