(PHP 4, PHP 5)
ereg_replace — Replace regular expression
$pattern
   , string $replacement
   , string $string
   )
   This function scans string for matches to
   pattern, then replaces the matched text
   with replacement.
  
This function has been DEPRECATED as of PHP 5.3.0. Relying on this feature is highly discouraged.
patternA POSIX extended regular expression.
replacement
       If pattern contains parenthesized substrings,
       replacement may contain substrings of the form
       \digit, which will be
       replaced by the text matching the digit'th parenthesized substring; 
       \0 will produce the entire contents of string.
       Up to nine substrings may be used. Parentheses may be nested, in which
       case they are counted by the opening parenthesis.
      
stringThe input string.
   The modified string is returned. If no matches are found in 
   string, then it will be returned unchanged.
  
For example, the following code snippet prints "This was a test" three times:
Example #1 ereg_replace() example
<?php
$string = "This is a test";
echo str_replace(" is", " was", $string);
echo ereg_replace("( )is", "\\1was", $string);
echo ereg_replace("(( )is)", "\\2was", $string);
?>
   One thing to take note of is that if you use an integer value as
   the replacement parameter, you may not get
   the results you expect. This is because
   ereg_replace() will interpret the number as
   the ordinal value of a character, and apply that. For instance:
  
Example #2 ereg_replace() example
<?php
/* This will not work as expected. */
$num = 4;
$string = "This string has four words.";
$string = ereg_replace('four', $num, $string);
echo $string;   /* Output: 'This string has   words.' */
/* This will work. */
$num = '4';
$string = "This string has four words.";
$string = ereg_replace('four', $num, $string);
echo $string;   /* Output: 'This string has 4 words.' */
?>
Example #3 Replace URLs with links
<?php
$text = ereg_replace("[[:alpha:]]+://[^<>[:space:]]+[[:alnum:]/]",
                     '<a href="\\0">\\0</a>', $text);
?>
Note:
As of PHP 5.3.0, the regex extension is deprecated in favor of the PCRE extension. Calling this function will issue an
E_DEPRECATEDnotice. See the list of differences for help on converting to PCRE.
ereg_replace() is deprecated as of PHP 5.3.0. preg_replace() is the suggested alternative to this function.