- file channels ?pattern?
This should really be channel names ?pattern? since it returns more than just files: also sockets, stdin, stdout, etc). As of Tcl 8.5, it indeed also comes under the name chan names, which is ugly but probably close enough.AMG: Ugly? How so?
The pattern is somewhat useful, in that it allows you to find only open sockets (use a pattern of sock*) or reflected channels (use a pattern of rc*) but otherwise it can only really be used to determine non-destructively whether a channel is still open (i.e., still existing). What it currently can't do is tell you whether a channel is a pipe or not; this may change in the future.
See also edit
RS 2008-04-07: Looking at the result of file channels, e.g. from a console, can help to detect bugs where files were opened but not closed, which can "leak" considerable memory.