问题描述：

I\'m trying to apply a regex constraint to a Symfony form input. The requirement for the input is that the start of the string and all commas must be followed by zero or more whitespace, then a # or @ symbol, except when it\'s the empty string.

As far as I can tell, there is no way to tell the constraint to use preg_match_all instead of just preg_match, but it does have the ability to negate the match. So, I need a regular expression that preg_match will NOT MATCH for the given scenario: any string containing the start of the string or a comma, followed by zero or more whitespace, followed by any character that is not a # or @ and is not the end of the string, but will match for everything else. Here are a few examples:

preg_match(..., \'\');              // No match
preg_match(..., \'#yolo\');         // No match
preg_match(..., \'#yolo,  #swag\'); // No match
preg_match(..., \'#yolo,@swag\');   // No match
preg_match(..., \'#yolo, @swag,\'); // No match
preg_match(..., \'yolo\');        // Match
preg_match(..., \'swag,#yolo\');  // Match
preg_match(..., \'@swag, yolo\'); // Match

I would\'ve thought for sure that /(^|,)\\s*[^@#]/ would work, but it\'s failing in every case with 1 or more spaces and it appears to be because of the asterisk. If I get rid of the asterisk, preg_match(\'/(^|,)\\s[^@#]/\', \'#yolo, @swag\') does not match (as desired) when there\'s exactly once space, but as as soon as I reintroduce the asterisk it breaks for any quantity of spaces > 0.

My theory is that the regex engine is interpreting the second space as a character that is not in the character set [@#], but that\'s just a theory and I don\'t know what to do about it. I know that I could create a custom constraint to use preg_match_all instead to get around this, but I\'d like to avoid that if possible.

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感谢您的意见，我们尽快改进~

功能建议

我正在尝试将正则表达式约束应用于Symfony表单输入。 对输入的要求是字符串的开头和所有逗号必须后跟零或更多的空格，然后是＃</ code>或 @ </ code>符号，除非它是空的 字符串。</ p>

据我所知，没有办法告诉约束使用 preg_match_all </ code>而不仅仅是 preg_match </ code>， 但它确实有能力否定比赛。 所以，我需要一个正则表达式 preg_match </ code>将不匹配给定的场景：包含字符串开头或逗号的任何字符串，后跟零个或多个空格，后跟任何字符 这不是＃或@并且不是字符串</ code>的结尾，但会匹配其他所有内容。 以下是一些示例：</ p>

  preg_match（...，\'\'）;  //没有匹配
preg_match（...，\'＃yolo\'）;  //没有匹配
preg_match（...，\'＃yolo，＃swag\'）;  //没有比赛
preg_match（...，\'＃yolo，@ swag\'）;  //没有匹配
preg_match（...，\'＃yolo，@ swag，\'）;  //没有匹配
preg_match（...，\'yolo\'）;  //匹配
npreg_match（...，\'swag，＃yolo\'）;  //匹配
preg_match（...，\'@ swag，yolo\'）;  //匹配
</ code> </ pre> 
我肯定会想到 /（^ |，）\\ s * [^ @＃] / </ code> 会工作，但它在每种情况下失败，有一个或多个空格，它似乎是因为星号。 如果我摆脱了星号， preg_match（\'/（^ |，）\\ s [^ @＃] /\'，\'＃yolo，@ swag\'）</ code>与（当需要时）不匹配 那里只有一次空间，但是当我重新引入星号时，它会打破任何数量的空间＆gt;  0。</ p> 
我的理论是正则表达式引擎将第二个空格解释为不在字符集 [@＃] </ code>中的字符，但这只是 一个理论，我不知道该怎么做。 我知道我可以使用 preg_match_all </ code>创建一个自定义约束来解决这个问题，但是如果可能的话我想避免这种情况。</ p> 
</ div> 
网友观点：
You may use
\'~(?:^|,)\\s*+[^#@]~\'
Here, the + symbol defines a *+ possessive quantifier matching 0 or more occurrences of whitespace chars, and disallowing the regex engine to backtrack into \\s* pattern if [^@#] cannot match the subsequent char.
See the regex demo.
Details
(?:^|,) - either start of string or ,
\\s*+ - zero or more whitespace chars, possessively matched (i.e. if the next char is not matched with [^#@] pattern, the whole pattern match will fail)
[^@#] - a negated character class matching any char but @ and #.
PHP正则表达式核心技术完全详解 第4节 php正则查找匹配处理函数使用技巧与学习心得
作者：极客小俊  一个专注于web技术的80后
我不用拼过聪明人，我只需要拼过那些懒人 我就一定会超越大部分人!
知乎@极客小俊，官方首发原创文章
Bilibili: 极客小俊GeekerJun


在我们说php系统自带的正则处理函数之前，我们先要回忆一下在PHP中正则表达式的组成元素有哪些? 如下:
定界符号
原子
元字符、量词
模式修正符
例如:一个匹配URL的正则表达式如下