hostapd_cli: 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/sbin/hostapd_cli - from package: hostapd

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

On Debian possible default full paths are:

/usr/sbin/hostapd_cli - from package: hostapd

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

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