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

Substitution

Processing...

Code Generator

Language

Generated Code

re = /(?:^|\b)(?<number>(?:\d+|\d{1,3}(?:,\d{3})+)(?:\.\d+)?)(?<replace> ?|&[^;]{2,7};)(?<dimensions>(?<mathjax>\$[^\n\$]+\$)|(?<unit>(?<si>(?!as)(?:[QRYZEPTGMkhdcmµnpfazyrq]|da)?(?:mol|cd|Hz|Pa|Wb|lm|lx|Bq|Gy|Sv|kat|[mgsAKNJWCVFΩSTHL]))|(?<imperial>mil|P|in|ft|yd|mi|le|ftm|nmi|oz|lbs?|t|tsp|tbsp|c|fl oz|pt|qt|gal|(?:sq|cu) ?(?:in|ft|yd|mi)|ft-lbf?|lbf?-ft|deg|Btu|psi|Ly)|(?<common>mph|kph|rad|sr)|(?<binary>(?:(?:[KMGTPEZY])i?)?B)))(?=\b|$| |[.,:;()\[\]{}=\/*+—–-])/m str = 'I have a 30 $m^2$ pumpernickle More precisely it\'s 29.87$m^2$. Traveling over 4,000 km, to where once there was ...in the year 2016 as a new method of... He crashed at 50mph They collided at speeds of over 200m/s The reading is 2kHz. The range is 20kHz–1MHz (1,000.3 kHz). Just 4M words at 30MB.' subst = '$<number>&#x202f;$<dimensions>' 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