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

r"
"
gm

Test String

Substitution

Processing...

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 = "(?:^ *(?:/\\*\\*[^/\\n]*\\r?\\n(?:[^/\\n]*\\r?\\n)*[^/\\n]*\\*/ *|//.*)\\r?\\n)+(?: *[\\r?\\n])*#ifdef BUILD_FLAG\\r?\\n[\\s\\S]*?^#endif\\r?\\n"; final String string = " Code here\n" + " and here\n\n" + "//this is s comment block\n" + "/**\n" + "*and a nested comment block\n" + "*/\n\n" + "//-----------------------------------------------------------------------------\n" + "// this comment block should not be captured\n" + "//-----------------------------------------------------------------------------\n\n" + "//-----------------------------------------------------------------------------\n" + "// this whole comment block and the conditional block below should be captured\n" + "//-----------------------------------------------------------------------------\n" + "/**\n" + " * @brief Some comment \n" + " * \n" + " xxxxx\n" + " * @return \n" + " */\n" + "//-----------------------------------------------------------------------------\n" + "#ifdef BUILD_FLAG\n" + "...\n" + "#endif\n\n" + " More code\n" + "More code\n\n" + "//---------------------------------------------------------\n" + "// this whole comment block and the conditional block below should be captured\n" + "// --------------------------------------------------------\n" + "#ifdef BUILD_FLAG\n" + "...\n" + "#endif\n\n" + "More code\n\n" + " //-------------------------------------------------------------------------\n" + " /**\n" + " * @name this whole block comment should be captured.\n" + " * @{\n" + " */\n\n" + "#ifdef BUILD_FLAG\n" + "...\n" + "#endif\n"; final String subst = ""; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); final Matcher matcher = pattern.matcher(string); // The substituted value will be contained in the result variable final String result = matcher.replaceAll(subst); System.out.println("Substitution result: " + result); } }

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