vreg: 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/vreg - from package: perl-SystemC-Vregs

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

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