PHP验证规则

shirobert

Regular Expression	Will match...
foo	The string "foo"
^foo	"foo" at the start of a string
foo$	"foo" at the end of a string
^foo$	"foo" when it is alone on a string
[abc]	a, b, or c
[a-z]	Any lowercase letter
[^A-Z]	Any character that is not a uppercase letter
(gif|jpg)	Matches either "gif" or "jpeg"
[a-z]+	One or more lowercase letters
[0-9\.\-]	Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$	Any word of at least one letter, number or _
([wx])([yz])	wy, wz, xy, or xz
[^A-Za-z0-9]	Any symbol (not a number or a letter)
([A-Z]{3}|[0-9]{4})	Matches three letters or four numbers

　　Perl-Compatible Regular Expressions emulate the Perl syntax forpatterns, which means that each pattern must be enclosed in a pair ofdelimiters. Usually, the slash (/) character is used. For instance,/pattern/.
　　The PCRE functions can be divided in several classes: matching, replacing, splitting and filtering.

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Matching Patterns
　　The preg_match()function performs Perl-style pattern matching on a string. preg_match()takes two basic and three optional parameters. These parameters are, inorder, a regular expression string, a source string, an array variablewhich stores matches, a flag argument and an offset parameter that canbe used to specify the alternate place from which to start the search:
preg_match ( pattern, subject [, matches [, flags [, offset]]])
　　The preg_match()function returns 1 if a match is found and 0 otherwise. Let's search the string "Hello World!" for the letters "ll":
<?php
if (preg_match("/ell/", "Hello World!", $matches)) {
  echo "Match was found <br />";
  echo $matches[0];
}
?>
　　The letters "ll" exist in "Hello", so preg_match()returns1 and the first element of the $matches variable is filled withthe string that matched the pattern. The regular expression in the nextexample is looking for the letters "ell", but looking for them withfollowing characters:
<?php
if (preg_match("/ll.*/", "The History of Halloween", $matches)) {
  echo "Match was found <br />";
  echo $matches[0];
}
?>
　　Now let's consider more complicated example. The most popular use ofregular expressions is validation. The example below checks if thepassword is "strong", i.e. the password must be at least 8 charactersand must contain at least one lower case letter, one upper case letterand one digit:
<?php
$password = "Fyfjk34sdfjfsjq7";

if (preg_match("/^.*(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$/", $password)) {
    echo "Your passwords is strong.";
} else {
    echo "Your password is weak.";
}
?>
　　The ^ and $ are looking for something at the start and the end ofthe string. The ".*" combination is used at both the start and the end.As mentioned above, the .(dot) metacharacter means any alphanumericcharacter, and * metacharacter means "zero or more". Between aregroupings in parentheses. The "?=" combination means "the next textmust be like this". This construct doesn't capture the text. In thisexample, instead of specifying the order that things should appear,it's saying that it must appear but we're not worried about the order.
　　The first grouping  is (?=.*{8,}). This checks if there are at least8 characters in the string. The next grouping (?=.*[0-9]) means "anyalphanumeric character can happen zero or more times, then any digitcan happen". So this checks if there is at least one number in thestring. But since the string isn't captured, that one digit can appearanywhere in the string. The next groupings (?=.*[a-z]) and (?=.*[A-Z])are looking for the lower case and upper case letter accordinglyanywhere in the string.
　　Finally, we will consider regular expression that validates an email address:
<?php
$email = firstname.lastname@aaa.bbb.com;
$regexp = "/^[^0-9][A-z0-9_]+([.][A-z0-9_]+)*[@][A-z0-9_]+([.][A-z0-9_]+)*[.][A-z]{2,4}$/";

if (preg_match($regexp, $email)) {
    echo "Email address is valid.";
} else {
    echo "Email address is <u>not</u> valid.";
}
?>
　　This regular expression checks for the number at the beginning andalso checks for multiple periods in the user name and domain name inthe email address. Let's try to investigate this regular expressionyourself.
　　For the speed reasons, the preg_match()function matchesonly the first pattern it finds in a string. This means it is veryquick to check whether a pattern exists in a string. An alternativefunction, preg_match_all(), matches a pattern against a string as many times as the pattern allows, and returns the number of times it matched.

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Replacing Patterns
　　In the above examples, we have searched for patterns in a string, leaving the search string untouched. The preg_replace()function looks for substrings that match a pattern and then replaces them with new text. preg_replace()takes three basic parameters and an additional one. These parametersare, in order, a regular expression, the text with which to replace afound pattern, the string to modify, and the last optional argumentwhich specifies how many matches will be replaced.
preg_replace( pattern, replacement, subject [, limit ])
　　The function returns the changed string if a match was found or anunchanged copy of the original string otherwise. In the followingexample we search for the copyright phrase and replace the year withthe current.
<?php
echo preg_replace("/([Cc]opyright) 200(3|4|5|6)/", "$1 2007", "Copyright 2005");
?>
　　In the above example we use back references in the replacementstring. Back references make it possible for you to use part of amatched pattern in the replacement string. To use this feature, youshould use parentheses to wrap any elements of your regular expressionthat you might want to use. You can refer to the text matched bysubpattern with a dollar sign ($) and the number of the subpattern. Forinstance, if you are using subpatterns, $0 is set to the whole match,then $1, $2, and so on are set to the individual matches for eachsubpattern.
　　In the following example we will change the date format from "yyyy-mm-dd" to "mm/dd/yyy":
<?php
echo preg_replace("/(\d+)-(\d+)-(\d+)/", "$2/$3/$1", "2007-01-25");
?>
　　We also can pass an array of strings as subjectto make thesubstitution on all of them. To perform multiple substitutions on thesame string or array of strings with one call to preg_replace(), we should pass arrays of patterns and replacements. Have a look at the example:
<?php
$search = array ( "/(\w{6}\s\(w{2})\s(\w+)/e",
                  "/(\d{4})-(\d{2})-(\d{2})\s(\d{2}:\d{2}:\d{2})/");

$replace = array ('"$1 ".strtoupper("$2")',
                  "$3/$2/$1 $4");

$string = "Posted by John | 2007-02-15 02:43:41";     

echo preg_replace($search, $replace, $string);?>
　　In the above example we use the other interesting functionality -you can say to PHP that the match text should be executed as PHP codeonce the replacement has taken place. Since we have appended an "e" tothe end of the regular expression, PHP will execute the replacement itmakes. That is, it will take strtoupper(name) and replace it with theresult of the strtoupper()function, which is NAME.

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Array Processing
　　PHP's preg_split()function enables you to break a stringapart basing on something more complicated than a literal sequence ofcharacters. When it's necessary to split a string with a dynamicexpression rather than a fixed one, this function comes to the rescue.The basic idea is the same as preg_match_all()except that,instead of returning matched pieces of the subject string, it returnsan array of pieces that didn't match the specified pattern. Thefollowing example uses a regular expression to split the string by anynumber of commas or space characters:
<?php
$keywords = preg_split("/[\s,]+/", "php, regular expressions");
print_r( $keywords );
?>
　　Another useful PHP function is the preg_grep()functionwhich returns those elements of an array that match a given pattern.This function traverses the input array, testing all elements againstthe supplied pattern. If a match is found, the matching element isreturned as part of the array containing all matches. The followingexample searches through an array and all the names starting withletters A-J:
<?php
$names = array('Andrew','John','Peter','Nastin','Bill');
$output = preg_grep('/^[a-m]/i', $names);
print_r( $output );
?>