hash and it's keys...

stan2004 has asked for the wisdom of the Perl Monks concerning the following question:

Hi reader !
I got such problem - I want retrieve keys of hash, but seems like I got something wrong:

@hash{'one'} = "123";
@hash{'two'} = "123";
@hash{'three'} = "123";

foreach ($key = keys(%hash))
 {
     print "key is - $key\n";
 }
[download]

I'm excpecting:

one
two
three
[download]

but, I got number of keys.

Why ? Where I'm wrong ?

Thanks for any answers.

20040729 Edit by ysth: use code, p, and br tags instead of pre

Comment on hash and it's keys... Select or Download Code

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Re: hash and it's keys... by Limbic~Region (Chancellor) on Jul 29, 2004 at 19:52 UTC
stan2004, Well, you have both done it wrong and done it right. The correct syntax of a for loop of this type is: `# pseudo for <variable> ( list ) { # some code presumably using variable } # real for my $key ( keys %hash ) { print "$key\n"; }` [download] You may omit the <variable> and perl will happily stick the current alias from the list into $_ (see perldoc perlvar). You have chosen not use warnings and strictures so you didn't get told about the other things you did wrong. This is a testimony to how far Perl will go to do what you mean. The correct way to assign a value to a hash key is: `#psuedo $hash{<key>} = <value>; #read $hash{foo} = 'bar';` [download] You can however assign multiple values to multiple keys at once using a hash slice. The syntax is `#pseudo @hash{<list of keys>} = <list of values>; #real @hash{ @keys } = @values;` [download] Finally, keys returns a list of keys in a hash in list context, but the number of keys in scalar context. That is why you got the list of keys. It sounds like you still have a lot to learn. See the various perldocs, check out the tutorials section, check out http://learn.perl.org. Cheers - L~R	[reply] [d/l] [select]
Re: hash and it's keys... by gaal (Parson) on Jul 29, 2004 at 19:49 UTC
In versions of Perl up to and including 5, the proper way to refer to a hash element is `$hash{elem}`. Using a `@` works but is less efficient; if you run perl with warnings (-w) you'll get a notice to that effect. The `foreach` line should be spelled like this: `foreach my $key (keys %hash) {` [download] Hope this helps.	[reply] [d/l] [select]
Re: hash and it's keys... by ysth (Canon) on Jul 29, 2004 at 19:52 UTC
First of all, put "use warnings;" at the top of your code; it will help you immensely with all kinds of problems. @hash{'one'} = "123" does work, but is better said as $hash{'one'} = "123". $key = keys... is calling keys in a scalar context (asking for only one value). keys is documented to return the number of keys in the hash in this case. Say foreach my $key (keys %hash) instead, or while (my $key = each %hash).	[reply]
Re: hash and it's keys... by Fletch (Bishop) on Jul 29, 2004 at 19:51 UTC
You either mean to use `for my $key ( keys %hash ) { ... }` or `while( my $key = each %hash ) { ... }`. You get the number of keys in the hash when you use it in a scalar context. See `perldoc -f keys`. And also `@hash{'one'}` is wrong; that's a one key hash slice, when what you really mean is `$hash{'one'}`.	[reply] [d/l] [select]
Re: hash and it's keys... by Anonymous Monk on Jul 30, 2004 at 04:59 UTC
The problem in your code is, you are assigning the number of keys in the hash to the variable $key. Use, `foreach $key (keys %hash){ print $key."\n" }` [download]	[reply] [d/l]