purge: 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/purge - from package: squid34

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

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