API UnitAttackPower

Returns the unit's melee attack power and modifiers.
 base, posBuff, negBuff = UnitAttackPower(unit)
==Arguments==
:;unit: : UnitId - The unit to get information from. (Does not work for "target" - Possibly only "player" and "pet")
==Returns==
:;base: - The unit's base attack power
:;posBuff: - The total effect of positive buffs to attack power.
:;negBuff: - The total effect of negative buffs to the attack power (a negative number)
==Example==
Displays the player's current attack power in the default chat window.
local base, posBuff, negBuff = UnitAttackPower("player")
local effective = base + posBuff + negBuff
print("Your current attack power: "..effective)