passing global variable by reference?

[Don S]

I'm trying to stick my frequently used subroutines into a Sysadmin.pm
module. Of course the first one I tried uses global variables and I
wondering if someone can guide me though referencing and derefrencing.

It's to walk a tree and call a subroutine on files/links/directories.
(I think I actually got the original code from the camel book.)
Anyway,
I also need to use global variables such as the level of directories
being descended but I take it I also want to "use strict" as a good
programming practice.


I've read in the camel book and it notes the \$ reference and
$$dereference but doesn't outline usage in subroutines.

I'm trying to call it like this:

vvvvvvv
&tree_walk($top_dir,\$level,\&du_info,1,0,0);

the heart of the subroutine is (with errors):

my($path,$$level,$sub,$d_flag,$f_flag,$l_flag) = @_;

&tree_walk($newpath,$level,$sub,$d_flag,$f_flag,$l _flag); # ... go
recursive
$level--;

and the actual subroutine is:

sub tree_walk{
my($path,$$level,$sub,$d_flag,$f_flag,$l_flag) = @_;
my($newpath,$entry,@entries);

# Get all objects in the directory

opendir(DIR,"$path"); # open the
directory
my(@entries) = readdir(DIR); # get all entries
closedir(DIR); # close it

# Check all of the objects

foreach $entry (@entries) {
unless( $entry eq "." || $entry eq "..") { # filter always
$newpath="$path/$entry"; # create full
path
#-------- action on dirs, files, links ----------

if( -d "$newpath" && $d_flag == 1) { # DIRECTORIES
unless( -l "$newpath" ) { # ignore links
&$sub($newpath,'d');
}
}

#--------- recursively read directories ---------

unless( -l "$newpath" ) { # stay away
from links
if( -d $newpath ) { # if it is a
dir ...
&tree_walk($newpath,$level,$sub,$d_flag,$f_flag,$l _flag);
# ... go recursive
$level--;
}
}

}
}
}

Thanks,
Don

[thumb_42@yahoo.com]

Don S <dshesnicky@yahoo.com> wrote:

> I'm trying to stick my frequently used subroutines into a Sysadmin.pm
> module. Of course the first one I tried uses global variables and I
> wondering if someone can guide me though referencing and derefrencing.

My newsreader wrapped your code and I couldn't read it very well, but..

I believe this may be your problem:

my($path,$$level,$sub,$d_flag,$f_flag,$l_flag) = @_;

If you change it to:

my($path,$level,$sub,$d_flag,$f_flag,$l_flag) = @_;

and do a $$level--;

You may have better luck.



Personally, with recursive subs, or subs that need to work close together
I'll often use anonymous sub(s) from within a block:

sub do_something {
my(@arguments) = @_;
my($level);
..
.. Set variables that you'll need to keep between calls ..
..
my($worker) = sub {
# .. Perform work here
--$level; # Access $level, almost as though it were global.
};
return($worker->(@arguments)); # This actually runs it.
}

You get the general idea.

If you're using an OOP module, you can also put stuff like that in $self.
$self->{__level}; However, there is a performance penalty for using
hashes. Its minor, but if calling it several thousand times pr. second, it
can add up, Data::Dumper might show you a mysterious __level entry when
examining your object for other reasons, causing you to wonder where it
came from.

Jamie

[Don S]

> I believe this may be your problem:

>
> my($path,$$level,$sub,$d_flag,$f_flag,$l_flag) = @_;
>
> If you change it to:
>
> my($path,$level,$sub,$d_flag,$f_flag,$l_flag) = @_;
>
> and do a $$level--;
>

That pretty much seemed to work, should have tried
a couple of more permutations to stumble on it :)
documentation/smockumentation. Relevant code is:

sub tree_walk {
my($level,$path,$sub,$d_flag,$f_flag,$l_flag) = @_;
<snip>
$$level++;
&tree_walk($level,$newpath,$sub,$d_flag,$f_flag,$l _flag);
$level--;
<snip>

}

I would have thought I needed a $$level or \$level when
I recursively called tree_walk but I guess it makes sense
that you have a pointer like object and once it's set you
only need to dereference it when used via $$.

Don