horde-clear-cache: 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/horde-clear-cache - from package: php-horde-horde

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

On Debian possible default full paths are:

/usr/bin/horde-clear-cache - from package: php-horde

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

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