Is it bad to use regex?
Regular expressions can be a good tool, but if you try apply them to every situation, you’ll be in for a world of hurt and confusion down the line. Regex isn’t suited to parse HTML because HTML isn’t a regular language. Regex probably won’t be the tool to reach for when parsing source code.
Why do people hate regular expressions?
The only reason why regular expressions (RegEx) is considered bad is because it might not be completely clear to the average programmer. However it generally does its job rather effectively. Take for example, when you want to check if the input is a number (both whole and/or decimal):
Why are regular expressions fast?
Why is that? A good indicator is that it is longer. Good regular expressions are often longer than bad regular expressions because they make use of specific characters/character classes and have more structure. This causes good regular expressions to run faster as they predict their input more accurately.
Should we use regex?
Regular expressions are useful in search and replace operations. The typical use case is to look for a sub-string that matches a pattern and replace it with something else. Most APIs using regular expressions allow you to reference capture groups from the search pattern in the replacement string.
Why is regex so slow compared to non regex?
A simple non-regex solution would be to split () each line and compare the 6th element. (Much faster: 9 microseconds per string.) The reason the regex is so slow is that the “*” quantifier is greedy by default, and so the first “.*” tries to match the whole string, and after that begins to backtrack character by character.
How are regular expressions interpreted by regular expressions engines?
Let’s see how the engine interprets quantifiers, showing performance characteristic of each one of them. Regular expressions are interpreted by regular expressions engines. Those engines may be treated as virtual machines for the language of regular expressions.
How do greedy quantifiers work in regex?
When a regex engine applies greedy quantifiers ( .* .+ ), it takes as many characters as possible. If the engine cannot match the rest of the pattern, it backtracks on the greedy operator.
Which parts of a regex pattern cause the biggest performance penalty?
It’s the repetition (\\d+I?)+ that may cause the biggest performance penalty, so we focus on the inner part of the pattern. For the sake of simplicity, we’ll stick to the most basic of the regex version with only one allowed separator (a comma) and no prefixes nor suffixes: (\\d+,?)+.