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"^@ heading2$[\s\S]*?^(?:field2: \"?((?<=\")[^\"\\]*(?:\\.[^\"\\]*)*(?=\"$)|(?<!\").*(?!\")$)\"?$|)?$[\s\S]*?(?=@ [^\s]*?|\Z)", flags=re.MULTILINE) test_str = ("@ heading1\n" "field1: \"single-line strings are quoted only sometimes.\"\n" "field2: \"strings that span\n" "multiple lines\n" "are always quoted.\"\n" "field3: this single-line string is unquoted.\n\n" "@ heading2\n" "field1: field names can be repeated among headings.\n" "field2: \"Regex is harder when I add an\n" "@ in a multi-line string, or if I add\n" "backslash-escaped characters like \\\" and \\'.\n\n" "What happens if I have an empty line in a string?\n\n" "Also,\n" "[this line]\n" "isn't actually a section.\"\n" "field3: this field comes after field2\n" "[sectionname]\n" "field1: the same field name under a different section.\n" "[anothersection]\n" "field1: a second section under the same heading\n" "field4: field number four\n\n" "@ heading3\n" "field1: value value value value value\n" "field2: \"quoted string\n" "quoted string\n" "quoted string\"\n" "unique: unique field name") 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