不包含连续字符的正则表达式 [英] Regex for not containing consecutive characters

问题描述

我想不出满足所有这些要求的 javascript 正则表达式:

I can't figure out javascript regex that would satisfy all those requirements:

字符串只能包含下划线和字母数字字符.必须以字母开头，不能包含空格，不能以下划线结尾，并且不能包含两个连续的下划线.

这是我来的，但不包含连续的下划线"部分是最难添加的.

This is as far as I came, but 'not containing consecutive underscores' part is the hardest to add.

^[a-zA-Z][a-zA-Z0-9_]+[a-zA-Z0-9]$

推荐答案

您可以使用多个前瞻(在本例中为否定的):

You could use multiple lookaheads (neg. ones in this case):

^(?!.*__)(?!.*_$)[A-Za-z]\w*$

请参阅 regex101.com 上的演示.<小时>分解为:

See a demo on regex101.com.

---

Broken down this says:

^           # start of the line
(?!.*__)    # neg. lookahead, no two consecutive underscores (edit 5/31/20: removed extra Kleene star)
(?!.*_$)    # not an underscore right at the end
[A-Za-z]\w* # letter, followed by 0+ alphanumeric characters
$           # the end

<小时>作为 JavaScript 片段:

let strings = ['somestring', '_not_this_one', 'thisone_', 'neither this one', 'but_this_one', 'this__one_not', 'this_one__yes']

var re = /^(?!.*__)(?!.*_$)[A-Za-z]\w*$/;
strings.forEach(function(string) {
    console.log(re.test(string));
});

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