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preg_replace
(PHP 4, PHP 5) preg_replace — Perform a regular expression search and replace
Description
mixed preg_replace
( mixed $pattern
, mixed $replacement
, mixed $subject
[, int $limit
[, int &$count
]] )
Parameters
-
pattern
-
The pattern to search for. It can be either a string or an array with
strings.
The e modifier makes preg_replace()
treat the replacement
parameter as PHP code after
the appropriate references substitution is done. Tip: make sure that
replacement
constitutes a valid PHP code string,
otherwise PHP will complain about a parse error at the line containing
preg_replace().
-
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
pattern
s will be replaced by an empty string.
replacement
may 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.
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 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
like.
-
subject
-
The 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.
-
limit
-
The maximum possible replacements for each pattern in each
subject
string. 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 NULL if an error occurred.
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:
Example #2 Using indexed arrays with preg_replace()
<?php
$string = 'The quick brown fox jumped over the lazy dog.';
$patterns[0] = '/quick/';
$patterns[1] = '/brown/';
$patterns[2] = '/fox/';
$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:
Example #4 Using the 'e' modifier
<?php
preg_replace("/(<\/?)(\w+)([^>]*>)/e",
"'\\1'.strtoupper('\\2').'\\3'",
$html_body);
?>
This would capitalize all HTML tags in the input text.
Example #5 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 #6 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:
Notes
Note:
When using arrays with pattern
and
replacement
, 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 which
pattern
should be replaced by which
replacement
, you should perform a
ksort() on each array prior to calling
preg_replace().
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