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 = /(?<=^|[^_])__(((\\_)|((?![\s_])(?:(?:[^_]|_(?!_))+?)?[^\s_]))+)__(?=[^_]|$)/m str = '-- funciona __foo bar__ __f o o b a r__ **teste __lorem ipsum__ dolor sit** __teste **lorem ipsum** dolor sit__ abc__xyz__teste -- não funcionava na primeira versão __foo_bar__ __a__ __*__ __foo_*bar__ -- não é para funcionar __ foo bar__ __foo bar __ _foo__ __ foo __ _foo_ __foo_ __ __ __a____ ____a__ _____ -- corner case: aninhado (não tratei pois não sei o que deveria fazer) __abc__xyz__123__ __abc __xyz__ 123__ -- corner case: escape (chega a reconhecer alguns casos, mas não substitui "\\_" por "_" __\\___ __a\\___ __abc\\___ __\\_abc_\\__ -- errado, mas não consegui tratar' subst = '<i>\\1<\\i>' 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