Appendix: POSIX Paths

A POSIX path is a string which is used to identify a directory or file in an operating system independent manner. Unlike a URL it does not specify the protocol which is to be used to access the directory or file, it is usually the case that they are accessed through the operating specific mechanisms. The BNF grammar for a POSIX path is as follows, for the reader unfamiliar with BNF grammars refer to Appendix :

path ::= [root] [relative-path]
root ::= [root-directory]
root-directory ::= "/"
relative-path ::= path-element { "/" path-element } ["/"]
path-element ::= name | parent-directory | directory-placeholder
name ::= char { char }
directory-placeholder ::= "."
parent-directory ::= ".."

This grammar is supplemented with the restriction that char may not be `' or `' and an empty path is also valid. The optional trailing ``'' in a relative-path is allowed as a notational convenience. It has no semantic meaning and is simply discarded.