numgrep: 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 Debian possible default full paths are:

/usr/bin/numgrep - from package: num-utils

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

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