Variable inside regular expression php

Question

I a stuck with regular expression and i need help. So basically i want to do somethning like this:

$data = "hi";
$number = 4;

$reg = '/^[a-z"]{1,4}$/';


if(preg_match($reg,$data)) {
    echo 'Match';   
}else {
    echo 'No match';
}

But i want to use variable

$reg = '/^[a-z"]{1, variable here }$/';

I have tried:

$reg = '/^[a-z"]{1, '. $number .'}$/';

$reg = "/^[a-z\"]{1, $number}$/";

But not getting right result.

Tnx for help

In the first example, you are using single quotes which prevents PHP from parsing your variable as a variable. — Alex W
– Alex W, Commented Sep 12, 2014 at 17:54
@AlexW - it doesn't matter which quotes did he use, since he split the string to two parts and add $number via . operator — Drecker
– Drecker, Commented Sep 12, 2014 at 18:00
@Drecker I was referring to the example above that. Where he put variable here. — Alex W
– Alex W, Commented Sep 12, 2014 at 18:01

Your Common Sense · Accepted Answer · 2023-08-31 07:36:55Z

40

In the first example you have an extra space where you shouldn't have one.

Also, you should always quote such variable as it may contain special characters recognized by regex. You should have:

$reg = '/^[a-z"]{1,'. preg_quote($number) .'}$/';

then it would work just fine.

edited Aug 31, 2023 at 7:36

Your Common Sense

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answered Sep 12, 2014 at 17:57

Drecker

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1 Comment

Jonathan J. Pecany Over a year ago

I had a problem with this where when I tried putting variables inside it, it doesn't work but when I put in the text from the variable to the correct location, it works quite find.

Atural · Accepted Answer · 2017-12-21 17:29:14Z

4

Another way to use variables in regex is through the use of sprintf.

For example:

$nonWhiteSpace = "^\s";
$pattern = sprintf("/[%s]{1,10}/",$nonWhiteSpace);
var_dump($pattern); //gives you /[^\s]{1,10}/

edited Dec 21, 2017 at 17:29

Atural

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answered Dec 21, 2017 at 17:10

cbernard73

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