First things first—figure out where the program starts. To execute a program, the loader (typically an operating system) will pass control of the process to a program’s entry point, which begins the run-time execution of the application.
The entry point is the place where a program begins, and it’s important to know what the program is doing once it begins executing the code. When you follow a program from the entry point, you’ll be able to follow the application as it boots up and configures itself to do whatever work it was designed to do.
Some programming languages may enforce conventions for how or where a program should start, while others may give more freedom in how a program is executed.
C-family languages, such as C, C++, and Rust, and JVM languages such as Java contain a predefined function called main.
Once your program has control of the process and has begun execution, it will be able to access command-line arguments and environment variables that can be used to dynamically configure the behavior of your application during run time. The program may contain specific logic to check for these arguments or environment variables in order to change the run-time behavior of the application without needing to recompile or redeploy the application.
It’s important to know where and how your program starts because that may give you valuable information as to how the program is configured, which could affect how the program behaves. If you don’t know what run-time configurations your program is using, you may not fully understand what it’s doing, so this is always a good first step.