my $filename = "some.txt";
my @stats = stat( $filename );
open( FILE, ">$filename" ) or die $!;
# do your magic to the file....
close( FILE );
chmod $stats[2], $filename oe die $!;   # mode is stored in stat field 2
chown $stats[4], $stats[5], $filename or die $!;     # uid in 4, gid in 5