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PHP Regular Expressions Learn note sharing:

1. Creating Regular Expressions

$regex = '/\d/i ';
It's a bit like the first way in JavaScript, but the word 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 matches for pattern. Its value will be 0 times (mismatch) or 1 times, because Preg_match () will stop the search after the first match .

$subject = "Dd133aa2";
$pattern = '/\d+/';
Preg_match ($pattern, $subject, $matches, preg_offset_capture);
Print_r ($matches);

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

Preg_match_all:

Performs a "global" regular expression match

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

The following code $subject and $pattern are the same as the above, the only difference is that Preg_match replaced by Preg_match_all.

Preg_match_all ($pattern, $subject, $matches, preg_offset_capture);
Print_r ($matches);

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

preg_replace:

Performs 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 in other cases the subject is returned unchanged. Returns NULL if an error occurs.

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

$subject = Array ("Dd133aa2", "KK1FF3");
$pattern = '/\d+/';
$result = Preg_replace ($pattern, ' Z ', $subject);
Print_r ($result);

Preg_replace_callback:

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

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

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

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

Preg_grep:

Returns an array entry for a matching pattern

Returns an array that is indexed using the key in input.

In the example code below, I added a "DDSDFD" in the $subject array, which doesn't contain numbers, and when I do a match, I filter out the numbers.

and $RESULT2 print out exactly the opposite, is the filter printed out, but the key is still 2, not 0.

$subject = Array ("Dd133aa2", "KK1FF3", "DDSDFD");
$pattern = '/\d+/';
$result = Preg_grep ($pattern, $subject);
$result 2 = Preg_grep ($pattern, $subject, Preg_grep_invert);
Print_r ($result);
Print_r ($result 2);

Preg_split:

Separating strings with a regular expression

Returns an array of substrings that are separated by a pattern boundary subject.

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

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

Preg_last_error:

Returns the error code generated by the last Pcre execution

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

Preg_quote:

Escape Regular Expression characters

Returns the escaped string .

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

The $result print out is "dd\.a\?a2cc", and in $result2, an extra parameter "a" is added, so that "a" is also escaped, "dd\.\a\?\a2cc"

$subject = "dd.a?a2cc";
$result = Preg_quote ($subject);
$result 2 = preg_quote ($subject, ' a ');
Print_r ($result);
Print_r ($result 2);

4, Mode modifier

The above is about the PHP regular expression of all the contents of the introduction, I hope that the learning of all help.