Possible bug in os.date when using format qualifiers

[Nick Gammon <nick@...>]

Hi!


Version 5.1.2 introduced a problem when using os.date which was not  
present in 5.5.1.

There was a change made in response to a bug I had earlier reported  
about an error being reported if os.date was called with an empty  
string.

Previously, the string supplied to os.date was passed to strftime in  
one piece.

Now, os.date breaks up the supplied string by looking for %x and  
calls strftime for each individual item.

However this breaks the behaviour as described in the Reference  
Manual, that the date is "formatted according to the same rules as  
the C function strftime".

Depending on which system you run "man strftime" you get slightly  
different information, but the gist is that:

"Some conversion  specifiers can be modified by preceding them by the  
E or O modifier to indicate that an alternative format should  be   
used.". For example, "%Ec, %EC, %Ex, %EX, %Ry".

Unfortunately the new coding does not allow for the optional letter  
between the % and the format specifier.

I also had the idea in my head that you used to be able to do  
something like this: os.date ("%#I")

This is supposed to drop leading zeroes. In fact, the MSDN  
documentation for strftime mentions exactly that.

I suggest that you do one of:

* revert to a single call of strftime (which would make the function  
behave as documented "like strftime"), handling the case of an empty  
string as an exception; or

* allow for modifiers "E", "O" and "#" between the % and the format  
specifier; or

* modify the documentation to make it clear that only %x is supported  
without something between the % and the x - in other words, remove  
the reference to "the same rules as ... strftime".



- Nick Gammon