ncl_grib2nc: 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/ncl_grib2nc - from package: ncl

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

On Debian possible default full paths are:

/usr/bin/ncl_grib2nc - from package: ncl-ncarg

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

Error in other languages:
ncl_grib2nc: bevel nie gevind nie
ncl_grib2nc: comandă negăsită
ncl_grib2nc: comando não encontrado
ncl_grib2nc: commande introuvable
ncl_grib2nc: command not found
ncl_grib2nc: käsku ei ole
ncl_grib2nc: không tìm thấy lệnh
ncl_grib2nc: komanda nerasta
ncl_grib2nc: Kommando nicht gefunden.
ncl_grib2nc: kommandot finns inte
ncl_grib2nc: komut yok
ncl_grib2nc: nie znaleziono polecenia
ncl_grib2nc: níor aimsíodh an t-ordú
ncl_grib2nc: no se encontró la orden
ncl_grib2nc: no s'ha trobat l'ordre
ncl_grib2nc: opdracht niet gevonden
ncl_grib2nc: parancs nem található
ncl_grib2nc: perintah tidak ditemukan
ncl_grib2nc: príkaz nenájdený
ncl_grib2nc: příkaz nenalezen
ncl_grib2nc: команда не найдена
ncl_grib2nc: командата не е открита
ncl_grib2nc: 命令找不到
ncl_grib2nc: コマンドが見つかりません