I am rather new to regex and am stuck on the following where I try to use greg_match_all to count the number of hello after world.

if I use "world". (hello), it counts to the in the last hello; "world".*?(hello) stops in the first hello, both giving one count.

blah blah blah
hello
blah blah blah
class="world" 
blah blah blah
hello 
blah blah
hello
blah blah blah
hello
blah blah blah

Please advise.

CodePudding user response：

Another option with simple regexes:

if(preg_match('/"world".*/s', $str, $out)) {
  echo preg_match_all('/\bhello\b/', $out[0]);
}

See demo at tio.run

CodePudding user response：

You can use a single preg_match_all call here:

$text = "blah blah blah\nhello\nblah blah blah\nclass=\"world\" \nblah blah blah\nhello \nblah blah\nhello\nblah blah blah\nhello\nblah blah blah";
echo preg_match_all('~(?:\G(?!^)|\bworld\b).*?\K\bhello\b~s', $text);

See the regex demo and the PHP demo. Details:

• (?:\G(?!^)|\bworld\b) - end of the previous match (\G(?!^) does this check: \G matches either start of the string or end of the previous match position, so we need to exclude the start of string position, and this is done with the (?!^) negative lookahead) or a whole word world
• .*? - any zero or more chars, as few as possible
• \K - discards all text matched so far
• \bhello\b - a whole word hello.

NOTE: If you do not need word boundary check, you may remove \b from the pattern.

If hello and world are user-defined patterns, you must preg_quote them in the pattern:

$start = "world";
$find = "hello";
$text = "blah blah blah\nhello\nblah blah blah\nclass=\"world\" \nblah blah blah\nhello \nblah blah\nhello\nblah blah blah\nhello\nblah blah blah";
echo preg_match_all('~(?:\G(?!^)|' . preg_quote($start, '~') . '\b).*?\K' . preg_quote($find, '~') . '~s', $text);

CodePudding user response：

One approach might be to first strip off the leading portion of the string up to, and including, the first occurrence of world. Then call preg_match_all as you already are doing and get the count of occurrences of hello.

$input = "blah blah blah
hello
blah blah blah
class=\"world\" 
blah blah blah
hello 
blah blah
hello
blah blah blah
hello
blah blah blah";

$input = preg_replace("/^.*?\bworld/", "", $input);
preg_match_all("/\bhello\b/", $input, $matches);
echo sizeof($matches[0]);  // 4