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There are lots of posts about regexs to match a potentially empty string, but I couldn't readily find any which provided a regex which only matched an empty string.
I know that ^ will match the beginning of any line and $ will match the end of any line as well as the end of the string. As such, /^$/ matches far more than the empty string such as "\n", "foobar\n\n", etc.
I would have thought, though, that /\A\Z/ would match just the empty string, since \A matches the beginning of the string and \Z matches the end of the string. However, my testing shows that /\A\Z/ will also match "\n". Why is that?
577
regex is not empty string.
An empty regular expression matches everything. > var empty = new RegExp(""); > empty.test("abc") true > empty.test("") true As you probably know, you should only use the RegExp constructor when you are dynamically creating a regular expression.
Find Whitespace Using Regular Expressions in Java The most common regex character to find whitespaces are \s and \s+ . The difference between these regex characters is that \s represents a single whitespace character while \s+ represents multiple whitespaces in a string.
I would use a negative lookahead for any character:
^(?![\s\S]) This can only match if the input is totally empty, because the character class will match any character, including any of the various newline characters.
174
It's as simple as the following. Many of the other answers aren't understood by the RE2 dialect used by C and golang.
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