gst: 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/gst - from package: gnu-smalltalk

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

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