package my_first; 
use Debug; # Imports in sub debug
our $DEBUG_FLAG =1;
debug("Print me"); #prints: Print me
1;

package my_second; 
use Debug; 
our $DEBUG_FLAG =0;
debug("Print me"); #prints none
1;

package Debug; 
our $DEBUG_FLAG =0; #Default value 
sub debug($) {
if(DEBUG_FLAG){
say $_[0]; 
}
}
1;