regtest: 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/regtest - from package: gcpegg

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

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