Search for partial string in PHP array? Search value contains hashtag

Question

Example:

$array = array('alpha beta','beta gamma','delta phi', '#alpha phi', 'beta phi');
$searchword = 'alpha';
$results = array_filter($array, function($var) use ($searchword) { return preg_match("/\b$searchword\b/i", $var); });
print_r($results);

Array ( [0] => alpha beta [3] => #alpha phi )

I would like to find only the elements containing #alpha, not alpha.

The result I want is Array ( [3] => #alpha phi ).

However, this doesn't work:

$array = array('alpha beta','beta gamma','delta phi', '#alpha phi', 'beta phi');
$searchword = '#alpha';
$results = array_filter($array, function($var) use ($searchword) { return preg_match("/\b$searchword\b/i", $var); });
print_r($results);

Array ( )

I also tried $searchword = preg_quote('#alpha'); but that doesn't work either. I'm not familiar enough with regex to figure this out-- there must be some regex rule I'm missing out on?

Note: I am not looking to find all the hashtag keywords in the array. I want to search for a specific hashtag keyword.

Credit: I used one of the answers from here: Search for PHP array element containing string

Answer 1

Remove the starting \b

preg_match("/$searchword\b/i", $var);

or

Use \B

preg_match("/\B$searchword\b/i", $var);

Why?

It's all about word boundaries \b matches between word char and a non-word char or vice-versa. Since the first character is # which is a non-word character and before that character there exists the start of the line boundary. \B is the suitable one for this, which matches between two non-word chars or two word chars. Here start of the line , # so there must exists \B in-between not \b.

Answer 2

Or you can also use strpos instead of preg_match as

$searchword = '#alpha';
$results = array_filter($array, function($var) use ($searchword) { return (strpos($var,$searchword)>-1); });