disper: 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 CentOS possible default full paths are:

/usr/bin/disper - from package: disper

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/disper - from package: disper

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

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