How do create a variable in another package in Perl?

[PerlOnTheWay]

Specifically,what's the right way to create a scalar/array/hash in another package in Perl?

Thank you very much

[moritz]

There's no real need to "create" variables in another packages, because they are entries in the symbol table that can autovivify. Nonetheless you can do something like @YourPackge::VariableName = (1, 2, 3);

Though it is rare that this is a useful and a good idea. Maybe try to explain what you want to achieve in the end, then we can think about better approaches. It could be an XY Problem.

(For example it might be better to export variables from a module that you use in the namespace in question.)

[PerlOnTheWay]

This is needed when the VariableName and the value of the variable(here (1,2,3)) are both determined on the fly

[GrandFather]

In which case it isn't needed. Use a hash instead, or maybe some other construct entirely. Show us sample code where you think such a thing is needed and we'll show you a much better way to do it.

[moritz]

Please read Why it's stupid to `use a variable as a variable name'

You haven't given enough to context to say for sure, but it might very well apply in your case.

[Anonymous Monk]

Hello, I have small joke for you :D

<GoodHumor>

I agree with moritz :) there is a strong suggestion of an interface design problem, a strong suggestion for a need to just pass args

Here is my complete analysis

• +1 key phrase "in another package"
• +1 newbee key phrase "in Perl"
• +1 asking for the syntax
• +1 while posessing the key keyword (package) to find the correct syntax
• +1 key phrase "is needed"
• +1 key phrase "on the fly"

[Anonymous Monk]

The right way is to don't! :) See

Config::Config{osname} and Config{osname}

Tutorials: Variable Scoping in Perl: the basics, Coping with Scoping

• varvarname Why it's stupid to `use a variable as a variable name'
• varvarname2 A More Direct Explanation of the Problem
• varvarname3 What if I'm Really Careful?

every page with keyword "namespace" in Modern Perl Book

[Corion]

In addition to Mark Jason Dominus' paper discouraging using a name to create a variable, you can look at eval or just plain access the variable through its fully qualified name:

my $varname = "Foo::Bar::my_var";

{
  no strict 'refs';
  my @array = @{ $varname } = (1,2,3);
  my %hash = %{ $varname } = (1 => 2);
  my $scalar = ${ $varname } = "Hello World";
}

use Data::Dumper;
eval <<'EOF';
    print Dumper \@Foo::Bar::my_var;
    print Dumper \%Foo::Bar::my_var;
    print Dumper \$Foo::Bar::my_var;

EOF

Most likely, you will use this technique for the wrong thing. It is very, very rarely needed to create variables in a package whose name you don't know yet. The one situation I know and accept is to set up @ISA for another package.

[Anonymous Monk]

The one situation I know and accept is to set up @ISA for another package.

Me too, and like Modern Perl Book, you probably just want to use Module::Pluggable :)