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

/
/
gmi

Test String

Code Generator

Language

Generated Code

const regex = /^\s*(#*)\s*(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s+([a-zA-Z0-9\.\- ]+)([^#]*#?\w*\s*)$/gmi; // Alternative syntax using RegExp constructor // const regex = new RegExp('^\\s*(#*)\\s*(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})\\s+([a-zA-Z0-9\\.\\- ]+)([^#]*#?\\w*\\s*)$', 'gmi') const str = `# Copyright (c) 1993-2009 Microsoft Corp. # # This is a sample HOSTS file used by Microsoft TCP/IP for Windows. # # This file contains the mappings of IP addresses to host names. Each # entry should be kept on an individual line. The IP address should # be placed in the first column followed by the corresponding host name. # The IP address and the host name should be separated by at least one # space. # # Additionally, comments (such as these) may be inserted on individual # lines or following the machine name denoted by a '#' symbol. # # For example: # # 102.54.94.97 rhino.acme.com # source server # 38.25.63.10 x.acme.com # x client host # localhost name resolution is handled within DNS itself. # 127.0.0.1 localhost # ::1 localhost 127.0.0.1 jw smartsite.jw 127.0.0.1 dev.filepresso.com dev.filepresso.com.pl dev.filepresso.pl dev.filefly.pl #### 89.31.66.248 sp.biatelbit.pl 192.168.72.51 subversion.biatel.com.pl # 127.0.0.1 bip.smartsite.bit-sa.pl # 127.0.0.1 bip.augustow.wrotapodlasia.pl 127.0.0.1 rpowp.smartsite.bit-sa.pl 127.0.0.1 cms.smartsite.bit-sa.pl 127.0.0.1 cms-test.smartsite.bit-sa.pl ############################################################ # # UMWP # ############################################################ ############################################################ # ST - test - UMWP ############################################################ #10.200.14.70 ST-sapp1 #10.200.14.70 tv.smartsite.bit-sa.pl wp.smartsite.bit-sa.pl cms.smartsite.bit-sa.pl test.smartsite.bit-sa.pl bip.smartsite.bit-sa.pl si.smartsite.bit-sa.pl sspw.wrotapodlasia.pl #10.200.14.70 radny.smartsite.bit-sa.pl stats.smartsite.bit-sa.pl test9.smartsite.bit-sa.pl `; // 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