spf_example: 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/spf_example - from package: libspf2-progs

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

On Debian possible default full paths are:

/usr/bin/spf_example - from package: spfquery

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

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