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"^(\w{3}\s*\d)\s*(\d\d:\d\d:\d\d)\s*(\w+)" test_str = ("Aug 1 18:27:49 knight sshd[20327]: Failed password for illegal user guest from 218.49.183.17 port 49090 ssh2\n" "Aug 1 18:27:49 knight sshd[20327]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:27:52 knight sshd[20329]: Failed password for admin from 218.49.183.17 port 49266 ssh2\n" "Aug 1 18:27:56 knight sshd[20331]: Failed password for admin from 218.49.183.17 port 49468 ssh2\n" "Aug 1 18:27:58 knight sshd[20334]: Illegal user user from 218.49.183.17\n" "Aug 1 18:27:59 knight sshd[20334]: Failed password for illegal user user from 218.49.183.17 port 49680 ssh2\n" "Aug 1 18:27:59 knight sshd[20334]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:28:02 knight sshd[20336]: Failed password for root from 218.49.183.17 port 49869 ssh2\n" "Aug 1 18:28:05 knight sshd[20347]: Failed password for root from 218.49.183.17 port 50063 ssh2\n" "Aug 1 18:28:12 knight sshd[20349]: Failed password for root from 218.49.183.17 port 50245 ssh2\n" "Aug 1 18:28:14 knight sshd[20352]: Illegal user test from 218.49.183.17\n" "Aug 1 18:28:19 knight sshd[20352]: Failed password for illegal user test from 218.49.183.17 port 50671 ssh2\n" "Aug 1 18:28:19 knight sshd[20352]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:29:55 knight sshd[20402]: Illegal user test from 218.49.183.17\n" "Aug 1 18:29:56 knight sshd[20402]: Failed password for illegal user test from 218.49.183.17 port 52244 ssh2\n" "Aug 1 18:29:56 knight sshd[20402]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:29:58 knight sshd[20404]: Illegal user guest from 218.49.183.17\n" "Aug 1 18:30:02 knight sshd[20406]: Illegal user test from 218.49.183.17\n" "Aug 1 18:30:03 knight sshd[20404]: Failed password for illegal user guest from 218.49.183.17 port 52416 ssh2\n" "Aug 1 18:30:03 knight sshd[20404]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:30:03 knight sshd[20406]: Failed password for illegal user test from 218.49.183.17 port 52558 ssh2\n" "Aug 1 18:30:03 knight sshd[20406]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:30:05 knight sshd[20439]: Failed password for illegal user guest from 218.49.183.17 port 52818 ssh2\n" "Aug 1 18:30:05 knight sshd[20439]: Illegal user guest from 218.49.183.17\n" "Aug 1 18:30:05 knight sshd[20439]: error: Could not get shadow information for NOUSER\n" "Aug 1 18:30:06 knight sshd[20441]: Failed password for admin from 218.49.183.17 port 52851 ssh2\n" "Aug 1 18:30:08 knight sshd[20443]: Failed password for admin from 218.49.183.17 port 53014 ssh2\n" "Aug 1 18:30:09 knight sshd[20445]: Failed password for admin from 218.49.183.17 port 53040 ssh2\n" "Aug 1 18:30:11 knight sshd[20447]: Failed password for admin from 218.49.183.17 port 53192 ssh2") 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