PHP: Regular Expression Functions (Perl-Compatible) - Manual
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Last updated: Wed, 29 Jan 2003

LXXXVIII. Regular Expression Functions (Perl-Compatible)

Introduction

The syntax for patterns used in these functions closely resembles Perl. The expression should be enclosed in the delimiters, a forward slash (/), for example. Any character can be used for delimiter as long as it's not alphanumeric or backslash (\). If the delimiter character has to be used in the expression itself, it needs to be escaped by backslash. Since PHP 4.0.4, you can also use Perl-style (), {}, [], and <> matching delimiters.

The ending delimiter may be followed by various modifiers that affect the matching. See Pattern Modifiers.

PHP also supports regular expressions using a POSIX-extended syntax using the POSIX-extended regex functions..

Requirements

Regular expression support is provided by the PCRE library package, which is open source software, written by Philip Hazel, and copyright by the University of Cambridge, England. It is available at .

Installation

Beginning with PHP 4.2.0 these functions are enabled by default. You can disable the pcre functions with --without-pcre-regex. Use --with-pcre-regex=DIR to specify DIR where PCRE's include and library files are located, if not using bundled library. For older versions you have to configure and compile PHP with --with-pcre-regex[=DIR] in order to use these functions.

The windows version of PHP has built in support for this extension. You do not need to load any additional extension in order to use these functions.

Runtime Configuration

This extension has no configuration directives defined in php.ini.

Resource Types

This extension has no resource types defined.

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

표 1. PREG constants

constantdescription
PREG_PATTERN_ORDER Orders results so that $matches[0] is an array of full pattern matches, $matches[1] is an array of strings matched by the first parenthesized subpattern, and so on. This flag is only used with preg_match_all().
PREG_SET_ORDER Orders results so that $matches[0] is an array of first set of matches, $matches[1] is an array of second set of matches, and so on. This flag is only used with preg_match_all().
PREG_OFFSET_CAPTURE See the description of PREG_SPLIT_OFFSET_CAPTURE. This flag is available since PHP 4.3.0 .
PREG_SPLIT_NO_EMPTY This flag tells preg_split() to only return only non-empty pieces.
PREG_SPLIT_DELIM_CAPTURE This flag tells preg_split() to capture parenthesized expression in the delimiter pattern as well. This flag is available since PHP 4.0.5 .
PREG_SPLIT_OFFSET_CAPTURE If this flag is set, for every occuring match the appendant string offset will also be returned. Note that this changes the return value in an array where very element is an array consisting of the matched string at offset 0 and it's string offset into subject at offset 1. This flag is available since PHP 4.3.0 and is only used for preg_split().

Examples

예 1. Examples of valid patterns

  • /<\/\w+>/

  • |(\d{3})-\d+|Sm

  • /^(?i)php[34]/

  • {^\s+(\s+)?$}

예 2. Examples of invalid patterns

  • /href='(.*)' - missing ending delimiter

  • /\w+\s*\w+/J - unknown modifier 'J'

  • 1-\d3-\d3-\d4| - missing starting delimiter

차례
Pattern Modifiers -- Describes possible modifiers in regex patterns
Pattern Syntax -- Describes PCRE regex syntax
preg_grep --  Return array entries that match the pattern
preg_match_all -- Perform a global regular expression match
preg_match -- Perform a regular expression match
preg_quote -- Quote regular expression characters
preg_replace_callback -- Perform a regular expression search and replace using a callback
preg_replace -- Perform a regular expression search and replace
preg_split -- Split string by a regular expression


User Contributed Notes
Regular Expression Functions (Perl-Compatible)
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arpadffy at polarfox dot com
14-Jul-2000 05:59

... so I find the solution for PCRE under Linux. Download the source code. Compile it with --with-pcre-regexmake parameter. It's working just fine with PHP 4.0.1pl2. One more time I learned: the safest (and the fastest) way is build your own code from the source. :-)
jensaxel at soegaard dot net
24-Jul-2000 10:13

Please add a link from the ordinary regular expressions to these. Otherwise they are easy to miss, when looking for regex functions, due the abreviation.
bigfart at asia dot com
12-Mar-2001 11:09

Ever wondered how to use a function within a PCRE?  here's how:

$content = preg_replace("/\*(\w+)\*/e", "lookupImageCode($1)", $content);

This code replaces all instances of *text*, where text is a code for an image, with the output of function lookupImageCode().  The /e and the quotes around the function name and arguments are essential to make this work :-)

I use this on one of my websites to query a database and cross-reference image filenames with special codes input by press release writers in our client's company.  They type the code of an image (displayed in a catalogue onscreen on the site's backend) and this little wonder of code changes it to an img src tag on the fly as the page is loaded.

Enjoy!

p.s.  thanks to the guys on #php who helped sort this out at 4am in the morning my time! (donut, jfk, cardinal) Contact me if you like.

gilh at mudbuginfo dot com
22-Aug-2001 01:09

There is some really good/simple documentation of Perl regular expressions at
hrz at geodata dot soton dot ac dot uk
06-Mar-2002 06:33

If you're venturing into new regular expression territory with a lack of useful examples then it would pay to get familiar with this page:


clay at killersoft dot com
12-Mar-2002 07:56

Here's a translation of Friedl's email address matching regexp:



Friedl's perl original is available here:


superzouz at hotmail dot com
14-Jun-2002 04:47

This is the easiest tutorial for regular expressions I have found yet.
Beginners should start here.
This tutorial is originally written for Jscript, but I think everything applies to PHP.
(I had to chop the following url into small pieces to be able to post it here)



script56/html/js56reconRegularExpressions.asp

kingn at oclc dot org
31-Jul-2002 06:18

Back References should be escaped: such as \\1 \\2

Example:
preg_match("/<(\w+)(.*?)>(.+)<\/\\1>/s", $data, $regs);

This attempts to parse XML/HTML like data... Where:
$regs[1] is the tag name
$regs[2] are any tag properties
$regs[3] is the data within the tag

This handles the base case for an algorithm that could parse an entire XML form recursively.

mrPuta at yahoo dot com dot au
19-May-2003 04:42

How to have optional spaces. For beginners like me.
I finally found the solution.
I need this so a surname like mine will 'match'. eg. 'De David'

<?function eregi_alpha_sp( $data ) {
if (   eregi('^[[:alpha:]| ]+$', $data)        ) {return true;}
return false; }?>

The spaces bit, is '| ]'. The 'pipe' meaning OR and a space.
So, the expression is Alpha OR Space

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 Last updated: Wed, 29 Jan 2003
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