Programming PHP

Perl-Compatible Regular Expressions

Perl has long been considered the benchmark for powerful regular expressions. PHP uses a C library called pcre to provide almost complete support for Perl’s arsenal of regular expression features. Perl regular expressions include the POSIX classes and anchors described earlier. A POSIX-style character class in a Perl regular expression works and understands non-English characters using the Unix locale system. Perl regular expressions act on arbitrary binary data, so you can safely match with patterns or strings that contain the NUL-byte (\x00).

Delimiters

Perl-style regular expressions emulate the Perl syntax for patterns, which means that each pattern must be enclosed in a pair of delimiters. Traditionally, the slash (/) character is used; for example, / pattern /. However, any nonalphanumeric character other than the backslash character (\) can be used to delimit a Perl-style pattern. This is useful when matching strings containing slashes, such as filenames. For example, the following are equivalent:

preg_match('/\/usr\/local\//', '/usr/local/bin/perl'); // returns true
preg_match('#/usr/local/#', '/usr/local/bin/perl');    // returns true

Parentheses (( )), curly braces ({}), square brackets ([]), and angle brackets (<>) can be used as pattern delimiters:

preg_match('{/usr/local/}', '/usr/local/bin/perl');    // returns true

Section 4.10.8 discusses the single-character modifiers you can put after the closing delimiter to modify the behavior ...