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..
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
ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/.
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.
以下的常數由此延伸定義, 只在這個延伸被編譯成PHP或實行時期被動態載入時有效。
表格 1. PREG constants