tomcat6-digest: 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/tomcat6-digest - from package: tomcat6

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

Error in other languages:
tomcat6-digest: bevel nie gevind nie
tomcat6-digest: comandă negăsită
tomcat6-digest: comando não encontrado
tomcat6-digest: commande introuvable
tomcat6-digest: command not found
tomcat6-digest: käsku ei ole
tomcat6-digest: không tìm thấy lệnh
tomcat6-digest: komanda nerasta
tomcat6-digest: Kommando nicht gefunden.
tomcat6-digest: kommandot finns inte
tomcat6-digest: komut yok
tomcat6-digest: nie znaleziono polecenia
tomcat6-digest: níor aimsíodh an t-ordú
tomcat6-digest: no se encontró la orden
tomcat6-digest: no s'ha trobat l'ordre
tomcat6-digest: opdracht niet gevonden
tomcat6-digest: parancs nem található
tomcat6-digest: perintah tidak ditemukan
tomcat6-digest: príkaz nenájdený
tomcat6-digest: příkaz nenalezen
tomcat6-digest: команда не найдена
tomcat6-digest: командата не е открита
tomcat6-digest: 命令找不到
tomcat6-digest: コマンドが見つかりません