open my $file, '+>', 'testfile' or die "Can't write testfile: $!\n";
print $file 'test!';
seek $file, 0, 0;
print <$file> . "\n";
seek $file, 0, 0;
truncate $file, 0 or die "Can't truncate testfile: $!\n";
close $file or die "Can't save testfile: $!\n";