The behavior of this function is almost identical to
preg_replace(), except for the fact that instead of
replacement parameter, one should specify a
callback that will be called and passed an array of
matched elements in the subject string. The callback should return the
replacement string.
Example 1. preg_replace_callback() example
<?php // this text was used in 2002 // we want to get this up to date for 2003 $text = "April fools day is 04/01/2002\n"; $text.= "Last christmas was 12/24/2001\n"; // the callback function function next_year($matches) { // as usual: $matches[0] is the complete match // $matches[1] the match for the first subpattern // enclosed in '(...)' and so on return $matches[1].($matches[2]+1); } echo preg_replace_callback( "|(\d{2}/\d{2}/)(\d{4})|", "next_year", $text); // result is: // April fools day is 04/01/2003 // Last christmas was 12/24/2002 ?>
You'll often need the callback function
for a preg_replace_callback() in just one place.
In this case you can use create_function() to
declare an anonymous function as callback within the call to
preg_replace_callback(). By doing it this way
you have all information for the call in one place and do not
clutter the function namespace with a callback functions name
not used anywhere else.
<?php /* a unix-style command line filter to convert uppercase * letters at the beginning of paragraphs to lowercase */ $fp = fopen("php://stdin", "r") or die("can't read stdin"); while (!feof($fp)) { $line = fgets($fp); $line = preg_replace_callback( '|<p>\s*\w|', create_function( // single quotes are essential here, // or alternative escape all $ as \$ '$matches', 'return strtolower($matches[0]);' ), $line ); echo $line; } fclose($fp); ?>
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Php preg replace callback syntax tutorial
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