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  ANSI Common Lisp   20 Files   20.1 File System Concepts   20.1.3 Truenames

20.1.3.1 Examples of Truenames

For example, a DEC TOPS-20 system with files PS:<JOE>FOO.TXT.1 and PS:<JOE>FOO.TXT.2 might permit the second file to be referred to as PS:<JOE>FOO.TXT.0, since the ".0" notation denotes "newest" version of several files. In the same file system, a "logical device" "JOE:" might be taken to refer to PS:<JOE>" and so the names JOE:FOO.TXT.2 or JOE:FOO.TXT.0 might refer to PS:<JOE>FOO.TXT.2. In all of these cases, the truename of the file would probably be PS:<JOE>FOO.TXT.2.

If a file is a symbolic link to another file (in a file system permitting such a thing), it is conventional for the truename to be the canonical name of the file after any symbolic links have been followed; that is, it is the canonical name of the file whose contents would become available if an input stream to that file were opened.

In the case of a file still being created (that is, of an output stream open to such a file), the exact truename of the file might not be known until the stream is closed. In this case, the function truename might return different values for such a stream before and after it was closed. In fact, before it is closed, the name returned might not even be a valid name in the file system - for example, while a file is being written, it might have version :newest and might only take on a specific numeric value later when the file is closed even in a file system where all files have numeric versions.


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