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
Processing...

Test String

Substitution
Processing...

Code Generator

Language

Generated Code

re = /\b(?<!X-MAS\s)TREE\b/ str = 'X-MAS TREE //this sentence should be excluded BLA BLA TREE //this sentence should be recognized XMAS TREE X-MASTREE X-TREE X-MASTREE How to exclude "X-MAS TREE"? Because all of those regex, will be replace with "X-MAS TREE" If I search with keyword "TREE", it will be infinite loop, because "X-MAS TREE" has "TREE" I tried with this combination, but not working: \\b(XMAS TREE|X\\-MASTREE|X\\-TREE|TREE|(?!X\\-MAS TREE)\\b \\b(XMAS TREE|X\\-MASTREE|X\\-TREE|(?!X\\-MAS \\s)TREE)\\b \\b(XMAS TREE|X\\-MASTREE|X\\-TREE|((?!X\\-MAS )|\\w*)TREE)\\b \\b(XMAS TREE|X\\-MASTREE|X\\-TREE|(?:(?!X\\-MAS) )TREE)\\b' subst = 'X-MAS TREE' result = str.gsub(re, subst) # Print the result of the substitution puts 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 Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html