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

const regex = /\b(?![1-4](?:\.\d+)?px)(?<!(?<!\S)\.)(\d*)(\d)(?:\.(\d+))?px\b/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('\\b(?![1-4](?:\\.\\d+)?px)(?<!(?<!\\S)\\.)(\\d*)(\\d)(?:\\.(\\d+))?px\\b', 'gm') const str = `font-size: 10px; border: 0px; margin-top: 4px; // dont touch margin-bottom: 12px; margin-right: 50%; margin-left: -12px; padding-left: 120px; padding-right: 8px; border-radius: calc(50% - 1px); // dont touch grid-template-columns: 1fr 44px 1fr; margin-top: 36.4px; border-width: 10.5px; border-width: .3px; // dont touch border-width: .6px; // dont touch border-width: 3.3px; // dont touch border-width: 6.6px 4px 8000px .34px; margin-left: -1px; // dont touch`; const subst = `$1.$2$3rem`; // 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