How can I print the contents of a hash in Perl?

Question

I keep printing my hash as # of buckets / # allocated. How do I print the contents of my hash?

Without using a while loop would be most preferable (for

Answer 1

Looping:

foreach(keys %my_hash) { print "$_ / $my_hash{$_}\n"; }

Functional

map {print "$_ / $my_hash{$_}\n"; } keys %my_hash;

But for sheer elegance, I'd have to choose wrang-wrang's. For my own code, I'd choose my foreach. Or tetro's Dumper use.

Answer 2

If you want to be pedantic and keep it to one line (without use statements and shebang), then I'll sort of piggy back off of tetromino's answer and suggest:

print Dumper( { 'abc' => 123, 'def' => [4,5,6] } );

Not doing anything special other than using the anonymous hash to skip the temp variable ;)

Answer 3

The answer depends on what is in your hash. If you have a simple hash a simple

print map { "$_ $h{$_}\n" } keys %h;

or

print "$_ $h{$_}\n" for keys %h;

will do, but if you have a hash that is populated with references you will something that can walk those references and produce a sensible output. This walking of the references is normally called serialization. There are many modules that implement different styles, some of the more popular ones are:

• Data::Dumper
• Data::Dump::Streamer
• YAML::XS
• JSON::XS
• XML::Dumper

Due to the fact that Data::Dumper is part of the core Perl library, it is probably the most popular; however, some of the other modules have very good things to offer.

Answer 4

Data::Dumper is your friend.

use Data::Dumper;
my %hash = ('abc' => 123, 'def' => [4,5,6]);
print Dumper(\%hash);

will output

$VAR1 = {
          'def' => [
                     4,
                     5,
                     6
                   ],
          'abc' => 123
        };

Answer 5

Easy:

print "$_ $h{$_}\n" for (keys %h);

Elegant, but actually 30% slower (!):

while (my ($k,$v)=each %h){print "$k $v\n"}