use warnings;
use strict;
print "\n";
print 'Enter a five digit number: ' ;
my $num = <>;
$num ~= s/\d/$1 /g;
print $num;
### Or you can also do this:
$num ~= s/\d/$1 /g;
$num ~= s/ $//; ## To remove the last space added in previous line
or
chomp($num); ## To remove the last space added in previous line
print $num;
perldoc -f substr