Programming :: Storing Grep Output To Feed Awk To Retrieve Entire Records Matching Variable

I have two files :

FileA
prot1
prot5
prot9
prot15

[Code]....

What I need to do is to extract from fileB the fields containing only the strings in fileA.

I thought awk could do the job easily with :

Code:
awk 'BEGIN { RS = "###" } /'$variable'/' fileB > output

where variable would maybe be the output of grep from fileA. So can I store the output of grep in a variable to use it afterwards with awk ?

something like that:

Code:
result=`grep prot. fileA` ; awk 'BEGIN { RS = "###" } /'$result'/' fileB > output
but that doesn't work. I'm always getting the entire fileB.

The output of grep get stored in the variable, I verified that with echo. So there is something that I just don't get... It seems to me that the above line should work.