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

I am passing a hash to a subroutine as a reference, e.g. &thing(\%hash); The subroutine then pulls in the hash values with my $args = shift; and I call the values using $args->{key}. Is there a manner of running thru the "keys" of this hash reference, even though its now a scalar, rather than an actual hash?

thanks -c

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Re: foreach keys possible using a hash reference?
by Abigail-II (Bishop) on Jul 04, 2002 at 17:10 UTC
    The rule on what the syntax is when dealing with references is very simple. Wherever you use something of the form sigil followed by the name of a variable (scalar, hash, array, subroutine), you may replace the name of the variable with a block whose result is a reference to the appropriate type.

    So, where you normally would write 

        keys %hash

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    you now replace hash with a block returning a reference to a hash, and you get: 
        keys %{$hashref}

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    The block has a very, very simple statement, the statement is just an expression consisting of a single variable. As an extra feature, in such a simple expression, you may omit the braces, so you will end up with: 
        keys %$hashref

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    Abigail

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Re: foreach keys possible using a hash reference?
by gav^ (Curate) on Jul 04, 2002 at 17:03 UTC
    Something like this would do the trick: 
    foreach (keys %$args) {
  # do something 
}

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    gav^

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Re: foreach keys possible using a hash reference?
by amphiplex (Monk) on Jul 04, 2002 at 17:04 UTC
    this should do: 
    my %h = (
  'a' => 1,
  'b' => 2,
  'c' => 3,
);

print_hash(\%h);

sub print_hash {
  my $h = shift;
  for (keys %$h) {
    print "$_: $h->{$_}\n";
  }
}

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    ---- kurt
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Re: foreach keys possible using a hash reference?
by impossiblerobot (Deacon) on Jul 04, 2002 at 21:53 UTC
    I would also suggest perlreftut, which details five simple rules for creating and de-referencing references, and really simplifies things.

    Impossible Robot
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Re: foreach keys possible using a hash reference?
by Juerd (Abbot) on Jul 04, 2002 at 19:48 UTC
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