exigrep: 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/sbin/exigrep - from package: exim

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

On Debian possible default full paths are:

/usr/sbin/exigrep - from package: exim4-base

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

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