问题
I want to test that a given string does not belong to the following group of strings: 22 75.
Could anyone please tell why PHP's preg_match("/[^(22|75)]/", "25") returns 0?
The weirdest thing is that preg_match("/[^(22|76)]/", "25") returns 1 as expected...
Edit: I guess I understand the reason and the nature of my mistake, not how to make a check that a given two-digit number does not match 20,21,22,23,24, 75,76,77,78,79,80 ? I need to assemble an expression to check a given age against the list of allowed ages (this presumes only two-digit numbers)
I can not use anything other than preg_match() (!preg_match() is not available in my case), I can only play with RegEx pattern.
回答1:
Time for a Regular Expressions Lesson!
Explanation of your regular expressions
[^(22|75)]
Matches false because it is looking for the following:
- A single character NOT in this list of characters:
|()275
[^(22|76)]
Matches true because it is looking for:
- A single character NOT in this list of characters:
|()276
Why does it do this?
You wrapped your regex in a character class (click for more info)
To give an example of how character classes work, look at this regex:
[2222222222222221111111199999999999]
This character class will only match ONE character, if it is a 2,1 or a 9.
How to make it work for you:
To match the number 25 (or 22, 52, and 55), you can use this character class:
[25]{2}
This will match a 2 digit number containing either 2 or 5 at either place.
回答2:
What are character classes
A character class is a collection of characters (not strings). With a character class, you're telling the regex engine to match only one out of several characters.
For example, if you wanted to match an a or e, you'd write [ae]. If you wanted to match grey or gray, you'd write gr[ae]y.
Explanation for first regex
[^(22|75)]
As said above, character classes match a single character from the list. Here, you're using ^ to get a negated character class, so this will match a single character that's not in the supplied list. In this case, our list contains the following characters:
( 2 2 | 7 5 )
Multiple characters are only counted once. So this effectively becomes:
( 2 | 7 5 )
25 is the string you're matching against. The regular expression asks: Does the supplied string contains a single character that's not in the above list? 2 and 5 are in the list, so the answer is No. That explains why preg_match() returns false (not false, 0 to be precise).
Explanation for second regex
/[^(22|76)]/
It is same as above. The only difference here is that 5 changed to 6. It now checks for the absense of any of the following characters:
( 2 | 7 6 )
The supplied string is still the same as before - 25. Does the string contain any character that's not in the list above? Yes! It does contain 5 (which is not in the list anymore). That explains why preg_match() returns 1.
Difference between character classes and alternation
They look similar but they do different things. Alternation can be used when you want to match a single regular expression out of several possible regular expressions. Unlike character classes, alternation works with a regex. A simple string, say foo is also a valid regular expression. It matches f followed by o, followed by o.
Use character class when you want to match one of the included characters. Use alternation when you want to match between n number of strings.
How should you modify the regex to obtain correct results
Negate your preg_match() call and use the regex (22|75):
if (!preg_match('/(22|75)/', '25')) {
# code...
}
This is the easiest approach. If you want to achieve this directly using a regex, then you may want to use look-arounds.
Alternative solution
If this is exactly what you're trying to do, then you don't need a regular expression at all. Leverage PHP's built-in functions for string manipulation! Not only it will be faster, it will be more readable too.
In this case, a simple in_array() should suffice:
if(!in_array('25', array(25,75))) {
# code ...
}
回答3:
In regular expression, [...] match any character inside the bracket.
To be more correct:
[^...]: match any charcter not listed inside the bracket. (^: negate)
Remove the [, and ] if you want to match string that starts with 22 or 76.
回答4:
Your regex is asking "does the string contain a character that is not (, 2, 7, 5, | or )?"
This is obviously not what you want.
Try this:
if( !in_array("25", array("22","75")))
回答5:
^ inside of [...] is a negation of a character list. (22|76)
Regex multiple character negation is a very tricky subject and can't be easily resolved.
But you could invert the return result of preg_match function ie.:
if(!preg_match('@22|76@', '25', $matches))
doSomething();
来源：https://stackoverflow.com/questions/21881626/why-preg-match-2275-25-returns-false