passing hash ref to a function

ovedpo15 has asked for the wisdom of the Perl Monks concerning the following question:

Hello,

My code is sending a hash by reference to a function and adds an element to it. The problem is that the new element isn't in the hash that I sent.

my %hash = (
    'animal' => 'bear',
    'plant' => 'oak',
    'fungus' => 'truffle',
);
test(\%hash);

print join(",", keys (%hash)),"\n";

sub test {
    my ($ref) = @_;
    my %ref_hash = %{$ref};
    $ref_hash{'new'} = 'new_v';
    print join(",", keys (%ref_hash)),"\n";
}
[download]

Output:

plant,new,fungus,animal                                               
+                                                                     
+                                        
plant,animal,fungus
[download]

I want the 'new' element to be also in the new one. I think I didn't quit understand how references work.

Output I want:

plant,new,fungus,animal                                               
+                                                                     
+                                        
plant,new,fungus,animal
[download]

2018-03-22 Athanasius Added code and paragraph tags

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Re: passing hash ref to a function by hippo (Archbishop) on Mar 16, 2018 at 17:08 UTC
`my %ref_hash = %{$ref};` When you do that you are creating a copy. Don't do that if you want to modify the arguments. `sub test { my ($ref) = @_; $ref->{'new'} = 'new_v'; print join(",", keys (%$ref)),"\n"; }` [download]	[reply] [d/l] [select]
Re: passing hash ref to a function by ovedpo15 (Pilgrim) on Mar 16, 2018 at 19:29 UTC
Hello, I would like to run a perl script inside a perl script. I know how to do so with brackets but I don't want to hardcode the path to the other script. For example I have p1 script and p2 script. I want to run p2 in p1. Assume that $path_to_p2 is the path to the p2 script. Until now I did it like this: `$path_to_p2` and it works but, I had to define $path_to_p2 in the file (hardcode) and it's a bad practice. Full Code Example: my $path_to_p2 = "~/path/to/p2.pl"; # BAD because if the path changed, it won't work. my output = `$path_to_p2"`; If p1 and p2 are in the same folder, can I use FindBin module in order to find p2 and run it somehow?	[reply]
Re^2: passing hash ref to a function by poj (Abbot) on Mar 16, 2018 at 19:50 UTC
Pease edit your title 'passing hash ref to a function' Where is p2 script located relative to p1 script. Are they are they both in the same folder ? ~~they just use~~ ~~my $output = `p2.pl`;~~ Update If yes, FindBin can locate the path to `p1.pl` which can be used to run `p2.pl`. #!perl # p1.pl use strict; use FindBin; my $p2 = $FindBin::Bin.'/p2.pl'; my $output = `$p2`; print $output; [download] poj	[reply] [d/l] [select]
Re^2: passing hash ref to a function by alexander_lunev (Pilgrim) on Mar 16, 2018 at 20:11 UTC
`use Cwd 'cwd'; my $path_to_p2 = cwd() . '/p2.pl';` [download]	[reply] [d/l]
Re^3: passing hash ref to a function by haukex (Archbishop) on Mar 17, 2018 at 10:17 UTC
`my $path_to_p2 = cwd() . '/p2.pl';` I don't see the advantage of this over just the relative `'p2.pl'` (unless the script is chdiring over its run).	[reply] [d/l] [select]
Re^2: passing hash ref to a function by Anonymous Monk on Mar 17, 2018 at 03:25 UTC
If you need to "run another script" within "a script," and you find that it actually matters to you that the script in question is a Perl script, versus any-ol' executable that you might wish to run on some system somewhere, then I would frankly suggest that you are dealing with a broken-design that needs to be "properly fixed, once and for all."	[reply]