htdig: 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/htdig - from package: htdig

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

On Debian possible default full paths are:

/usr/bin/htdig - from package: htdig

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

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