very simple preg_replace doesnt work

Question

I have this code, is working in all the tester I'm using for regex, but later, in my real php code it doesn't work. What I want is to replace the number in the link for something else

     $value='/something.html?helperid=252';
     //patern
     $patternHelperId='/(?<=helperid=)\d{1,}/';
     //replace
     preg_replace($patternHelperId, "mynewreplacement",  $value);

     //debug
     echo "\n$value\n";//  /something.html?helperid=252????? aggain???

What's wrong??

Answer 1

You should assign the result of preg_replace back to $value , like this:

$value = preg_replace($patternHelperId, "mynewreplacement",  $value);

And, as a sidenote, \\d{1,} can be replaced with \\d+ .

Answer 2

preg_replace returns the result. It does not modify the variable in-place

Answer 3

You have forgotten to take the result of the preg_replace function:

$newValue = preg_replace($patternHelperId, "mynewreplacement",  $value);

echo "\n$newvalue\n";

A better pattern:

$patternHelperId='/helperid=\K\d++/';