Operating System Tutorial
Chapter 4, Writing and editing

Filenames

Filenames

Filenames can be up to 256 characters long. You can use any characters you like in a filename, except for the following metacharacters, which have a special meaning to the shell:

! ? * " ' ` ; / $ < > ( ) | { } [ ]

It is a good idea to choose meaningful filenames to make it easier to remember what the files contain. 

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 Examples of legal filenames   Examples of illegal filenames
 -----------------------------------------------------------------------
 qtrone                        qtr(one)
 report.127                    report|127
 annualreport_1994             annualreport~1994
Filenames only have to be unique within a directory. In other words, you can have as many files named report as you like, as long as there is only one report per directory.