proguardgui: command not found

Have You tried accessing the binary with the full path?

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/proguardgui - from package: proguard

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