php-preg-1

Q. Regular expression

Regular expression is composed of atoms, metacharacters and pattern modification. Atoms are just ordinary characters.

Metacharacters:

d: Match any decimal digit [0-9]

s: Match any whitespace character

w: Match any number, letter, underscore [0-9a-zA-Z_]

.: Match any character except the newline character

?: Match 0 or once

+: Match the preceding atom 1 or more times

*: Match any number of times

|: Match two Or multiple branch choices, used to separate multiple-choice patterns

b: Match word boundaries

B: Non-word boundaries

^: Match the beginning of the input string

$: Match the end of the input string Position

(): Pattern unit, multiple atoms are composed of large atoms as one unit. This will store relevant matches in a cache that can be retrieved for later use. The buffers in which submatches are stored are numbered starting from 1 and going up to 99. Each buffer can be accessed using n. Pay attention to escaping when using in regular expression patterns. For example: "/^d{4}(W)d{2}1d{2}$/". Non-storage mode can be set using ?:s in parentheses.

The inner workings of the regular expression engine

Knowing how the regular expression engine works can help you quickly understand why a certain regular expression doesn't work as you expect.

<code>  有两种类型的引擎：文本导向(text-directed)的引擎和正则导向(regex-directed)的引擎。Jeffrey Friedl把他们称作DFA和NFA引擎。本文谈到的是正则导向的引擎。这是因为一些非常有用的特性，如“惰性”量词(lazy quantifiers)和反向引用(backreferences)，只能在正则导向的引擎中实现。所以毫不意外这种引擎是目前最流行的引擎。
</code>

You can easily tell whether the engine used is text-oriented or regular-oriented. If backreferences or "lazy" quantifiers are implemented, you can be sure that the engine you are using is regex-oriented. You can do the following test: change the regular expression <

The above has introduced php-preg-1, including various aspects. I hope it will be helpful to friends who are interested in PHP tutorials.