Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
gm

Test String

Code Generator

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(\\*\\*NOTE\\*\\*: )_([^_]*)_\\n"; final String string = "JavaScript run in the browser has one set of rules when run in a\n" + "browser, and another set when run outside a browser. If you are using\n" + "JavaScript primarily to write client side scripts meant to be run in a\n" + "browser, then it is best to learn JavaScript, and develop JavaScript,\n" + "under that scenario. It is true that there are legitimate and important\n" + "ways to run JavaScript from outside the browser. For instance, you can\n" + "run JavaScript from the command prompt, or directly from inside some\n" + "IDEs. At first, however, such stratagems can lead to much confusion. As\n" + "a result, I suggest that you begin by developing JavaScript inside a\n" + "browser.\n\n" + "**NOTE**: _I should probably qualify what I say above. The basic syntax\n" + "of the language does not change when you switch from a browser to some\n" + "environment. (The only exception, of course, is when a browser has a\n" + "buggy implementation of JavaScript, and that still happens quite\n" + "frequently.) But even when everything works correctly, certain key\n" + "features of the language, such as the **this** keyword, have a\n" + "different significance inside a browser and outside a browser. Also, key\n" + "elements of the API, such as the **alert** function, are available in a\n" + "browser and not outside a browser. These and other differences become\n" + "manageable when you gain proficiency in the language, but at first, it\n" + "is best to avoid such subtle pitfalls by running JavaScript in the\n" + "environment in which you intend to use it. Of course, if you are\n" + "intending to write mostly server side JavaScript with **nodejs**, then\n" + "this advice is less convincing. I don't not think there are serious\n" + "disadvantages to learning JavaScript in a browser even if you want to\n" + "use it on the server side, but you will find that there are differences.\n" + "In general, I think it is easier to move from the browser to **nodejs**,\n" + "than it is to move from **nodejs** to the quirky world of browsers._\n\n" + "It turns out that the code you saw in the previous section provides a\n" + "good framework for beginning and intermediate level JavaScript\n" + "programmers who want to learn more about the langauge. Start out by\n" + "opening up code similar to what you see in Listing 3 and 4. As a matter\n" + "of fact, you can simply reuse VerySimple.html over and over again. As we\n" + "explore the JavaScript language, all you need do is change the name of\n" + "the JavaScript file that you are linking in. For instance, linking\n" + "VerySimple01.js for one program, then VerySimple02.js for the next\n" + "program. Better yet, follow best practices and rename each JavaScript\n" + "file to reflect its contents. For instance, ExploringLoops.js would be a\n" + "good name for a JavaScript file that you created when you wanted to\n" + "learn about how loops are written in JavaScript."; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html