The return value can be eval ed to get back the original reference structure. Bear in mind that a reference so created will not preserve pointer equalities with the original reference.
Handles self-referential structures correctly. Any references that are the
same as one of those passed in will be marked $VARI$VARI
In the extended usage form, the supplied references can be given
user-specified names. If a supplied name begins with a *, the output
will describe the dereferenced type of the supplied reference for hashes and
arrays.
Several styles of output are possible, all controlled by setting
$Data::Dumper::Indent
or using the corresponding method name. 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).
Methods
-
PACKAGE->new(ARRAYREF [, ARRAYREF])
-
Returns a newly created
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.
The prefix specified by
$Data::Dumper::Varname
will be used with a
numeric suffix if the name for a value is undefined.
-
$<
EM>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.
The second form, for convenience, simply calls the new method on its
arguments before dumping the object immediately.
-
$<
EM>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 to be dumped subsequently.
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.
-
$<
EM>OBJ->Values([ARRAYREF])
-
Queries or replaces the internal array of values that will be dumped.
-
$<
EM>OBJ->Names([ARRAYREF])
-
Queries or replaces the internal array of user supplied names for the values
that will be dumped.
-
$<
EM>OBJ->Reset
-
Clears the internal table of ``seen'' references.
Functions
-
Dumper(LIST)
-
Returns the stringified form of the values in the list, subject to the
configuration options below. The values will be named
$VARII
Configuration Variables/Methods
Several configuration variables can be used to control the kind of output
generated when using the procedural interface. These variables are usually
local
ized 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.
-
$Data::Dumper::Indent
or
$<
EM>OBJ->Indent([NEWVAL])
-
Controls the style of indentation. It can be set to 0, 1, 2 or 3. 2 is the
default.
-
$Data::Dumper::Purity
or
$<
EM>OBJ->Purity([NEWVAL])
-
Controls the degree to which the output can be
eval
ed 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
$<
EM>OBJ->Pad([NEWVAL])
-
Specifies the string that will be prefixed to every line of the output.
Empty string by default.
-
$Data::Dumper::Varname
or
$<
EM>OBJ->Varname([NEWVAL])
-
Contains the prefix to use for tagging variable names in the output. The
default is ``VAR''.
Exports
-
Dumper
-
EXAMPLE
use Data::Dumper;
package Foo;
sub new {bless {'a' => 1, 'b' => sub { return "foo" }}, $_[0]};
package Fuz; # a wierd 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];
$bar = eval(Dumper($boo));
print($@) if $@;
print Dumper($boo), Dumper($bar); # pretty print (no array indices)
$Data::Dumper::Indent = 0; # turn off all pretty print
print Dumper($boo), "\n";
$Data::Dumper::Indent = 1; # mild pretty print
print Dumper($boo);
$Data::Dumper::Indent = 3; # pretty print with array indices
print Dumper($boo);
# recursive structure
@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
$d = Data::Dumper->new([$a,$b], [qw(a b)]); # go OO
$d->Seen({'*c' => $c}); # stash a ref without printing it
$d->Indent(3);
print $d->Dump;
$d->Reset; # empty the seen cache
$d->Purity(0);
print $d->Dump;
BUGS
Due to limitations of Perl subroutine call semantics, you can't 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.
Dumper
cheats with CODE references. If a code reference is encountered in
the structure being processed, an anonymous subroutine returning the perl
string-interpolated representation of the original CODE reference 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 a dummy placeholder. Someday, perl will have a switch
to cache-on-demand the string representation of a compiled piece of code, I
hope.
SCALAR objects have the wierdest looking
bless
workaround.
AUTHOR
Gurusamy Sarathy gsar@umich.edu
Copyright (c) 1995 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 1.23 3 Dec 1995
SEE ALSO
perl(1)