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

`
`
mg

Test String

Code Generator

Language

Generated Code

const regex = new RegExp('(?P<time>\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}:\\d{2},\\d{0,3}) (?P<message>fail2ban.*(?P<gid>\\[\\d*\\]: )(?P<level>[A-Z]{4,7}) .*)', 'mg') const str = `2020-05-11 06:25:02,732 fail2ban.server [879]: INFO rollover performed on /var/log/fail2ban.log 2020-05-08 01:34:33,079 fail2ban.filter [16566]: INFO [sshd] Found 1.1.1.1 - 2020-05-08 01:34:33 2020-05-09 04:02:31,316 fail2ban.actions [16566]: NOTICE [sshd] Ban 1.0.0.1 2020-05-23 00:09:06,355 fail2ban.server [9474]: INFO Reload jail GHOST 2020-05-23 00:09:06,355 fail2ban.filter [9474]: INFO Removed logfile: '/opt/logs/ghost/https___nonsense_fyi_production.log' 2020-05-23 00:09:07,902 fail2ban.actions [9474]: NOTICE [GHOST] Flush ticket(s) with iptables-multiport 2020-05-23 00:09:07,902 fail2ban.actions [9474]: NOTICE [GHOST] Flush ticket(s) with iptables-allports 2020-05-23 00:09:09,699 fail2ban.jail [9474]: INFO Jail 'GHOST' stopped 2020-05-23 00:09:09,701 fail2ban.jail [9474]: INFO Creating new jail 'GHOST' 2020-05-23 00:09:09,701 fail2ban.jail [9474]: INFO Jail 'GHOST' uses pyinotify {} 2020-05-23 00:09:09,706 fail2ban.jail [9474]: INFO Initiated 'pyinotify' backend 2020-05-23 00:09:09,709 fail2ban.filter [9474]: INFO Added logfile: '/opt/logs/ghost/https___nonsense_fyi_production.log' (pos = 14909, hash = 7091b34995f750999f6c605cd6250439a2e0cde7) 2020-05-23 00:09:09,710 fail2ban.filter [9474]: INFO encoding: UTF-8 2020-05-23 00:09:09,711 fail2ban.filter [9474]: INFO maxRetry: 5 2020-05-23 00:09:09,711 fail2ban.filter [9474]: INFO findtime: 300 2020-05-23 00:09:09,712 fail2ban.actions [9474]: INFO banTime: 2592000 2020-05-23 00:09:09,714 fail2ban.jail [9474]: INFO Jail 'GHOST' started 2020-05-23 00:09:09,714 fail2ban.server [9474]: INFO Reload finished.`; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions