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

/
/
gmix

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

const regex = /((?:[ -$&(-[\]-~]|([%'\\])\2)*(%(\d+\$)?[-+\s0#]?(\d+|\*)?(\.\d+)?[bt]?[diuoxXfeEgGcs]+)+(?:(?!(?:[ -$&(-[\]-~]|([%'\\])\7)*(?:%(?:\d+\$)?[-+\s0#]?(?:\d+|\*)?(?:\.\d+)?[bt]?[diuoxXfeEgGcs]+)+)(?:[ -$&(-[\]-~]|([%'\\])\8)*)?) /gmi; // Alternative syntax using RegExp constructor // const regex = new RegExp('((?:[ -$&(-[\\]-~]|([%\'\\\\])\\2)*(%(\\d+\\$)?[-+\\s0#]?(\\d+|\\*)?(\\.\\d+)?[bt]?[diuoxXfeEgGcs]+)+(?:(?!(?:[ -$&(-[\\]-~]|([%\'\\\\])\\7)*(?:%(?:\\d+\\$)?[-+\\s0#]?(?:\\d+|\\*)?(?:\\.\\d+)?[bt]?[diuoxXfeEgGcs]+)+)(?:[ -$&(-[\\]-~]|([%\'\\\\])\\8)*)?) ', 'gmi') const str = `Color %s, we are looking for %%02droids %% number1 %d, number2 %05d, hex %#x, float %5.2f, unsigned value %u. I wanted to also add the ability to capture "any printable text characters besides %, ' and \\, unless these characters appear exactly twice". This needs to be captured both before the initial % and after the conversion character. any printable character: [ -~] besides %, ' and \\: (?![\\\\%']) these characters appear exactly twice: ( §§§§ |'{2}|\\\\{2}|%{2}) (§ = placeholder) I am having a problem with the "unless", that is, getting the negative look-ahead to discard single occurrences but allow double occurrences of the specified characters. Color %s, number1 %d, number2 %05d, hex %#x, float %5.2f, unsigned value %u. | | | | | | |`; const subst = `IMAGE REMOVED FROM CHROME\r\n`; // The substituted value will be contained in the result variable const result = str.replace(regex, subst); console.log('Substitution result: ', 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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions