Collision detection script help

I was attempting to change the knife into a close range weapon that pushes the player back when they are hitting an enemy or entity. currently it just pushes the player, which is progress, but it just allows them to fly due to allowing the hit to be registered regardless of if it's hitting an enemy or not. here is the code:

 ModCS.Bullet.Act[25] = function(bul)
    -- count1 is just a general-purpose variable
    -- Here it's being used to keep track of how long the bullet has lived
    bul.count1 = bul.count1 + 1
    if bul.count1 > bul.life_count then -- life_count is the "frames to live" in bullet properties
        -- Delete when reaching the end of its range
        ModCS.Bullet.Delete(bul)
        ModCS.Caret.Spawn(3, bul.x, bul.y, 0) -- Spawn effect 3 (shoot effect)
        return
    end

    -- This is atypical of bullets in general, but the vanilla Blade starts with the
    -- "ignore solid" flag and only removes it after a few frames
    if bul.count1 == 3 then
        ModCS.Bullet.UnsetBit(bul, 3) -- 2 is the "ignore solid" bit
    end

    -- Play a sound every so often
    if bul.count1 % 1 == 1 then
        ModCS.Sound.Play(12)
    end

    -- Using act_no like this lets us run some initialization code only on the first frame
    -- of the bullet's existence
    if bul.act_no == 0 then
        bul.act_no = 1
        -- Set movement velocity
        if bul.direct == 0
         then-- left -- 4 px/frame
            ModCS.Player.xm = 1112
            ModCS.Player.ym = -812
        elseif bul.direct == 1 then -- up
            bul.ym = -1
        elseif bul.direct == 2 then -- right
            bul.xm = 1
        elseif bul.direct == 3 then -- down
            bul.ym = 1
            ModCS.Player.ym = -1112
        else
        ModCS.Player.ym = 0 ModCS.Player.xm = 0
    end
        -- Move the bullet
        if ModCS.Player.direct == 0 then
            bul.x = -20 + ModCS.Player.x
            bul.y = ModCS.Player.y
        elseif ModCS.Player.direct == 2 then
            bul.x = 20 + ModCS.Player.x
            bul.y = ModCS.Player.y
        end

        local left_animation_frames = {
            ModCS.Rect.Create(0, 48, 16, 64),
            ModCS.Rect.Create(16, 48, 32, 64),
            ModCS.Rect.Create(32, 48, 48, 64),
            ModCS.Rect.Create(48, 48, 64, 64)
        }
        local right_animation_frames = {
            ModCS.Rect.Create(64, 48, 80, 64),
            ModCS.Rect.Create(80, 48, 96, 64),
            ModCS.Rect.Create(96, 48, 112, 64),
            ModCS.Rect.Create(112, 48, 128, 64)
        }

        -- Animate the bullet
        bul.ani_wait = bul.ani_wait + 1
        if bul.ani_wait > 1 then
            bul.ani_wait = 0
            bul.ani_no = bul.ani_no + 1
        end
        if bul.ani_no > 3 then
            bul.ani_no = 0
        end

        if bul.direct == 0 then
            ModCS.Bullet.SetRect(bul, left_animation_frames[bul.ani_no + 1])
        else
            ModCS.Bullet.SetRect(bul, right_animation_frames[bul.ani_no + 1])
        end
    end
end

 

apologies if i didn't get my point across clear enough, but i want to make the bullet only detect when it's hitting an enemy.