paw++-gfortran: 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/paw++-gfortran - from package: paw-gfortran

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

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