count number of lines in terminal output

Pipe the result to wc using the -l (line count) switch:

grep -Rl "curl" ./ | wc -l

Putting the comment of EaterOfCode here as an answer.

grep itself also has the -c flag which just returns the count

So the command and output could look like this.

$ grep -Rl "curl" ./ -c
24

EDIT:

Although this answer might be shorter and thus might seem better than the accepted answer (that is using wc). I do not agree with this anymore. I feel like remembering that you can count lines by piping to wc -l is much more useful as you can use it with other programs than grep as well.