Access to hash ref element

[Anonymous Monk]

Hi there Monks!
Its a question of doing it better, so I am confused!
How to access or better print the value of "name" from this simple sample code structure:

use strict;
use warnings;
use Data::Dumper;

my $data = [

{
'name' => 'Mary'
},

];

#my $test = $data[0]{1};
#my $test = $ { $data} { name };
#my $test = @{ $data} { name };
my $test =  $data->{ name };
print "\n - $test \n";
warn Dumper $test;

Thanks for looking!

[choroba]

The [ at the beginning of the structure means it is an array reference. The following { tells us there is a hash reference inside. Therefore, the following should work:

my $test = $data->[0]->{'name'};

which can be shortened to

my $test = $data->[0]{name};

as arraows after ] and } are optional and simple alphanumeric keys are quoted automatically.

[Anonymous Monk]

That's right! Thanks for it!

[Laurent_R]

Hi, you could do:

 print $data->[0]{name};

Or, if you prefer:

print $data->[0]->{name}

EDIT: oops, I had not seen Choroba's answer.

[TomDLux]

Seems to be a popular question for newcomers to ask how to access some component of a complicated structures.

The answer is to user the built-in debugger.

tlegrady@rw-q318:~$ perl -d t.pl

Loading DB routines from perl5db.pl version 1.3
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(t.pl:5):    my $data = [
  DB<1> n
main::(t.pl:16):    my $test =  $data->{ name };
  DB<1> x $data
0  ARRAY(0x70b910)
   0  HASH(0x70b970)
      'name' => 'Mary'
  DB<2> x $data->[0]
0  HASH(0x70b970)
   'name' => 'Mary'
  DB<3> x $data->[0]{name}
0  'Mary'

When the debugger starts, it shows that it's about to execute line 5. I do a "next" ( 'n') to complete that, and then it's going to execute line 16. I query the debugger to show the value of $data, and then of its components. Since you're looking right at it, it's easy to tell you want array element '0', hash tag 'name'.

[davido]

Another "answer" is simply Data::Dumper. It produces a dump that shows both the structure's content, and how to access individual elements. All that needs to be done is to dump the structure, and see how it's built.

[Laurent_R]

I fully agree. The debugger (and especially the x command to unfold data structure) is of tremendous help for all such cases and has helped me out many times. But, for some reason, many people seem to be afraid to use it, although it is in fact a very simple tool to use. Many questions on many developping forums would never be asked if the OP had "dared" to use the debugger to figure out what is going on. But there is nothing "daring" there, and it is increedibly helpful.

Having said that, the Data::Dumper is also a very useful way of understanding complicated data structure. But for the purpose of debugging, I think the debugger is the right tool.

[Anonymous Monk]

the debugger may be great for debugging your own programs, but not particularly friendly for sharing on forums -- Dumper fits that bill better

[AnomalousMonk]

... and if you want to interpolate it into a string before you print it, such scalar elements of arrays and hashes, however deeply nested or directly or indirectly referenced, interpolate like any other scalar:

>perl -wMstrict -le
"my $data = [ {'name' => 'Mary'} ];
 ;;
 print qq{---$data->[0]{name}---};
"
---Mary---