gdcmdiff: 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/gdcmdiff - from package: libgdcm-tools

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

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