mygrep: 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/share/dotlrn/packages/acs-lang/bin/mygrep - from package: dotlrn
/usr/share/openacs/packages/acs-lang/bin/mygrep - from package: openacs

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

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