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][A-Z] matches one digit followed by one capital letter

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

([0-9][A-Z]|[A-Z][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.