正则表达式用于检查 a-z' A-Z' 0-9、-、_，但不超过 5 个数字

的正则表达式是

^[a-zA-Z0-9_-]{0,5}$

它匹配最多五个字符的任意字符组合。

几种可能性：

~'A(?:[a-z_-]*[0-9]){0,5}[a-z_-]*'z(?<=.)~i

或

~'A(?!(?:.*[0-9]){6})['w-]+'z~

这两种模式假定不允许使用空字符串。

第一种模式：

~                        # pattern delimiter
'A                       # anchor for the start of the string
(?:[a-z_-]*[0-9]){0,5}   # repeat this group between 0 or 5 times (so 5 digits max)
[a-z_-]*                 # zero or more allowed characters
'z                       # end of the string
(?<=.)                   # lookbehind that checks there is at least one character
~
i                        # make the pattern case insensitive

第二种模式：

~
'A
(?!                  # negative lookahead that checks there is not
    (?:.*[0-9]){6}   # 6 digits in the string
)  
['w-]+
'z
~