httex: 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/httex - from package: tetex-tex4ht

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

On Debian possible default full paths are:

/usr/bin/httex - from package: tex4ht

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

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