grep-available: 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/grep-available - from package: dctrl-tools

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

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