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

/
/
gm

Test String

Code Generator

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "^((\\s+|)(\\/\\/|#)|$)"; final String string = "##################################################################\n" + "#### /etc/apt/apt.conf.d/50unattended-upgrades ###\n" + "// Automatically upgrade packages from these (origin:archive) pairs\n" + "//\n" + "// Note that in Ubuntu security updates may pull in new dependencies\n" + "// from non-security sources (e.g. chromium). By allowing the release\n" + "// pocket these get automatically pulled in.\n" + "Unattended-Upgrade::Allowed-Origins {\n" + " \"${distro_id}:${distro_codename}\";\n" + " \"${distro_id}:${distro_codename}-security\";\n" + " // Extended Security Maintenance; doesn't necessarily exist for\n" + " // every release and this system may not have it installed, but if\n" + " // available, the policy for updates is such that unattended-upgrades\n" + " // should also install from here by default.\n" + " \"${distro_id}ESMApps:${distro_codename}-apps-security\";\n" + " \"${distro_id}ESM:${distro_codename}-infra-security\";\n" + "// \"${distro_id}:${distro_codename}-updates\";\n" + "// \"${distro_id}:${distro_codename}-proposed\";\n" + "// \"${distro_id}:${distro_codename}-backports\";\n" + "};\n\n" + "// Python regular expressions, matching packages to exclude from upgrading\n" + "Unattended-Upgrade::Package-Blacklist {\n" + " // The following matches all packages starting with linux-\n" + "// \"linux-\";\n\n" + " // Use $ to explicitely define the end of a package name. Without\n" + " // the $, \"libc6\" would match all of them.\n" + "// \"libc6$\";\n" + "// \"libc6-dev$\";\n" + "// \"libc6-i686$\";\n\n" + " // Special characters need escaping\n" + "// \"libstdc\\+\\+6$\";\n\n" + " // The following matches packages like xen-system-amd64, xen-utils-4.1,\n" + " // xenstore-utils and libxenstore3.0\n" + "// \"(lib)?xen(store)?\";\n\n" + " // For more information about Python regular expressions, see\n" + " // https://docs.python.org/3/howto/regex.html\n" + "};\n\n" + "// This option controls whether the development release of Ubuntu will be\n" + "// upgraded automatically. Valid values are \"true\", \"false\", and \"auto\".\n" + "Unattended-Upgrade::DevRelease \"auto\";\n\n\n" + "##################################################################\n" + "#### /etc/cron.weekly/man-db ###\n\n" + "#!/bin/sh\n" + "#\n" + "# man-db cron weekly\n\n" + "set -e\n\n" + "if [ -d /run/systemd/system ]; then\n" + " # Skip in favour of systemd timer.\n" + " exit 0\n" + "fi\n\n" + "iosched_idle=\n" + "# Don't try to change I/O priority in a vserver or OpenVZ.\n" + "if ! egrep -q '(envID|VxID):.*[1-9]' /proc/self/status && \\\n" + " ([ ! -d /proc/vz ] || [ -d /proc/bc ]); then\n" + " iosched_idle='--iosched idle'\n" + "fi\n\n" + "if ! [ -d /var/cache/man ]; then\n" + " # Recover from deletion, per FHS.\n" + " install -d -o man -g man -m 0755 /var/cache/man\n" + "fi\n\n" + "# regenerate man database\n" + "if [ -x /usr/bin/mandb ]; then\n" + " # --pidfile /dev/null so it always starts; mandb isn't really a daemon,\n" + " # but we want to start it like one.\n" + " start-stop-daemon --start --pidfile /dev/null \\\n" + " --startas /usr/bin/mandb --oknodo --chuid man \\\n" + " $iosched_idle \\\n" + " -- --quiet\n" + "fi\n\n" + "exit 0"; 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