htdigest: 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/htdigest - from package: httpd-tools

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

On Debian possible default full paths are:

/usr/bin/htdigest - from package: apache2-utils

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

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