\W – matches any non-word (that is non-alphanumeric) character and is shorthand for.\D – matches any non-digit and is the same as.\s – matches any white space character.\w – matches any alphanumeric character which could be a letter, a digit, or an underscore.\d – matches any decimal digit and is shorthand for.In addition to the metacharacters we have looked at, here are some of the most commonly used ones: Search for a stand-alone word that begins and end with the pattern wardĬonsole.log(text3.match(regexPattern3)) // Output: Search for a word that ends with the pattern wardĬonsole.log(text2.match(regexPattern2)) // Output: Search for a word that begins with the pattern wardĬonsole.log(text1.match(regexPattern1)) // Output: The word is matched according to the position of the metacharacter. \b matches the start or end of a word.You use the metacharacters b and B to assert a word boundary. You can think of them as a word-based version of ^ and $. Word Boundaries are metacharacters that match the start and end position of a word – a sequence of alphanumeric characters. Note that anchors characters ^ and $ match just the position of the characters in the pattern and not the actual characters themselves. For example:Ĭonsole.log(regexPattern.test('The mouse and the cat')) // Output: trueĬonsole.log(regexPattern.test('The cat and mouse')) // Output: false $ matches the end of a line and anchors a literal at the end of that line.Without the ^ in the pattern, the output will return trueĬonsole.log(regexPattern2.test('The cat and mouse')) // Output: true For example:Ĭonsole.log(regexPattern1.test('cat and mouse')) // Output: trueĬonsole.log(regexPattern1.test('The cat and mouse')) // Output: false because the line does not start with cat ^ matches the start of a line and anchors a literal at the beginning of that line.You use them to assert where a boundary should be. Anchors and Boundaries:Īnchors are metacharacters that match the start and end of a line of text they are examining. Let's take a look at each subgroup and the characters that go with them. These characters fit into different subgroups that perform similar functions. Using special characters, you can do more than just find a direct match.įor example, if you want to match a character in a string that may or may not appear once or multiple times, you can do this with special characters. How to Use Regular Expression Special CharactersĪ special character in a regular expression is a character with a reserved meaning. One way to solve this could be: function isPattern(userInput) `, 'gi') Ĭonsole.log(str.match(regExpConst)) // Output: Here's a scenario: you want to verify that the telephone number entered by a user on a form matches a format, say, #-#-# (where # represents a number). With regular expressions, you can do things like find and replace text, verify that input data follows the format required, and and other similar things. Regular expressions are patterns that allow you to describe, match, or parse text. Let’s get to it! What Are Regular Expressions? In this article, you will learn about the fundamentals of regular expressions, regular expression pattern notation, how you can interpret a simple regex pattern, and how to write your own regex pattern. Knowing how to solve problems using regex is helpful to you as a developer and improves your productivity. They are key to efficient text processing. This usually complicates developers.Regular expressions (regex) are a useful programming tool. The single-line and multiline modes set up by the flags s and m respectively, have nothing to do with one another. Why would a flag do something that's already there by default? In fact, treating a string as a sequence of multiple lines of characters is the default behavior of a regular expression. To many of you, multiline mode would seem to be the opposite of this - a given test string is treated as a sequence of multiple lines of characters. In the previous section, we saw how the s flag serves to put a regular expression into single line mode, where a given test string is treated as one single line of characters. But with the m flag in place, they instead do this for every line in the string. The flag m stands for multiline mode and serves to make the boundary tokens ^ and $ match the beginning and end of each line.īy default, the ^ and $ characters in an expression match the beginning and ending boundaries of a given test string.
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