PHP preg_replace

function make_links_blank($text)
{
  return  preg_replace(
     array(
       '/(?(?=<a[^>]*>.+<\/a>)
             (?:<a[^>]*>.+<\/a>)
             |
             ([^="\']?)((?:https?|ftp|bf2|):\/\/[^<> \n\r]+)
         )/iex',
       '/<a([^>]*)target="?[^"\']+"?/i',
       '/<a([^>]+)>/i',
       '/(^|\s)(www.[^<> \n\r]+)/iex',
       '/(([_A-Za-z0-9-]+)(\\.[_A-Za-z0-9-]+)*@([A-Za-z0-9-]+)
       (\\.[A-Za-z0-9-]+)*)/iex'
       ),
     array(
       "stripslashes((strlen('\\2')>0?'\\1<a href=\"\\2\">\\2</a>\\3':'\\0'))",
       '<a\\1',
       '<a\\1 target="_blank">',
       "stripslashes((strlen('\\2')>0?'\\1<a href=\"http://\\2\">\\2</a>\\3':'\\0'))",
       "stripslashes((strlen('\\2')>0?'<a href=\"mailto:\\0\">\\0</a>':'\\0'))"
       ),
       $text
   );
}

I was writing a replacement pattern to parse HTML text which sometimes
contained PHP variable-like strings. Various initial solutions yeilded
either escaped quotes or fatal errors due to these variable-like strings
being interpreted as poorly formed variables.

"Tim K." and "steven -a-t- acko dot net" provide some detailed
discussion of preg_replace's quote escaping in the comments below,
including the use of str_replace() to remove the preg_replace added
slash-quote.  However, this suggestion is applied to the entire text
AFTER the preg_match.  This isn't a robust solution in that it is
conceivable that the text unaffected by the preg_replace() may contain
the string \\" which should not be fixed.  Furthermore, the addition of
escaped quotes within preg_replaces with multiple patterns/replacements
(with arrays) may break one of the following patterns.

The solution, then, must fix the quote-escaped text BEFORE replacing it
in the target, and possibly before it is passed to a function within the
replacement code.  Since the replacement string is interpreted as PHP
code, just use str_replace('\\"','"','$1') where you need an
unadulterated $1 to appear.  The key is to properly escape the necessary
characters.  Three variations appear in the examples below, as well as a
set of incorrect examples.  I haven't seen this solution posted before,
so hopefully this will be helpful rather than covering old ground.

Try this example code:

<?php
/*
   Using preg_replace with the /e modifier on ANY text, regardless of single
   quotes, double quotes, dollar signs, backslashes, and variable interpolation.

Tested on PHP 5.0.4 (cli), PHP 5.1.2-1+b1 (cli), and PHP 5.1.2 for Win32.

Solution?
       1.  Use single quotes for the replacement string.
       2.  Use escaped single quotes around the captured text variable (\\'$1\\').
       3.  Use str_replace() to remove the escaped double quotes
           from within the replacement code (\\" -> ").
*/

function _prc_function1($var1,$var2,$match) {
   $match = str_replace('\\"','"',$match);
   // ... do other stuff ...
   return $var1.$match.$var2;
}
function _prc_function2($var1,$var2,$match) {
   // ... do other stuff ...
   return $var1.$match.$var2;
}

$v1 = '(';
$v2 = ')';
// Lots of tricky characters:
$text = "<xxx>...\\$varlike_text[_'\\\\\\""\\"'...</xxx>";
$pattern = '/<xxx>(.*?)</xxx>/e';

echo $text . " Original.<br>\\n";

// Example #1 - Processing in place.
// returns (...$varlike_text['"""\\'...)
echo preg_replace(
   $pattern,
   '$v1 . str_replace(\\'\\\\"',\\'"\\',\\'$1\\') . $v2',
   $text) . " Escaped double quotes replaced with str_replace. (Good.)<br>n";

// Example #2 - Processing within a function.
// returns (...$varlike_text['\\"""'...)
echo preg_replace(
   $pattern,
   '_prc_function1($v1,$v2,'$1\\')',
   $text) . " Escaped double quotes replaced in a function. (Good.)<br>\\n";

// Example #3 - Preprocessing before a function.
// returns (...$varlike_text['"""\\'...)
echo preg_replace(
   $pattern,
   '_prc_function2($v1,$v2,str_replace(\\'\\\\"',\\'"\\',\\'$1\\'))',
   $text) . " Escaped double quotes replaced with str_replace before sending match to a function. (Good.)<br>n";

// Example #4 - INCORRECT implementations
//  a. returns (...$varlike_text[_'\\\\""\\"'...)
//  b. returns (...$varlike_text[_'"\\\\""\\'...)
//  c. returns (...$varlike_text[_'\\\\""\\"'...)
//  d. Causes a syntax+fatal error, unexpected T_BAD_CHARACTER...
echo preg_replace( $pattern, "\\$v1 . '$1' . \\$v2", $text)," Enclosed in double/single quotes. (Wrong!  Extra slashes.)<br>\\n";
echo preg_replace( $pattern, "\\$v1 . '$1' . \\$v2", $text)," Enclosed in double/single quotes, $ escaped. (Wrong!  Extra slashes.)<br>\\n";
echo preg_replace( $pattern, '$v1 . '$1\\' . $v2', $text)," Enclosed in single/single quotes. (Wrong!  Extra slashes.)<br>\\n";
echo preg_replace( $pattern, '$v1 . "$1" . $v2', $text)," Enclosed in single quotes. (Wrong!  Dollar sign in text is interpreted as variable interpolation.)<br>\\n";

?>

;-) Klemens

Note that most user examples on php.net I have read, only replace
selected characters, such as single and double quotes. This replaces all
high characters, including greek characters, arabian characters,
smilies, whatever.

It took me ages to get it just downto two regular expressions, but it handles all high level characters properly.

$text = preg_replace('/([\xc0-\xdf].)/se', "'&#' .
((ord(substr('$1', 0, 1)) - 192) * 64 + (ord(substr('$1', 1, 1)) - 128))
. ';'", $text);
$text = preg_replace('/([\xe0-\xef]..)/se', "'&#' .
((ord(substr('$1', 0, 1)) - 224) * 4096 + (ord(substr('$1', 1, 1)) -
128) * 64 + (ord(substr('$1', 2, 1)) - 128)) . ';'", $text);

I wanted to have a function that extracts only wanted parameters out of a
http query string, and they had to be flexible, eg 'updateItem=1'
should be replaced, as well as 'updateCategory=1', but i sometimes ended
up having too much replaced from the query.

example:

my query string: 'updateItem=1&itemID=14'

ended up in a query string like this: '4' , which was not really covering the plan ;)

i was using this regexp:

preg_replace('/&?update.*=1&?/','',$query_string);

i discovered, that preg_replace matches the longest possible string,
which means that it replaces everything from the first u up to the 1
after itemID=

I assumed, that it would take the shortest possible match.

$str = preg_replace('/<tag[^>](.*)>(.*)<\/tag>/ims','<!-- edited -->', $str);

<?php

$value = '<a href="http://www.domain.com/123.html">123</a>';

echo preg_replace('/<a href="(.*?)">(.*?)<\\/a>/i', '$2', $value);

//Output
// 123

?>

$search = array('/,/','/\$/');

$replace = array('','');

$data['amount_limit'] = preg_replace($search,'',$data['amount_limit']);

<?php
function make_links_blank( $text )
{
 return  preg_replace(
     array(
       '/(?(?=<a[^>]*>.+<\/a>)
             (?:<a[^>]*>.+<\/a>)
             |
             ([^="\'])((?:https?|ftp):\/\/[^<> \n\r]+)
         )/iex',
       '/<a([^>]*)target="?[^"\']+"?/i',
       '/<a([^>]+)>/i'
       ),
     array(
       "stripslashes((strlen('\\2')>0?'\\1<a href=\"\\2\">\\2</a>\\3':'\\0'))",
       '<a\\1',
       '<a\\1 target="_blank">'
       ),
       $text
   );
}

?>

This function replaces links (http(s)://, ftp://) with respective html anchor tag, and also makes all anchors open in a new window.

"Go to the [Blender3D Homepage|http://www.blender3d.org] for more Details"

To get this into a link, use:

$new = preg_replace('/\[(.*?)\|(.*?)\]/', '<a href="$2" target="_blank">$1</a>', $new);

[quote]if you're new to this function, and getting an error like  'delimiter must not alphanumeric backslash ...[/quote]

Note that if you use arrays for search and replace then you will want to
quote your searching expression with / or you will get this error.

However, if you use a single string to search and replace then you will
not recieve this error if you do not quote your regular expression in /

The regexp is essentially the same but now I deal with problems that it
couldn't handle, such as urls, which tended to screw things up, and the
odd placement of a : or ; in the body text, by using functions. This
makes it easier to expand to take account of all the things I know I've
not taken account of. But here it is in its essential glory. Or
mediocrity. Take your pick.

<?php

define('PARSER_ALLOWED_STYLES_',
'text-align,font-family,font-size,text-decoration');

function strip_styles($source=NULL) {
  $exceptions = str_replace(',', '|', @constant('PARSER_ALLOWED_STYLES_'));

/* First we want to fix anything that might potentially break the styler stripper, sow e try and replace
   * in-text instances of : with its html entity replacement.
   */

function Replacer($text) {
   $check = array (
       '@:@s',
   );
   $replace = array(
       ':',
   );

return preg_replace($check, $replace, $text[0]);
  }

$source = preg_replace_callback('@>(.*)<@Us', 'Replacer', $source);

$regexp =

'@([^;"]+)?(?<!'. $exceptions. ')(?<!\>\w):(?!\/\/(.+?)\/|<|>)((.*?)[^;"]+)(;)?@is';

$source = preg_replace($regexp, '', $source);

$source = preg_replace('@[a-z]*=""@is', '', $source);

return $source;
}

?>

Increment the limit to be sure it's larger than a subject lenght.

function make_links_blank( $text )
{
 
 return  preg_replace( array(
               "/[^\"'=]((http|ftp|https):\/\/[^\s\"']+)/i",
               "/<a([^>]*)target=\"?[^\"']+\"?/i",
               "/<a([^>]+)>/i"
       ),
         array(
               "<a href=\"\\1\">\\1</a>",
               "<a\\1",
               "<a\\1 target=\"_blank\" >"
           ),
       $text
       );
}

Replacing letters of badword for a definite character.
View example:

<?php

function censured($string, $aBadWords, $sChrReplace) {

foreach ($aBadWords as $key => $word) {

// Regexp for case-insensitive and use the functions
       $aBadWords[$key] = "/({$word})/ie";

}

// to substitue badwords for definite character
   return preg_replace($aBadWords,
                       "str_repeat('{$sChrReplace}', strlen('\\1'))",
                       $string
                       );

}

// To show modifications
print censured('The nick of my friends are rand, v1d4l0k4, P7rk, ferows.',
               array('RAND', 'V1D4L0K4', 'P7RK', 'FEROWS'),
               '*'
               );
  
?>

<?php

/* The string would normally be a form-submitted html file or text string */

$string = '<span
style="font-family:arial; font-size:20pt; text-decoration:underline;
sausage:bueberry;" width="200">Hello there</span> This is some
<div style="display:inline;">test text</div>';

/* Array of styles to allow. */

$except = array('font-family', 'text-decoration');

$allow = implode($except, '|');

/* The monster beast regexp. I was up all night trying to figure this one out. */

$regexp = '@([^;"]+)?(?<!'.$allow.'):(?!\/\/(.+?)\/)((.*?)[^;"]+)(;)?@is';

print str_replace('<', '<', $regexp).'<br/><br/>';

$out = preg_replace($regexp, '', $string);

/* Now lets get rid of any unwanted empty style attributes */

$out = preg_replace('@[a-z]*=""@is', '', $out);

print $out;

?>

This should produce the following:

<span style="font-family:arial; text-decoration:underline;"
width="200">Hello there</span> This is some <div >test
text</div>

Now, I'm a relative newbie at this so I'm sure there's a better way to do it. There's *always* a better way.

note that whatever is in $pattern (and only $pattern, not $string, or
$replacement) must be enclosed by '/  /' (note the forward slashes)

e.g.
$pattern = '/and/';
$replacement = 'sandy';
$string = 'me and mine';

generates 'me sandy mine'

seems to be obvious to everyone else, but took me a while to figure out!!

$replaces = 0;

$return .= preg_replace('/(\b' . $substr . ')/ie', '"<$tag>$1<$end_tag>" . (substr($replaces++,0,0))', $s2, $limit);

<?

function unicode_unescape(&$var, $convert_to_cp1251 = false){
   $var = preg_replace(
       '#%u([\da-fA-F]{4})#mse',
       $convert_to_cp1251 ? '@iconv("utf-16","windows-1251",pack("H*","\1"))' : 'pack("H*","\1")',
       $var
   );
}

//

$str = 'to %u043B%u043E%u043F%u0430%u0442%u0430 or not to %u043B%u043E%u043F%u0430%u0442%u0430';

unicode_unescape($str, true);

echo $str;

?>

When I try to use the 'empty' function in the replacement string (when
using the 'e' modifier, of course) the regexp interpreter get stucked at
that point.

An examplo of this failure:

<?php
echo $test = preg_replace( "/(bla)/e", "empty(123)", "bla bla ble" );

# it should print something like:
# "1 1 ble"
?>

Very odd, huh?

This allows for the user to enter variations:

[url=http://www.foo.org]The link[/url]
[url="http://www.foo.org"]The link[/url]
[url='http://www.foo.org']The link[/url]

or even

[url=#http://www.foo.org#]The link[/url]
[url=!http://www.foo.org!]The link[/url]

$full_text = preg_replace('/\[p=(\d+)\]/e',
  "\"<a href=\\\"./test.php?person=$1\\\">\"
   .get_name($1).\"</a>\"",
   $short_text);

I hope that it comes out correctly this time :-)

This is my solution:

$expanded_text = preg_replace('/\\[p=(\d+)\\]/e',
   "\\"<a href=\\\\\\"./test.php?person=$1\\\\\\">\\".get_name($1).\\"</a&>\\"",
       $short_text);

It took me some time to work out the proper number of quotes and backslashes.

regards, Leif.

You could put this in 1 replace for faster execution as well:

<?php

/*
 * Removes all blank lines from a string.
 */
function removeEmptyLines($string)
{
   return preg_replace("/(^[\r\n]*|[\r\n]+)[\s\t]*[\r\n]+/", "\n", $string);
}

?>

function decraper($htm, $delstyles=false) {
   $commoncrap = array('&quot;'
   ,'font-weight: normal;'
   ,'font-style: normal;'
   ,'line-height: normal;'
   ,'font-size-adjust: none;'
   ,'font-stretch: normal;');
   $replace = array("'");
   $htm = str_replace($commoncrap, $replace, $htm);
     $pat = array();
   $rep = array();
   $pat[0] = '/(<table\s.*)(width=)(\d+%)(\D)/i';
   $pat[1] = '/(<td\s.*)(width=)(\d+%)(\D)/i';
   $pat[2] = '/(<th\s.*)(width=)(\d+%)(\D)/i';
   $pat[3] = '/<td( colspan="[0-9]+")?( rowspan="[0-9]+")?
( width="[0-9]+")?( height="[0-9]+")?.*?>/i';
   $pat[4] = '/<tr.*?>/i';
   $pat[5]=
'/<\/st1:address>(<\/st1:\w*>)?
<\/p>[\n\r\s]*<p[\s\w="\']*>/i';
   $pat[6] = '/<o:p.*?>/i';
   $pat[7] = '/<\/o:p>/i';
   $pat[8] = '/<o:SmartTagType[^>]*>/i';
   $pat[9] = '/<st1:[\w\s"=]*>/i';
   $pat[10] = '/<\/st1:\w*>/i';
   $pat[11] = '/<p[^>]*>(.*?)<\/p>/i';
   $pat[12] = '/ style="margin-top: 0cm;"/i';
   $pat[13] = '/<(\w[^>]*) class=([^ |>]*)([^>]*)/i';
   $pat[14] = '/<ul(.*?)>/i';
   $pat[15] = '/<ol(.*?)>/i';
   $pat[17] = '/<br \/>&nbsp;<br \/>/i';
   $pat[18] = '/&nbsp;<br \/>/i';
   $pat[19] = '/<!-.*?>/';
   $pat[20] = '/\s*style=(""|\'\')/';
   $pat[21] = '/ style=[\'"]tab-interval:[^\'"]*[\'"]/i';
   $pat[22] = '/behavior:[^;\'"]*;*(\n|\r)*/i';
   $pat[23] = '/mso-[^:]*:"[^"]*";/i';
   $pat[24] = '/mso-[^;\'"]*;*(\n|\r)*/i';
   $pat[25] = '/\s*font-family:[^;"]*;?/i';
   $pat[26] = '/margin[^"\';]*;?/i';
   $pat[27] = '/text-indent[^"\';]*;?/i';
   $pat[28] = '/tab-stops:[^\'";]*;?/i';
   $pat[29] = '/border-color: *([^;\'"]*)/i';
   $pat[30] = '/border-collapse: *([^;\'"]*)/i';
   $pat[31] = '/page-break-before: *([^;\'"]*)/i';
   $pat[32] = '/font-variant: *([^;\'"]*)/i';
   $pat[33] = '/<span [^>]*><br \/><\/span><br \/>/i';
   $pat[34] = '/" "/';
   $pat[35] = '/[\t\r\n]/';
   $pat[36] = '/\s\s/s';
   $pat[37] = '/ style=""/';
   $pat[38] = '/<span>(.*?)<\/span>/i';
//empty (no attribs) spans
   $pat[39] = '/<span>(.*?)<\/span>/i';
//twice, nested spans
   $pat[40] = '/(;\s|\s;)/';
   $pat[41] = '/;;/';
   $pat[42] = '/";/';
   $pat[43] = '/<li(.*?)>/i';
   $pat[44] =
'/(<\/b><b>|<\/i><i>|<\/em><em>|
<\/u><u>|<\/strong><strong>)/i';
   $rep[0] = '$1$2"$3"$4';
   $rep[1] = '$1$2"$3"$4';
   $rep[2] = '$1$2"$3"$4';
   $rep[3] = '<td$1$2$3$4>';
   $rep[4] = '<tr>';
   $rep[5] = '<br />';
   $rep[6] = '';
   $rep[7] = '<br />';
   $rep[8] = '';
   $rep[9] = '';
   $rep[10] = '';
   $rep[11] = '$1<br />';
   $rep[12] = '';
   $rep[13] = '<$1$3';
   $rep[14] = '<ul>';
   $rep[15] = '<ol>';
   $rep[17] = '<br />';
   $rep[18] = '<br />';
   $rep[19] = '';
   $rep[20] = '';
   $rep[21] = '';
   $rep[22] = '';
   $rep[23] = '';
   $rep[24] = '';
   $rep[25] = '';
   $rep[26] = '';
   $rep[27] = '';
   $rep[28] = '';
   $rep[29] = '';
   $rep[30] = '';
   $rep[31] = '';
   $rep[32] = '';
   $rep[33] = '<br />';
   $rep[34] = '""';
   $rep[35] = '';
   $rep[36] = '';
   $rep[37] = '';
   $rep[38] = '$1';
   $rep[39] = '$1';
   $rep[40] = ';';
   $rep[41] = ';';
   $rep[42] = '"';
   $rep[43] = '<li>';
   $rep[44] = '';
   if($delstyles===true){
       $pat[50] = '/ style=".*?"/';
       $rep[50] = '';
   }
   ksort($pat);
   ksort($rep);
   return $htm;
}

Hope it helps, critics are more than welcome.

<?php
$url = '<a attr="garbage" href="http://us3.php.net/preg_replace">preg_replace - php.net</a>';
$url = preg_replace( '/<.*href="?(.*:\/\/)?([^ \/]*)([^ >"]*)"?[^>]*>(.*)(<\/a>)/', '<a href="$1$2$3">$4</a> [$2]', $url );
?>

Will output:

<a href="http://us3.php.net/preg_replace">preg_replace - php.net</a> [us3.php.net]

<?php

function removeEvilStyles($tagSource)
{
   // this will leave everything else, but:
   $evilStyles = array('font', 'font-family', 'font-face', 'font-size', 'font-size-adjust', 'font-stretch', 'font-variant');

$find = array();
   $replace = array();
  
   foreach ($evilStyles as $v)
   {
       $find[]    = "/$v:.*?;/";
       $replace[] = '';
   }
  
   return preg_replace($find, $replace, $tagSource);
}

function removeEvilTags($source)
{
   $allowedTags = '<h1><h2><h3><h4><h5><a><img><label>'.
       '<p><br><span><sup><sub><ul><li><ol>'.
       '<table><tr><td><th><tbody><div><hr><em><b><i>';
   $source = strip_tags(stripslashes($source), $allowedTags);
   return trim(preg_replace('/<(.*?)>/ie', "'<'.removeEvilStyles('\\1').'>'", $source));
}

?>

$body = preg_replace("[\[(.*?)\]]", "", $body);

The following example escapes only unescaped single quotes:

<?php
$a = "I'm using regex";
$b = "I\'m using regex";

$patt = "/(?<!\\\)\'/";
$repl = "\\'";

print "a:  ".preg_replace ($patt, $repl, $a)."\n";
print "b:  ".preg_replace ($patt, $repl, $b)."\n";
?>

and prints:
a:  I\'m using regex
b:  I\'m using regex

Remark: matching a backslashe require a triple backslash (\\\).

"wordLimit" trims a string down to a certain number of words, and adds
an ellipsis after the last word, or returns the string if the limit is
larger than the number of words in the string.

"stringLimit" trims a string down to a certain number of characters, and
adds an ellipsis after the last word, without truncating any words in
the middle (it will instead leave it out), or returns the string if the
limit is larger than the string size. The length of a string will
INCLUDE the length of the ellipsis.

<?php

function wordLimit($string, $length = 50, $ellipsis = '...') {
   return count($words = preg_split('/\s+/', ltrim($string), $length + 1)) > $length ?
       rtrim(substr($string, 0, strlen($string) - strlen(end($words)))) . $ellipsis :
       $string;
}

function stringLimit($string, $length = 50, $ellipsis = '...') {
   return strlen($fragment = substr($string, 0, $length + 1 - strlen($ellipsis))) < strlen($string) + 1 ?
       preg_replace('/\s*\S*$/', '', $fragment) . $ellipsis : $string;
}

echo wordLimit('  You can limit a string to only so many words.', 6);
// Output: "You can limit a string to..."
echo stringLimit('Or you can limit a string to a certain amount of characters.', 32);
// Output: "Or you can limit a string to..."

?>

Remember to install:

/usr/ports/devel/php4-pcre (or 5 for -- 5 ;)

That's all... enjoy - and save 30 mins. like I could have used :D

<?php
   $text = "PHP rocks!";
   $encoded = preg_replace(
           "'(.)'e"
         ,"dechex(ord('\\1'))"
         ,$text
   );
   print "ENCODED: $encoded\n";
?>
ENCODED: 50485020726f636b7321
<?php
   print "DECODED: ".preg_replace(
       "'([\S,\d]{2})'e"
     ,"chr(hexdec('\\1'))"
     ,$encoded)."\n";
?>
DECODED: PHP rocks!

<?php
$body = preg_replace('/\[([biu])\]/i', '<\\1>', $body);
$body = preg_replace('/\[\/([biu])\]/i', '</\\1>', $body);
?>

First line replaces [b] [B] [i] [I] [u] [U] with the appropriate html tags(<b>, <i>, <u>)

Second one does the same for closing tags...

For urls, I use...

<?php
$body = preg_replace('/\s(\w+:\/\/)(\S+)/', ' <a href="\\1\\2" target="_blank">\\1\\2</a>', $body);
?>

and for urls starting with www., i use...

<?php
$body = preg_replace('/\s(www\.)(\S+)/', ' <a href="http://\\1\\2" target="_blank">\\1\\2</a>', $body);
?>

Pop all these lines into a function that receives and returns the text you want 'forum coded' and away you go:)

<?php
function change_string($str)
   {
     $str = trim($str);
     $str = htmlspecialchars($str);
     $str = preg_replace('#(.*)\@(.*)\.(.*)#','<a href="mailto:\\1@\\2.\\3">Send email</a>',$str);
     $str = preg_replace('=([^\s]*)(www.)([^\s]*)=','<a href="http://\\2\\3" target=\'_new\'>\\2\\3</a>',$str);
     return $str;
   }
?>

$new = preg_replace('/\\\\/','\\\\\\\\',$old);

note the pattern uses 4 backslashes and the replacement uses 8!  the
reason for 4 slashses in the pattern part has already been explained on
this page, but nobody has yet mentioned the need for the same logic in
the replacement part in which backslashes are also doubly parsed, once
by PHP and once by the PCRE extension.  so the eight slashes break down
to four slashes sent to PCRE, then two slashes put in the final output.

<?php
function convert_links($str) {
       $replace = <<<EOPHP
'<a href="'.htmlentities('\\1').htmlentities('\\2').//remove line break
'">'.htmlentities('\\1').htmlentities('\\2').'</a>'
EOPHP;
   $str = preg_replace('#(http://)([^\s]*)#e', $replace, $str);
   return $str;
}
?>

<?php

function auto_url($txt){

# (1) catch those with url larger than 71 characters

  $pat = '/(http|ftp)+(?:s)?:(\\/\\/)'

       .'((\\w|\\.)+)(\\/)?(\\S){71,}/i';

  $txt = preg_replace($pat, "<a href=\"\\0\" target=\"_blank\">$1$2$3/...</a>",

$txt);

# (2) replace the other short urls provided that they are not contained inside an html tag already.

  $pat = '/(?<!href=\")(http|ftp)+(s)?:' .

     .'(\\/\\/)((\\w|\\.)+) (\\/)?(\\S)/i';

  $txt = preg_replace($pat,"<a href=\"$0\" target=\"_blank\">$0</a> ",

  $txt);

return $txt;

}

?>

Note the negative look behind expression added in the second
instance for exempting those that are preceded with ' href=" ' (meaning
that they were already put inside appropiate html tags by the previous
expression)

(get rid of the space between question mark and the last parenthesis
group in both regex, I need to put it like that to be able to post this
comment)

$pattern = array('/one/', '/two/');
$replace = array('uno', 'dos');
$subject = "test one, one two, one two three";

echo preg_replace($pattern, $replace, $subject, 1);
?>

If limit were applied to the whole array (which it isn't), it would return:
test uno, one two, one two three

However, in reality this will actually return:
test uno, one dos, one two three

<?php
$string = "Don't split words";
echo substr($string, 0, 10); // Returns "Don't spli"

$pattern = "/(^.{0,10})(\W+.*$)/";
$replacement = "\${1}";
echo preg_replace($pattern, $replacement, $string); // Returns "Don't"
?>

http://www.php.net/manual/en/function.parse-url.php

- J.

The example in the docs for /e suffers from this mistake in fact.

With /e, the replacement string is a PHP expression. So when you use a
backreference in the replacement expression, you need to put the
backreference inside quotes, or otherwise it would be interpreted as PHP
code. Like the example from the manual for preg_replace:

preg_replace("/(<\/?)(\w+)([^>]*>)/e",
             "'\\1'.strtoupper('\\2').'\\3'",
             $html_body);

To make this easier, the data in a backreference with /e is run through
addslashes() before being inserted in your replacement expression. So if
you have the string

He said: "You're here"

It would become:

He said: \"You\'re here\"

...and be inserted into the expression.
However, if you put this inside a set of single quotes, PHP will not strip away all the slashes correctly! Try this:

print ' He said: \"You\'re here\" ';
 Output: He said: \"You're here\"

This is because the sequence \" inside single quotes is not recognized as anything special, and it is output literally.

Using double-quotes to surround the string/backreference will not help
either, because inside double-quotes, the sequence \' is not recognized
and also output literally. And in fact, if you have any dollar signs in
your data, they would be interpreted as PHP variables. So double-quotes
are not an option.

The 'solution' is to manually fix it in your expression. It is easiest
to use a separate processing function, and do the replacing there (i.e.
use "my_processing_function('\\1')" or something similar as replacement
expression, and do the fixing in that function).

If you surrounded your backreference by single-quotes, the double-quotes are corrupt:
$text = str_replace('\"', '"', $text);

People using preg_replace with /e should at least be aware of this.

I'm not sure how it would be best fixed in preg_replace. Because
double-quotes are a really bad idea anyway (due to the variable
expansion), I would suggest that preg_replace's auto-escaping is
modified to suit the placement of backreferences inside single-quotes
(which seemed to be the intention from the start, but was incorrectly
applied).

Escaping a backslash (\) really involves not two, not three, but four backslashes to work properly.

So to match a single backslash, one should use:

preg_replace('/(\\\\)/', ...);

or to, say, escape single quotes not already escaped, one could write:

preg_replace("/([^\\\\])'/", "\$1\'", ...);

Anything else, such as the seemingly correct

preg_replace("/([^\\])'/", "\$1\'", ...);

gets evaluated as escaping the ] and resulting in an unterminated character class.

I'm not exactly clear on this issue of backslash proliferation, but it
seems to involve the combination of PHP string processing and PCRE
processing.