How to decipher a regular expression?

Question

preg_match_all('/({\$([^}]+)})/', $result, $matches)

Can someone please help decipher the regular expression in this call?

Regular expressions are not my best. As far as I can tell it's looking for matches that look like {$foo} but I think I am missing something?

Answer 1

Here, we have a rather simple expression that passes pretty much all chars, bounded from left with { and $ and bounded from right with }. It collects almost all chars in between:

DEMO

RegEx

If this expression wasn't desired, it can be modified or changed in regex101.com. For example, we can restrict it and fail special chars, if we like:

({\$\w+})

DEMO

RegEx Circuit

jex.im visualizes regular expressions:

Demo

const regex = /({\$\w+})/gm;
const str = `{\$foo}
{\$foo_090_}
{\$foo_@#\$%_5678}
{\$foo_@#\$%_{+[]:}`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

PHP Test

$re = '/({\$\w+})/m';
$str = '{$foo}
{$foo_090_}
{$foo_@#$%_5678}
{$foo_@#$%_{+[]:}';

preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);

// Print the entire match result
var_dump($matches);