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
No Match

/
/
gm

Test String

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^@ heading2$[\s\S]*?^(?:field2: \"?((?<=\")[^\"\\]*(?:\\.[^\"\\]*)*(?=\"$)|(?<!\").*(?!\")$)\"?$|)?$[\s\S]*?(?=@ [^\s]*?|\Z)" 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 = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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