preg_replace

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 timesMore 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 \EEven 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)

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 123echo preg_replace('#(?<digits>\d+)#', '\digits $digits ${digits}', '123');// \digits $digits ${digits}?>To use named backreferences, you have to use preg_replace_callback:<?phpecho preg_replace_callback('#(?<digits>\d+)#', function( $m ){  return "$m[1] $m[digits] {$m['digits']}";}, '123');// 123 123 123echo 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

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:<?phpfunction expandCamelCase($source) {  return preg_replace('/(?<!^)([A-Z][a-z]|(?<=[a-z])[^a-z]|(?<=[A-Z])[0-9_])/', ' $1', $source);}?>Before:  ExpandCamelCaseAPIDescriptorPHP5_3_4Version3_21BetaAfter:  Expand Camel Case API Descriptor PHP 5_3_4 Version 3_21 Beta

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 theirnormal 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, suchas "אנני" which would start off as "אןןי". Note that there's still theproblem of acronyms with gershiim but that's not a difficult oneto solve. The code is in use at http://gibberish.co.il which you canuse to translate wrongly-encoded Hebrew, transliterize, and someother Hebrew-related functions.To ensure that there will be no regular characters at the end of aword, just convert all regular characters to their final forms, thenrun this function. Enjoy!

A delimiter can be any ASCII non-alphanumeric, non-backslash, non-whitespace character:  !"#$%&'*+,./:;=?@^_`|~-  and  ({[<>]})

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"

How to replace all comments inside code without remove crln  = \r\n or cr \r each line?<?php$txt_target=<<<t1this;//    dsdsds    nope    /*    ok    */is;huge/*text bla*/    /*bla*/ t1;/*=======================================================================expected result:=======================================================================this;    nopeis;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 LF74 68 69 73 3b 0a 09 6e 6f 70 65 0d 0a 0d 0a 69 73 3b 68 75 67 65 0d 0aI 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);?>

Sample for replacing bracketed short-codesThe 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:<?phpfunction 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