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 single character of: a, b, c or d
    [[ab][cd]]
  • 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

import re regex = re.compile(r"(?=(?:....)*$)") test_str = ("<html>\n" "<head>\n" "<title>Credit Card Test</title>\n" "</head>\n\n" "<body>\n" "<h1>Credit Card Test</h1>\n\n" "<form>\n" "<p>Please enter your credit card number:</p>\n\n" "<p><input type=\"text\" size=\"20\" name=\"cardnumber\"\n" " onkeyup=\"validatecardnumber(this.value)\"></p>\n\n" "<p id=\"notice\">(no card number entered)</p>\n" "</form>\n\n" "<script>\n" "function validatecardnumber(cardnumber) {\n" " // Strip spaces and dashes\n" " cardnumber = cardnumber.replace(/[ -]/g, '');\n" " // See if the card is valid\n" " // The regex will capture the number in one of the capturing groups\n" " var match = /^(?:(4[0-9]{12}(?:[0-9]{3})?)|(5[1-5][0-9]{14})|↵\n" "(6(?:011|5[0-9]{2})[0-9]{12})|(3[47][0-9]{13})|(3(?:0[0-5]|[68][0-9])↵\n" "[0-9]{11})|((?:2131|1800|35[0-9]{3})[0-9]{11}))$/.exec(cardnumber);\n" " if (match) {\n" " // List of card types, in the same order as the regex capturing groups\n" " var types = ['Visa', 'MasterCard', 'Discover', 'American Express',\n" " 'Diners Club', 'JCB'];\n" " // Find the capturing group that matched\n" " // Skip the zeroth element of the match array (the overall match)\n" " for (var i = 1; i < match.length; i++) {\n" " if (match[i]) {\n" " // Display the card type for that group\n" " document.getElementById('notice').innerHTML = types[i - 1];\n" " break;\n" " }\n" " }\n" " } else {\n" " document.getElementById('notice').innerHTML = '(invalid card number)';\n" " }\n" "}\n" "</script>\n" "</body>\n" "</html>\n") subst = "-" result = regex.sub(subst, test_str) if result: print(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 Python, please visit: https://docs.python.org/3/library/re.html