PHP and regular expression series: regular expressions in PHP. Starting today, we will begin to get a series of articles in the PHP Tutorial series, mainly for regular expressions. The approximate content sorting is arranged as follows: 1. regular expression in PHP 2. eight Practical PHP regular expressions will begin to get a series of PHP tutorials today. it is mainly for regular expressions.
The approximate content sorting is arranged as follows:
1. regular expressions in PHP
2. eight Practical PHP regular expressions
3. how to write PHP regular expressions that are easier to read
4. half an hour proficient in regular expressions
5. Application of regular expressions in the document collection system and FAQs
6... more planning...
In terms of the source of the article content, some old articles on this site have been reorganized, and some English documents have been translated (thanks for your help in Canada! OEL students). some of them are personal experiences.
My personal abilities are limited and there must be some mistakes. please remind me and make some corrections when I find myself. I will not mislead new users. if the article can give you some reference, it will be very satisfying.
PHP and regular expression series: regular expressions in PHP
Introduction to regular expressions and the role of regular expressions in PHP
Regular expressions are a way to express rules. using these rules in PHP allows you to flexibly match, verify, replace, and string. This article covers the basics of PCRE and how to use the preg_match (), preg_replace (), and preg_split () functions.
Next, let's start from the instance step by step to learn how to use these functions.
Rule match preg_match
With preg_match (), we can complete string rule matching. If a match is found, the preg_match () function returns 1; otherwise, 0. Another optional third parameter allows you to store the matched part in an array. This function can be very useful when verifying data.
$ String = "football ";
If (preg_match ('/foo/', $ string )){
// The matching is correct.
}
The above example will be matched successfully because the word football contains foo. Now let's try a more complex one, such as verifying an Email address.
$ String = "first.last@domain.uno.dos ";
If (preg_match (
'/^ [^ 0-9] [a-zA-Z0-9 _] + ([.] [a-zA-Z0-9 _] +) * [@] [a-zA-Z0-9 _] + ([.] [a-zA-Z0-9 _] +) * [.] [a-zA-Z] {2, 4} $ /',
$ String )){
// Verify the Email address
}
This example verifies that the Email address is in the correct format. Now let's take a look at the various rules represented by this regular expression.
PCRE, as its name implies, has the same syntax as the regular expression in Perl, so each regular expression must have a pair of delimiters. We generally use the separator.
The ^ at the beginning and $ at the end let PHP check from the beginning of the string to the end. If there is no $, the program will still match to the end of the Email.
[And] are used to limit the allowed input type. For example, a-z allows all lowercase letters, A-Z allows all uppercase letters, 0-9 all numbers, and so on, and more other types.
{And} are used to limit the expected number of characters. For example, {2, 4} indicates that each section of a string can contain 2-4 characters, such as .com.cn or. info. Here, "." is not a single character, because the allowed input type defined earlier than {2, 4} only contains uppercase and lowercase letters, so the segment only matches uppercase and lowercase letters.
(And) is used to merge sections and define the characters that must exist in strings. (A | B | c) can match a, B, or c.
(.) Will match all characters, and [.] will only match "." itself.
To use some symbols, you must add one in front. These characters are: () []. *? + ^ | $
Rule replacement preg_replace
Preg_replace allows you to replace the regular expression that matches your definition in the string. A simple annotation removal function:
Preg_replace ('[(/*) +. + (*/)]', '', $ val );
This code can remove multiple comments using/* comments */format in PHP and CSS. The three parameters are the regular expression, the string to be replaced, and the target string to be replaced (here the removal function is required, so it is a blank string-> ''). If you want to match sub-rules, you can use $0 to represent all matches, $1, $2, and so on.
Rule segmentation preg_split
Preg_split splits the entire string into multiple segments of 1, 2, or more characters according to the matched regular expression. For example, to obtain tags, whether they are separated by spaces or commas:
$ Tags = preg_split ('/[,]/', 'My, tags, venvenly, spaced ');
Print_r ($ tags );
Regular expressions are a practical technique that allows you to focus on the expected content.
However, it is annoying to have a regular expression that does not give you the expected results, so I will attach some simple grammar guides in the second article of this series to help you.
Appendix: PCRE syntax guide
/Delimiter
^ String header
$ String tail
[A-z] all lowercase letters
[A-Z] all uppercase letters
[0-9] All numbers
? Zero or a forward character
* Zero or multiple leading characters
+ One or more leading characters
{4} 4 leading characters
{4, 8} 4-8 followed by the first character
. Any character
(Red | green | blue) Red, green, or blue (red, green, or blue)
S space
Special characters (must be prefixed)
() []. *? + ^ | $
Regular expressions. The approximate sorting of content is arranged as follows: 1. regular expression in PHP 2. eight Practical PHP regular expressions...
