Final answer:
The .gitignore file prevents entire files from being tracked in your repository, it is not limited to managed packages, and it does not work with files that are already being tracked without extra steps.
Step-by-step explanation:
When considering the function of a .gitignore file, the correct option is a: It prevents entire files from being tracked in your repository. The .gitignore file is a text file that Git checks to determine which files and directories to ignore when performing operations such as commits and builds. When a file is listed in .gitignore, it instructs the Git version control system to disregard that file and prevent it from being tracked. This means that any changes made to that file will not appear in your staging area or commits, effectively keeping it out of version control.
Option b is not true because .gitignore is not limited to only files that are part of managed packages. It can include any files or directories in your project that you do not want to track, such as compiled binary files, log files, or personal configuration files.
Option c is also incorrect, as once a file is being tracked by Git, adding it to .gitignore will not automatically exclude it from being tracked. It will still be tracked until it is removed from the repository index. If you want to stop tracking a file that is already being tracked by Git, you must explicitly remove it from the index using the git rm --cached command for changes to .gitignore to take effect.