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

Code Generator

Language

Generated Code

import re regex = re.compile(r"(err\s*?\d{1})|[^\d]\s+(\d{3})(?:$|\s+(?!\d))", flags=re.MULTILINE | re.IGNORECASE) test_str = ("The below items should match:\n" "-----------------------------\n" "123\n" "456 123\n" "123 324 324\n" "Match the number in this sentence 123 as well\n" "999\n\n" "The below items should NOT match:\n" "---------------------------------\n" "1234\n" "12345\n" "123456\n" "1234567\n\n" "£123\n" "$456\n\n" "Err404\n" "ERR404\n" "err404\n" "Err 404\n" "ERR 404\n" "err 404\n\n" "there is err 404 on page\n" "this err 1232222222222 as well\n\n" "a string 12323 like this\n" "asd\n" "4444333322221111\n" "4444 3333 2222 1111\n" "Err123\n\n" "02012341234\n" "920 1234 1234") 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