问题描述
"\\w+@\\w+[.]\\w+"和"^\\w+@\\w+[.]\\w+$"有什么区别?我已经尝试过用Google搜索它，但是没有运气.
What is the difference between "\\w+@\\w+[.]\\w+" and "^\\w+@\\w+[.]\\w+$"? I have tried to google for it but no luck.
推荐答案
^的意思是匹配字符串的开头"(更确切地说，是 position 在字符串的第一个字符之前，因此它与实际字符不匹配.
^ means "Match the start of the string" (more exactly, the position before the first character in the string, so it does not match an actual character).
$的意思是匹配字符串的末尾"(字符串中最后一个字符之后的位置).
$ means "Match the end of the string" (the position after the last character in the string).
两者都称为锚，并确保整个字符串都匹配，而不是仅匹配子字符串.
Both are called anchors and ensure that the entire string is matched instead of just a substring.
因此，在您的示例中，第一个正则表达式将报告[email protected]的匹配项，但匹配的文本将为[email protected]，可能不是您期望的.第二个正则表达式将完全失败.
So in your example, the first regex will report a match on [email protected], but the matched text will be [email protected], probably not what you expected. The second regex will simply fail.
请注意，因为某些正则表达式实现将正则表达式隐式地锚定在字符串的开头/结尾(例如，如果使用的话，例如Java的.matches()).
Be careful, as some regex implementations implicitly anchor the regex at the start/end of the string (for example Java's .matches(), if you're using that).
如果设置了多行选项(例如，使用(?m)标志或通过执行Pattern.compile("^\\w+@\\w+[.]\\w+$", Pattern.MULTILINE))，则^和$也会在行的开头和结尾匹配.
If the multiline option is set (using the (?m) flag, for example, or by doing Pattern.compile("^\\w+@\\w+[.]\\w+$", Pattern.MULTILINE)), then ^ and $ also match at the start and end of a line.
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