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Dumper (3)
  • >> Dumper (3) ( Solaris man: Библиотечные вызовы )
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    NAME

         Data::Dumper - stringified perl data structures, suitable
         for both printing and eval
    
    
    

    SYNOPSIS

             use Data::Dumper;
    
             # simple procedural interface
             print Dumper($foo, $bar);
    
             # extended usage with names
             print Data::Dumper->Dump([$foo, $bar], [qw(foo *ary)]);
    
             # configuration variables
             {
               local $Data::Dump::Purity = 1;
               eval Data::Dumper->Dump([$foo, $bar], [qw(foo *ary)]);
             }
    
             # OO usage
             $d = Data::Dumper->new([$foo, $bar], [qw(foo *ary)]);
                ...
             print $d->Dump;
                ...
             $d->Purity(1)->Terse(1)->Deepcopy(1);
             eval $d->Dump;
    
    
    
    

    DESCRIPTION

         Given a list of scalars or reference variables, writes out
         their contents in perl syntax. The references can also be
         objects.  The contents of each variable is output in a
         single Perl statement.  Handles self-referential structures
         correctly.
    
         The return value can be evaled to get back an identical copy
         of the original reference structure.
    
         Any references that are the same as one of those passed in
         will be named $VARn (where n is a numeric suffix), and other
         duplicate references to substructures within $VARn will be
         appropriately labeled using arrow notation.  You can specify
         names for individual values to be dumped if you use the
         Dump() method, or you can change the default $VAR prefix to
         something else.  See $Data::Dumper::Varname and
         $Data::Dumper::Terse below.
    
         The default output of self-referential structures can be
         evaled, but the nested references to $VARn will be
         undefined, since a recursive structure cannot be constructed
         using one Perl statement.  You should set the Purity flag to
         1 to get additional statements that will correctly fill in
         these references.
    
         In the extended usage form, the references to be dumped can
         be given user-specified names.  If a name begins with a *,
         the output will describe the dereferenced type of the
         supplied reference for hashes and arrays, and coderefs.
         Output of names will be avoided where possible if the Terse
         flag is set.
    
         In many cases, methods that are used to set the internal
         state of the object will return the object itself, so method
         calls can be conveniently chained together.
    
         Several styles of output are possible, all controlled by
         setting the Indent flag.  See the section on Configuration
         Variables or Methods below for details.
    
         Methods
    
         PACKAGE->new(ARRAYREF [, ARRAYREF])
             Returns a newly created Data::Dumper object.  The first
             argument is an anonymous array of values to be dumped.
             The optional second argument is an anonymous array of
             names for the values.  The names need not have a leading
             $ sign, and must be comprised of alphanumeric
             characters.  You can begin a name with a * to specify
             that the dereferenced type must be dumped instead of the
             reference itself, for ARRAY and HASH references.
    
             The prefix specified by $Data::Dumper::Varname will be
             used with a numeric suffix if the name for a value is
             undefined.
    
             Data::Dumper will catalog all references encountered
             while dumping the values. Cross-references (in the form
             of names of substructures in perl syntax) will be
             inserted at all possible points, preserving any
             structural interdependencies in the original set of
             values.  Structure traversal is depth-first,  and
             proceeds in order from the first supplied value to the
             last.
    
         $OBJ->Dump  or  PACKAGE->Dump(ARRAYREF [, ARRAYREF])
             Returns the stringified form of the values stored in the
             object (preserving the order in which they were supplied
             to new), subject to the configuration options below.  In
             an array context, it returns a list of strings
             corresponding to the supplied values.
    
             The second form, for convenience, simply calls the new
             method on its arguments before dumping the object
             immediately.
    
         $OBJ->Dumpxs  or  PACKAGE->Dumpxs(ARRAYREF [, ARRAYREF])
             This method is available if you were able to compile and
             install the XSUB extension to Data::Dumper. It is
             exactly identical to the Dump method above, only about 4
             to 5 times faster, since it is written entirely in C.
    
         $OBJ->Seen([HASHREF])
             Queries or adds to the internal table of already
             encountered references.  You must use Reset to
             explicitly clear the table if needed.  Such references
             are not dumped; instead, their names are inserted
             wherever they are encountered subsequently.  This is
             useful especially for properly dumping subroutine
             references.
    
             Expects a anonymous hash of name => value pairs.  Same
             rules apply for names as in new.  If no argument is
             supplied, will return the "seen" list of name => value
             pairs, in an array context.  Otherwise, returns the
             object itself.
    
         $OBJ->Values([ARRAYREF])
             Queries or replaces the internal array of values that
             will be dumped.  When called without arguments, returns
             the values.  Otherwise, returns the object itself.
    
         $OBJ->Names([ARRAYREF])
             Queries or replaces the internal array of user supplied
             names for the values that will be dumped.  When called
             without arguments, returns the names.  Otherwise,
             returns the object itself.
    
         $OBJ->Reset
             Clears the internal table of "seen" references and
             returns the object itself.
    
         Functions
    
         Dumper(LIST)
             Returns the stringified form of the values in the list,
             subject to the configuration options below.  The values
             will be named $VARn in the output, where n is a numeric
             suffix.  Will return a list of strings in an array
             context.
    
         DumperX(LIST)
             Identical to the Dumper() function above, but this calls
             the XSUB implementation.  Only available if you were
             able to compile and install the XSUB extensions in
             Data::Dumper.
    
    
         Configuration Variables or Methods
    
         Several configuration variables can be used to control the
         kind of output generated when using the procedural
         interface.  These variables are usually localized in a block
         so that other parts of the code are not affected by the
         change.
    
         These variables determine the default state of the object
         created by calling the new method, but cannot be used to
         alter the state of the object thereafter.  The equivalent
         method names should be used instead to query or set the
         internal state of the object.
    
         The method forms return the object itself when called with
         arguments, so that they can be chained together nicely.
    
         $Data::Dumper::Indent  or  $OBJ->Indent([NEWVAL])
             Controls the style of indentation.  It can be set to 0,
             1, 2 or 3.  Style 0 spews output without any newlines,
             indentation, or spaces between list items.  It is the
             most compact format possible that can still be called
             valid perl.  Style 1 outputs a readable form with
             newlines but no fancy indentation (each level in the
             structure is simply indented by a fixed amount of
             whitespace).  Style 2 (the default) outputs a very
             readable form which takes into account the length of
             hash keys (so the hash value lines up).  Style 3 is like
             style 2, but also annotates the elements of arrays with
             their index (but the comment is on its own line, so
             array output consumes twice the number of lines).  Style
             2 is the default.
    
         $Data::Dumper::Purity  or  $OBJ->Purity([NEWVAL])
             Controls the degree to which the output can be evaled to
             recreate the supplied reference structures.  Setting it
             to 1 will output additional perl statements that will
             correctly recreate nested references.  The default is 0.
    
         $Data::Dumper::Pad  or  $OBJ->Pad([NEWVAL])
             Specifies the string that will be prefixed to every line
             of the output.  Empty string by default.
    
         $Data::Dumper::Varname  or  $OBJ->Varname([NEWVAL])
             Contains the prefix to use for tagging variable names in
             the output. The default is "VAR".
    
         $Data::Dumper::Useqq  or  $OBJ->Useqq([NEWVAL])
             When set, enables the use of double quotes for
             representing string values.  Whitespace other than space
             will be represented as [\n\t\r], "unsafe" characters
             will be backslashed, and unprintable characters will be
             output as quoted octal integers.  Since setting this
             variable imposes a performance penalty, the default is
             0.  The Dumpxs() method does not honor this flag yet.
    
         $Data::Dumper::Terse  or  $OBJ->Terse([NEWVAL])
             When set, Data::Dumper will emit single, non-self-
             referential values as atoms/terms rather than
             statements.  This means that the $VARn names will be
             avoided where possible, but be advised that such output
             may not always be parseable by eval.
    
         $Data::Dumper::Freezer  or  $OBJ->Freezer([NEWVAL])
             Can be set to a method name, or to an empty string to
             disable the feature.  Data::Dumper will invoke that
             method via the object before attempting to stringify it.
             This method can alter the contents of the object (if,
             for instance, it contains data allocated from C), and
             even rebless it in a different package.  The client is
             responsible for making sure the specified method can be
             called via the object, and that the object ends up
             containing only perl data types after the method has
             been called.  Defaults to an empty string.
    
         $Data::Dumper::Toaster  or  $OBJ->Toaster([NEWVAL])
             Can be set to a method name, or to an empty string to
             disable the feature.  Data::Dumper will emit a method
             call for any objects that are to be dumped using the
             syntax bless(DATA, CLASS)-METHOD()>.  Note that this
             means that the method specified will have to perform any
             modifications required on the object (like creating new
             state within it, and/or reblessing it in a different
             package) and then return it.  The client is responsible
             for making sure the method can be called via the object,
             and that it returns a valid object.  Defaults to an
             empty string.
    
         $Data::Dumper::Deepcopy  or  $OBJ->Deepcopy([NEWVAL])
             Can be set to a boolean value to enable deep copies of
             structures.  Cross-referencing will then only be done
             when absolutely essential (i.e., to break reference
             cycles).  Default is 0.
    
         $Data::Dumper::Quotekeys  or  $OBJ->Quotekeys([NEWVAL])
             Can be set to a boolean value to control whether hash
             keys are quoted.  A false value will avoid quoting hash
             keys when it looks like a simple string.  Default is 1,
             which will always enclose hash keys in quotes.
    
         $Data::Dumper::Bless  or  $OBJ->Bless([NEWVAL])
             Can be set to a string that specifies an alternative to
             the bless builtin operator used to create objects.  A
             function with the specified name should exist, and
             should accept the same arguments as the builtin.
             Default is bless.
    
         Exports
    
         Dumper
    
    
    

    EXAMPLES

         Run these code snippets to get a quick feel for the behavior
         of this module.  When you are through with these examples,
         you may want to add or change the various configuration
         variables described above, to see their behavior.  (See the
         testsuite in the Data::Dumper distribution for more
         examples.)
    
             use Data::Dumper;
    
             package Foo;
             sub new {bless {'a' => 1, 'b' => sub { return "foo" }}, $_[0]};
    
             package Fuz;                       # a weird REF-REF-SCALAR object
             sub new {bless \($_ = \ 'fu\'z'), $_[0]};
    
             package main;
             $foo = Foo->new;
             $fuz = Fuz->new;
             $boo = [ 1, [], "abcd", \*foo,
                      {1 => 'a', 023 => 'b', 0x45 => 'c'},
                      \\"p\q\'r", $foo, $fuz];
    
             ########
             # simple usage
             ########
    
             $bar = eval(Dumper($boo));
             print($@) if $@;
             print Dumper($boo), Dumper($bar);  # pretty print (no array indices)
    
             $Data::Dumper::Terse = 1;          # don't output names where feasible
             $Data::Dumper::Indent = 0;         # turn off all pretty print
             print Dumper($boo), "\n";
    
             $Data::Dumper::Indent = 1;         # mild pretty print
             print Dumper($boo);
    
             $Data::Dumper::Indent = 3;         # pretty print with array indices
             print Dumper($boo);
    
    
    
             $Data::Dumper::Useqq = 1;          # print strings in double quotes
             print Dumper($boo);
    
    
             ########
             # recursive structures
             ########
    
             @c = ('c');
             $c = \@c;
             $b = {};
             $a = [1, $b, $c];
             $b->{a} = $a;
             $b->{b} = $a->[1];
             $b->{c} = $a->[2];
             print Data::Dumper->Dump([$a,$b,$c], [qw(a b c)]);
    
    
             $Data::Dumper::Purity = 1;         # fill in the holes for eval
             print Data::Dumper->Dump([$a, $b], [qw(*a b)]); # print as @a
             print Data::Dumper->Dump([$b, $a], [qw(*b a)]); # print as %b
    
    
             $Data::Dumper::Deepcopy = 1;       # avoid cross-refs
             print Data::Dumper->Dump([$b, $a], [qw(*b a)]);
    
    
             $Data::Dumper::Purity = 0;         # avoid cross-refs
             print Data::Dumper->Dump([$b, $a], [qw(*b a)]);
    
    
             ########
             # object-oriented usage
             ########
    
             $d = Data::Dumper->new([$a,$b], [qw(a b)]);
             $d->Seen({'*c' => $c});            # stash a ref without printing it
             $d->Indent(3);
             print $d->Dump;
             $d->Reset->Purity(0);              # empty the seen cache
             print join "----\n", $d->Dump;
    
    
             ########
             # persistence
             ########
    
             package Foo;
             sub new { bless { state => 'awake' }, shift }
             sub Freeze {
                 my $s = shift;
                 print STDERR "preparing to sleep\n";
                 $s->{state} = 'asleep';
                 return bless $s, 'Foo::ZZZ';
             }
    
             package Foo::ZZZ;
             sub Thaw {
                 my $s = shift;
                 print STDERR "waking up\n";
                 $s->{state} = 'awake';
                 return bless $s, 'Foo';
             }
    
             package Foo;
             use Data::Dumper;
             $a = Foo->new;
             $b = Data::Dumper->new([$a], ['c']);
             $b->Freezer('Freeze');
             $b->Toaster('Thaw');
             $c = $b->Dump;
             print $c;
             $d = eval $c;
             print Data::Dumper->Dump([$d], ['d']);
    
    
             ########
             # symbol substitution (useful for recreating CODE refs)
             ########
    
             sub foo { print "foo speaking\n" }
             *other = \&foo;
             $bar = [ \&other ];
             $d = Data::Dumper->new([\&other,$bar],['*other','bar']);
             $d->Seen({ '*foo' => \&foo });
             print $d->Dump;
    
    
    
    

    BUGS

         Due to limitations of Perl subroutine call semantics, you
         cannot pass an array or hash.  Prepend it with a \ to pass
         its reference instead.  This will be remedied in time, with
         the arrival of prototypes in later versions of Perl.  For
         now, you need to use the extended usage form, and prepend
         the name with a * to output it as a hash or array.
    
         Data::Dumper cheats with CODE references.  If a code
         reference is encountered in the structure being processed,
         an anonymous subroutine that contains the string '"DUMMY"'
         will be inserted in its place, and a warning will be printed
         if Purity is set.  You can eval the result, but bear in mind
         that the anonymous sub that gets created is just a
         placeholder.  Someday, perl will have a switch to cache-on-
         demand the string representation of a compiled piece of
         code, I hope.  If you have prior knowledge of all the code
         refs that your data structures are likely to have, you can
         use the Seen method to pre-seed the internal reference table
         and make the dumped output point to them, instead.  See the
         EXAMPLES manpage above.
    
         The Useqq flag is not honored by Dumpxs() (it always outputs
         strings in single quotes).
    
         SCALAR objects have the weirdest looking bless workaround.
    
    
    

    AUTHOR

         Gurusamy Sarathy        gsar@umich.edu
    
         Copyright (c) 1996-98 Gurusamy Sarathy. All rights reserved.
         This program is free software; you can redistribute it
         and/or modify it under the same terms as Perl itself.
    
    
    

    VERSION

         Version 2.10    (31 Oct 1998)
    
    
    

    SEE ALSO

         perl(1)
    
    
    
    


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