How can I write or append to a text file using sql?

as follows you can do it

exec master..xp_cmdshell 'echo pranay test application > d:\file.txt'

      

        
        
        
      

    

more on this: http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/how-to-copy-data-append-data-into-files-