flipdiff: 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/flipdiff - from package: patchutils

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

On Debian possible default full paths are:

/usr/bin/flipdiff - from package: patchutils

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

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