gdcmviewer: 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/gdcmviewer - from package: libvtkgdcm-tools

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

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