[BiO BB] restrict the blast result by e-value?

[NewGene]

Hi, group,
        If I do a blast search and want only hits with 100% identity 
between query and subject, how can I specify the e-value or other 
parameters for this purpose? I am not familiar with the underlying 
statistics of Blast, but it seems that the query sequences with same length 
have the same e-values for perfect match. If there is a formula available 
to predict this e-value, it will help to put it into scripts run my 
localblast automatically using any length sequence.

	Thanks in advance for your help.
	
CL