FreeFem++-nw: 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/FreeFem++-nw - from package: freefem++

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

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