Tips on using PHP regular expressions_PHP tutorial

Definition of PHP regular expression:

A grammatical rule used to describe character arrangement and matching patterns. It is mainly used for pattern segmentation, matching, search and replacement operations of strings.

Regular functions in PHP:

There are two sets of regular functions in PHP, both of which have similar functions, namely:

One set is composed of PCRE (Perl Compatible Regular Expression ) library provided. Functions named with the prefix "preg_";

A set of functions provided by POSIX (Portable Operating System Interface of Unix) extensions. Use functions named with the prefix "ereg_"; (POSIX regular function library is no longer recommended for use since PHP 5.3, and will be removed from PHP 6)

Due to the upcoming history of POSIX regular function Stage, and the forms of PCRE and perl are similar, which is more convenient for us to switch between perl and php, so here we focus on the use of PCRE regularity.

PCRE regular expression

PCRE stands for Perl Compatible Regular Expression, which means Perl compatible regular expression.

In PCRE, the pattern expression (i.e. regular expression) is usually enclosed between two backslashes "/", such as "/apple/".

Several important concepts in regular expressions are: metacharacters, escapes, pattern units (repetitions), antonyms, references and assertions. These concepts can be easily understood and mastered in the article [1].

Commonly used meta-characters:

Meta-character Description

/A Matches the atom at the beginning of the string

/Z Matches characters The atom at the end of the string

/b Matches the boundary of the word //bis/ Matches the string whose head is is /is/b/ Matches the string whose end is is //bis/b/ Delimited

/B Matches any character except word boundaries //Bis/ Matches "is" in the word "This"

/d Matches a number; equivalent to [0-9]

/D Matches any character except numbers; equivalent to [^0-9]

/w Matches an English letter, number or underscore; equivalent to [0-9a-zA -Z_]

/W Matches any character except English letters, numbers and underscores; equivalent to [^0-9a-zA-Z_]

/s Matches a blank character; Equivalent to [/f/t/v]

/S Matches any character except whitespace characters; Equivalent to [^/f/t/v]

/f Matches one The form feed character is equivalent to /x0c or /cL

matches a newline character; equivalent to /x0a or /cJ

matches a carriage return character and is equivalent to /x0d or /cM

/t Matches a tab character; equivalent to /x09/ or /cl

/v Matches a vertical tab character; equivalent to /x0b or /ck

/oNN Matches an octal number

/xNN Matches a hexadecimal number

/cC Matches a control character

Pattern Modifiers:

Pattern modifiers are especially used in ignoring case and matching multiple lines. Mastering this modifier can often solve many problems we encounter.

i - Can match both uppercase and lowercase letters

M - Treat the string as multiple lines

S - Treat the string as a single line, and treat newlines as ordinary characters , making "." match any character

X - Blanks in the pattern are ignored

U - Match the nearest string

e - Replace the string as Expressions use the

format: /apple/i matches "apple" or "Apple", etc., ignoring case. /i

PCRE pattern unit:

//1 Extract the first attribute

/^/d{2} ([/W])/d{ 2}//1/d{4}$ matches strings such as "12-31-2006", "09/27/1996", and "86 01 4321". But the above regular expression does not match the format of "12/34-5678". This is because the result "/" of pattern "[/W]" has already been stored. When the next position "/1" is quoted, its matching pattern is also the character "/".

Use the non-storage pattern unit "(?:)" when there is no need to store the matching results

For example /(?:a|b|c)(D|E|F)// 1g/ will match "aEEg". In some regular expressions, it is necessary to use non-storage mode units. Otherwise, the order of subsequent references needs to be changed. The above example can also be written as /(a|b|c)(C|E|F)/2g/.

PCRE regular expression function:

The following is the quoted content:

preg_match() and preg_match_all()
preg_quote()
preg_split()
preg_grep()
preg_replace()

The specific use of the function can be found through the PHP manual. Here are some regular expressions we have accumulated:

Match action attribute

The following is the quoted content:

$str = '';
$match = '';
preg_match_all('//s+action=/"(?!http:)(.*?)/"/s/', $str, $match);
print_r($match);

Use the callback function in the regular expression

The following is the quoted content:

/**  
   * replace some string by callback function  
   *  
  */
function callback_replace() {
$url = 'http://esfang.house.sina.com.cn';
$str = '';
$str = preg_replace ( '/(?<=/saction=/")(?!http:)(.*?)(?=/"/s)/e', 'search(/$url, //1)', $str );
                                                                                                                                                  ; . $match; 🎜> $str = 'xxxxxx.com.cn bold font
paragraph text

';
preg_match_all ( '/(?<=<(/w{1})>) .*(?=)/', $str, $match );
echo "Match the content in HTML tags without attributes:";
print_r ( $match );

Replace the address in the HTML source code

The following is the quoted content:

$form_html = preg_replace ( '/(?<=/saction= /"|/ssrc=/"|/shref=/")(?!http:|javascript)(.*?)(?=/"/s)/e', 'add_url(/$url, /'/ /1/')', $form_html );

Finally, although the regular tool is powerful, in terms of efficiency and writing time, sometimes it may not be more direct than explode. For some urgent or less demanding tasks, a simple, crude approach may be better.

http://www.bkjia.com/PHPjc/371448.html

www.bkjia.com

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http: //www.bkjia.com/PHPjc/371448.html

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Definition of PHP regular expression: A grammatical rule used to describe character arrangement and matching patterns. It is mainly used for pattern segmentation, matching, search and replacement operations of strings. Positive in PHP...