redis-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/bin/redis-cli - from package: redis

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

On Debian possible default full paths are:

/usr/bin/redis-cli - from package: redis-tools

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

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