dehtmldiff: 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/dehtmldiff - from package: patchutils

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

On Debian possible default full paths are:

/usr/bin/dehtmldiff - from package: patchutils

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

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