unwrapdiff: 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/unwrapdiff - from package: patchutils

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

On Debian possible default full paths are:

/usr/bin/unwrapdiff - from package: patchutils

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

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