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A dot . in a regular expression matches any single character. In order for regex to match a dot, the dot has to be escaped: \.
It has been pointed out to me that inside square brackets [] a dot does not have to be escaped. For example, the expression:
[.]{3} would match ... string.
Doesn't it, really? And if so, is it true for all regex standards?
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(dot) metacharacter, and can match any single character (letter, digit, whitespace, everything). You may notice that this actually overrides the matching of the period character, so in order to specifically match a period, you need to escape the dot by using a slash \. accordingly.
Operators: * , + , ? , | Anchors: ^ , $ Others: . , \ In order to use a literal ^ at the start or a literal $ at the end of a regex, the character must be escaped.
in regex is a metacharacter, it is used to match any character. To match a literal dot in a raw Python string ( r"" or r'' ), you need to escape it, so r"\." Unless the regular expression is stored inside a regular python string, in which case you need to use a double \ ( \\ ) instead.
If you want the dot or other characters with a special meaning in regexes to be a normal character, you have to escape it with a backslash. Since regexes in Java are normal Java strings, you need to escape the backslash itself, so you need two backslashes e.g. \\.
In a character class (square brackets) any character except ^, -, ] or \ is a literal.
This website is a brilliant reference and has lots of info on the nuances of different regex flavours. http://www.regular-expressions.info/refcharclass.html
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