Question

<?php
    $string = '395095427174400_558374047513203';
    if(preg_match("/^[0-9][_][0-9]$/",$string)){
        echo "True";
    }else{
        echo "False";
    }
?>

Why does my regex not match and underscore between numbers?

Answer 1

You need to use quantifier to match more number of digits before an underscore. And you don’t really need to have your underscore in a character class.

You can try this regex: –

/^[0-9]+_[0-9]+$/