patch: 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/patch - from package: patch

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

On Debian possible default full paths are:

/usr/bin/patch - from package: patch

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

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