Returns 1 if the first unit can attack the second, nil otherwise.

canAttack = UnitCanAttack(attacker, attacked);

Parameters

Arguments

attacker 

UnitId - the unit that would initiate the attack (e.g., "player" or "target")

attacked 

UnitId - the unit that would be attacked (e.g., "player" or "target")

Returns

canAttack 

Bool - 1 if the attacker can attack the attacked, nil otherwise.

Example

if ( UnitCanAttack("player", "target") ) then
 DEFAULT_CHAT_FRAME:AddMessage("You can attack " .. UnitName("target") .. ".");
end

Result

If the player can attack their target, a message stating so is displayed in the default chat frame.