avahi-discover: 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/avahi-discover - from package: avahi-ui-tools

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

On Debian possible default full paths are:

/usr/bin/avahi-discover - from package: avahi-discover

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

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