append: 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/share/doc/mh-book/examples/mh/bin/append - from package: mh-book

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

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