The easiest way to do it (assuming you don't need to have humans interpret it) is to just use the numeric return value from time():

my $filename = $directory . '/' . time() . '.ext';
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Otherwise, you can put together the various numbers from localtime:

my @lt = localtime(time);
my $filename = sprintf "%s/%04d%02d%02d%02d%02d%02d", $directory, $lt[
+5]+1900, $lt[4]+1, @lt[3,2,1,0];
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