NAME
    UUID - Universally Unique Identifier library for Perl

SYNOPSIS
        use UUID qw(uuid);    # see EXPORTS
        my $str = uuid();     # generate version 4 UUID string

        $str = uuid1();                   # new version 1 UUID string
        $str = uuid4();                   # new version 4 UUID string
        $str = uuid6();                   # new version 6 UUID string
        $str = uuid7();                   # new version 7 UUID string

        UUID::generate_v1($bin);          # new version 1 binary UUID
        UUID::generate_v4($bin);          # new version 4 binary UUID
        UUID::generate_v6($bin);          # new version 6 binary UUID
        UUID::generate_v7($bin);          # new version 7 binary UUID

        UUID::parse($str, $bin);          # map string to binary UUID

        UUID::unparse($bin, $str);        # stringify $bin; prefer lowercase

        UUID::compare($bin1, $bin2);      # compare binary UUIDs
        UUID::copy($dst, $src);           # copy binary UUID from $src to $dst

        UUID::clear($bin);                # set binary UUID to NULL
        UUID::is_null($bin);              # compare binary UUID to NULL

        UUID::time($bin);                 # return UUID time
        UUID::type($bin);                 # return UUID type
        UUID::variant($bin);              # return UUID variant
        UUID::version($bin);              # return UUID version

        UUID::generate($bin);             # alias for generate_v1()
        UUID::generate_time($bin);        # alias for generate_v1()
        UUID::generate_random($bin);      # alias for generate_v4()

        UUID::unparse_lower($bin, $str);  # force lowercase stringify
        UUID::unparse_upper($bin, $str);  # force uppercase stringify

        # NAMESPACE is 'dns', 'url', 'oid', or 'x500'; case-insensitive.
        $str = uuid3(dns => 'www.example.com');
        $str = uuid5(url => 'https://www.example.com/foo.html');

        UUID::generate_v3($bin, dns => 'www.example.com');
        UUID::generate_v5($bin, url => 'https://www.example.com/foo.txt');

DESCRIPTION
    The UUID library is used to generate unique identifiers for objects that
    may be accessible beyond the local system. For instance, they could be
    used to generate unique HTTP cookies across multiple web servers without
    communication between the servers, and without fear of a name clash.

    The generated UUIDs can be reasonably expected to be unique within a
    system, and unique across all systems, and are compatible with those
    created by the Open Software Foundation (OSF) Distributed Computing
    Environment (DCE).

    All generated UUIDs are either version 1, 3, 4, 5, 6, or version 7. And
    all are variant 1, meaning compliant with the OSF DCE standard as
    described in RFC4122.

    Versions 6 and 7 are not yet standardized. They are presented here as
    proposed in RFC4122bis, version 14, and may change in the future.
    RFC4122bis is noted to replace RFC4122, if approved.

FUNCTIONS
    Most of the UUID functions expose the historically underlying libuuid
    C interface rather directly. That is, many return their values in their
    parameters and nothing else.

    Not very Perlish, but it's been like that for a long time so not likely
    to change any time soon.

    All take or return UUIDs in either binary or string format. The string
    format resembles the following:

        21b081a3-de83-4480-a14f-e89a1dcf8f0f

    Or, in terms of printf(3) format:

        "%08x-%04x-%04x-%04x-%012x"

    The binary form is simply a packed 16 byte binary value.

  clear( $uuid )
    Sets binary $uuid equal to the value of the NULL UUID.

  compare( $uuid1, $uuid2 )
    Compares two binary UUIDs.

    Returns an integer less than, equal to, or greater than zero if $uuid1
    is less than, equal to, or greater than $uuid2.

    If one is defined and the other not, the defined value is deemed the
    larger.

    If either operand is not a binary UUID, falls back to a simple string
    comparison returning similar values.

  copy( $dst, $src )
    Copies the binary $src UUID to $dst.

    If $src isn't a UUID, $dst is set to the NULL UUID.

  generate( $uuid )
    Alias for generate_v4().

    Prior to version 0.33, this function provided either a binary version 4
    UUID or fell back to version 1 in some cases. This is no longer the
    case. The fallback feature was removed with the addition of an onboard
    crypto-strength number generator.

  generate_random( $uuid )
    Alias for generate_v4().

  generate_time( $uuid )
    Alias for generate_v1().

  generate_v1( $uuid )
    Generates a new version 1 binary UUID using the current time and the
    local ethernet MAC address, if available.

    If the MAC address is not available at startup, or a randomized address
    is requested (see :mac in EXPORTS), a random address is used. The
    multicast bit of this address is set to avoid conflict with addresses
    returned from network cards.

  generate_v3( $uuid, NAMESPACE => NAME )
    Generate a new version 3 binary UUID using the given namespace and name
    hashed through the MD5 algorithm.

    Namespace is one of "dns", "url", "oid", or "x500", and
    case-insensitive. It is used to select the namespace UUID to hash with
    the name.

    Name should be an entity from the given namespace, but can really be any
    text.

  generate_v4( $uuid )
    Generates a new version 4 binary UUID using mostly random data. There
    are 6 bits used for the UUID format, leaving 122 bits for randomness.

  generate_v5( $uuid, NAMESPACE => NAME )
    Generate a new version 5 binary UUID using the given namespace and name
    hashed through the SHA1 algorithm.

    Namespace is one of "dns", "url", "oid", or "x500", and
    case-insensitive. It is used to select the namespace UUID to hash with
    the name.

    Name should be an entity from the given namespace, but can really be any
    text.

  generate_v6( $uuid )
    Generates a new version 6 binary UUID using the current time and the
    local ethernet MAC address, if available.

    If the MAC address is not available at startup, or a randomized address
    is requested (see :mac in EXPORTS), a random address is used. The
    multicast bit of this address is set to avoid conflict with addresses
    returned from network cards.

    Version 6 is the same as version 1, with reversed time fields to make it
    more database friendly.

  generate_v7( $uuid )
    Generates a new version 7 binary UUID using the current time and random
    data. There are 6 bits used for the UUID format and 48 bits for
    timestamp, leaving 74 bits for randomness.

    Version 7 is the same as version 6, in that it uses reversed timestamp
    fields, but also uses a Unix epoch time base instead of Gregorian.

  is_null( $uuid )
    Compares the value of $uuid to the NULL UUID.

    Returns 1 if NULL, and 0 otherwise.

  parse( $string, $uuid )
    Converts the string format UUID in $string to binary and returns in
    $uuid. The previous content of $uuid, if any, is lost.

    Returns 0 on success and -1 on failure. Additionally on failure, the
    content of $uuid is unchanged.

  time( $uuid )
    Returns the time element of a binary UUID in seconds since the epoch,
    the same as Perl's time function.

    Keep in mind this only works for version 1, 6, and version 7 UUIDs.
    Values returned from other versions are always 0.

  type( $uuid )
    Alias for version().

  unparse( $uuid, $string )
    Alias for unparse_lower().

    Prior to version 0.32, casing of the return value was system-dependent.
    Later versions are lowercase, per RFC4122.

  unparse_lower( $uuid, $string )
    Converts the binary UUID in $uuid to string format and returns in
    $string. The previous content of $string, if any, is lost.

  unparse_upper( $uuid, $string )
    Same as unparse_lower() but $string is forced to upper case.

  uuid()
    Alias for uuid4().

  uuid0()
    Returns a new string format NULL UUID.

  uuid1()
    Returns a new string format version 1 UUID. Functionally the equivalent
    of calling generate_v1() then unparse(), but throwing away the
    intermediate binary UUID.

  uuid3(NAMESPACE = NAME)>
    Same as uuid1() but version 3. See generate_v3().

  uuid4()
    Same as uuid1() but version 4.

  uuid5(NAMESPACE = NAME)>
    Same as uuid1() but version 5. See generate_v5().

  uuid6()
    Same as uuid1() but version 6.

  uuid7()
    Same as uuid1() but version 7.

  variant( $uuid )
    Returns the variant of binary $uuid.

    This module only generates variant 1 UUIDs. Others may be found in the
    wild.

    Known variants:

        0  NCS
        1  DCE
        2  Microsoft
        3  Other

  version( $uuid> )
    Returns the version of binary $uuid.

    This module only generates version 1, 3, 4, 5, 6, and version 7 UUIDs.
    Others may be found in the wild.

    Known versions:

        v1  date/time and node address
        v2  date/time and node address, security version
        v3  namespace based, MD5 hash
        v4  random
        v5  namespace based, SHA-1 hash
        v6  reverse date/time and node address
        v7  reverse unix date/time and random
        v8  custom

RANDOM NUMBERS
    Version 4 and 7 UUIDs are partially filled with random numbers, as well
    as versions 1 and 6 when used with the :mac option.

    Prior to version 0.33, UUID obtained randomness from the system's
    /dev/random device, or similar interface. On some platforms it called
    getrandom() and on others it read directly from /dev/urandom. And of
    course, Win32 did something completely different.

    Starting in version 0.33, UUID generates random numbers itself using the
    ChaCha20 algorithm which is considered crypto-strength in most circles.
    This is the same algo used as the basis for many modern kernel RNGs,
    albeit without the same entropy gathering ability.

    To compensate, UUID mixes the output from ChaCha with output from
    another RNG, Xoshiro. The idea is that by mixing the two, the true
    output from either is effectively hidden, making discovery of either's
    key much more unlikely than it already is. And without the keys, you
    can't predict the future.

    Well, that's the theory anyway.

    Starting in version 0.38, the whole mix is initially seeded from the
    best platform-specific source available which could be one or more of:

        arc4random()
        BCryptGenRandom()
        CryptGenRandom()
        getentropy()
        getrandom()
        /dev/urandom
        /dev/random

TIME
    Time-based UUIDs are formed with time-of-day information gathered from
    Time::HiRes. This provides a portable timestamp with 1us resolution
    facilitating generation rates up to 1M UUIDs/sec without further action.

    If UUIDs are required faster than 1us (i.e. > 1M UUIDs/sec), an internal
    counter simulates 100ns intervals, which is the UUID resolution limit.
    Each UUID within the same 1us tick will thus appear to be at successive
    100ns intervals, which probably isn't true.

    Should the internal counter exceed 9 within the same 1us period, it is
    reset to 0 and the UUID sequence field is incremented, thus guaranteeing
    uniqueness even though the time sequence will repeat.

    This scheme raises the limit of time-based uniqueness to over 16G
    UUIDs/sec, which is well beyond the best benchmarks seen to date.
    (~14M/sec for v6 binary UUIDs on commodity hardware.)

    Starting in version 0.38, the internal counter is moved to shared
    memory, ensuring uniqueness among time-based UUIDs in forked or threaded
    environments. Note that UUID must be loaded before forking or creating
    threads for this guarantee to hold.

NAMESPACES
    Versions 3 and 5 generate UUIDs within namespaces. What this really
    means is that the NAME value is concatenated with a dedicated
    NAMESPACE UUID before hashing.

    Available namespaces and UUIDs:

        dns   6ba7b810-9dad-11d1-80b4-00c04fd430c8
        url   6ba7b811-9dad-11d1-80b4-00c04fd430c8
        oid   6ba7b812-9dad-11d1-80b4-00c04fd430c8
        x500  6ba7b814-9dad-11d1-80b4-00c04fd430c8

    For example, if you need to create some UUIDs within your own
    "questions" and "answers" namespaces using SHA1:

        $ns_base = uuid5( dns => 'www.example.com' );

        $ns_questions = uuid5( $ns_base, 'questions' );
        $ns_answers   = uuid5( $ns_base, 'answers'   );

        for $topic ( next_qa_aref() ) {
            ($q, $a) = @$topic;
            $uuid_question = uuid5( $ns_questions, $q );
            $uuid_answer   = uuid5( $ns_answers,   $a );
            ...
        }

    This way, you can deterministically convert existing (and likely
    colliding) namespaces over to one UUID namespace, which is often useful
    when merging datasets.

    You also don't need to publish your base and namespace UUIDs. Anyone
    using the same logic can generate the same question and answer UUIDs.

MAINTAINING STATE
    Internal state is optionally maintained for timestamped UUIDs (versions
    1, 6, and 7) via a file designated by the :persist export tag. See
    EXPORTS for details.

    The file records various internal states at the time the last UUID is
    generated, preventing future instances from overlapping the prior UUID
    sequence. This allows the sequence to absolutely survive reboots and,
    more importantly, backwards resetting of system time.

    If :persist is not used, time resets will still be detected while the
    module is loaded and handled by incrementing the UUID clock_seq field.
    The clock_seq field is randomly initialized in this case anyway, so the
    chance of overlap is low but still exists since clock_seq is only 14
    bits wide. Using a random MAC will help (see :mac in EXPORTS), adding an
    additional 48 bits of randomness.

    NOTE: Using :persist incurs a serious performance penalty, in excess of
    95% on tested platforms. You can run "make compare" in the distribution
    directory to see how this might affect your application, but unless you
    need many thousands of UUIDs/sec it's probably a non-issue.

EXPORTS
    None by default. All functions may be imported in the usual manner,
    either individually or all at once using the :all tag.

    Beware that importing :all clobbers Perl's time(), not to mention a
    few other commonly used subs, like copy() from File::Copy.

  :mac=mode
    The MAC address used for MAC-inclusive UUIDS (versions 1 and 6) is
    forced to always be random in one of two modes:

        random The MAC address is generated once at startup and used
        through the lifetime of the process. This is the default if a real
        MAC cannot be found.

        unique A new MAC address is generated for each new UUID. It is not
        guaranteed to be unique beyond the probability of randomness.

  :persist=path/to/state.txt
    Path to timestamp state maintenance file. (See MAINTAINING STATE.) The
    path may be either relative or absolute.

    If the file does not exist, it will be created provided the path exists
    and the user has permission.

    If the file cannot be opened, cannot be created, or is a symlink, UUID
    will ignore it. No state will be maintained.

    WARNING: Do not :persist in a public directory. See CVE-2013-4184. UUID
    attempts to avoid this, but nothing is foolproof. Only YOU can prevent
    symlink attacks!

  :defer[=N]
    Persistence of state is deferred N seconds when generating time-based
    UUIDs. More precisely, state is only saved every N seconds. If UUIDs
    are generated more often, those within the N second window will not
    save state.

    Defer values greater than some platform-specific interval greatly reduce
    the performance penalty introduced through persistence. While the
    default, :defer=0.001, is probably fine, you can run make persist in the
    distribution directory to see the effect of various values.

THREAD SAFETY
    This module is believed to be thread safe.

UUID LIBRARY
    Releases prior to UUID-0.32 required libuuid or similar be installed
    first. This is no longer the case. Version 0.33 bundled the e2fsprogs
    UUID code, and version 0.34 removed it altogether.

BENCHMARKS
    There are a few benchmarks in the distribution ubin directory which can
    be run either standalone or through the Makefile.

  make compare
    Runs all three of the following tests.

  make speeds
    Runs ubin/cmp_speeds.pl to compare the speeds of various UUID versions.

  make styles
    Runs ubin/cmp_styles.pl to compare different UUID calling styles.

  make persist
    Runs ubin/cmp_persist.pl to compare different deferral values for
    persistent state.

COPYRIGHT AND LICENSE
    This software is Copyright (c) 2014-2026 by Rick Myers.

    This is free software, licensed under:

      The Artistic License 2.0 (GPL Compatible)

    Details of this license can be found within the 'LICENSE' text file.

AUTHOR
    Current maintainer:

      Rick Myers <jrm@cpan.org>.

    Authors and/or previous maintainers:

      Lukas Zapletal <lzap@cpan.org>

      Joseph N. Hall <joseph.nathan.hall@gmail.com>

      Colin Faber <cfaber@clusterfs.com>

      Peter J. Braam <braam@mountainviewdata.com>

CONTRIBUTORS
    David E. Wheeler

    William Faulk

    gregor herrmann

    Slaven Rezic

    twata

    Christopher Rasch-Olsen Raa

    Petr Pisar

    Kurt Starsinic

SEE ALSO
    RFC4122 - <https://www.rfc-editor.org/rfc/rfc4122>

    RFC4122bis -
    <https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bis-14.html>

    perl(1).

