gvimdiff: 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/gvimdiff - from package: vim-X11

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

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