Can I use a 7805 as a current regulator?
Can I use 7805 as current regulator?


Yes, but it's a very inefficient solution. A regulator with only 1.2 or 1.3 V feedback voltage can be used as a current regulator with much less power lost in the sense resistor.


  My input is 12-14 vdc (battery) and I require output 5v and 500mA or adjustable. ...  Is there any thing that can control both voltage and current?


You can control the voltage or the current, but you can't control both --- the load will determine whichever one you don't control. See this old question.


  Can zener sove the problem because it can limit the voltage.


A zener can be used as a shunt regulator, which will control the voltage applied to the load (but then the load itself will determine the current drawn). It can also be set up as a voltage source with a maximum current limit (but if the load draws more than the limit, the voltage will drop in response).


  design requirement for emergency (disaster struck areas) is Low cost. 


The price difference between a TI and a LT regulator will be much much much lower than the cost of delivering the parts to a disaster zone at short notice. I wouldn't worry about it.