how to use php regular expression

Question

I wanted to count asterisks from a string starting with foo 'fooarbazlujabazlewis*bazbazlewbaz' and i should be able to count asterisk from another string starting with luja in short I wanted the starting string to be changed programmatically

I tried below code, but it counts any asterisk even if foo is not at the beginning

preg_match_all('/(^foo\*)*(\*)/', '*foo*arbaz*luj*abaz*lewis*bazbazlewbaz'); 

the result is 6. but in this case, I wanted it to fail since foo is not at the beginning.

Answer 1

It is not the best application for a regex, but you can use

preg_match_all('~(?:\G(?!\A)|^foo)[^*]*\K\*~', $string, $matches)

See the regex demo. Details:

• (?:\G(?!\A)|^foo) - either the end of the previous successful match or foo at the start of string
• [^*]* - zero or more chars other than *
• \K - discard the text matched so far
• \* - an asterisk.

See the PHP demo:

$string = "foo*arbaz*luj*abaz*lewis*bazbazlewbaz";
echo preg_match_all('~(?:\G(?!\A)|^foo)[^*]*\K\*~', $string, $matches);
// => 5

Without a regex, you could simply check if foo appears at the start of string (using strpos) and then use substr_count to count the occurrences of asterisks:

$string = "foo*arbaz*luj*abaz*lewis*bazbazlewbaz";
if (strpos($string, "foo") === 0 ) {
    echo substr_count($string, "*");
}

See this PHP demo.