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

/
/
gm

Test String

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^((\s+|)(\/\/|#)|$)" test_str = ("##################################################################\n" "#### /etc/apt/apt.conf.d/50unattended-upgrades ###\n" "// Automatically upgrade packages from these (origin:archive) pairs\n" "//\n" "// Note that in Ubuntu security updates may pull in new dependencies\n" "// from non-security sources (e.g. chromium). By allowing the release\n" "// pocket these get automatically pulled in.\n" "Unattended-Upgrade::Allowed-Origins {\n" " \"${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") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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 Python, please visit: https://docs.python.org/3/library/re.html