demo.bat: 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/share/doc/libcommons-launcher-java/examples/example/src/bin/demo.bat - from package: libcommons-launcher-java

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

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