What is necessary to execute a program directly in the terminal?

To execute a program directly in the terminal, it must be in the system's PATH. The PATH is an environment variable that contains a list of directories where the shell looks for executable files when a command is entered. If the executable file is located in one of these directories, you can simply type its name at the command prompt and the shell will be able to locate and run it.

When a program is not in the PATH, you would need to specify the full path to the executable, or change to the directory where the program is located. This demonstrates the convenience of having executables in the PATH, as it allows users to execute programs without needing to remember their exact locations or having to navigate through the file system.

Other options do not encapsulate the requirement for executing a program efficiently. A program does not necessarily have to be in the current directory to run directly if it is located in the PATH. The .sh extension is commonly associated with shell scripts but is not required for execution; a program can have different file extensions or no extension at all and still be executable. Similarly, while script files can be executed, it is not a requirement for all executable programs.