Regex: Is the string starting with capital letter (not only in A-Z)?

Question

How can I check if a string starts with a capital letter, in cases where the first letter might not be in A-Z range but from other languages also AND simultaneously if the first character is not a number?

examples:

"This is string" - match
"this is string" - not match
"5 not good" - not match
"Увеличи starts capital" - match
"мащабиране no capital" - not match

in php:

if (preg_math('/??/i', $str) ) {
  echo 'yeeee haaa';
}

Answer 1

Use this regex:

preg_match('#^\p{Lu}#u', $str)

\p{Lu} will match any character that has Unicode character property of uppercase letter.

Demo on regex101 (please ignore the flags m and g, they are for demonstration purpose only)

When you are dealing with a Unicode string (or more specifically, in the case of preg_ functions, the Unicode string must be in UTF-8 encoding), you must always use the u flag to make the engine treat the input string and the pattern with character semantics. Otherwise, by default, preg_ functions treat the pattern and input string as an array of bytes and produce an unexpected result for characters outside the ASCII range.