htproxy: 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/htproxy - from package: 3proxy

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

On Debian possible default full paths are:

/usr/bin/htproxy - from package: httest

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

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