¿Cómo creo una expresión regular en línea?

How do I create an online regex?

RegExr is an online tool to learn, build, & test Regular Expressions (RegEx / RegExp).

1. Supports JavaScript & PHP/PCRE RegEx.
2. Results update in real-time as you type.
3. Roll over a match or expression for details.
4. Validate patterns with suites of Tests.
5. Save & share expressions with others.

Method to prove that a language L is not regular

1. At first, we have to assume that L is regular.
2. So, the pumping lemma should hold for L.
3. Use the pumping lemma to obtain a contradiction − Select w such that |w| ≥ c. Select y such that |y| ≥ 1. Select x such that |xy| ≤ c. Assign the remaining string to z.

Learning Regular Expressions. The best way to learn regular expressions is to give the examples a try yourself, then modify them slightly to test your understanding. It is common to make mistakes in your patterns while you are learning. When this happens typically every line will be matched or no lines will be matched or some obscure set.

A regular expression, regex or regexp (sometimes called a rational expression) is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for “find” or “find and replace” operations on strings, or for input validation.

You’ll find that regular expressions are used in three different ways: Regular text match, search and replace and splitting. The latter is basicly the same as the reverse match i.e. everything the regular expression did not match.

A regular expression (or “regex”) is a search pattern used for matching one or more characters within a string. It can match specific characters, wildcards, and ranges of characters. Regular expressions were originally used by Unix utilities, such as vi and grep.