guilt-diff: 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/guilt-diff - from package: guilt

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

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