mysqldiff: 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/mysqldiff - from package: mysql-utilities

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

On Debian possible default full paths are:

/usr/bin/mysqldiff - from package: mysql-utilities

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

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