cgnsdiff: 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 Debian possible default full paths are:

/usr/bin/cgnsdiff - from package: cgns-convert

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

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