是否可以使用正则表达式编辑字符串？

I want to edit string like below example :

$str = '$variable$123'

Convert to

$str = '$variable$*123'

I tried below code :

<?php

$str = '$variable$123';
$str= preg_replace('/(\$\w*\$.[0-9]*)+/i', '$1*$2', $str);
echo $str;

?>

But didn't get as i want...

Please help.....

I got the answer.

<?

$str1 = '$variable$123$variable2$';    
echo replace($str1);

$str2 = '$variable$123';
echo replace($str2);

function replace($str)
{
    $str = preg_replace('/(\$\w*\$)(\d+)/i', '$1*$2', $str);
    $str = preg_replace('/(\d+)(\$\w*\$)/i', '$1*$2', $str);        
    return $str
}

?>

output :

$variable$*123*$variable2$

$variable$*123

$str = preg_replace('/(\$\w+\$)(\d+)/', '$1*$2', $str);

Another (simpler) version that may fit the exemple given in comment

$str = preg_replace('/(\$\w+\$)/', '$1*', $str);