yapp: 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 CentOS possible default full paths are:

/usr/bin/yapp - from package: perl-Parse-Yapp

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/yapp - from package: libparse-yapp-perl

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

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