xgrep: 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/xgrep - from package: xgrep

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

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