expressionEngine php parsing str_replace not working

I have a template with php enabled on output. However i can't get str_replace to work. See below code. If i just put {title} without any php then it works. But when i include php and place {title} inside the str_replace function, i get nothing displayed. I tried php with simple echo 'test'; an开发者_如何学Cd it worked. It's just not parsing {title} or other field tags.

{exp:channel:entries channel="one" url_title="{segment_2}"}
  <?php
    echo str_replace('old', 'new', '{title}');
  ?>
{/exp:channel:entries}

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This may sound preposterous, but have you tried removing the url_title parameter from the {exp:channel:entries} tag to ensure the rest of your code and logic is working properly?

The following code should output the entry title of "old test" (without quotes):

{exp:channel:entries channel="channel_name" entry_id="xx" dynamic="off"}
    {title} 
{/exp:channel:entries}

Given the same entry title of "old test", this should output: "new test" (again, without the quotes):

{exp:channel:entries channel="channel_name" entry_id="xx" dynamic="off"}
    <?php
        echo str_replace('old', 'new', '{title}');
    ?>
{/exp:channel:entries}

This was tested successfully in a new, blank template with PHP Enabled and set to Output.

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You might try embedding the template that has your PHP in it and sending the variable that way. The parsing on input/output still doesn't matter with certain elements sometimes.