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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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"^[a-zA-Z]\d{4}$" test_str = ("# The CMS, who maintain these codes, describe the format as:-\n" "# \"HCPCS Level II codes (also known as alpha-numeric codes) consist of a single alphabetical letter followed by 4 numeric digits.\"\n" "# (https://www.cms.gov/medicare/coding-billing/healthcare-common-procedure-system)\n" "# NOTE: This regex will not identify HCPCS Level I codes (AKA CPT codes)\n" "# Also, some sources say the single letter ranges only from A-V (this regex follows A-Z)\n" "# Finally, this regex does not match procedure modifiers, which are 2 digit codes that follow a HCPCS code (with hyphen). \n" "# (https://www.aapc.com/resources/what-are-medical-coding-modifiers)\n" "# A separate regex has been created on regex101 supporting these modifiers\n\n" "# Genuine codes\n" "E8015\n" "A6410\n" "C5278\n" "G2102\n" "M1221\n" "V2623\n" "V2756\n" "c5278\n" "g2102\n" "m1221\n" "v2623\n" "v2756\n" "# Should fail\n" "EE8015\n" "6410\n" "E641O\n" "[6410\n" "_6510\n" "g212\n" "C52789\n") 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