Latest rules

You definitely need a mask to enter a shop and most shops have the hand gel at the door.
Outside in the streets you don't need a mask on but masks will still be required in outdoor situations where it is not possible to maintain a safety distance of 1.5 meters between people.  

I don't know the rules for bars and restaurants etc.

This is the correct information. For bars and restaurants you need to wear a mask on entry and exit, as well as moving about from your table, such as going to the toilets or to the bar to order drinks. In addition, there is a limit of 50% + 1 for travel in cars where the occupants are not residing together.

Hope this helps and the conditions are not too onerous.

Also I believe mandatory on public transport and public buildings indoors.

You need  a mask

Like the UK mabdatory for shops plus also to enter a bar, even to use the toilet. Walking outside a mask is not required assuming you can keep a safe distance but my experience over the last 7 weeks is that the majority wear a mask most times. 

Its not mandatory to wear a mask anymore in the UK for entering shops, I still do as many other do out of respect for the people who are at risk. 

Does anyone know if the exemption from wearing a mask - health reasons - is allowed as it is in UK ?

Unless it has changed, the only exemption on medical grounds was on production of a doctors note which confirms that the person should be exempt. There was not a self diagnosis option, as was available in in the UK. Others may be aware of a change in the rules that I have not seen. 
hope this helps

Hi we are in Spain at the moment, apart from shops entering and leaving a pub or going to the toilet, and public transport it is not necessary to ware a mask outside some people do, but I guess it is because they want to, the only other place we have been asked to ware one is as you enter an outdoor market, but honestly it is not a problem and we are glad we came,i hope

this helps you a little. 

I wasn't aware that there was self diagnosis, I understood it was mainly those severely vulnerable and usually with respiratory ailments. If a doctor's letter is necessary then that's ok. - but not very visable.