bd_pgsql_purge: 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/sbin/bd_pgsql_purge - from package: bandwidthd-pgsql

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

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