What is bad regex?
What you call an “evil” regex is a regex that exhibits catastrophic backtracking. The linked page (which I wrote) explains the concept in detail. Basically, catastrophic backtracking happens when a regex fails to match and different permutations of the same regex can find a partial match.
Is it safe to use regex?
An attacker can then cause a program using a Regular Expression to enter these extreme situations and then hang for a very long time. Specifically with preg_match there is a known issue that can cause a PHP Segmentation Fault. So the answer is no, it is not safe because of issues such as these.
What is the most accurate description of a regular expression C#?
In C#, Regular Expression is a pattern which is used to parse and check whether the given input text is matching with the given pattern or not. In C#, Regular Expressions are generally termed as C# Regex. The . Net Framework provides a regular expression engine that allows the pattern matching.
Is regex frowned upon?
Not only it is a bad idea in general to implement it, but you may be tempted to do it using regular expressions, and you’ll do it wrong. There are plenty of ways an human can write a word, a number, a sentence and will be understood by another human, but not your regular expression.
What does it mean when regex does not contain certain characters?
Where [<>] means any of < or > and [^<>] means any that is not of < or >. And of course the mandatory link. Thanks for contributing an answer to Stack Overflow!
Can you match any character with regex dot?
Match any character using regex ‘.’ character will match any character without regard to what character it is. The matched character can be an alphabet, number of any special character. By default, period/dot character only matches a single character.
Is it possible to avoid an evil regex?
You may not always be able to avoid these types of regexes, but if your regex engine is built right, then it is less of a problem. See this blog series for a great deal of information on the topic of regex engines. Note the caveat at the bottom of the article, in that backtracking is an NP-Complete problem.
Can a regex match only one uppercase character?
Matches only a single uppercase character in range from ‘A’ to ‘Z’. Matches only a single character in range from ‘a’ to ‘z’, case-insensitive. Matches only a single number in range from ‘0’ to ‘9’.