demo.sh: 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.sh - from package: libcommons-launcher-java

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

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