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

const regex = /^(?'DateTime'(?'Month'[A-Za-z]+)\s+(?'Day'0?[1-9]|[12][0-9]|3[01])\s+(?'Time'[0-9]{2}:[0-9]{2}:[0-9]{2}(\.[0-9]{1,3})?))\W(?'Full_Host'[alnum]|(?:(?'Host_prefix'(?:[A-Za-z])-?)(?'Host'[A-Za-z]+)-*(?'Host_suffix'-{1}[A-Za-z]+)))\W(?'Msg_Sender'(?:\s?\S+:\s)+)?(?'Log_Msg'[[:blank:][:alnum:][:punct:]]+)/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('^(?\'DateTime\'(?\'Month\'[A-Za-z]+)\\s+(?\'Day\'0?[1-9]|[12][0-9]|3[01])\\s+(?\'Time\'[0-9]{2}:[0-9]{2}:[0-9]{2}(\\.[0-9]{1,3})?))\\W(?\'Full_Host\'[alnum]|(?:(?\'Host_prefix\'(?:[A-Za-z])-?)(?\'Host\'[A-Za-z]+)-*(?\'Host_suffix\'-{1}[A-Za-z]+)))\\W(?\'Msg_Sender\'(?:\\s?\\S+:\\s)+)?(?\'Log_Msg\'[[:blank:][:alnum:][:punct:]]+)', 'gm') const str = `May 18 11:02:26 example-host-name kernel: Linux version 6.9.0-gentoo-x86_64 (root@example-host-builder) (x86_64-pc-linux-gnu-gcc (Gentoo Hardened 13.2.1_p20240210 p14) 13.2.1 20240210, GNU ld (Gentoo 2.42 p3) 2.42.0) #1 SMP PREEMPT_DYNAMIC Fri May 17 01:42:56 PDT 2024 May 18 11:02:26 example-host-name kernel: Kernel is locked down from Kernel configuration; see man kernel_lockdown.7 May 18 11:02:26 example-host-name kernel: Command line: BOOT_IMAGE=(lvm/vg0-gentoo--root--two)/boot/vmlinuz-6.9.0-gentoo-x86_64.signed root=/dev/dm-4 May 18 11:02:26 example-host-name kernel: x86/split lock detection: #AC: crashing the kernel on kernel split_locks and warning on user-space split_locks May 18 11:02:26 example-host-name kernel: BIOS-provided physical RAM map: May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x0000000000000000-0x000000000009dfff] usable May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x000000000009e000-0x000000000009efff] reserved May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x000000000009f000-0x000000000009ffff] usable May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x0000000000100000-0x000000003aae7fff] usable May 18 11:02:26 example-host-name kernel: BIOS-e820: [mem 0x000000003aae8000-0x000000004395efff] reserved `; 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