To match a string that contains only those characters (or an empty string), try This works for .NET regular expressions, and probably a lot of other languages as well. Breaking it down: If you don’t want to allow empty strings, use + instead of *. As others have pointed out, some regex languages have a shorthand form … Read more
Works that way. The expression contains non-latin characters, so it usually fails. You’ve got to decode into Unicode and use re.U (Unicode) flag. I’m a beginner too and I faced that issue a couple of times myself.
will match a single character that is NOT a digit or whitespace. will match a single character that IS a non-digit or non-whitespace. Since every character is either not a digit or not whitespace, the second regex will match any character. It’s equivalent to the difference between: and Note that the following would be equivalent … Read more
I would like to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores.
I managed to figure out this solution: omit group() for the situation where the searchbox reply is “No results” and thus doesn’t match the Regex.
Assuming you want the whole regex to ignore case, you should look for the i flag. Nearly all regex engines support it: Check the documentation for your language/platform/tool to find how the matching modes are specified. If you want only part of the regex to be case insensitive (as my original answer presumed), then you … Read more
I think this is what you want: I’ve used the -P switch to get perl regex.
The fully RFC 822 compliant regex is inefficient and obscure because of its length. Fortunately, RFC 822 was superseded twice and the current specification for email addresses is RFC 5322. RFC 5322 leads to a regex that can be understood if studied for a few minutes and is efficient enough for actual use. One RFC 5322 compliant regex … Read more
\t is not equivalent to \s+, but \s+ should match a tab (\t). The problem in your example is that the second pattern \s\s+ is looking for two or more whitespace characters, and \t is only one whitespace character. Here are some examples that should help you understand: \s\s+ would also match ‘ \t’, ‘\n\t’, ‘ \n \t \t\n’. Also, \s\s* is equivalent to \s+. Both will match one or more whitespace … Read more
What does /\S/ mean in a regex?