I am a studying in a engineering college ....... there we are having linux operating system in the server and that was shared to all by installing putty in every system ........every student has their own login id's and passwords .my question is how to copy a file from one user to another user...... plz reply............plz

You should create a new thread instead of injecting your own requests in a totally unrelated thread.

scp path/to/sourcefile user@hostname:path/to/destfile

As above, but don't forget to make sure you have the correct permissions on the destination folder.