preg match to get text after @ symbol and before next space using php

I need help to find out the strings from a text which starts with @ and till the next immediate space by preg_match in php

Ex : I want to get @string from this line as separate. In this example, I need to extract "@string" alone from this line.

Could any body help me to find out the solutions for this.

Thanks in advance!

PHP and Python are not the same in regard to searches. If you've already used a function like strip_tags on your capture, then something like this might work better than the Python example provided in one of the other answers since we can also use look-around assertions.

<?php
$string = <<<EOT
I want to get @string from this line as separate.
In this example, I need to extract "@string" alone from this line.

@maybe the username is at the front.

Or it could be at the end @whynot, right!

dog@cat.com would be an e-mail address and should not match.        

EOT;

echo $string."<br>";

preg_match_all('~(?<=[\s])@[^\s.,!?]+~',$string,$matches);
print_r($matches);
?>

Output results

Array
(
    [0] => Array
        (
            [0] => @string
            [1] => @maybe
            [2] => @whynot
        )

)       

Update

If you're pulling straight from the HTML stream itself, looking at the Twitter HTML it's formatted like this however:

<s>@</s><b>UserName</b>

So to match a username from the html stream you would match with the following:

<?php

$string = <<<EOT
<s>@</s><b>Nancy</b> what are you on about?

I want to get <s>@</s><b>string</b> from this line as separate. In this example, I need to extract "@string" alone from this line.

<s>@</s><b>maybe</b> the username is at the front.

Or it could be at the end <s>@</s><b>WhyNot</b>, right!

dog@cat.com would be an e-mail address and should not match.        

EOT;

$matchpattern = '~(<s>(@)</s><b\>([^<]+)</b>)~';
preg_match_all($matchpattern,$string,$matches);


$users = array();
foreach ($matches[0] as $username){
    $cleanUsername = strip_tags($username);
    $users[]=$cleanUsername;
}

print_r($users);

Output

Array
(
    [0] => @Nancy
    [1] => @string
    [2] => @maybe
    [3] => @WhyNot
)