Is there a difference between single and double quotes in PHP?

Yes, the main difference is content processing. In double quotes, PHP performs variable interpolation and escapes sequences, while in single quotes, it does not.

• Single quotes ('): The content is taken literally. Variables are not substituted, and escaped characters (except \' and \\) are not processed.

  <?php
  $name = 'World';
  echo 'Hello, $name!\n'; // Will output: Hello, $name!\n
  ?>
  

• Double quotes ("): Content is parsed syntactically. Variables (including array elements and object properties) are substituted, and escaped sequences (\n, \t, \) are interpreted.

  <?php
  $name = 'World';
  echo "Hello, $name!\n"; // Will output: Hello, World! (and a newline)
  ?>
  

Summary comparison:

Feature	Single quotes	Double quotes
Variable interpolation	No	Yes
Processing \n, \t, etc.	No	Yes
Processing \' and \\	Yes	Yes
Performance	Slightly faster	Slightly slower (due to parsing)