Naming files is very simple: any ASCII character can be used.
It is, however, recommended that no metacharacters (
, {,
}, [, ], 
, $, 
,
~ , >, <, |, &) be used.
It is also recommended to simply use letters, digits, underscore (_),
hyphen (-) and the dot (.).
By convention, files ending with .c are C language files. File names ending with .p, .f, .s are respectively PASCAL, FORTRAN, and assembler program files. Header (include) files usually end with .h.
File names beginning with a . (dot) are hidden files: they do not appear when files are listed. Those files are typically configuration files. Usually, their name consists of the package they represent followed by the rc (run command) string. .mailrc and .newsrc are two examples.
Any file names may contain many dots and/or underscores. These are NOT separators.