yelp-new: 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/yelp-new - from package: yelp-tools

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

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