wgrib: 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/wgrib - from package: wgrib

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

On Debian possible default full paths are:

/usr/bin/wgrib - from package: grads

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

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