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

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 = "^rgba?\\((?:\\s+)?(?<r>\\d+(?<unit>%?))(?:\\s+)?(?<separator>[\\s|,])(?:\\s+)?(?<g>\\d+\\k<unit>)(?:\\s+)?\\k<separator>(?:\\s+)?(?<b>\\d+\\k<unit>)(?:\\s+)?(?:(?<=(?:,.+))(?:,(?:\\s+)?(?<a>(?:\\d+)?(?:\\.?\\d+)))?(?:\\s+)?)?\\)$"; final String string = "// Valid\n" + "rgb(120 , 42 , 55)\n" + "rgb(23%, 100%, 0%)\n" + "rgb(120 42 55)\n" + "rgb(23% 100% 0%)\n" + "rgb(0 0 0)\n" + "rgba(23, 53, 0)\n\n" + "// Invalid\n" + "rgb(255, 120 0)\n" + "rgb(100% 32 75)\n\n" + "// When an alpha channel is defined, separator must be comma (not sure why but you can try it in browser to see for yourself)\n\n" + "// Valid\n" + "rgb(255, 255, 255, 1)\n" + "rgb(255, 255, 255, .643)\n" + "rgb(255, 255, 255, 1.324 )\n" + "rgba(255, 255, 255, 1)\n" + "rgba(255, 255, 255, .643)\n" + "rgba(255, 255, 255, 1.324 )\n\n" + "// Invalid\n" + "rgb(255, 255, 255, )\n" + "rgb(255, 255, 255, .)\n" + "rgba(255 255 255 1)\n" + "rgba(255 255 255, 1)"; 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