The application of regular expression in PHP
in PHP applications, regular expressions are used primarily for:
• Regular match: matches the corresponding content according to the regular expression
• Regular substitution: matching content based on regular expressions and replacing
• Regular segmentation: Splitting strings based on regular expressions
There are two types of regular expression functions in PHP, one is Perl-compatible regular expression functions, the other is POSIX-extended regular expression functions. There is little difference, and Perl-compatible regular expression functions are recommended, so the following are examples of Perl-compatible regular expression functions.
delimiters
A regular expression function in Perl compatibility mode whose regular expression needs to be written in a delimiter. Any character that is not a letter, number, or backslash () can be used as a delimiter, and usually we use/as a delimiter. See the example below for specific use.
Tips
Although the regular expression is very powerful, if you can do it with a normal string handler, try not to use regular expression functions, because regular expressions are much less efficient. About normal string processing functions.
Preg_match ()
The Preg_match () function is used to match a regular expression, successfully returning 1, otherwise returning 0.
Syntax:
int Preg_match (string pattern, string subject [, array matches])
parameter Description:
| Parameters |
Description |
| Pattern |
Regular expressions |
| Subject |
Objects that need to match the retrieved |
| Matches |
Optionally, stores an array of matching results, $matches [0] will contain text that matches the entire pattern, $matches [1] will contain text that matches the child pattern in the first captured bracket, and so on |
Example 1:
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<?php
if (Preg_match ("/php/i", "PHP is the Web scripting language of choice.", $matches))
Print "A match was found:". $matches [0];
} else {
Print "A match is not found.";
}
?>
Browser Output:
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In this example, because the I modifier is used, it is case-insensitive to match PHP in the text.
Tips
Preg_match () stops the match after the first match succeeds, and the Preg_match_all () function is used if you want to achieve a match for all the results, that is, to the end of the subject.
Example 2, get the host domain name from a URL:
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<?php
Get host name from URL
Preg_match ("/^" (http://)? [^/]+)/I "," http://www.jb51.net/index.html ", $matches);
$host = $matches [2];
To get the following two segments from the host name
Preg_match ("/[^./]+.[ ^./]+$/", $host, $matches);
echo "domain name: {$matches [0]}";
?>
Browser Output:
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The domain name is: jb51.net
Preg_match_all ()
The Preg_match_all () function is used to make a regular expression global match, successfully returning the number of times the entire pattern match (possibly 0), or FALSE if the error returns.
Syntax:
int Preg_match_all (string pattern, string subject, array matches [, int flags])
parameter Description:
| Parameters |
Description |
| Pattern |
Regular expressions |
| Subject |
Objects that need to match the retrieved |
| Matches |
An array that stores matching results |
| Flags |
Optionally, specify the order in which the matching results are placed in the matches, and the optional tags are:
- Preg_pattern_order: By default, the result is sorted so that $matches [0] matches all patterns, $matches [1] is an array of strings that match the child pattern in the first bracket, and so on
- Preg_set_order: Sort results by making $matches [0] An array of the first set of matches, $matches [1] as an array of the second set of matches, and so on
- Preg_offset_capture: If you set this tag, the matching result for each occurrence also returns its attached string offset
|
The following example shows the keyword (PHP) in all <pre></pre> tags in the text to be displayed in red.
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<?php
$str = "<pre> learning PHP is a happy thing." </pre><pre> all the phper need to work together! </pre> ";
$kw = "PHP";
Preg_match_all ('/<pre> (ss]*?) </pre>/', $str, $mat);
For ($i =0 $i <count ($mat [0]); $i + +) {
$mat [0][$i] = $mat [1][$i];
$mat [0][$i] = str_replace ($kw, ' <span style= ' color: #ff0000 ' > '. $kw. ' </span> ', $mat [0][$i]);
$str = Str_replace ($mat [1][$i], $mat [0][$i], $str);
}
Echo $str;
?>
Regular matching Chinese characters
Regular matching Chinese characters vary slightly according to page encoding:
gbk/gb2312 Encoding: [x80-xff>]+ or [xa1-xff]+
utf-8 encoding: [x{4e00}-x{9fa5}]+/u
Example:
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<?php
$STR = "Learning php is a happy thing." ";
Preg_match_all ("/[x80-xff]+/", $str, $match);
UTF-8 use:
Preg_match_all ("/[x{4e00}-x{9fa5}]+/u", $str, $match);
Print_r ($match);
?>
output:
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Array
(
[0] => Array
(
[0] => study
[1] => is a happy thing.
)
)
