hpi_shell: 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/hpi_shell - from package: openhpi32
/usr/bin/hpi_shell - from package: openhpi

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

On Debian possible default full paths are:

/usr/bin/hpi_shell - from package: openhpi-clients

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

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