What is Perl's equivalent to PHP's print_r()?

Question

I find print_r in PHP extremely useful, but wonder if there is anything remotely equivalent in Perl?

Answer 1

Data::Dumper

A snippet of the examples shown in the above link.

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);

Answer 2

As usually with Perl, you might prefer alternative solutions to the venerable Data::Dumper:

• Data::Dump::Streamer has a terser output than Data::Dumper, and can also serialize some data better than Data::Dumper,
• YAML (or Yaml::Syck, or an other YAML module) generate the data in YAML, which is quite legible.

And of course with the debugger, you can display any variable with the 'x' command. I particularly like the form 'x 2 $complex_structure' where 2 (or any number) tells the debugger to display only 2 levels of nested data.

Answer 3

An alternative to Data::Dumper that does not produce valid Perl code but instead a more skimmable format (same as the x command of the Perl debugger) is Dumpvalue. It also consumes a lot less memory.

As well, there is Data::Dump::Streamer, which is more accurate in various edge and corner cases than Data::Dumper is.

Answer 4

I use Data::Dump, it's output is a bit cleaner than Data::Dumper's (no $VAR1), it provides quick shortcuts and it also tries to DTRT, i.e. it will print to STDERR when called in void context and return the dump string when not.

Answer 5

I went looking for the same thing and found this lovely little Perl function, explicitly meant to generate results like print_r().

The author of the script was asking your exact question in a forum here.

print objectToString($json_data);

Gives this output:

HASH {
time                             => 1233173875
error                            => 0
node                             => HASH {
    vid                              => 1011
    moderate                         => 0
    field_datestring                 => ARRAY {
        HASH {
            value                            => August 30, 1979
        }
    }

    field_tagged_persons             => ARRAY {
        HASH {
            nid                              => undef
        }
    }

...and so on...