正则表达式在大写字母前面强调

Question

I created this regexp that will add an underscore infront of all capital letters except for the first one if it's in the beginning of the string

$string = preg_replace('/(?!^)[A-Z]/', '_$0', $string);
// Hello --> Hello
// HelloHello --> Hello_Hello
// aHelloHello --> a_Hello_Hello
// HELLO --> H_E_L_L_O
// hello --> hello
// HHEllo --> H_Hello

I would like the regexp to skip all continuous capital characters at the beginning of the string:

// HHello --> HHello
// HEllO --> HEll_O
// aHEllo --> a_H_Ello
// HHHHHHHHHHellO --> HHHHHHHHHHell_O

In short: a regexp that adds an underscore infront of all capital letters but ignores all continuous capital letters from the beginning of the string.

Answer 1

Regex:

^[A-Z]+(*SKIP)(*F)|[A-Z]

Replacement string:

_$0

DEMO

If you want to done the samething in python then you need to use regex module which allows quantifiers in a lookbehind,

>>> import regex
>>> m = regex.sub(r'(?<!^[A-Z]+|^)([A-Z])', r'_\1', 'HHHHHHHHHHHHHeLLO')
>>> m
'HHHHHHHHHHHHHe_L_L_O'