print join ",",keys %{$data[0]};
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See perlfunc for docs on the use of keys.

I guess you want to traverse the array, and then traverse each hash elements. One solution could be:

for my $hash (@data) {
    for (keys %$hash) { ... }
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If you simply want to list the keys of a hash, you can do:

my @keys = keys %{$data[0]}; # or [1], or [2], ...
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Hope this helps.

I guess you want to traverse the array, and then traverse each hash elements.

Depending on what the data's being used for, for quickly printing any complex data structure you can often avoid writing any loops yourself just by using YAML (or Data::Dumper if you prefer):

use YAML qw<Dump>;
print Dump \@data;
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Smylers

my %allKeys;
foreach my $i ( 0 .. $#data ){
  my $hash = $data[$i];
  for (keys %$hash) {
    push @{$allKeys{$_}}, $i;
  }
}

foreach my $key ( sort keys %allKeys ){
  my $locations = $allKeys{$key};
  printf "Key '%s' was seen %d times at these indices: %s\n",
    $key, scalar @$locations, join(", ", @$locations);
}
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for ( my $i=0; $i<=$#data; $i++ ) {
    my $href = $data[$i];
    for ( keys %$href ) {
        print "$_\n";
    }
}
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-S

Most monks would suggest the more natural foreach for something like this, as it tends to cut down on "one-off" errors. Also, it tends to be more intuitive (at least after you've learned Perl; I can see how your way would be more intutitive to a person coming from C or Java).

foreach my $href ( @data ) {
    for ( keys %$href ) {
        print "$_\n";
    }
}
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    -Bryan