Re: Better way to define global variables

[kcott]

G'day govindkailas,

It's generally not a good idea to export by default (i.e. with @EXPORT) — see the Exporter documentation sections: Selecting What to Export and What Not to Export. Instead, consider using @EXPORT_OK and %EXPORT_TAGS.

Here's an example of Utilities.pm that does that:

package Utilities;

use strict;
use warnings;

use Exporter qw{import};

my @sys_exports = qw{$SYS_DIR $SYS_OTHER};
my @util_exports = qw{$UTIL_THIS $UTIL_THAT};

our @EXPORT_OK = (@sys_exports, @util_exports);
our %EXPORT_TAGS = (SYS => [@sys_exports], UTIL => [@util_exports]);

our $SYS_DIR = "sys_dir";
our $SYS_OTHER = "sys_other";
our $UTIL_THIS = "util_this";
our $UTIL_THAT = "util_that";

1;

Here's some sample runs showing how to use it.

No namespace pollution unless specifically requested:

$ perl -Mstrict -Mwarnings -E '
    use Utilities;                     
    say $SYS_DIR;
'
Global symbol "$SYS_DIR" requires explicit package name at -e line 3.
Execution of -e aborted due to compilation errors.

Request a specific item:

$ perl -Mstrict -Mwarnings -E '
    use Utilities qw{$SYS_DIR};        
    say $SYS_DIR;
'
sys_dir

Request multiple items using a tag:

$ perl -Mstrict -Mwarnings -E '
    use Utilities qw{:SYS};            
    say $SYS_DIR;
'
sys_dir

Mix specific and tag requests:

$ perl -Mstrict -Mwarnings -E '
    use Utilities qw{:UTIL $SYS_OTHER};
    say $SYS_OTHER;
    say $UTIL_THAT;
'
sys_other
util_that