This is a first-order differential equation. To solve it, we will use the method of separation of variables. First, rewrite the equation as:
\[
\frac{dy}{dx} = e^{x} \cdot e^{-y}
\]
Now, separate the variables:
\[
e^{y} \, dy = e^{x} \, dx
\]
Integrating both sides:
\[
\int e^{y} \, dy = \int e^{x} \, dx
\]
This gives:
\[
e^{y} = e^{x} + C
\]
Where \( C \) is the constant of integration. Thus, the solution to the differential equation is:
\[
e^{y} = e^{x} + C
\]