I want to find out the files that are older than a given file in the current
directory ...Can anyone help

thanks buddy !! but it also prints the file itself ( yourfile)which acts as the input.....also it gives output as this
-------------
.
./a.txt
./b.txt
----------

can i avoid the "./ "

Try: where" __ " is double underscore.

Well that works fine !! is _(underscore) a substitute for "/" in sed command.
As sed has the following syntax sed -e 's/a/b'

Yes "_" is delimiter here, I used it because "/" was in our search string also, so to avoid confusion it was "_" there, you can use any character as delimiter, but you have to take care of it in your syntax later on.

Regards,
Tayyab