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 \\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("$2")'). Make sure you are aware of PHP's string syntax to know exactly how the interpreted string will look.
-
subject -
The string or an array with strings to search and replace.
If
subjectis an array, then the search and replace is performed on every entry ofsubject, and the return value is an array as well. -
limit -
The maximum possible replacements for each pattern in each
subjectstring. Defaults to -1 (no limit). -
count -
If specified, this variable will be filled with the number of replacements done.
Return Values
preg_replace() returns an array if the
subject parameter is an array, or a string
otherwise.
If matches are found, the new subject will
be returned, otherwise subject will be
returned unchanged or NULL if an error occurred.
Errors/Exceptions
An E_DEPRECATED level error is emitted when
passing in the "\e" modifier.
Changelog
| Version | Description |
|---|---|
| 5.5.0 | The /e modifier is deprecated. Use preg_replace_callback() instead. See the PREG_REPLACE_EVAL documentation for additional information about security risks. |
| 5.1.0 |
Added the count parameter
|
| 4.0.4 |
Added the '$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
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().
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
Коментарии
Be aware that when using the "/u" modifier, if your input text contains any bad UTF-8 code sequences, then preg_replace will return an empty string, regardless of whether there were any matches.
This is due to the PCRE library returning an error code if the string contains bad UTF-8.
From what I can see, the problem is, that if you go straight and substitute all 'A's wit 'T's you can't tell for sure which 'T's to substitute with 'A's afterwards. This can be for instance solved by simply replacing all 'A's by another character (for instance '_' or whatever you like), then replacing all 'T's by 'A's, and then replacing all '_'s (or whatever character you chose) by 'A's:
<?php
$dna = "AGTCTGCCCTAG";
echo str_replace(array("A","G","C","T","_","-"), array("_","-","G","A","T","C"), $dna); //output will be TCAGACGGGATC
?>
Although I don't know how transliteration in perl works (though I remember that is kind of similar to the UNIX command "tr") I would suggest following function for "switching" single chars:
<?php
function switch_chars($subject,$switch_table,$unused_char="_") {
foreach ( $switch_table as $_1 => $_2 ) {
$subject = str_replace($_1,$unused_char,$subject);
$subject = str_replace($_2,$_1,$subject);
$subject = str_replace($unused_char,$_2,$subject);
}
return $subject;
}
echo switch_chars("AGTCTGCCCTAG", array("A"=>"T","G"=>"C")); //output will be TCAGACGGGATC
?>
Below is a function for converting Hebrew final characters to their
normal equivelants should they appear in the middle of a word.
The /b argument does not treat Hebrew letters as part of a word,
so I had to work around that limitation.
<?php
$text="עברית מבולגנת";
function hebrewNotWordEndSwitch ($from, $to, $text) {
$text=
preg_replace('/'.$from.'([א-ת])/u','$2'.$to.'$1',$text);
return $text;
}
do {
$text_before=$text;
$text=hebrewNotWordEndSwitch("ך","כ",$text);
$text=hebrewNotWordEndSwitch("ם","מ",$text);
$text=hebrewNotWordEndSwitch("ן","נ",$text);
$text=hebrewNotWordEndSwitch("ף","פ",$text);
$text=hebrewNotWordEndSwitch("ץ","צ",$text);
} while ( $text_before!=$text );
print $text; // עברית מסודרת!
?>
The do-while is necessary for multiple instances of letters, such
as "אנני" which would start off as "אןןי". Note that there's still the
problem of acronyms with gershiim but that's not a difficult one
to solve. The code is in use at http://gibberish.co.il which you can
use to translate wrongly-encoded Hebrew, transliterize, and some
other Hebrew-related functions.
To ensure that there will be no regular characters at the end of a
word, just convert all regular characters to their final forms, then
run this function. Enjoy!
Because i search a lot 4 this:
The following should be escaped if you are trying to match that character
\ ^ . $ | ( ) [ ]
* + ? { } ,
Special Character Definitions
\ Quote the next metacharacter
^ Match the beginning of the line
. Match any character (except newline)
$ Match the end of the line (or before newline at the end)
| Alternation
() Grouping
[] Character class
* Match 0 or more times
+ Match 1 or more times
? Match 1 or 0 times
{n} Match exactly n times
{n,} Match at least n times
{n,m} Match at least n but not more than m times
More Special Character Stuff
\t tab (HT, TAB)
\n newline (LF, NL)
\r return (CR)
\f form feed (FF)
\a alarm (bell) (BEL)
\e escape (think troff) (ESC)
\033 octal char (think of a PDP-11)
\x1B hex char
\c[ control char
\l lowercase next char (think vi)
\u uppercase next char (think vi)
\L lowercase till \E (think vi)
\U uppercase till \E (think vi)
\E end case modification (think vi)
\Q quote (disable) pattern metacharacters till \E
Even More Special Characters
\w Match a "word" character (alphanumeric plus "_")
\W Match a non-word character
\s Match a whitespace character
\S Match a non-whitespace character
\d Match a digit character
\D Match a non-digit character
\b Match a word boundary
\B Match a non-(word boundary)
\A Match only at beginning of string
\Z Match only at end of string, or before newline at the end
\z Match only at end of string
\G Match only where previous m//g left off (works only with /g)
If you would like to remove a tag along with the text inside it then use the following code.
<?php
preg_replace('/(<tag>.+?)+(<\/tag>)/i', '', $string);
?>
example
<?php $string='<span class="normalprice">55 PKR</span>'; ?>
<?php
$string = preg_replace('/(<span class="normalprice">.+?)+(<\/span>)/i', '', $string);
?>
This will results a null or empty string.
<?php
$string='My String <span class="normalprice">55 PKR</span>';
$string = preg_replace('/(<span class="normalprice">.+?)+(<\/span>)/i', '', $string);
?>
This will results a " My String"
To split Pascal/CamelCase into Title Case (for example, converting descriptive class names for use in human-readable frontends), you can use the below function:
<?php
function expandCamelCase($source) {
return preg_replace('/(?<!^)([A-Z][a-z]|(?<=[a-z])[^a-z]|(?<=[A-Z])[0-9_])/', ' $1', $source);
}
?>
Before:
ExpandCamelCaseAPIDescriptorPHP5_3_4Version3_21Beta
After:
Expand Camel Case API Descriptor PHP 5_3_4 Version 3_21 Beta
A delimiter can be any ASCII non-alphanumeric, non-backslash, non-whitespace character: !"#$%&'*+,./:;=?@^_`|~- and ({[<>]})Sample for replacing bracketed short-codes
The used short-codes are purely used for educational purposes for they could be shorter as in 'italic' to 'i' or 'bold' to 'b'.
Sample text
----
This sample shows how to have [italic]italic[/italic], [bold]bold[/bold] and [underline]underlined[/underline] and [strikethrough]striked[/striketrhough] text.
with this function:
<?php
function textDecoration($html)
{
$patterns = [
'/\[(italic)\].*?\[\/\1\] ?/',
'/\[(bold)\].*?\[\/\1\] ?/',
'/\[(underline)\].*?\[\/\1\] ?/'
];
$replacements = [
'<i>$1</i>',
'<strong>$1</strong>',
'<u>$1</u>'
];
return preg_replace($patterns, $replacements, $html);
}
$html = textDecoration($html);
echo $html; // or return
?>
results in:
----
This sample shows how to have <i>italic</i>, <b>bold</b> and <u>underlined</u> and [strikethrough]striked[/striketrhough] text.
Notice!
There is no [strikethrough]striked[/striketrhough] fallback in the patterns and replacements array
How to replace all comments inside code without remove crln = \r\n or cr \r each line?
<?php
$txt_target=<<<t1
this;// dsdsds
nope
/*
ok
*/
is;huge
/*text bla*/
/*bla*/
t1;
/*
=======================================================================
expected result:
=======================================================================
this;
nope
is;huge
=======================================================================
visualizing in a hex viewer .. to_check_with_a_hex_viewer.txt ...
t h i s ; LF TAB n o p e CR LF CR LF i s ; h u g e CR LF
74 68 69 73 3b 0a 09 6e 6f 70 65 0d 0a 0d 0a 69 73 3b 68 75 67 65 0d 0a
I used F3 (viewer + options 3: hex) in mythical TOTAL COMMANDER!
=======================================================================
*/
echo '<hr><pre>';
echo $txt_target;
echo '</pre>';
// a single line '//' comments
$txt_target = preg_replace('![ \t]*//.*[ \t]*!', '', $txt_target);
// /* comment */
$txt_target = preg_replace('/\/\*([^\/]*)\*\/(\s+)/smi', '', $txt_target);
echo '<hr><pre>';
echo $txt_target;
echo '</pre><hr>';
file_put_contents('to_check_with_a_hex_viewer.txt',$txt_target);
?>
You can only use numeric backreferences in the replacement string, but not named ones:
<?php
echo preg_replace('#(\d+)#', '\1 $1 ${1}', '123');
// 123 123 123
echo preg_replace('#(?<digits>\d+)#', '\digits $digits ${digits}', '123');
// \digits $digits ${digits}
?>
To use named backreferences, you have to use preg_replace_callback:
<?php
echo preg_replace_callback('#(?<digits>\d+)#', function( $m ){
return "$m[1] $m[digits] {$m['digits']}";
}, '123');
// 123 123 123
echo preg_replace_callback('#(?<digits>\d+)#', fn($m) => "$m[1] $m[digits] {$m['digits']}", '123');
// 123 123 123
?>
See https://bugs.php.net/bug.php?id=81469