PHP Regular Expression Learning notes, regular expression learning notes _php Tutorial

PHP Regular Expression Learning notes, regular expression learning notes

PHP Regular Expression Learning notes sharing:

1. Create a regular expression

$regex = '/\d/i ';
It's a bit like the first way in JavaScript, but here is a string.

2. Special characters in regular expressions

Special characters are: . \ + *? [ ^ ] $ ( ) { } = ! < > | : -

3. Functions in regular expressions

There are 8 methods,Preg_match and Preg_match_all,preg_replace and Preg_replace_callback,preg_grep, Preg_split, Preg_last_ Error and Preg_quote.

Preg_match:

Performs a regular expression match

returns the number of occurrences of pattern . Its value will be 0 times (mismatched) or 1 times, because Preg_match () will stop searching after the first match .

$subject = "Dd133aa2"; $pattern = '/\d+/';p reg_match ($pattern, $subject, $matches, preg_offset_capture);p Rint_r ($ matches);

The example code above adds the parameter "preg_offset_capture" so that there is an additional offset in the $matches. For example, the following "2"

Preg_match_all:

Performs a "global" regular expression match

Returns the complete number of matches (possibly 0), or False if an error occurs.

In the code below, $subject and $pattern are the same as above, and the only difference is that Preg_match is replaced with Preg_match_all.

Preg_match_all ($pattern, $subject, $matches, preg_offset_capture);p Rint_r ($matches);

The number of returns is 2, matched to two times, and then the input in the array $matches, with two. One more than the above.

preg_replace:

Perform a search and replace of a regular expression

If subject is an array, preg_replace () returns an array, and in other cases returns a string.

If the match is found, the replaced subject is returned, and other cases return unchanged subject. If an error occurs, NULL is returned.

In the code, $subject is an array with two sets of strings, followed by replacing multiple numbers with uppercase "Z".

$subject = Array ("Dd133aa2", "KK1FF3"), $pattern = '/\d+/'; $result = preg_replace ($pattern, ' Z ', $subject);p Rint_r ($ result);

Preg_replace_callback:

Performs a regular expression search and replaces it with a "callback"

The behavior of this function, in addition to specifying a callback substitution replacement for substitution string calculations, is equivalent to Preg_replace (), including the returned result.

The following code is also replaced with uppercase "Z", the contents of each $matches in the callback function is the part of the comment in the code, the first time is 133, the second time is 2.

$subject = "Dd133aa2"; $pattern = '/\d+/'; $result = Preg_replace_callback ($pattern, function ($matches) {    //$matches [0] = = 133    //$matches [0] = 2    return ' Z ';   

Preg_grep:

Returns an array entry for the matching pattern

Returns an array that is indexed using key in input.

In the following example code, in the $subject array I added a "DDSDFD", which does not contain numbers, in the match, the number of the filter out.

and $result2 print out of the exact opposite, is to print out the filter, but the key is still 2, not 0.

$subject = Array ("Dd133aa2", "KK1FF3", "DDSDFD"); $pattern = '/\d+/'; $result = Preg_grep ($pattern, $subject); $result 2 = pr Eg_grep ($pattern, $subject, Preg_grep_invert);p rint_r ($result);p Rint_r ($result 2);

Preg_split:

Separating strings with a regular expression

Returns an array of substrings that are made using the pattern boundary to separate subject.

In the following code, I enclose the expression in $pattern with parentheses in order to capture it in $RESULT2.

$subject = "dd133aa2cc"; $pattern = '/(\d+)/'; $result = Preg_split ($pattern, $subject); $result 2 = Preg_split ($pattern, $ Subject, NULL, preg_split_delim_capture);p rint_r ($result);p Rint_r ($result 2);

Preg_last_error:

Returns the error code generated by the last Pcre regular execution

Preg_match ('/(?: \ d+|<\d+>) *[!?] /', ' foobar foobar foobar '); $result = Preg_last_error ();//preg_backtrack_limit_error call backtracking limit exceeds print_r ($result);

Preg_quote:

Escaping regular expression characters

Returns the escaped string .

In the following code, there are two characters in the $subject that need to be escaped, "." and "?".

After the $result is printed out is "dd\.a\?a2cc", and in $result2, add a parameter "a", so that "a" will also be escaped, "dd\.\a\?\a2cc"

$subject = "dd.a?a2cc"; $result = Preg_quote ($subject); $result 2 = Preg_quote ($subject, ' a ');p Rint_r ($result);p Rint_r ($ RESULT2);

4. Mode modifier

The above is about the PHP regular expression of the full content of the introduction, I hope that everyone's learning has helped.

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