How do I redirect grep output to a variable?

I have a pipe. For example, I have this pipe:

user@user:~$ cal | head -1 | grep -oP "[A-Za-z]+"

      

        
        
        
      

    

For this channel, I get this result:

September

      

        
        
        
      

    

I want to store this result in a variable. I write the following commands:

user@user:~$ cal | head -1 | month=$(grep -oP "[A-Za-z]+") | echo $month

      

        
        
        
      

    

And I am getting an empty string. What is the problem?