Php regular expression sub-mode reverse reference learning Notes

You must use a regular expression to obtain the title of a string. The title label is h1 ~ H6.
Use a regular expression: "@

Example 1

 

The code is as follows:	Copy code
<? Php $ Str = 'Preg_match_all ("@ Print_r ($ all ); ?> Result Array ( [0] => Array         ( [0] => [1] => [2] => [3] =>         ) [1] => Array         ( [0] => 1 [1] => 2 [2] => 3 [3] => 4         ) [2] => Array         ( [0] => php php1 [1] => php php2 [2] => php php3 [3] => php php4         ) )

Example 2

Mixed preg_replace (mixed pattern, mixed replacement, mixed subject [, int limit])

Function

Search for matches in pattern in subject and replace them with replacement. If limit is specified, only limit matches are replaced. If limit is omitted or its value is-1, all matches are replaced.
Replacement can contain reverse references in the \ n or $ n format. n can be 0 to 99, and \ n indicates text that matches the nth subpattern of pattern, \ 0 indicates the text that matches the entire pattern.

Sub-mode

The regular expression enclosed by parentheses in the $ pattern parameter. The number of child patterns is the number of left-to-right parentheses. (Pattern is the pattern)

Example 1: The simplest and most useful example is to determine the position of two identical words consecutively in the text.

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<? Php $ String = "Is the cost of gasoline going up "; $ Pattern = "/\ B ([a-z] +) \ 1 \ B/I"; // \ 1 here cannot be used \ $1 or $1 $ Str = preg_replace ($ pattern, "\ 1", $ string); // Here \ 1 can be used \ $1 or $1 to reference the first child match Echo $ str; // the result Is the cost of gasoline going up ?>

In this example, the subexpression is an item in parentheses. \ B matches the start or end of a word. + Repeat once or more times.
This subexpression matches one or more letter words, that is, '[a-z] +.

The second part of the regular expression is a reference to the previously captured sub-match, that is, the second occurrence word matched by the append expression, use '\ 1' to reference the first child Match. The First \ is an escape character.

I is the modifier in the regular expression. I: case insensitive.

Example 3:

The reverse reference ($0-99 or \ 0-99) and submode of the regular expression start.
$0 indicates the matching items of all matching modes. $1 is a 1st child match, and $2 to $99 are 2nd to 99th child matches in sequence.
If the character behind the submatch is a number, use curly brackets to separate it. Example: $ {1} 1.

The code is as follows:

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<? Php $ String = "{April 15,200 3 }"; // 'W' matches letters, numbers, and underscores, 'D' matches 0-99 numbers, and '+' matches multiple or more times. $ Pattern = "/{(\ w +) (\ d +), (\ d +)}/I"; // match to be searched in the string $ Replacement1 = "\$ {1} 1, \ $3 "; $ Replacement2 = "\ $0 "; $ Replacement3 = "\ $1 "; $ Replacement4 = "\ $2 "; $ Replacement5 = "\ $3 "; Echo "<BR> "; // The string is replaced with the text that matches the substring pattern in the nth captured parentheses Print preg_replace ($ pattern, $ replacement1, $ string ); Echo "<BR> "; Print preg_replace ($ pattern, $ replacement2, $ string ); Echo "<BR> "; Print preg_replace ($ pattern, $ replacement3, $ string ); Echo "<BR> "; Print preg_replace ($ pattern, $ replacement4, $ string ); Echo "<BR> "; Print preg_replace ($ pattern, $ replacement5, $ string ); Echo "<BR> "; // General expression Print preg_replace ("/\ w +/I", "j", $ string ); ?> Effect: April1, 2003 {10000l 15,200 3} Else L 15 2003 {J, j}

The test has passed.