带有计数位的正则表达式

Question

Here is my code

<?php
    $str='salamsalam';
    echo preg_match('/salam{1,1}/',$str);
?>

I write in regex one time min and max but I don't know why it prints 1(true),

And one more question:

I would like to accept just exactly 4 digit (no more, no less) now my code is here:

<?php
    $num=234567 ;
    echo preg_match('/[0-9]{4,4}/',$num); 
?>

That it is not correct, it also accept 234567 .

Answer 1

The problem in both expressions is that you just match somewhere in the text. If you want to make sure that there is nothing before and after what you match with the expression, you need to include the start and end markers there:

<?php
$str = 'salamsalam';
echo preg_match('/^salam$/', $str);

and:

<?php
$num = 234567;
echo preg_match('/^[0-9]{4}$/', $num);

Note that you don’t need to use {min,max} if you want match exactly a specific number of times. Then you can just use {num}. And if you want to match only once, you don’t need to add any specifier.

Answer 2

PROBLEM

Your regex is correct in both cases.

The problem is, preg_match() returns true if there is any match found --- if there is more than one match found, then it will still print true.

---

SOLUTION

You can add a ^ to match the beginning and a $ to match the end in your regex so that it will match the whole string (or not).

/^salam$/
/^[0-9]{4}$/