How to escape # using preg_match. Simple backslash doesn't seem to work?

I'm using Twilio and when an incoming text contains certain keywords ie: #today, #yesterday, #week or #month, I'm responding back with how many car deals were done in that period of time. So the user texts just the one word with the pound sign in front so my app knows its an instruction and not just a 'word' like yesterday.

I test the $to number to be sure its an admin phone number, than check the
$body = $_REQUEST['Body']; against those keywords.

Kind of like:
if( preg_match('/^(today)$/i', $body) ){
send back deals today
} else if if( preg_match('/^(yesterday)$/i', $body) ){
send back yesterdays deal count
} else {
do whatever
}

Works fine until I add in the # pound sign.

I tried placing the slash but didn't seem to work:
if( preg_match('/^(/#yesterday$/i', $body) ){

just didn't return anything.

I understand the issue; I just need to see the actual test data.  You can get this with var_dump().  Then use view source and copy/paste the information here.  When your regex has the ^ and $ at the beginning and end, you're telling the engine to evaluate the entire string.  If there are any other characters, even invisible whitespace, the match will fail.

Philosophy on why the test data matters (much more than the failing code):
https://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_7830-A-Quick-Tour-of-Test-Driven-Development.html

That worked perfectly as the how to example. Thanks again.

Great!  Thanks for the points and thanks for using EE, ~Ray