Question

Write a PHP regular expression pattern that matches a string that satisfies the following description:
The string must begin with the (uppercase) letter A. Any three alphanumeric characters
must follow. After these, the letter B (uppercase or lowercase) must be repeated one or more times,
and the string must end with two digits.

Answer 1

ANSWER :

$pattern = "A[\w]{3}[bB]{1,}[0-9]{2}"

A means it matches the character A literally(case sensitive)

[\w]{3} -> {3} is a quantifier means that the preceding word(or characters) matches exactly 3 times
[\w] matches any word character (equal to [a-zA-Z0-9_])

[bB]{1,} -> {1} is a quantifier that matches between one and unlimited times(as many times as possible)
[bB] matches a single character in the list bB (case sensitive)

[0-9]{2} -> {2} is a quantifier means that the preceding word(or characters) matches or must come exactly 2 times
[0-9] Matches a single digit between 0 and 9

Hope it helps... thank you:)