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ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       Storable - persistence for Perl data structures

        use Storable;
        store \%table, 'file';
        $hashref = retrieve('file');

        use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);

        # Network order
        nstore \%table, 'file';
        $hashref = retrieve('file');   # There is NO nretrieve()

        # Storing to and retrieving from an already opened file
        store_fd \@array, \*STDOUT;
        nstore_fd \%table, \*STDOUT;
        $aryref = fd_retrieve(\*SOCKET);
        $hashref = fd_retrieve(\*SOCKET);

        # Serializing to memory
        $serialized = freeze \%table;
        %table_clone = %{ thaw($serialized) };

        # Deep (recursive) cloning
        $cloneref = dclone($ref);

        # Advisory locking
        use Storable qw(lock_store lock_nstore lock_retrieve)
        lock_store \%table, 'file';
        lock_nstore \%table, 'file';
        $hashref = lock_retrieve('file');

       The Storable package brings persistence to your Perl data
       structures containing SCALAR, ARRAY, HASH or REF objects,
       i.e. anything that can be conveniently stored to disk and
       retrieved at a later time.

       It can be used in the regular procedural way by calling
       "store" with a reference to the object to be stored, along
       with the file name where the image should be written.

       The routine returns "undef" for I/O problems or other
       internal error, a true value otherwise. Serious errors are
       propagated as a "die" exception.

       To retrieve data stored to disk, use "retrieve" with a
       file name.  The objects stored into that file are recre-
       ated into memory for you, and a reference to the root
       object is returned. In case an I/O error occurs while
       reading, "undef" is returned instead. Other serious errors
       are propagated via "die".

perl v5.8.5                 2002-11-06                          1

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       Since storage is performed recursively, you might want to
       stuff references to objects that share a lot of common
       data into a single array or hash table, and then store
       that object. That way, when you retrieve back the whole
       thing, the objects will continue to share what they origi-
       nally shared.

       At the cost of a slight header overhead, you may store to
       an already opened file descriptor using the "store_fd"
       routine, and retrieve from a file via "fd_retrieve". Those
       names aren't imported by default, so you will have to do
       that explicitly if you need those routines.  The file
       descriptor you supply must be already opened, for read if
       you're going to retrieve and for write if you wish to

               store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
               $hashref = fd_retrieve(*STDIN);

       You can also store data in network order to allow easy
       sharing across multiple platforms, or when storing on a
       socket known to be remotely connected. The routines to
       call have an initial "n" prefix for network, as in
       "nstore" and "nstore_fd". At retrieval time, your data
       will be correctly restored so you don't have to know
       whether you're restoring from native or network ordered
       data.  Double values are stored stringified to ensure
       portability as well, at the slight risk of loosing some
       precision in the last decimals.

       When using "fd_retrieve", objects are retrieved in
       sequence, one object (i.e. one recursive tree) per associ-
       ated "store_fd".

       If you're more from the object-oriented camp, you can
       inherit from Storable and directly store your objects by
       invoking "store" as a method. The fact that the root of
       the to-be-stored tree is a blessed reference (i.e. an
       object) is special-cased so that the retrieve does not
       provide a reference to that object but rather the blessed
       object reference itself. (Otherwise, you'd get a reference
       to that blessed object).

       The Storable engine can also store data into a Perl scalar
       instead, to later retrieve them. This is mainly used to
       freeze a complex structure in some safe compact memory
       place (where it can possibly be sent to another process
       via some IPC, since freezing the structure also serializes
       it in effect). Later on, and maybe somewhere else, you can
       thaw the Perl scalar out and recreate the original complex
       structure in memory.

       Surprisingly, the routines to be called are named "freeze"

perl v5.8.5                 2002-11-06                          2

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       and "thaw".  If you wish to send out the frozen scalar to
       another machine, use "nfreeze" instead to get a portable

       Note that freezing an object structure and immediately
       thawing it actually achieves a deep cloning of that struc-

           dclone(.) = thaw(freeze(.))

       Storable provides you with a "dclone" interface which does
       not create that intermediary scalar but instead freezes
       the structure in some internal memory space and then imme-
       diately thaws it out.

       The "lock_store" and "lock_nstore" routine are equivalent
       to "store" and "nstore", except that they get an exclusive
       lock on the file before writing.  Likewise,
       "lock_retrieve" does the same as "retrieve", but also gets
       a shared lock on the file before reading.

       As with any advisory locking scheme, the protection only
       works if you systematically use "lock_store" and
       "lock_retrieve".  If one side of your application uses
       "store" whilst the other uses "lock_retrieve", you will
       get no protection at all.

       The internal advisory locking is implemented using Perl's
       flock() routine.  If your system does not support any form
       of flock(), or if you share your files across NFS, you
       might wish to use other forms of locking by using modules
       such as LockFile::Simple which lock a file using a
       filesystem entry, instead of locking the file descriptor.

       The heart of Storable is written in C for decent speed.
       Extra low-level optimizations have been made when manipu-
       lating perl internals, to sacrifice encapsulation for the
       benefit of greater speed.

       Normally, Storable stores elements of hashes in the order
       they are stored internally by Perl, i.e. pseudo-randomly.
       If you set $Storable::canonical to some "TRUE" value,
       Storable will store hashes with the elements sorted by
       their key.  This allows you to compare data structures by
       comparing their frozen representations (or even the com-
       pressed frozen representations), which can be useful for
       creating lookup tables for complicated queries.

       Canonical order does not imply network order; those are
       two orthogonal settings.

perl v5.8.5                 2002-11-06                          3

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       Since Storable version 2.05, CODE references may be seri-
       alized with the help of B::Deparse. To enable this fea-
       ture, set $Storable::Deparse to a true value. To enable
       deserializazion, $Storable::Eval should be set to a true
       value. Be aware that deserialization is done through
       "eval", which is dangerous if the Storable file contains
       malicious data. You can set $Storable::Eval to a subrou-
       tine reference which would be used instead of "eval". See
       below for an example using a Safe compartment for deseri-
       alization of CODE references.

       If $Storable::Deparse and/or $Storable::Eval are set to
       false values, then the value of $Storable::forgive_me (see
       below) is respected while serializing and deserializing.

       This release of Storable can be used on a newer version of
       Perl to serialize data which is not supported by earlier
       Perls.  By default, Storable will attempt to do the right
       thing, by "croak()"ing if it encounters data that it can-
       not deserialize.  However, the defaults can be changed as

       utf8 data
           Perl 5.6 added support for Unicode characters with
           code points > 255, and Perl 5.8 has full support for
           Unicode characters in hash keys.  Perl internally
           encodes strings with these characters using utf8, and
           Storable serializes them as utf8.  By default, if an
           older version of Perl encounters a utf8 value it can-
           not represent, it will "croak()".  To change this
           behaviour so that Storable deserializes utf8 encoded
           values as the string of bytes (effectively dropping
           the is_utf8 flag) set $Storable::drop_utf8 to some
           "TRUE" value.  This is a form of data loss, because
           with $drop_utf8 true, it becomes impossible to tell
           whether the original data was the Unicode string, or a
           series of bytes that happen to be valid utf8.

       restricted hashes
           Perl 5.8 adds support for restricted hashes, which
           have keys restricted to a given set, and can have val-
           ues locked to be read only.  By default, when Storable
           encounters a restricted hash on a perl that doesn't
           support them, it will deserialize it as a normal hash,
           silently discarding any placeholder keys and leaving
           the keys and all values unlocked.  To make Storable
           "croak()" instead, set $Storable::downgrade_restricted
           to a "FALSE" value.  To restore the default set it
           back to some "TRUE" value.

       files from future versions of Storable
           Earlier versions of Storable would immediately croak

perl v5.8.5                 2002-11-06                          4

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

           if they encountered a file with a higher internal ver-
           sion number than the reading Storable knew about.
           Internal version numbers are increased each time new
           data types (such as restricted hashes) are added to
           the vocabulary of the file format.  This meant that a
           newer Storable module had no way of writing a file
           readable by an older Storable, even if the writer
           didn't store newer data types.

           This version of Storable will defer croaking until it
           encounters a data type in the file that it does not
           recognize.  This means that it will continue to read
           files generated by newer Storable modules which are
           careful in what they write out, making it easier to
           upgrade Storable modules in a mixed environment.

           The old behaviour of immediate croaking can be re-
           instated by setting $Storable::accept_future_minor to
           some "FALSE" value.

       All these variables have no effect on a newer Perl which
       supports the relevant feature.

       Storable uses the "exception" paradigm, in that it does
       not try to workaround failures: if something bad happens,
       an exception is generated from the caller's perspective
       (see Carp and "croak()").  Use eval {} to trap those

       When Storable croaks, it tries to report the error via the
       "logcroak()" routine from the "Log::Agent" package, if it
       is available.

       Normal errors are reported by having store() or retrieve()
       return "undef".  Such errors are usually I/O errors (or
       truncated stream errors at retrieval).


       Any class may define hooks that will be called during the
       serialization and deserialization process on objects that
       are instances of that class.  Those hooks can redefine the
       way serialization is performed (and therefore, how the
       symmetrical deserialization should be conducted).

       Since we said earlier:

           dclone(.) = thaw(freeze(.))

       everything we say about hooks should also hold for deep
       cloning. However, hooks get to know whether the operation
       is a mere serialization, or a cloning.

perl v5.8.5                 2002-11-06                          5

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       Therefore, when serializing hooks are involved,

           dclone(.) <> thaw(freeze(.))

       Well, you could keep them in sync, but there's no guaran-
       tee it will always hold on classes somebody else wrote.
       Besides, there is little to gain in doing so: a serializ-
       ing hook could keep only one attribute of an object, which
       is probably not what should happen during a deep cloning
       of that same object.

       Here is the hooking interface:

       "STORABLE_freeze" obj, cloning
           The serializing hook, called on the object during
           serialization.  It can be inherited, or defined in the
           class itself, like any other method.

           Arguments: obj is the object to serialize, cloning is
           a flag indicating whether we're in a dclone() or a
           regular serialization via store() or freeze().

           Returned value: A LIST "($serialized, $ref1, $ref2,
           ...)" where $serialized is the serialized form to be
           used, and the optional $ref1, $ref2, etc... are extra
           references that you wish to let the Storable engine

           At deserialization time, you will be given back the
           same LIST, but all the extra references will be point-
           ing into the deserialized structure.

           The first time the hook is hit in a serialization
           flow, you may have it return an empty list.  That will
           signal the Storable engine to further discard that
           hook for this class and to therefore revert to the
           default serialization of the underlying Perl data.
           The hook will again be normally processed in the next

           Unless you know better, serializing hook should always

               sub STORABLE_freeze {
                   my ($self, $cloning) = @_;
                   return if $cloning;         # Regular default serialization

           in order to keep reasonable dclone() semantics.

       "STORABLE_thaw" obj, cloning, serialized, ...
           The deserializing hook called on the object during
           deserialization.  But wait: if we're deserializing,

perl v5.8.5                 2002-11-06                          6

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

           there's no object yet... right?

           Wrong: the Storable engine creates an empty one for
           you.  If you know Eiffel, you can view "STORABLE_thaw"
           as an alternate creation routine.

           This means the hook can be inherited like any other
           method, and that obj is your blessed reference for
           this particular instance.

           The other arguments should look familiar if you know
           "STORABLE_freeze": cloning is true when we're part of
           a deep clone operation, serialized is the serialized
           string you returned to the engine in
           "STORABLE_freeze", and there may be an optional list
           of references, in the same order you gave them at
           serialization time, pointing to the deserialized
           objects (which have been processed courtesy of the
           Storable engine).

           When the Storable engine does not find any
           "STORABLE_thaw" hook routine, it tries to load the
           class by requiring the package dynamically (using the
           blessed package name), and then re-attempts the
           lookup.  If at that time the hook cannot be located,
           the engine croaks.  Note that this mechanism will fail
           if you define several classes in the same file, but
           perlmod warned you.

           It is up to you to use this information to populate
           obj the way you want.

           Returned value: none.


       Predicates are not exportable.  They must be called by
       explicitly prefixing them with the Storable package name.

           The "Storable::last_op_in_netorder()" predicate will
           tell you whether network order was used in the last
           store or retrieve operation.  If you don't know how to
           use this, just forget about it.

           Returns true if within a store operation (via
           STORABLE_freeze hook).

           Returns true if within a retrieve operation (via
           STORABLE_thaw hook).

perl v5.8.5                 2002-11-06                          7

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)


       With hooks comes the ability to recurse back to the
       Storable engine.  Indeed, hooks are regular Perl code, and
       Storable is convenient when it comes to serializing and
       deserializing things, so why not use it to handle the
       serialization string?

       There are a few things you need to know, however:

       o   You can create endless loops if the things you serial-
           ize via freeze() (for instance) point back to the
           object we're trying to serialize in the hook.

       o   Shared references among objects will not stay shared:
           if we're serializing the list of object [A, C] where
           both object A and C refer to the SAME object B, and if
           there is a serializing hook in A that says freeze(B),
           then when deserializing, we'll get [A', C'] where A'
           refers to B', but C' refers to D, a deep clone of B'.
           The topology was not preserved.

       That's why "STORABLE_freeze" lets you provide a list of
       references to serialize.  The engine guarantees that those
       will be serialized in the same context as the other
       objects, and therefore that shared objects will stay

       In the above [A, C] example, the "STORABLE_freeze" hook
       could return:

               ("something", $self->{B})

       and the B part would be serialized by the engine.  In
       "STORABLE_thaw", you would get back the reference to the
       B' object, deserialized for you.

       Therefore, recursion should normally be avoided, but is
       nonetheless supported.

       Deep Cloning

       There is a Clone module available on CPAN which implements
       deep cloning natively, i.e. without freezing to memory and
       thawing the result.  It is aimed to replace Storable's
       dclone() some day.  However, it does not currently support
       Storable hooks to redefine the way deep cloning is per-

Storable magic
       Yes, there's a lot of that :-) But more precisely, in UNIX
       systems there's a utility called "file", which recognizes
       data files based on their contents (usually their first
       few bytes).  For this to work, a certain file called magic

perl v5.8.5                 2002-11-06                          8

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       needs to taught about the signature of the data.  Where
       that configuration file lives depends on the UNIX flavour;
       often it's something like /usr/share/misc/magic or
       /etc/magic.  Your system administrator needs to do the
       updating of the magic file.  The necessary signature
       information is output to STDOUT by invoking
       Storable::show_file_magic().  Note that the GNU implemen-
       tation of the "file" utility, version 3.38 or later, is
       expected to contain support for recognising Storable files
       out-of-the-box, in addition to other kinds of Perl files.

       Here are some code samples showing a possible usage of

               use Storable qw(store retrieve freeze thaw dclone);

               %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);

               store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";

               $colref = retrieve('mycolors');
               die "Unable to retrieve from mycolors!\n" unless defined $colref;
               printf "Blue is still %lf\n", $colref->{'Blue'};

               $colref2 = dclone(\%color);

               $str = freeze(\%color);
               printf "Serialization of %%color is %d bytes long.\n", length($str);
               $colref3 = thaw($str);

       which prints (on my machine):

               Blue is still 0.100000
               Serialization of %color is 102 bytes long.

       Serialization of CODE references and deserialization in a
       safe compartment:

               use Storable qw(freeze thaw);
               use Safe;
               use strict;
               my $safe = new Safe;
               # because of opcodes used in "use strict":
               $safe->permit(qw(:default require));
               local $Storable::Deparse = 1;
               local $Storable::Eval = sub { $safe->reval($_[0]) };
               my $serialized = freeze(sub { 42 });
               my $code = thaw($serialized);
               $code->() == 42;

       If you're using references as keys within your hash
       tables, you're bound to be disappointed when retrieving

perl v5.8.5                 2002-11-06                          9

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       your data. Indeed, Perl stringifies references used as
       hash table keys. If you later wish to access the items via
       another reference stringification (i.e. using the same
       reference that was used for the key originally to record
       the value into the hash table), it will work because both
       references stringify to the same string.

       It won't work across a sequence of "store" and "retrieve"
       operations, however, because the addresses in the
       retrieved objects, which are part of the stringified ref-
       erences, will probably differ from the original addresses.
       The topology of your structure is preserved, but not hid-
       den semantics like those.

       On platforms where it matters, be sure to call "binmode()"
       on the descriptors that you pass to Storable functions.

       Storing data canonically that contains large hashes can be
       significantly slower than storing the same data normally,
       as temporary arrays to hold the keys for each hash have to
       be allocated, populated, sorted and freed.  Some tests
       have shown a halving of the speed of storing -- the exact
       penalty will depend on the complexity of your data.  There
       is no slowdown on retrieval.

       You can't store GLOB, FORMLINE, etc.... If you can define
       semantics for those operations, feel free to enhance
       Storable so that it can deal with them.

       The store functions will "croak" if they run into such
       references unless you set $Storable::forgive_me to some
       "TRUE" value. In that case, the fatal message is turned in
       a warning and some meaningless string is stored instead.

       Setting $Storable::canonical may not yield frozen strings
       that compare equal due to possible stringification of num-
       bers. When the string version of a scalar exists, it is
       the form stored; therefore, if you happen to use your num-
       bers as strings between two freezing operations on the
       same data structures, you will get different results.

       When storing doubles in network order, their value is
       stored as text.  However, you should also not expect non-
       numeric floating-point values such as infinity and "not a
       number" to pass successfully through a nstore()/retrieve()

       As Storable neither knows nor cares about character sets
       (although it does know that characters may be more than
       eight bits wide), any difference in the interpretation of
       character codes between a host and a target system is your
       problem.  In particular, if host and target use different
       code points to represent the characters used in the text

perl v5.8.5                 2002-11-06                         10

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       representation of floating-point numbers, you will not be
       able be able to exchange floating-point data, even with

       "Storable::drop_utf8" is a blunt tool.  There is no facil-
       ity either to return all strings as utf8 sequences, or to
       attempt to convert utf8 data back to 8 bit and "croak()"
       if the conversion fails.

       Prior to Storable 2.01, no distinction was made between
       signed and unsigned integers on storing.  By default
       Storable prefers to store a scalars string representation
       (if it has one) so this would only cause problems when
       storing large unsigned integers that had never been
       coverted to string or floating point.  In other words val-
       ues that had been generated by integer operations such as
       logic ops and then not used in any string or arithmetic
       context before storing.

       64 bit data in perl 5.6.0 and 5.6.1

       This section only applies to you if you have existing data
       written out by Storable 2.02 or earlier on perl 5.6.0 or
       5.6.1 on Unix or Linux which has been configured with 64
       bit integer support (not the default) If you got a precom-
       piled perl, rather than running Configure to build your
       own perl from source, then it almost certainly does not
       affect you, and you can stop reading now (unless you're
       curious). If you're using perl on Windows it does not
       affect you.

       Storable writes a file header which contains the sizes of
       various C language types for the C compiler that built
       Storable (when not writing in network order), and will
       refuse to load files written by a Storable not on the same
       (or compatible) architecture.  This check and a check on
       machine byteorder is needed because the size of various
       fields in the file are given by the sizes of the C lan-
       guage types, and so files written on different architec-
       tures are incompatible.  This is done for increased speed.
       (When writing in network order, all fields are written out
       as standard lengths, which allows full interworking, but
       takes longer to read and write)

       Perl 5.6.x introduced the ability to optional configure
       the perl interpreter to use C's "long long" type to allow
       scalars to store 64 bit integers on 32 bit systems.  How-
       ever, due to the way the Perl configuration system gener-
       ated the C configuration files on non-Windows platforms,
       and the way Storable generates its header, nothing in the
       Storable file header reflected whether the perl writing
       was using 32 or 64 bit integers, despite the fact that
       Storable was storing some data differently in the file.
       Hence Storable running on perl with 64 bit integers will

perl v5.8.5                 2002-11-06                         11

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       read the header from a file written by a 32 bit perl, not
       realise that the data is actually in a subtly incompatible
       format, and then go horribly wrong (possibly crashing) if
       it encountered a stored integer.  This is a design fail-

       Storable has now been changed to write out and read in a
       file header with information about the size of integers.
       It's impossible to detect whether an old file being read
       in was written with 32 or 64 bit integers (they have the
       same header) so it's impossible to automatically switch to
       a correct backwards compatibility mode.  Hence this
       Storable defaults to the new, correct behaviour.

       What this means is that if you have data written by
       Storable 1.x running on perl 5.6.0 or 5.6.1 configured
       with 64 bit integers on Unix or Linux then by default this
       Storable will refuse to read it, giving the error Byte
       order is not compatible.  If you have such data then you
       you should set $Storable::interwork_56_64bit to a true
       value to make this Storable read and write files with the
       old header.  You should also migrate your data, or any
       older perl you are communicating with, to this current
       version of Storable.

       If you don't have data written with specific configuration
       of perl described above, then you do not and should not do
       anything.  Don't set the flag - not only will Storable on
       an identically configured perl refuse to load them, but
       Storable a differently configured perl will load them
       believing them to be correct for it, and then may well
       fail or crash part way through reading them.

       Thank you to (in chronological order):

               Jarkko Hietaniemi <jhiATiki.fi>
               Ulrich Pfeifer <pfeiferATcharly.de>
               Benjamin A. Holzman <bahATecnvantage.com>
               Andrew Ford <A.FordATford-mason.uk>
               Gisle Aas <gisleATaas.no>
               Jeff Gresham <gresham_jeffreyATjpmorgan.com>
               Murray Nesbitt <murrayATactivestate.com>
               Marc Lehmann <pcgATopengroup.org>
               Justin Banks <justinbATwamnet.com>
               Jarkko Hietaniemi <jhiATiki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
               Salvador Ortiz Garcia <sogATmsg.mx>
               Dominic Dunlop <domoATcomputer.org>
               Erik Haugan <erikATsolbors.no>

       for their bug reports, suggestions and contributions.

       Benjamin Holzman contributed the tied variable support,
       Andrew Ford contributed the canonical order for hashes,

perl v5.8.5                 2002-11-06                         12

ext::Storable::StPerllProgrammers Refeext::Storable::Storable(3p)

       and Gisle Aas fixed a few misunderstandings of mine
       regarding the perl internals, and optimized the emission
       of "tags" in the output streams by simply counting the
       objects instead of tagging them (leading to a binary
       incompatibility for the Storable image starting at version
       0.6--older images are, of course, still properly under-
       stood).  Murray Nesbitt made Storable thread-safe.  Marc
       Lehmann added overloading and references to tied items

       Storable was written by Raphael Manfredi &lt;Raphael_Man-
       fredi@pobox.com&gt; Maintenance is now done by the
       perl5-porters &lt;perl5-porters@perl.org&gt;

       Please e-mail us with problems, bug fixes, comments and
       complaints, although if you have complements you should
       send them to Raphael.  Please don't e-mail Raphael with
       problems, as he no longer works on Storable, and your mes-
       sage will be delayed while he forwards it to us.


perl v5.8.5                 2002-11-06                         13