(PHP 4, PHP 5, PHP 7, PHP 8)
preg_replace — Perform a regular expression search and replace
$pattern,$replacement,$subject,$limit = -1,&$count = null
Searches subject for matches to
pattern and replaces them with
replacement.
To match an exact string, rather than a pattern, consider using str_replace() or str_ireplace() instead of this function.
patternThe pattern to search for. It can be either a string or an array with strings.
Several PCRE modifiers are also available.
replacement
The string or an array with strings to replace. If this parameter is a
string and the pattern parameter is an array,
all patterns will be replaced by that string. If both
pattern and replacement
parameters are arrays, each pattern will be
replaced by the replacement counterpart. If
there are fewer elements in the replacement
array than in the pattern array, any extra
patterns will be replaced by an empty string.
replacement may contain references of the form
\n or
$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.
Note that backslashes in string literals may require to be escaped.
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
\1 notation 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.
subjectThe string or an array with strings to search and replace.
If subject is an array, then the search and
replace is performed on every entry of subject,
and the return value is an array as well.
If the subject array is associative, keys
will be preserved in the returned value.
limit
The maximum possible replacements for each pattern in each
subject string. Defaults to
-1 (no limit).
countIf specified, this variable will be filled with the number of replacements done.
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 null if an error occurred.
Using the "\e" modifier is an error;
an E_WARNING is emitted in this case.
If the regex pattern passed does not compile to a valid regex, an E_WARNING is emitted.
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 jumps 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, $string);
?>The above example will output:
The bear black slow jumps over the lazy dog.
By ksorting patterns and replacements, we should get what we wanted.
<?php
ksort($patterns);
ksort($replacements);
echo preg_replace($patterns, $replacements, $string);
?>The above example will output:
The slow black bear jumps 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
Note:
When using arrays with
patternandreplacement, the keys are processed in the order they appear in the array. This is not necessarily the same as the numerical index order. If you use indexes to identify whichpatternshould be replaced by whichreplacement, you should perform a ksort() on each array prior to calling preg_replace().
Note:
When both
patternandreplacementare arrays, matching rules will operate sequentially. That is, the secondpattern/replacementpair will operate on the string that results from the firstpattern/replacementpair, not the original string. If you want to simulate replacements operating in parallel, such as swapping two values, replace one pattern by an intermediary placeholder, then in a later pair replace that intermediary placeholder with the desired replacement.<?php
$p = array('/a/', '/b/', '/c/');
$r = array('b', 'c', 'd');
print_r(preg_replace($p, $r, 'a'));
// prints d
?>