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Regular Expression Functions (Perl-Compatible)


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. See Pattern Syntax for detailed explanation.

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.

Note: This extension maintains a global per-thread cache of compiled regular expressions (up to 4096).


You should be aware of some limitations of PCRE. Read » for more info.


Ingen eksterne libraries er nødvendige for at kompilere denne udvidelse.


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.

Windows versionen af PHP har indbygget support for denne udvidelse. Du behøver ikke indsætte ekstra udvidelser for at bruge disse funktioner.

Runtime Konfiguration

Virkemåden af disse funktioner er berørt af indstillinger i php.ini.

PCRE Configuration Options
Name Default Changeable Changelog
pcre.backtrack_limit "100000" PHP_INI_ALL Available since PHP 5.2.0.
pcre.recursion_limit "100000" PHP_INI_ALL Available since PHP 5.2.0.
For flere detaljer og definationer af PHP_INI_* constanterne, se ini_set() dokumentation.

Her er en kort forklaring på konfigurations-direktiverne.

pcre.backtrack_limit integer

PCRE's backtracking limit.

pcre.recursion_limit integer

PCRE's recursion limit. Please note that if you set this value to a high number you may consume all the available process stack and eventually crash PHP (due to reaching the stack size limit imposed by the Operating System).


Denne udvidelse har ingen ressourcetyper defineret.

Foruddefinerede Konstanter

Konstanterne nedenunder er defineret af denne udvidelse, og vil kun være tilgængelige når denne udvidelse enten er blevet kompileret ind i PHP eller dynamisk indsat under runtime.

PREG constants
constant description
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 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 occurring match the appendant string offset will also be returned. Note that this changes the return values in an array where every element is an array consisting of the matched string at offset 0 and its string offset within subject at offset 1. This flag is available since PHP 4.3.0 and is only used for preg_split().
PREG_NO_ERROR Returned by preg_last_error() if there were no errors. Available since PHP 5.2.0.
PREG_INTERNAL_ERROR Returned by preg_last_error() if there was an internal PCRE error. Available since PHP 5.2.0.
PREG_BACKTRACK_LIMIT_ERROR Returned by preg_last_error() if backtrack limit was exhausted. Available since PHP 5.2.0.
PREG_RECURSION_LIMIT_ERROR Returned by preg_last_error() if recursion limit was exhausted. Available since PHP 5.2.0.
PREG_BAD_UTF8_ERROR Returned by preg_last_error() if the last error was caused by malformed UTF-8 data (only when running a regex in UTF-8 mode). Available since PHP 5.2.0.
PCRE_VERSION PCRE version and release date (e.g. "7.0 18-Dec-2006"). Available since PHP 5.2.4.


Example#1 Examples of valid patterns

  • /<\/\w+>/
  • |(\d{3})-\d+|Sm
  • /^(?i)php[34]/
  • {^\s+(\s+)?$}

Example#2 Examples of invalid patterns

  • /href='(.*)' - missing ending delimiter
  • /\w+\s*\w+/J - unknown modifier 'J'
  • 1-\d3-\d3-\d4| - missing starting delimiter

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