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
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"^(?=.{1,39}$)^[a-zA-Z\d]+(?:-[a-zA-Z\d]+)*$", flags=re.MULTILINE) test_str = ("-username\n" "_username_\n" "__us_ername\n" "us_er\n" "username-\n" "1user--name\n" "132uname-\n" "-uname1234\n" "-username-\n" "user--name\n" "av34axc-\n" "1234567890A1234567890B1234567890C1234567890D\n\n" "Username\n" "a-a\n" "aBc\n" "BaC\n" "1-1\n" "1-2-3-4\n" "q-1-2-3\n" "q-q-q-q-q\n" "username\n" "123username123\n" "username3123\n" "1234\n" "user-name\n" "13-13\n" "q1-q2-q3\n" "a\n" "A\n" "1234567890A1234567890B1234567890C123456\n" "1234567890A123456-7890B1234567890C12345") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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