$$\lim_{x \to \frac{\pi}{2}^-}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = 0$$
More at x→pi/2 from the left$$\lim_{x \to \frac{\pi}{2}^+}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = 0$$
$$\lim_{x \to \infty}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right)$$
More at x→oo$$\lim_{x \to 0^-}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = -1$$
More at x→0 from the left$$\lim_{x \to 0^+}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = -1$$
More at x→0 from the right$$\lim_{x \to 1^-}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = \frac{-1 + \cos{\left(1 \right)} \tan{\left(1 \right)}}{\cos{\left(1 \right)}}$$
More at x→1 from the left$$\lim_{x \to 1^+}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right) = \frac{-1 + \cos{\left(1 \right)} \tan{\left(1 \right)}}{\cos{\left(1 \right)}}$$
More at x→1 from the right$$\lim_{x \to -\infty}\left(\tan{\left(x \right)} - \sec{\left(x \right)}\right)$$
More at x→-oo