References in perl are a bit different from C or other languages.

What you have passed is like a scalar with the reference to an array; so the ways to retrieve it are:

sub spawn_proc_prog {
    my ($r, $command, $argv) = @_;

    # to access the elements of $argv you do
    my $first = $argv->[0];
    my $second = $argv->[1];

    # or
    my @argv = @{$argv};

    # and there's a lot more..
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Update: try perldoc perlref for more information about references in perl.

I seem to have asked the question incorrectly. spawn_proc_prog will spawn (like the "system" call) the program specified in $command and send it arguments in the argv array. What I want to do is read the content of the argv array in the program that receives it (the one in $command), and $r is the apache request object...

My usage looks something like :

$command = "foo.pl";
@args = qw(1 2 3 4 5);
spawn_proc_prog($r, $command, \@argv);


Now I want to be able to read the argv array in foo.pl. I get the referent, but it arrives as an empty array...

Thanks
- BGa

Since it's being handled as a command, did you look in @ARGV of foo.pl?

This is reinforced by the module doc that says:

The third optional argument is a reference to an array which if passed becomes ARGV to the spawned program.



--Bob Niederman, http://bob-n.com

I don't think perl automagically will allow two (or more) processes to read and write to the same memory. The solution? Look into the IPC::Shareable module. It provides routines to tie variables to Shared memory, and lock and unlock access to avoid race conditions. If I get some time I'll post sample code.

Just because @argv is passed by reference, it doesn't always mean that @argv will be modified for you to read the changes. @argv is probably passed by reference simply to prevent the copying of a potentially long list of values or perhaps to make the API for that function easier to change/extend or even to make it possible to detect certain usage mistakes (or perhaps due to all of the above).

In the Unix 'spawn' interface (see exec and/or "man exec"; 'spawn' also involves fork but that part doesn't affect 'argv') argv is clearly copied to the program being invoked and not copied back.