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# LXXXIV. 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.

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

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

> Note: The Perl-compatible regular expression functions are available in PHP 4 and in PHP 3.0.9 and up.

> 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/.

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