unshield: 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/unshield - from package: unshield

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

On Debian possible default full paths are:

/usr/bin/unshield - from package: unshield

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

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