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

use strict; my $str = 'Aug 1 18:27:49 knight sshd[20327]: Failed password for illegal user guest from 218.49.183.17 port 49090 ssh2 Aug 1 18:27:49 knight sshd[20327]: error: Could not get shadow information for NOUSER Aug 1 18:27:52 knight sshd[20329]: Failed password for admin from 218.49.183.17 port 49266 ssh2 Aug 1 18:27:56 knight sshd[20331]: Failed password for admin from 218.49.183.17 port 49468 ssh2 Aug 1 18:27:58 knight sshd[20334]: Illegal user user from 218.49.183.17 Aug 1 18:27:59 knight sshd[20334]: Failed password for illegal user user from 218.49.183.17 port 49680 ssh2 Aug 1 18:27:59 knight sshd[20334]: error: Could not get shadow information for NOUSER Aug 1 18:28:02 knight sshd[20336]: Failed password for root from 218.49.183.17 port 49869 ssh2 Aug 1 18:28:05 knight sshd[20347]: Failed password for root from 218.49.183.17 port 50063 ssh2 Aug 1 18:28:12 knight sshd[20349]: Failed password for root from 218.49.183.17 port 50245 ssh2 Aug 1 18:28:14 knight sshd[20352]: Illegal user test from 218.49.183.17 Aug 1 18:28:19 knight sshd[20352]: Failed password for illegal user test from 218.49.183.17 port 50671 ssh2 Aug 1 18:28:19 knight sshd[20352]: error: Could not get shadow information for NOUSER Aug 1 18:29:55 knight sshd[20402]: Illegal user test from 218.49.183.17 Aug 1 18:29:56 knight sshd[20402]: Failed password for illegal user test from 218.49.183.17 port 52244 ssh2 Aug 1 18:29:56 knight sshd[20402]: error: Could not get shadow information for NOUSER Aug 1 18:29:58 knight sshd[20404]: Illegal user guest from 218.49.183.17 Aug 1 18:30:02 knight sshd[20406]: Illegal user test from 218.49.183.17 Aug 1 18:30:03 knight sshd[20404]: Failed password for illegal user guest from 218.49.183.17 port 52416 ssh2 Aug 1 18:30:03 knight sshd[20404]: error: Could not get shadow information for NOUSER Aug 1 18:30:03 knight sshd[20406]: Failed password for illegal user test from 218.49.183.17 port 52558 ssh2 Aug 1 18:30:03 knight sshd[20406]: error: Could not get shadow information for NOUSER Aug 1 18:30:05 knight sshd[20439]: Failed password for illegal user guest from 218.49.183.17 port 52818 ssh2 Aug 1 18:30:05 knight sshd[20439]: Illegal user guest from 218.49.183.17 Aug 1 18:30:05 knight sshd[20439]: error: Could not get shadow information for NOUSER Aug 1 18:30:06 knight sshd[20441]: Failed password for admin from 218.49.183.17 port 52851 ssh2 Aug 1 18:30:08 knight sshd[20443]: Failed password for admin from 218.49.183.17 port 53014 ssh2 Aug 1 18:30:09 knight sshd[20445]: Failed password for admin from 218.49.183.17 port 53040 ssh2 Aug 1 18:30:11 knight sshd[20447]: Failed password for admin from 218.49.183.17 port 53192 ssh2'; my $regex = qr/^(\w{3}\s*\d)\s*(\d\d:\d\d:\d\d)\s*(\w+)/mp; if ( $str =~ /$regex/g ) { print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n"; # print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n"; # print "Capture Group 2 is $2 ... and so on\n"; } # ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p' # Named capture groups can be called via $+{name}

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 Perl, please visit: http://perldoc.perl.org/perlre.html