Matching a sentence with grep

I'm trying to grep for the full sentence containing a search term. I've tried

grep (^.|\.\s).*searchterm.*(\.\s|\n)

but it's not working and I'm not sure why.

To clarify: I want stdout to print the full sentence of the search term. I am using grep to search through a single text file.

As an example, if my file has

"Foo blah. Blah blah searchterm blah blah. Foo bar."

I want stdout to print Blah blah searchterm blah blah

Tried this on my sh-compatible terminal:

$ grep --only-matching --perl-regexp "[^.]*searchterm[^.]*" \
       <<< "Foo blah. Blah blah searchterm blah blah. Foo bar."
Blah blah searchterm blah blah
$ 

Can be abbreviated to grep -oP.

I think the problem with the regex you provided is specifying .*to how greedy you wanted it to be (as stated by bertieb). What I did was just reformulate your request from "anything as long as it ends with dot" to "anything that's not a dot"