can't understand the difference between * and + quantifiers in REGEX [duplicate] - php

Question

This question already has answers here:
Difference between * and + regex
(7 answers)
Closed 4 years ago.
I am new to regex, and as i have studied, the * matches zero or more and + matches one or more, so i started to test this:
<?php
preg_match("/a/", 'bbba',$m);
preg_match("/a*/", 'bbba',$o);
preg_match("/a+/", 'bbba',$p);
echo '<pre>';
var_dump($m);
var_dump($o);
var_dump($p);
echo '</pre>';
?>
but the result is that * didn't match any thing and returned empty while the letter a exists:
array(1) {
[0]=>
string(1) "a"
}
array(1) {
[0]=>
string(0) ""
}
array(1) {
[0]=>
string(1) "a"
}
so what i miss here.

Answer 1

/a/ matches the first a in bbba
/a*/ matches 0 or more a characters. There are 0 a characters between the start of the string and the first b so it matches there.
/a+/ matches 1 or more a characters so it matches the first a character
The thing to note here is that a regex will try and match as early in the string it is checking as possible.

Answer 2

a* means match string which may NOT contain a because * matches zero or more, hence pattern a* will match even empty string.
To see all matches you can use preg_match_all, like:
<?php
preg_match_all("/a*/", 'bbba', $o);
var_dump($o);
as result you will see:
array(1) {
[0]=>
array(5) {
[0]=>
string(0) ""
[1]=>
string(0) ""
[2]=>
string(0) ""
[3]=>
string(1) "a"
[4]=>
string(0) ""
}
}
hope it will help you.

Answer 3

* means that the preceding item will be matched zero or more times.
+ means that the preceding item will be matched one or more times.
Also a* match empty, that why it shows an empty result. You can use preg_match_all("/a*/", 'bbba',$o); and then filter the results on the non-empty values of the array resulting.