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

r"
"
gm

Test String

Code Generator

Language

Generated Code

const regex = new RegExp('^(.*ext[2-4]|.*xfs)(\\s+)((([a-zA-Z\\=\\-]+)(?!noatime,nodireatime)).+)', 'gm') const str = `# Not match /dev/mapper/VolGroup00-root / ext4 errors=remount-ro,noatime,nodiratime 0 1 /dev/mapper/VolGroup00-home /home ext4 defaults,noatime,nodiratime 0 2 LABEL=cloudimg-rootfs / ext4 defaults,noatime,nodiratime 0 0 # /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> /dev/mapper/VolGroup00-root / ext4 errors=remount-ro 0 1 # /boot was on /dev/sda1 during installation UUID=72836e37-44d4-4612-90ef-0e545a0071a6 /boot ext4 defaults 0 2 /dev/mapper/VolGroup00-home /home ext4 defaults 0 2 /dev/mapper/VolGroup00-tmp /tmp ext4 defaults 0 2 /dev/mapper/VolGroup00-var /var ext4 defaults 0 2 /dev/mapper/VolGroup00-swap_1 none swap sw 0 0 /dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0 # Ubuntu OpenStack LABEL=cloudimg-rootfs / ext4 defaults 0 0 # Centos /dev/mapper/VolGroup00-lv_slash / xfs defaults 0 0 UUID=4534700a-a2b2-4d6c-9415-c372da0c39eb /boot xfs defaults 0 0 /dev/mapper/VolGroup00-lv_home /home xfs defaults 0 0 /dev/mapper/VolGroup00-lv_tmp /tmp xfs defaults 0 0 /dev/mapper/VolGroup00-lv_var /var xfs defaults 0 0 /dev/mapper/VolGroup00-lv_swap swap swap defaults 0 0 # Debian 7 /dev/mapper/VolGroup00-root / ext4 errors=remount-ro 0 1 # /boot was on /dev/sda1 during installation UUID=080670e3-93d1-4fdc-be7d-d8b05ad6d1e5 /boot ext4 defaults 0 2 /dev/mapper/VolGroup00-home /home ext4 defaults 0 2 /dev/mapper/VolGroup00-tmp /tmp ext4 defaults 0 2 /dev/mapper/VolGroup00-var /var ext4 defaults 0 2 /dev/mapper/VolGroup00-swap_1 none swap sw 0 0 /dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0 /dev/fd0 /media/floppy0 auto rw,user,noauto 0 0 # Debian 8 /dev/mapper/VolGroup00-root / ext4 errors=remount-ro 0 1 # /boot was on /dev/sda1 during installation UUID=18b29bfa-332a-409b-810c-5cc8a1dbb81e /boot ext4 defaults 0 2 /dev/mapper/VolGroup00-home /home ext4 defaults 0 2 /dev/mapper/VolGroup00-tmp /tmp ext4 defaults 0 2 /dev/mapper/VolGroup00-var /var ext4 defaults 0 2 /dev/mapper/VolGroup00-swap_1 none swap sw 0 0 /dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0 `; // 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