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

An exclamation mark '!' has no special meaning for hiding files in Linux; it is a valid filename character.

An underscore '_' is a regular character and does not cause a file to be hidden in Linux.

A tilde '~' is commonly used to represent a user's home directory or backup files, but it does not hide a file when placed at the beginning of a filename.

In Linux and Unix-like operating systems, files and directories whose names begin with a period ('.') are treated as hidden files and are not displayed by default in directory listings, such as with the 'ls' command, unless specific options like 'ls -a' are used. This convention is a simple way to conceal configuration files or other non-essential user-visible files.