vppreproc: 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/vppreproc - from package: perl-Verilog-Perl

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

On Debian possible default full paths are:

/usr/bin/vppreproc - from package: libverilog-perl

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

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