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-z\d](-?[a-z\d]){0,62})\.)*(([a-z\d](-?[a-z\d]){0,62})\.)([a-z](-?[a-z\d]){1,62})|((\d{1,3}\.){3}\d{1,3}))$", flags=re.MULTILINE) test_str = ("// Valid\n" "a-a.domain.com\n" "1a.domain.com\n" "a1.domain.com\n" "a.domain.com\n" "domain.com\n" "10.10.10.11\n" "// Invalid\n" "-a.domain.com\n" "a-.domain.com\n\n" "// Valid\n" "cname.do-main.com\n" "cname.1domain.com\n" "cname.domain1.com\n" "// Invalid\n" "cname.-domain.com\n" "cname.domain-.com\n\n" "// Valid\n" "cname.domain.tld\n" "cname.domain.co\n" "cname.domain.tld1\n" "cname.domain.tld-1\n" "// Invalid\n" "cname.domain.1tld\n" "cname.domain.tld-\n" "cname.domain.-tld") 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