To hide the file on a Linux system, you have to start the filename with a specific character. What is the character?

The exclamation mark has no special hiding semantics in Linux filenames and is treated as a regular character.

The underscore is a valid and visible filename character in Linux with no special hiding behavior.

A tilde prefix typically denotes backup files created by text editors and does not cause the file to be hidden from directory listings.

The period (.) prefix is the Unix/Linux convention for hiding files. When a filename starts with '.', tools like 'ls' omit it from standard output unless the '-a' or '-A' flag is used. This behavior is enforced at the shell and filesystem utility level, not the kernel level.