David Jeffries

Some PHP Abilities You May Not Know About

April 4th, 2008 | Tags:

Throughout my time programming PHP I've come across a few interesting things about the language. Coming from a primarily Java background, it seems quite strange to be able to do some of these things so easily.

Having said that, here are a few things with PHP that I've found interesting, and hopefully some of these things you've never heard about.

Call a PHP function from a string
PHP is an interesting language. To do the following in Java, it would be much more complex - around 5-10 lines of code. In PHP however, it is quite simple to call a function dynamically from a string.

<?php
  $call_this = "phpinfo";
  $call_this();
?>

You can even pass arguments to the variable like you were calling the function directly - it's pretty cool. Here's a practical example: Consider a function that accepts either a jpeg or png image file and resizes it (this is only a subset of the function).

<?php
  switch($imgType){
    case "jpeg":
      $create = "imagecreatefromjpeg";
      break;
    case "png":
      $create = "imagecreatefrompng";
      break;
  }
  $create($filename); //this will create either a jpeg or png
?>

This makes the code considerably cleaner by dynamically setting the function that will be called.

Ternary operator
This is a quick way to write an IF statement, without the structure and braces. The way it works is like a normal if statement, you pass it true or false (in the following case, ($test == true) == true), and then the ? means then and the : means else. It's pretty simple, and is nice to use for simple one liners, in cases like the following example.

<?php
  $test = true;
  echo $test == true ? "is true!" : "not true";
  //will print "is true!";
?>

A little bit nicer than

<?php
  $test = true;
  if($test == true){
    echo "is true!";
  }else{
    echo "not true";
  }
?>

Easily echo a variable
I don't really like this method, I prefer to just use <?php echo "string"; ?>, but maybe this way is faster - I'm not sure. Either way, pretty much all it does is echo the variable that is after the equals sign.

<?php
  $val = 50;
?>
<!-- some HTML or whatever -->
<?= $val ?>

Variable variables
Variable variables are variables that can be dynamically set with strings. In the following code, you will notice that we set the variable $val to "hello" and then set the variable variable (the string that $val holds ("hello")) to the string "variable variable". When we echo $hello, the text "variable variable" will be printed.

<?php
  $val = 'hello';
  $$val = 'variable variable';
  //the string that is set in $val is now the name of our variable.
  echo $hello; //will print 'variable variable'
?>

Calling a variable variable function
Expanding on the variable variables, you could actually combine that example with calling a PHP function by a string and do this:

<?php
  $val = 'show_info';
  $$val = 'phpinfo';
  echo $show_info(); //will echo phpinfo()
?>

Here, "show_info" is the name of the variable, and its pointing to "phpinfo" Writing $show_info() calls the function that the variable variable is pointing to. It's kind of confusing and would probably only be used in some really complex code, but it does work.