A brief analysis of the implementation of regular expression matching in PHP_PHP tutorial

A brief analysis of the implementation of PHP regular expression matching

PHP regular expression matching is the ultimate goal when we talk about the application of regular expressions in PHP, so how to implement PHP regular expression matching Woolen cloth? What specific method will be used? Let’s take a look at the specifics.

PHP inherits the tradition of UNIX and fully supports the processing of regular expressions. Regular expressions provide an advanced, but non-intuitive, method of string matching and processing. Friends who have used PERL's regular expressions know that regular expressions are very powerful, but they are not easy to learn.

PHP regular expression matching example application:

<ol class="dp-c"><li class="alt"><span><span>^.+@.+..+$  </span></span></li></ol>

This effective but incomprehensible code is enough to give some programmers a headache (me) or make them Give up using regular expressions. I believe that after you finish reading this tutorial, you will understand the meaning of this code.

Basic pattern matching of PHP regular expression matching

Everything starts from the most basic. Patterns are the most basic elements of regular expressions. They are a set of characters that describe the characteristics of a string. Patterns can be simple, consisting of ordinary strings, or very complex, often using special characters to represent a range of characters, recurrences, or to represent context. For example:

^once

This pattern contains a special character ^, which means that the pattern only matches those strings starting with once. For example, this pattern matches the string "once upon a time" but does not match "There once was a man from NewYork". Just like the ^ symbol indicates the beginning, the $ symbol matches strings that end with a given pattern.

bucket$

This pattern matches "Who kept all of this cash in a bucket" but does not match "buckets". When the characters ^ and $ are used together, they represent an exact match (strings are the same as patterns). For example:

^bucket$

only matches the string "bucket". If a pattern does not include ^ and $, then it matches any string that contains the pattern. For example: the pattern

once

matches the string

<ol class="dp-c">
<li class="alt"><span><span>There once was a man from NewYork  </span></span></li>
<li><span>Who kept all of his cash in a bucket. </span></li>
</ol>

.

The letters (o-n-c-e) in this pattern are literal characters, that is, they represent the letters themselves, and the same goes for numbers. Other slightly more complex characters, such as punctuation and white characters (spaces, tabs, etc.), require escape sequences. All escape sequences begin with a backslash (). The escape sequence for the tab character is: t. So if we want to detect whether a string starts with a tab character, we can use this pattern:

^t

Similarly, use n to represent "new line" , r means carriage return. Other special symbols can be used with a backslash in front, such as the backslash itself is represented by ., the period is represented by ., and so on.

This concludes the introduction to PHP regular expression matching. I hope it will be helpful for you to understand and learn PHP regular expression matching.

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