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preg_replace

(PHP 4, PHP 5, PHP 7, PHP 8)

preg_replace执行一个正则表达式的搜索和替换

说明

preg_replace(
    string|array $pattern,
    string|array $replacement,
    string|array $subject,
    int $limit = -1,
    int &$count = null
): string|array|null

搜索 subject 中匹配 pattern 的部分,以 replacement 进行替换。

参数

pattern

要搜索的模式。可以使一个字符串或字符串数组。

可以使用一些 PCRE 修饰符

replacement

用于替换的字符串或字符串数组。如果这个参数是一个字符串,并且 pattern 是一个数组,那么所有的模式都使用这个字符串进行替换。如果 patternreplacement 都是数组,每个 pattern 使用 replacement 中对应的元素进行替换。如果 replacement 中的元素比 pattern 中的少,多出来的 pattern 使用空字符串进行替换。

replacement 中可以包含后向引用 \\n$n,语法上首选后者。 每个这样的引用将被匹配到的第 n 个捕获子组捕获到的文本替换。 n 可以是0-99,\\0$0 代表完整的模式匹配文本。捕获子组的序号计数方式为:代表捕获子组的左括号从左到右, 从1开始数。如果要在 replacement 中使用反斜线,必须使用 4 个("\\\\",译注:因为这首先是 PHP 的字符串,经过转义后,是两个,再经过正则表达式引擎后才被认为是一个原文反斜线)。

当在替换模式下工作并且后向引用后面紧跟着需要是另外一个数字 (比如:在一个匹配模式后紧接着增加一个原文数字),不能使用 \\1 这样的语法来描述后向引用。比如,\\11将会使preg_replace() 不能理解你希望的是一个 \\1 后向引用紧跟一个原文 1,还是一个 \\11 后向引用后面不跟任何东西。 这种情况下解决方案是使用 ${1}1。这创建了一个独立的 $1 后向引用, 一个独立的原文 1

当使用被弃用的 e 修饰符时, 这个函数会转义一些字符 (即:'"\ 和 NULL) 然后进行后向引用替换。当这些完成后请确保后向引用解析完后没有单引号或双引号引起的语法错误 (比如: 'strlen(\'$1\')+strlen("$2")')。确保符合 PHP 的 字符串语法,并且符合 eval 语法。因为在完成替换后,引擎会将结果字符串作为 PHP 代码使用 eval 方式进行评估并将返回值作为最终参与替换的字符串。

subject

要进行搜索和替换的字符串或字符串数组。

如果 subject 是一个数组,搜索和替换回在 subject 的每一个元素上进行, 并且返回值也会是一个数组。

limit

每个模式在每个 subject 上进行替换的最大次数。默认是 -1(无限)。

count

如果指定,将会被填充为完成的替换次数。

返回值

如果 subject 是一个数组,preg_replace() 返回一个数组,其他情况下返回一个字符串。

如果匹配被查找到,替换后的 subject 被返回,其他情况下返回没有改变的 subject。如果发生错误,返回 null

错误/异常

"\e" 会并忽略,并产生 E_WARNING 错误。

范例

示例 #1 使用后向引用紧跟数值原文

<?php
$string 
'April 15, 2003';
$pattern '/(\w+) (\d+), (\d+)/i';
$replacement '${1}1,$3';
echo 
preg_replace($pattern$replacement$string);
?>

以上例程会输出:

April1,2003

示例 #2 preg_replace() 中使用基于索引的数组

<?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);
?>

以上例程会输出:

The bear black slow jumps over the lazy dog.

对模式和替换内容按 key 进行排序我们可以得到期望的结果。

<?php
ksort
($patterns);
ksort($replacements);
echo 
preg_replace($patterns$replacements$string);
?>

以上例程会输出:

The slow black bear jumps over the lazy dog.

示例 #3 替换一些值

<?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');
?>

以上例程会输出:

$startDate = 5/27/1999

示例 #4 剥离空白字符

这个例子剥离多余的空白字符

<?php
$str 
'foo   o';
$str preg_replace('/\s\s+/'' '$str);
// 将会改变为'foo o'
echo $str;
?>

示例 #5 使用参数 count

<?php
$count 
0;

echo 
preg_replace(array('/\d/''/\s/'), '*''xp 4 to', -$count);
echo 
$count//3
?>

以上例程会输出:

xp***to
3

注释

注意:

当使用数组形式的patternreplacement时, 将会按照key在数组中出现的顺序进行处理. 这不一定和数组的索引顺序一致. 如果你期望使用索引对等方式用replacementpattern 进行替换, 你可以在调用preg_replace()之前对两个数组各进行一次ksort()排序.

参见

add a note

User Contributed Notes 8 notes

up
737
arkani at iol dot pt
13 years ago
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)
up
2
bublifuk at mailinator dot com
4 years ago
A delimiter can be any ASCII non-alphanumeric, non-backslash, non-whitespace character:  !"#$%&'*+,./:;=?@^_`|~-  and  ({[<>]})
up
2
me at perochak dot com
11 years ago
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"
up
1
sternkinder at gmail dot com
14 years ago
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
?>
up
0
nik at rolls dot cc
9 years ago
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
up
0
php-comments-REMOVE dot ME at dotancohen dot com
14 years ago
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!
up
0
ismith at nojunk dot motorola dot com
15 years ago
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.
up
-2
mail at johanvandemerwe dot nl
2 years ago
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
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