grep-changelog: 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/grep-changelog - from package: emacs-common

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

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