If you use use or require, Perl makes sure that the module (or simply a codeblock of variable declarations) is loaded only once.  Note, however, that the loaded file has its own implicit lexical scope — which matters for variables declared with my or our ...

Unfortunately accessing an undeclared variable which was required from another file can lead to "undefined variable"-warnings.

Importing with use might be more complicated but it works with warnings enabled.

@OP: You may wanna have a look at Exporter

Cheers Rolf

UPDATE: added "undeclared"

...can lead to "undefined variable"-warnings

Could you provide an example?  I think you're fine as long as you make sure the code has loaded/compiled before you access the variables (using use or require within a BEGIN block):

---- X.pm ----
$::foo = "foo";
$::bar = "bar";
--------------

#!/usr/bin/perl
use strict;
use warnings;
use X;   # or BEGIN { require X; }

print "$::foo\n";   # no warnings
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do resp. require, both setting global variables. do will (re)load the file, while require seems to be closer in what it does to the name of include_once (which I don't know what it does).

#!/usr/bin/perl
use strict;
use vars qw/$NAME $AGE $DATE/;

$NAME = 'jim';
$AGE = 29;
$DATE = `date`;
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In that example, the variables reside in namespace main::, so that from anywhere in the program, $main::AGE will hit 29 in this example.

If this were a module..

package Sunflower;
use strict;
use vars qw/$NAME $AGE $DATE/;

$NAME = 'jim';
$AGE = 29;
$DATE = `date`;
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Then from anywhere in the code (there are some variations), you can access $Sunflower::AGE.

(You do have to realize that if you code a module (pm), then that example there, those values are set at compile time, before your code calling 'use Sunflower;' runs.. Worry about this later.)

I would say if you expect your values to change from time to time.. How about a YAML config file?

#!/usr/bin/perl
use strict;
use YAML;

my $abs_conf = '/etc/sunflower.conf';
my $config_data = YAML::LoadFile($abs_conf);

printf "Age is %s, name is %s, date is %s\n", 
   $config_data->{AGE}, $config_data->{NAME}, `date`;
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And in your /etc/sunflower.conf..

---
AGE: 29
NAME: jim