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

/
/
gs

Test String

Code Generator

Language

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "<!--(?:(?!<!--|-->).|(?R))*-->"; final String string = "Remove comments from some generated HTML which can be invalid with nested comments\n" + "==================================================================================\n\n" + "I would like to remove HTML comments from some generated content.\n" + "If I use the regex `/<!--(.*?)-->/` (ungreedy with the `?`) then it works for most cases such as this example:\n\n" + "```html\n" + "<!-- <h1> test </h1> --> not remove <!-- <h1> test 2 </h1> -->\n" + "```\n\n" + "It gets rid of the `<h1>` tags and leaves the \"*not remove*\" as desired.\n\n" + "But **if the comments are nested**, then it will not handle it properly as it will leave the last comment closing tag `'-->'`. The workaround would be to use a greedy pattern, but in this case it will not work for the first case, with multiple comments.\n\n" + "Example of nested comments (I know it's not valid HTML, but it's the backend which is generating it):\n\n" + "```html\n" + "text <!-- something <!-- <p> test </p> --> need remove -->\n" + "```\n\n" + "I've tried to find a solution, but I don't know how to solve this. Has anyone an idea how to handle it?\n\n" + "<!-- multiline\n" + "comment -->\n\n" + "<!-- <footer>Footer with\n" + " nested <!-- comment -->\n" + " on several lines.</footer>\n" + "-->"; final Pattern pattern = Pattern.compile(regex, Pattern.DOTALL); 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