preg_replace
(PHP 4, PHP 5)
preg_replace — Perform a regular expression search and replace
Description
$pattern ,
mixed $replacement ,
mixed $subject [,
int $limit = -1[,
int &$count ]] )
Searches subject for matches to pattern and replaces them with replacement.
Parameters
-
pattern -
The pattern to search for. It can be either a string or an array with strings.
Several PCRE modifiers are also available, including the deprecated 'e' (PREG_REPLACE_EVAL), which is specific to this function.
-
replacement -
The string or an array with strings to replace. If this parameter is a string and the
patternparameter is an array, all patterns will be replaced by that string. If bothpatternandreplacementparameters are arrays, eachpatternwill be replaced by thereplacementcounterpart. If there are fewer elements in thereplacementarray than in thepatternarray, any extrapatterns will be replaced by an empty string.replacementmay contain references of the form \\n or (since PHP 4.0.4) $n, with the latter form being the preferred one. Every such reference will be replaced by the text captured by the n'th parenthesized pattern. n can be from 0 to 99, and \\0 or $0 refers to the text matched by the whole pattern. Opening parentheses are counted from left to right (starting from 1) to obtain the number of the capturing subpattern. To use backslash in replacement, it must be doubled ("\\\\" PHP string).When working with a replacement pattern where a backreference is immediately followed by another number (i.e.: placing a literal number immediately after a matched pattern), you cannot use the familiar \\1notation for your backreference. \\11, for example, would confuse preg_replace() since it does not know whether you want the \\1 backreference followed by a literal 1, or the \\11 backreference followed by nothing. In this case the solution is to use \${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal.
When using the deprecated e modifier, this function escapes some characters (namely ', ", \ and NULL) in the strings that replace the backreferences. This is done to ensure that no syntax errors arise from backreference usage with either single or double quotes (e.g. 'strlen(\'$1\')+strlen("$2")'). Make sure you are aware of PHP's string syntax to know exactly how the interpreted string will look.
-
subject -
The string or an array with strings to search and replace.
If
subjectis an array, then the search and replace is performed on every entry ofsubject, and the return value is an array as well. -
limit -
The maximum possible replacements for each pattern in each
subjectstring. Defaults to -1 (no limit). -
count -
If specified, this variable will be filled with the number of replacements done.
Return Values
preg_replace() returns an array if the subject parameter is an array, or a string otherwise.
If matches are found, the new subject will be returned, otherwise subject will be returned unchanged or NULLif an error occurred.
Errors/Exceptions
An E_DEPRECATED level error is emitted when passing in the "\e" modifier.
Changelog
| Version | Description |
|---|---|
| 5.5.0 | The /e modifier is deprecated. Use preg_replace_callback() instead. See the PREG_REPLACE_EVALdocumentation for additional information about security risks. |
| 5.1.0 | Added the count parameter |
| 4.0.4 | Added the '$n' form for the replacement parameter |
| 4.0.2 | Added the limit parameter |
Examples
Example #1 Using backreferences followed by numeric literals
<?php
$string = 'April 15, 2003';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '${1}1,$3';
echo preg_replace($pattern, $replacement, $string);
?>
The above example will output:
April1,2003
Example #2 Using indexed arrays with preg_replace()
<?php
$string = 'The quick brown fox jumped over the lazy dog.';
$patterns = array();
$patterns[0] = '/quick/';
$patterns[1] = '/brown/';
$patterns[2] = '/fox/';
$replacements = array();
$replacements[2] = 'bear';
$replacements[1] = 'black';
$replacements[0] = 'slow';
echo preg_replace($patterns, $replacements, $string);
?>
The above example will output:
The bear black slow jumped over the lazy dog.
By ksorting patterns and replacements, we should get what we wanted.
<?php
ksort($patterns);
ksort($replacements);
echo preg_replace($patterns, $replacements, $string);
?>
The above example will output:
The slow black bear jumped over the lazy dog.
Example #3 Replacing several values
<?php
$patterns = array ('/(19|20)(\d{2})-(\d{1,2})-(\d{1,2})/',
'/^\s*{(\w+)}\s*=/');
$replace = array ('\3/\4/\1\2', '$\1 =');
echo preg_replace($patterns, $replace, '{startDate} = 1999-5-27');
?>
The above example will output:
$startDate = 5/27/1999
Example #4 Strip whitespace
This example strips excess whitespace from a string.
<?php
$str = 'foo o';
$str = preg_replace('/\s\s+/', ' ', $str);
// This will be 'foo o' now
echo $str;
?>
Example #5 Using the count parameter
<?php
$count = 0;
echo preg_replace(array('/\d/', '/\s/'), '*', 'xp 4 to', -1 , $count);
echo $count; //3
?>
The above example will output:
xp***to 3
Notes
See Also
- PCRE Patterns
- preg_filter() - Perform a regular expression search and replace
- preg_match() - Perform a regular expression match
- preg_replace_callback() - Perform a regular expression search and replace using a callback
- preg_split() - Split string by a regular expression
- preg_last_error() - Returns the error code of the last PCRE regex execution
