# caller:
StartCapture( { twigs => {filter => $filterTwig, capture => $captureTw
+ig},
                hashes => {filter => \%filterHash, capture => \%captur
+eHash},
                files => {filter => 'filter.txt', capture => 'capture.
+txt'},
                results => 'c:/temp.txt' } );

# ...

sub StartCapture
{
    my $hashref = shift;

    $$hashref{results} ||= 'c:/SomeDefault.txt';

#   ...
}
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Thanks. My optional parameters problem is solved, but I learned a new way of doing it by seeing your post

Here is an example. You pass the parmeter as a hash reference and access it as a hash reference in the function.

func({1=>'a', 
      2=>'a',
      'a'=>99,
      'f'=>'234',
      'xyzzy'=>'Grue be here.',
      'foo'=>'geww',});


sub func
  {
    my $hashref = shift;

    print "an item from hash: $hashref->{'xyzzy'}\n";
    printf("another item from hash: %s\n", $hashref->{'foo'});
  }
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I think you missed the @_ added to the end of the hash, which would effectively OVERWRITE the default values with the ones passed in.

Celebrate Intellectual Diversity

How to handle the optional parameters in this case?

Oh, From your response, it sounds like you are asking about a specific function that is part of a package? XML::Twig perhaps?

Adding that to the question will probably get you a better answer... Your question sounded like you were having trouble passing a has and using it within a function.

Hazah! I'm Employed!

At any rate, if you modify the call by removing the brackets like so it will work:

StartCapture(  
                twigs   => {filter => $filterTwig,  capture => $captur
+eTwig},
                hashes  => {filter => %filterHash,  capture => %captur
+eHash},
                files   => {filter => 'filter.txt', capture => 'captur
+e.txt'}, 
                results => 'c:/temp.txt'
               
);
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Result:

perl www.pl
results => c:/temp.txt
C:\Temp>
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It is important to use Data::Dumper or the like to analyze things that are being passed when you are doing things like this. For instance, how do you know you want the entire %captureDefaultHash, rather than just a bunch of elements in it?

#!/usr/bin/perl

use strict;

use Data::Dumper;

my_sub({foo => 'bar', oof => 'wha'});

sub my_sub {
    my $ref = shift;

    my %args = (
        foo => 'oop',
        pah => 'meh',
        oof => 'off',
        %{$ref}
    );

    warn Dumper(\%args);
}
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I am a beginner in Perl. Please correct me if I am wrong!
I want to do something like the following, so that I can alter only some values of the hash and call the function again and again. I am not sure whether the same thing can be done using a 'list' as suggested in the previous post.

#!/usr/bin/perl

use strict;
use Data::Dumper;

my %input = {foo => 'bar', oof => 'wha'};
my_sub(\%input);

$input{foo} = 'bar1';
my_sub(\%input);

sub my_sub {
    my $ref = shift;

    my %args = (
        foo => 'oop',
        pah => 'meh',
        oof => 'off',
        %{$ref}
    );

    warn Dumper(\%args);
}
[download]

Hrm, interesting question. It seems more like you want a global hash which gets reset to the default values each time the function is called with the exception of the values you pass in. I still don't think a reference is the way to go, but if it works, meh. What about this:

#!/usr/bin/perl

use strict;

use Data::Dumper;

my %hash = ();

my_sub(foo => 'bar', oof => 'wha');
my_sub(pah => 'eek');

sub my_sub {
    %hash = (
        foo => 'oop',
        pah => 'meh',
        oof => 'off',
        @_
    );

    warn Dumper(\%hash);
}
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