simplyhtml: 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/simplyhtml - from package: simplyhtml

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

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