Returns the value of the symbolic link given by name (i.e. the name of the file it points to). If name isn't a symbolic link or its value cannot be read, then an error is returned. On systems that don't support symbolic links this option is undefined.
AMG: Is there any difference between [file readlink $link] and [file link $link]?
GNU coreutils provides "readlink -f", which outputs the canonical location for a file. Here's a TCL proc that does the same:
http://ynform.org/w/Pub/TclFileCanonicalize (Dead link as of 12-02-2014)