如何使用 preg_match 只允许包含字母和数字字符的字符串？

Question

I need a regex to accept only strings that contain both alphabetic and numeric characters. For example:

ABCDEF: wrong 
123456: wrong
!##$%@.: wrong
ABCD123!@$: wrong
ABC12389IKEIIJ29: **correct**

How can I do it with PHP?

Answer 1

preg_match('/^[0-9A-Z]*([0-9][A-Z]|[A-Z][0-9])[0-9A-Z]*$/', $subject);

If you want to allow small and capital letters, add an i at the end of the pattern string.

Explanation:

[0-9][AZ] matches one digit followed by one capital letter

[AZ][0-9] matches one capital letter followed by one digit

([0-9][AZ]|[AZ][0-9]) matches one of these two sequences

[0-9A-Z]* matches 0-n digits and/or capital letters

The idea is: A string which contains both (and only), letters and numbers, has at least one subsequence where a letter follows a digit or a digit follows a letter. All the other characters (preceding and following) have to be digits or letters.

Answer 2

I feel the most professional and comprehensible way of doing this is to declare two lookaheads which individually demand a certain range of characters, then match one or more characters that satisfy both sets of whitelisted characters -- of course, all of this logic needs to be nested inside of start of string and end of string anchors.

I'll demonstrate with preg_grep() applied to an array of test strings, but you can use the same pattern with preg_match() on a single string.

Code: ( Demo )

$tests = [
    'ABCDEF',
    '123456',
    '9Z',
    '!##$%@.',
    'ABCD123!@$',
    'ABC12389IKEIIJ29',
];

var_export(
    preg_grep(
        '~^(?=.*[A-Z])(?=.*\d)[A-Z\d]+$~',
        $tests
    )
);

Output: (array of qualifying strings)

array (
  2 => '9Z',
  5 => 'ABC12389IKEIIJ29',
)