'edit ' is not recognised as an internal command,operable program or batch file in dos why?

Question

after installing oracle in my system I can not edit txt files in dos ( command prompt )

Answer 1

Assuming it has not be deleted (unlikely) your path may have been amended not to include your windows system32 directory which is where edit.com should be found

So %windir%\system32\edit.com should start it regardless of the path settings.

You can check/change your path on the Environment Variables section which is found on the Advanced tab of your System Properties. (ie Right-Click on My-Computer and select Properties)