essidscan: 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:

/sbin/essidscan - from package: ifscheme

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

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