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"
"
mg

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 = "^(?:\\t| )*(?:#|%|;|//|--|REM|C|!) (?:#{64} (.*)|#{32} (.*)|#{16} (.*)|#{8} (.*)|#{4} (.*)|#{2} (.*))$"; final String string = "Valid comments that start with \"#\":\n\n" + "# ################################################################ First Level\n" + "# ################################ Second Level\n" + "# ################ Third level\n" + "# ######## Fourth Level\n" + "# #### Fifth level\n" + "# ## Sixth level\n\n" + "Valid comments that start with different characters:\n\n" + "// ################################################################ 1st Level\n" + "; ################################ 2nd Level\n" + "REM ################ 3rd level\n" + "C ######## 4th Level\n" + "% #### 5th level\n" + "-- ## 6th level\n\n" + "Valid comments that start with spaces or tabs:\n" + " # ################################################################ 1st level\n" + " ; ################################ 2nd Level\n\n" + "Invalid comments:\n\n" + "################################################################ No initial character\n" + "; ################################################ Hashes not a power of 2\n" + "@ ################ Character not recognized\n" + "C ########No space after hashes\n" + "% %%%%%%%% No hashes\n" + ". # #### Period before spaces\n" + " ;#### No space after character"; 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