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  1. <?php
  2.  
  3. $string = '
  4. <!--
  5. this   is a comment
  6.  
  7. -->
  8.  
  9. <br/>    <br>
  10.  
  11. <!--
  12. this   is a comment
  13. -->
  14. <br/>   <br/>
  15. <!--
  16. this   is a comment
  17.  
  18. -->
  19. Hello    	world';
  20.  
  21. $new_string = preg_replace_callback('#(?(?!<!--).*?(?=<!--|$)|(<!--.*?-->))#s', function($m){
  22. 	if(!isset($m[1])){
  23. 		return preg_replace('#\s+#s', ' ', $m[0]);
  24. 	}
  25. 	return $m[0];
  26. },$string);
  27.  
  28. echo $new_string;
  29. ?>
Success #stdin #stdout 0.01s 20568KB
comments ()
stdin 
Standard input is empty
stdout 
 <!--
this   is a comment

--> <br/> <br> <!--
this   is a comment
--> <br/> <br/> <!--
this   is a comment

--> Hello world
https://ideone.com/cHdNS2
language:
PHP (php 7.3.5)
created:
11 years ago
visibility:
public

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