cec-client: 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/cec-client - from package: cec-utils

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

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