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 23:41:46)

 H107 - String Handling in PHP
  [2238] Handling nasty characters - Perl, PHP, Python, Tcl, Lua - (2009-06-14)
  [2165] Making Regular Expressions easy to read and maintain - (2009-05-10)
  [2046] Finding variations on a surname - (2009-02-17)
  [1799] Regular Expressions in PHP - (2008-09-16)
  [1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
  [1603] Do not SHOUT and do not whisper - (2008-04-06)
  [1533] Short and sweet and sticky - PHP form input - (2008-02-06)
  [1372] A taster PHP expression ... - (2007-09-30)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1195] Regular Express Primer - (2007-05-20)
  [1058] PHP Regular expression to extrtact link and text - (2007-01-31)
  [1008] Date conversion - PHP - (2006-12-26)
  [728] Looking ahead and behind in a Regular Expression - (2006-05-22)
  [716] Evaluating arithmetic expressions in configuration files - (2006-05-10)
  [642] How similar are two words - (2006-03-11)
  [608] Don't expose your regular expressions - (2006-02-15)
  [589] Robust PHP user inputs - (2006-02-03)
  [574] PHP - dividing a string up into pieces - (2006-01-23)
  [560] The fencepost problem - (2006-01-10)
  [558] Converting between acres and hectares - (2006-01-08)
  [493] Running a Perl script within a PHP page - (2005-11-12)
  [463] Splitting the difference - (2005-10-13)
  [422] PHP Magic Quotes - (2005-08-22)
  [337] the array returned by preg_match_all - (2005-06-06)
  [54] PHP and natural sorting - (2004-09-19)
  [31] Here documents - (2004-08-28)

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