Page 595 - Beginning PHP 5.3

Chapter 18: String Matching with Regular Expressions
Replacing Text

As you know from reading Chapter 5, searching strings is only half the story. Often you need to replace a
portion of a string with new text.
Simple search - and - replace functions like str_replace() are useful for replacing literal strings.
However, if you need to replace more complex patterns of text, you can use PHP ’ s regular expression
string replacement functions, preg_replace() and preg_replace_callback() . You explore these
two functions in the following sections.

Replacing Text with preg_replace()
preg_replace() lets you match a pattern against a target string, much like preg_match() , and replace
the matched text with different text. In its most basic form, preg_replace() takes three arguments:
❑ The regular expression to search for (as a string).

❑ The replacement text to replace any matched text with.
❑ The target string to search through.

preg_replace() returns the target string with any matched text replaced by the replacement text.
Here ’ s a simple example that searches for a dollar symbol followed by a number of digits, a dot, and two
more digits, and replaces this text with the string “ [CENSORED] “ :

$text = “The wholesale price is $89.50.”;

// Displays “The wholesale price is [CENSORED].”

echo preg_replace( “/\\$\d+\.\d{2}/”, “[CENSORED]”, $text );
Remember backreferences from using preg_match() earlier in the chapter? You can also use backreferences
within the replacement string — simply write a dollar ( $ ) symbol followed by the backreference number:

$text = “Author: Steinbeck, John”;

// Displays “Author: John Steinbeck”
echo preg_replace( “/(\w+), (\w+)/”, “$2 $1”, $text );

If you want to include the entire matched text in the replacement string, use $0 (a dollar followed
by zero):
$text = “Mouse mat: $3.99”;

// Displays “Mouse mat: Only $3.99”
echo preg_replace( “/\\$\d+\.\d{2}/”, “Only $0”, $text );

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