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"^((a{1,4}|a?b|ba){1,3}|(a{1,3}|b){1,4}|((a{2,3}|b){2}|aaba|abaa){2})$", flags=re.MULTILINE) test_str = ("Allowed:\n" "aaaaaaaaaaaa\n" "aaaaaaaaaaa\n" "abaaaaab\n" "baaaaaba\n" "abaaaaba\n" "bbbb\n" "bababa\n" "ababab\n" "aabaabaa\n" "abaabaaa\n" "baaaaaab\n" "baaaaab\n\n" "baaaaaaaaa\n" "abaaaaaaaa\n" "aabaaaaaaa\n" "aaabaaaaaa\n" "aaaabaaaaa\n" "aaaaabaaaa\n" "aaaaaabaaa\n" "aaaaaaabaa\n" "aaaaaaaaba\n" "aaaaaaaaab\n\n" "baaaaaba\n" "abaaaaab\n" "babaaaaa\n" "ababaaaa\n" "aababaaa\n" "aaaababa\n" "aaaaabab\n\n" "baaaabaa\n" "abaaaaba\n" "aabaaaab\n" "baabaaaa\n" "abaabaaa\n" "aabaabaa\n" "aaabaaba\n\n" "baaaaba\n" "abaaaab\n" "babaaaa\n" "ababaaa\n" "aababaa\n" "aaababa\n\n" "abba\n" "abbb\n" "bababa\n" "bbaab\n" "abbab\n" "abaabb\n" "baaabaa\n" "abaaaba\n" "aabaaab\n" "baabaaa\n" "abaabaa\n" "abaabaa\n" "aabaaba\n\n" "Disallowed:\n" "aaaaaaaaaaaaa\n" "aabaabaaa\n" "aababab\n" "bbbba\n" "bbabb\n" "baaaaaaab") 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