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

/
/
g

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"(?<=Received: from ).*(?= by)" test_str = ("Dec 25 21:44:10 ra-mx amavis[69766]: (69766-04) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <notification+kr4keges24xr@facebookmail.com> -> <sto@kingkong.network> SIZE=21892 BODY=8BITMIME Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <sto@kingkong.network>; Sun, 25 Dec 2016 21:44:10 +0100 (CET)\n" "Dec 25 21:47:27 ra-mx amavis[67599]: (67599-13) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T182139-67599-Iw5AO2Ei: <> -> <bounce@espeurope.net> SIZE=25924 Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <bounce@espeurope.net>; Sun, 25 Dec 2016 21:47:27 +0100 (CET)\n" "Dec 25 21:49:08 ra-mx amavis[67599]: (67599-14) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T182139-67599-Iw5AO2Ei: <> -> <noreply@espeurope.net> SIZE=7152 Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <noreply@espeurope.net>; Sun, 25 Dec 2016 21:49:08 +0100 (CET)\n" "Dec 25 22:12:07 ra-mx amavis[69766]: (69766-05) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <notification+kr4keges24xr@facebookmail.com> -> <sto@kingkong.network> SIZE=12043 BODY=8BITMIME Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <sto@kingkong.network>; Sun, 25 Dec 2016 22:12:07 +0100 (CET)\n" "Dec 25 22:24:12 ra-mx amavis[67599]: (67599-15) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T182139-67599-Iw5AO2Ei: <kh004r5582@blueyonder.co.uk> -> <bounce@espeurope.net> SIZE=5022 Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <bounce@espeurope.net>; Sun, 25 Dec 2016 22:24:12 +0100 (CET)\n" "Dec 25 22:43:12 ra-mx amavis[69766]: (69766-06) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <> -> <noreply@espeurope.net> SIZE=7185 Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <noreply@espeurope.net>; Sun, 25 Dec 2016 22:43:12 +0100 (CET)\n" "Dec 25 23:35:30 ra-mx amavis[67599]: (67599-16) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T182139-67599-Iw5AO2Ei: <> -> <bounce@espeurope.net> SIZE=3752 BODY=8BITMIME ENVID=0OIR003T4IP20A10@etrn.telekom.sk Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <bounce@espeurope.net>; Sun, 25 Dec 2016 23:35:30 +0100 (CET)\n" "Dec 25 23:35:35 ra-mx amavis[69766]: (69766-07) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <> -> <bounce@espeurope.net> SIZE=3751 BODY=8BITMIME ENVID=0OIR003U4IP80A10@etrn.telekom.sk Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <bounce@espeurope.net>; Sun, 25 Dec 2016 23:35:35 +0100 (CET)\n" "Dec 25 23:37:53 ra-mx amavis[69766]: (69766-08) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <notification+kr4keges24xr@facebookmail.com> -> <sto@kingkong.network> SIZE=17322 BODY=8BITMIME Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <sto@kingkong.network>; Sun, 25 Dec 2016 23:37:53 +0100 (CET)\n" "Dec 25 23:39:12 ra-mx amavis[69766]: (69766-09) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <maja.wahlen@sunrise.ch> -> <bounce@espeurope.net> SIZE=7695 BODY=7BIT Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <bounce@espeurope.net>; Sun, 25 Dec 2016 23:39:12 +0100 (CET)\n" "Dec 25 23:44:23 ra-mx amavis[69766]: (69766-10) ESMTP [193.203.199.10]:10024 /var/amavis/tmp/amavis-20161225T202928-69766-zqjUPXL8: <> -> <noreply@espeurope.net> SIZE=7138 Received: from ra-mx.espeurope.net ([193.203.199.10]) by ra-mx (ra-mx.espeurope.net [193.203.199.10]) (amavisd-new, port 10024) with ESMTP for <noreply@espeurope.net>; Sun, 25 Dec 2016 23:44:23 +0100 (CET)\n") matches = re.finditer(regex, test_str) 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