How to validate the string with only specific letter and number?

Question

I want to validate the string containing characters A , B . X & Y . The character A & B must follow by the number but X, Y should not be.

// correct 
"A11X",
"A45YA1X",
"A1XXA999YYA1",

// Not correct
"A1A1AAX12",
"1A1Y32A1",
"CA1A1",
"A1C1",

I am using following regex command.

$flags = PREG_SET_ORDER;
        preg_match_all('/A|B(\d+)|.+/i', trim($command), $operations, $flags);

If the string is correct, it must return true otherwise it should return error message.

Answer 1

You may use this regex:

^(?:[AB]\d+|[XY])+$

RegEx Demo

• This regex uses a non-capturing group that matches letter A or B followed by 1+ digits or using alternation matches letter X or Y .

• This group is repeated 1 or more times to allow repetitions of this sub-pattern in entire string.