too long

I have a regex, which is: /[0-9]+(,[0-9]+)*/.

It accepts only numbers, separated by a comma. For instance:

1,2,3,4 = good
,1,2,3,4 = bad
1,2,3,4, = bad
String = bad

But it also accepts a numbers with a space:

1, 2, 3, 4 = good

How to make regex that wouldn't allow to do so and would only let to enter a numbers, separated by a comma without spaces?

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Your regex is correct as is, you just need to use anchors so you check the full string, and not a partial match.

^[0-9]+(,[0-9]+)*$

https://regex101.com/r/zU22VX/1/

An alternative approach could be:

$string = '1,2,3,4';
$array = str_getcsv($string);
foreach($array as $number) {
    if(!is_numeric($number)) {
        echo 'Bad value' . $number;
        break;
    }
}

This should work:

/^\d(,\d)*$/

• ^ match the beginning of the string
• \d match a digit
• $ match the end of the string

Example:

if (preg_match("/^\d(,\d)*$/", $string))
    echo "good";
else
    echo "bad";

Use this:

^(\d,(?=\d))*\d$

How it works:

• ^: match strings which starts with..(what follows)
• (...)*: what inside the brackets can be repeated any number of times
• \d,(?=\d): this is the block that is allowed to repeat. It looks for a number from 0 to 9 followed by a comma which is followed by a number. The number following the comma is not included in the match.
• \d$: finally, the string must terminate with a number.