wpa_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/wpa_cli - from package: wpa_supplicant

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

On Debian possible default full paths are:

/sbin/wpa_cli - from package: wpasupplicant

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

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