expect_unbuffer: 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/expect_unbuffer - from package: expect

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

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