A detailed description of strings and regular expressions in PHP, PHP regular Expressions _php tutorial

A detailed description of the string and regular expressions in PHP, with a detailed description of the PHP regular expression

I. Characteristics of String types

1, PHP is a weakly typed language, other data types can be directly applied to string function operation.

<?php
echo substr ("123456", 2,4);  Output 345
echo substr (123456,2,4);    Output 345
echo Hello;                 Look for Hello constants first, and if not found, use Hello as a string
?>

2, the string can be used as an "array", is a collection of characters.

<?php
$str = "Www.jb51.net";
echo $str [0];
echo $str [1];
Echo $str [2];
?>

However, the string is not a true array, and the function of the array cannot be used. such as COUNT ($STR) does not return a string length. The PHP engine cannot differentiate between characters and arrays, resulting in two semantics. Since PHP4, curly braces have been used instead of square brackets.

<?php
To ensure backward compatibility, square brackets can still be used
$str = www.jb51.net;
echo $str {0};
echo $str {1};
echo $str {2};
?>

3. Double quotation mark variable parsing

In PHP, when you define a string with double quotes or delimiters, the variables are parsed.

<?php
$arr = Array (' name ' = = ' Dwqs ', ' add ' = ' www.ido321.com ');
echo "$arr [name]";  Can parse, but cannot use quotation marks in square brackets
echo "$arr [' name ']";  Error
echo "{$arr [' name ']}";  Can parse, with curly braces containing elements, name without quotation marks is also possible
Suppose there is an object $square
echo "$square->width"; Can parse
echo "$square->width00 cent"; Can not parse, with curly braces to solve
echo "{$square->width}width00 cent"; Can parse
?>

Second, the string output function

Iii. commonly used string format functions

Most of the string handling functions of ps:php do not modify the source string, but instead return the new string

Four, the regular expression

The regular expression describes a pattern of string matching, which is composed of three parts: Atomic, meta-character, and pattern modifier, through which the string is matched, searched, replaced, and delimited in a particular function.

In PHP, there are two regular library of processing functions: Pcre and POSIX. The former is named after the Preg_ prefix and is compatible with Perl; the latter is named after the Ereg_ prefix. The two functions are similar, but the efficiency of pcre is slightly higher.

The Perl language-compatible regular expression handler:

1. Grammar

1.1 delimiter: When using patterns in a Perl-compatible regular function, you must add a delimiter to the pattern. Any character other than letters, numbers, and backslashes (\) can be used as a bounding symbol

<?php
The following regularization is legal
echo $m 1 = '/<\/\w+/';
echo $m 2 = ' | (\d{3})-\d| Sm ';
echo $m 3 = '!^ (? i) php[34]! ';
echo $m 4 = ' {^\s+ (\s+)? $} ';
?>

1.2 Atoms: atoms contain ordinary characters, such as letters, numbers, nonprinting characters, such as spaces, carriage returns, special characters and metacharacters characters, such as quotation marks, *, +, etc., must be escaped with "\"; custom atomic tables such as [APJ], [A-z], universal character types, such as \d, \d.

<?php
The following are equivalent, matching e-mail
$mail 1 = '/^[0-9a-za-z]+@[0-9a-za-z]+ (\.[ 0-9a-za-z]+) {0,3}$/';
$mail 2 = '/^\w+@\w+ (\.\w+) {0,3}$/';
?>

1.3 Metacharacters: A character that is used to construct a regular expression with a special meaning. Perl can use a variety of meta-characters to search for matches, such as *, +,? Common meta characters are as follows

1.4 mode modifier: Used outside the regular delimiter, extending the function of the regular in matching, replacing, and so on.

2. perl-compatible regular expression functions

2.1 Preg_match (String pattern,string Subject[,array matches]): Used to find and match strings. Parameter description:

Pattern is a regular, subject is a string that needs to be processed, an optional matches is used to match the results of each sub-pattern stored in pattern, matches[0] preserves the overall content that matches the pattern, matches[1] Preserves the matching content in the first parenthesis in pattern, and so on.

<?php
Header ("Content-type:text/html;charset=utf8");
$pattern = '/(HTTP): \/\/(WWW) \. ([^\.\/]+)\. (com|net|org)/I ';
$subject = "My blog: http://www.ido321.com";
if (Preg_match ($pattern, $subject, $matches)) {
echo "Search URL is:". $matches [0]. "
";  The 1th element of the array holds the entire matching result
The protocol in the Echo "URL is:". $matches [1]. "
";//the 2nd element of the array holds the 1th-word expression
The host in the echo "URL is:". $matches [2]. "
";//the 3rd element of the array holds the 2nd-word expression
The domain name in the echo "URL is:". $matches [3]. "
";//the 4th element of the array holds the 3rd-word expression
The top field in the echo "URL is:". $matches [4]. "
";//the 5th element of the array holds the 4th-word expression
}
?>

Results

Preg_match_all () is similar to the Preg_match () function, where the former is matched to the end of the string, which stops matching after the first match.

2.2 Preg_grep (String Pattern,array iput): Matches an element in an array, returning an array cell that matches a regular match. Parameter description:

pattern is regular, and input is an array that needs to be matched.

<?php
$arr = Array (' Linux RedHat9.0 ', ' Apache2.2.9 ', ' MySQL5.0.51 ', ' PHP5.2.6 ', ' LAMP ', ' 100 ');
$version = Preg_grep ('/^[a-za-z]+ (\d|\.) +$/', $arr);
Output: Array ([1]=>apache2.2.9 [2]=>mysql5.0.51 [3]=>php5.2.6]

?>

2.3 preg_replace (mixed pattern,mixed replacement,mixed subject[,int limit]): string substitution. Description

The function searches the subject for a match with pattern and replaces it with replacement. Limit is used to restrict the number of matches, that is, the number of replacements.

<?php
$pattern = '/<[\/\!] *? [^<>]*?/is ';
$text = ' This text is bold and underlined and Italic ';
Echo preg_replace ($pattern, "", $text);  Replace all HTML tags with an empty
Echo preg_replace ($pattern, "", $text, 2); Value replaces first 2 HTML tags
?>

2.4 preg_split (String pattern,string subject[,int Limit[,int flags]): Splits the string. Description

The function returns an array. The array element contains a string that is split in subject with the pattern match as the boundary, and the limit means see 2.3,flags meaning refer to the documentation.

<?php
Split a string by any number of spaces
$kerwords = Preg_split ("/[\s,]+/", "hypertext Language,programming");
Output: Array ([0]=>hypertext [1]=>language,[2[=>programming]
Print_r ($kerwords);
?>

PHP Regular expression + string extraction problem

$str = ' {"A": 1234567890, "B": "U", "Birthday": "2000-01-01", "Gender": "1", "Location": "123456", "Login_ip": " 123.123.123.123 "," login_time ": 1234567890," id ":" 1234567 "," sign ":" 0bcbdea54d1f2c3c75b058eb5d2ae124 "} ';
$user _id= "";
if (Preg_match_all (' | ') ID ":" (\s+?) "|", $str, $reg))
{
$user _id= $reg [1][0];
}
echo "UserID is:". $user _id;
?>

Output Result:
UserID is:1234567

How do you use regular expressions to add content to a string in PHP?

You can use regular expressions, or directly with PHP, feel or PHP is more convenient:
$str = Str_replace ("

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