UUID(3pm) User Contributed Perl Documentation UUID(3pm)
NAME
UUID - Universally Unique Identifier library for Perl
SYNOPSIS
# SIMPLE
use UUID qw(uuid); # see EXPORTS
my $str = uuid(); # generate version 4 UUID string
# SPECIFIC
$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
# NAMESPACE is 'dns', 'url', 'oid', or 'x500'; case-insensitive.
$str = uuid3(dns => 'www.example.com');
$str = uuid5(url => 'https://www.example.com/foo.html');
UUID::generate_v1($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($bin); # new version 7 binary UUID
UUID::generate_v3($bin, dns => 'www.example.com');
UUID::generate_v5($bin, url => 'https://www.example.com/foo.txt');
UUID::generate($bin); # alias for generate_v1()
UUID::generate_time($bin); # alias for generate_v1()
UUID::generate_random($bin); # alias for generate_v4()
UUID::unparse($bin, $str); # stringify $bin; prefer lowercase
UUID::unparse_lower($bin, $str); # force lowercase stringify
UUID::unparse_upper($bin, $str); # force uppercase stringify
UUID::parse($str, $bin); # map string to binary UUID
UUID::compare($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
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 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
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.
RANDOM NUMBERS
Versions 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 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.
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.
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) 2014-2025 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
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).
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