clex: 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/clex - from package: clex

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

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