PHP - function associated with str_replace only run when needed - php

Question

I was using the str_replace() function to replace some contents within a text file. My code:
$txt = file_get_contents('script.txt');
function makefile() {
$file = fopen("test.txt","w");
fwrite($file,"Hello World. Testing!");
fclose($file);
return "Done!";
}
$templates = array("{{time}}", "{{PI}}", "{{make}}");
$applied = array(date("h:i:sa"), 22/7, makefile());
$str = str_replace($templates, $applied , $txt);
echo $str;
The script.txt contains:
The time is {{time}} <br>
The value of PI is {{PI}}
As you can see, it's just a simple templating system. the makefile() function is used only for testing purpose. The script.txt file has no {{make}} templates. So normally, the makefile function won't need to be called during replacement operation. But when I run the code, it creates the test.txt. Which mean makefile() runs. Is there any way to avoid this kind of unnecessary function operations? And run them only when needed?

Answer 1

You would need to add strpos check. strpos in php is used to find the position a substring occurs in a string, but if the substring never occurs, then it will return false. Leveraging that, we can do:
<?php
$txt = "The time is {{time}} <br>
The value of PI is {{PI}}";
function makefile() {
$file = fopen("test.txt","w");
fwrite($file,"Hello World. Testing!");
fclose($file);
return "Done!";
}
$templates = array("{{time}}", "{{PI}}", "{{make}}");
$applied = array(date("h:i:sa"), 22/7, strpos($txt,"{{make}}") ? makefile() : false);
$str = str_replace($templates, $applied , $txt);
echo $str;
?>