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

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

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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html