preg replace callback - How to create a pattern to use in preg_replace_callback() function in PHP

I am upgrading my PHP Application from PHP 5 to PHP 7 for which I am required to replace all the references of preg_replace() function to preg_replace_callback() function.

I am having a hard time creating the $pattern parameter for preg_replace_callback() function.

Below are the code details -

The string that I am trying to match -

$bandHdrs = "{format(26,num,4)}";
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Existing PHP 5 code:

$bandHFmtString = "#({)(format)([(]*)([0-9]*)([a-zA-Z0-9,']*)([)]*)(})#e";
$subBandHead = preg_replace_callback($bandHFmtString, '$this->formatSqlNumber($queryData[$r][' . "$4" . '],\'' . "$5" . '\',\'' . "$2" . '\')', $bandHdrs);

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New PHP 7 code:

$bandHFmtString = "#\{format\(\[0-9]*\,\[a-zA-Z0-9]*\,\[0-9]*\)\}#";
$subBandHead = preg_replace_callback($bandHFmtString, function ($matches) use ($value) {
                                                                                        $firstCommaPos = strpos($matches[0],",");
                                                                                        $closeParenPos = strpos($matches[0],")",$firstCommaPos + 1);
                                                                                        $formatStr = substr($matches[0],$firstCommaPos,$closeParenPos - $firstCommaPos);
                                                                                        return Report::formatSqlNumber($value,$formatStr,"format"); 
                                                        , $bandHdrs[$key]);

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Can someone help me create the $bandHFmtString pattern to match the $bandHdrs string?

Any help would be truly appreciated.

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