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Curly braces within double quoted strings in PHP

In PHP, you can include a variable name within a double quoted string and the variable will be expanded as the string is used - this means that double quotes are actually an operator, whereas single quotes mean a string literal. You can also put curly braces around a variable name to say, explicitly, "this is the variable", so:
  $place = "London";
  $course = "PHP";
  print ("We can run a $course course for you in ${place} next month");

will produce:
  We can run a PHP course for you in London next month

Somewhat surprisingly, you can also place the curly braces OUTSIDE the $, so the line:
  print ("We can run a $course course for you in {$place} next month");
would produce the same results.

This use of curly braces outside the $ is known as the "complex" form of variable expansion within double quotes. In the other (simple) form, you can expand a regular variable, or an array member with a constant or simple variable name as its subscript - a very useful facility - but one which is frustratingly limited at times. In the complex form you have somewhat more facilities - you can use double subscripts ("arrays of arrays") and you can access object properties too. So:
  print ("This is {$box->area()}\n");
is a valid (and very useful) syntax.

There's a full set of examples (with sample output) [here].
(written 2010-02-09, updated 2010-02-11)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
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  [463] Splitting the difference - (2005-10-13)
  [422] PHP Magic Quotes - (2005-08-22)
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  [54] PHP and natural sorting - (2004-09-19)
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