matita.opt: 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/matita.opt - from package: matita

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

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