igrep: 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/igrep - from package: OpenImageIO-utils

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

On Debian possible default full paths are:

/usr/bin/igrep - from package: openimageio-tools

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

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