Check out Clamv ( http://www.clamav.net/ )
It is a open source anti-virus, and you can scan a stream.
So you do not need to save the file for scanning it.
http://linux.die.net/man/1/clamscan
Scan a data stream:
cat testfile | clamscan –
So it is quite easy, start the clamscan process with the – arg. write the file content to the stdin, and wait for the result code.
During your testing, you can use the EICAR file, which is a file dedicated for checking if an anti-virus is working. http://en.wikipedia.org/wiki/EICAR_test_file