package moduleA;

@ISA = qw(Exporter);
@EXPORT_OK = qw($readMode $writeMode $appendMode openFile);
$readMode = '';
$writeMode = '>';
...
1;

##</code><code>##

use moduleA qw($appendMode openFile);
...
# calls moduleA::openFile() with parameter $moduleA::appendMode:
openFile(..., $appendMode); # note: no namespace qualifier needed