nydiff-gfortran: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/nydiff-gfortran - from package: patchy-gfortran

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