仅包含字母数字字符和下划线的正则表达式，以字母字符开头

Question

我正在尝试验证 Firebase 事件名称:

Event names can be up to 40 characters long, may only contain alphanumeric characters and underscores ("_"), and must start with an alphabetic character.

无效:

• 4foo(以数字开头)
• foo bar(包含一个空格)
• foo$@bar(包含特殊字符)

有效:

• foo
• foo_bar
• Foo_Bar

我试过 \d?[^A-Za-z0-9_]+ 如果有任何特殊字符和空格，它会匹配，但它不会匹配带有数字字符的字符串开始。

Answer 1

使用

^[A-Za-z][A-Za-z0-9_]{0,39}$

参见 regex proof .

同义词:

^[A-Za-z]\w{0,39}$
^\p{L}\w{0,39}$
^[[:alpha:]]\w{0,39}$

解释

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  [A-Za-z]                 any character of: 'A' to 'Z', 'a' to 'z'
--------------------------------------------------------------------------------
  [A-Za-z0-9_]{0,39}       any character of: 'A' to 'Z', 'a' to 'z',
                           '0' to '9', '_' (between 0 and 39 times
                           (matching the most amount possible))
--------------------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string