mce_grep: 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/mce_grep - from package: perl-MCE-tools

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

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