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]
  • Character class intersection
    [\w&&[^\d]]
  • 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

const regex = /(?<=(?:[^\d]|^))(\d{4}[ \t])(?:\d{4}[ \t]){2}(\d{4})(?=(?:[^\d]|$))/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<=(?:[^\\d]|^))(\\d{4}[ \\t])(?:\\d{4}[ \\t]){2}(\\d{4})(?=(?:[^\\d]|$))', 'gm') const str = `1234 1234 1234 1234 1234 5678 9101 1121 1234 84848 5454 4888 1111 2222 5555 4444 1111 2222 5555 44444 11111 2222 5555 4444 asa1111 2222 5555 4444dasda Вчера вечером со счета номер 4301 0234 2145 2140 был совершен перевод на счет 5042 2012 0532 2043 в размере \${payment_amount} рублей `; const subst = `$1 **** **** $2`; // 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