nydiff: 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/nydiff - from package: patchy

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

On Debian possible default full paths are:

/usr/bin/nydiff - from package: nypatchy

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

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