Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
Data::Dump(3)	      User Contributed Perl Documentation	 Data::Dump(3)

       Data::Dump - Pretty printing of data structures

	use Data::Dump qw(dump);

	$str = dump(@list);
	@copy_of_list =	eval $str;

	# or use it for	easy debug printout
	use Data::Dump;	dd localtime;

       This module provides a few functions that traverse their	argument list
       and return a string containing Perl code	that, when "eval"ed, produces
       a deep copy of the original arguments.

       The main	feature	of the module is that it strives to produce output
       that is easy to read.  Example:

	   @a =	(1, [2,	3], {4 => 5});


	   "(1,	[2, 3],	{ 4 => 5 })"

       If you dump just	a little data, it is output on a single	line. If you
       dump data that is more complex or there is a lot	of it, line breaks are
       automatically added to keep it easy to read.

       The following functions are provided (only the dd* functions are
       exported	by default):

       dump( ... )
       pp( ... )
	   Returns a string containing a Perl expression.  If you pass this
	   string to Perl's built-in eval() function it	should return a	copy
	   of the arguments you	passed to dump().

	   If you call the function with multiple arguments then the output
	   will	be wrapped in parenthesis "( ..., ... )".  If you call the
	   function with a single argument the output will not have the
	   wrapping.  If you call the function with a single scalar (non-
	   reference) argument it will just return the scalar quoted if
	   needed, but never break it into multiple lines.  If you pass
	   multiple arguments or references to arrays of hashes	then the
	   return value	might contain line breaks to format it for easier
	   reading.  The returned string will never be "\n" terminated,	even
	   if contains multiple	lines.	This allows code like this to place
	   the semicolon in the	expected place:

	      print '$obj = ', dump($obj), ";\n";

	   If dump() is	called in void context,	then the dump is printed on
	   STDERR and then "\n"	terminated.  You might find this useful	for
	   quick debug printouts, but the dd*()	functions might	be better
	   alternatives	for this.

	   There is no difference between dump() and pp(), except that dump()
	   shares its name with	a not-so-useful	perl builtin.  Because of this
	   some	might want to avoid using that name.

       quote( $string )
	   Returns a quoted version of the provided string.

	   It differs from "dump($string)" in that it will quote even numbers
	   and not try to come up with clever expressions that might shorten
	   the output.	If a non-scalar	argument is provided then it's just
	   stringified instead of traversed.

       dd( ... )
       ddx( ...	)
	   These functions will	call dump() on their argument and print	the
	   result to STDOUT (actually, it's the	currently selected output
	   handle, but STDOUT is the default for that).

	   The difference between them is only that ddx() will prefix the
	   lines it prints with	"# " and mark the first	line with the file and
	   line	number where it	was called.  This is meant to be useful	for
	   debug printouts of state within programs.

       dumpf( ..., \&filter )
	   Short hand for calling the dump_filtered() function of
	   Data::Dump::Filtered.  This works like dump(), but the last
	   argument should be a	filter callback	function.  As objects are
	   visited the filter callback is invoked and it can modify how	the
	   objects are dumped.

       There are a few global variables	that can be set	to modify the output
       generated by the	dump functions.	 It's wise to localize the setting of

	   This	holds the string that's	used for indenting multiline data
	   structures.	It's default value is "	 " (two	spaces).  Set it to ""
	   to suppress indentation.  Setting it	to "| "	makes for nice visuals
	   even	if the dump output then	fails to be valid Perl.

	   How long must a binary string be before we try to use the base64
	   encoding for	the dump output.  The default is 50.  Set it to	0 to
	   disable base64 dumps.

	   This	controls how wide the string should before we add a line
	   break.  The default is 60.

       Code references will be dumped as "sub {	... }".	Thus, "eval"ing	them
       will not	reproduce the original routine.	 The "..."-operator used will
       also require perl-5.12 or better	to be evaled.

       If you forget to	explicitly import the "dump" function, your code will
       core dump. That's because you just called the builtin "dump" function
       by accident, which intentionally	dumps core.  Because of	this you can
       also import the same function as	"pp", mnemonic for "pretty-print".

       The "Data::Dump"	module grew out	of frustration with Sarathy's in-most-
       cases-excellent "Data::Dumper".	Basic ideas and	some code are shared
       with Sarathy's module.

       The "Data::Dump"	module provides	a much simpler interface than
       "Data::Dumper".	No OO interface	is available and there are fewer
       configuration options to	worry about.  The other	benefit	is that	the
       dump produced does not try to set any variables.	 It only returns what
       is needed to produce a copy of the arguments.  This means that
       "dump("foo")" simply returns '"foo"', and "dump(1..3)" simply returns
       '(1, 2, 3)'.

       Data::Dump::Filtered, Data::Dump::Trace,	Data::Dumper, JSON, Storable

       The "Data::Dump"	module is written by Gisle Aas <>, based
       on "Data::Dumper" by Gurusamy Sarathy <>.

	Copyright 1998-2010 Gisle Aas.
	Copyright 1996-1998 Gurusamy Sarathy.

       This distribution is currenly maintained	by Breno G. de Oliveira.

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl v5.32.1			  2021-06-26			 Data::Dump(3)


Want to link to this manual page? Use this URL:

home | help