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UNIX terminal io incompatibility
- To: email@example.com
- Subject: UNIX terminal io incompatibility
- From: gray@GSWD-VMS
- Date: Tue, 01 Oct 85 12:21:30 CDT
- Cc: gray
Common Lisp maps poorly onto UNIX(tm) in the area of terminal io.
On pages 328 and 329 of CLtL it says:
"*standard-input*, *standard-output*, *error-output*, *trace-
output*, *query-io*, and *debug-io* are initially bound to
synonym streams that pass all operations on to the stream that is
the value of *terminal-io*." Earlier on, the specification
describes *query-io* and *debug-io* as always being interactive
These requirements cause problems under UNIX when you redirect
the output of a program, specifically when you redirect the
output of a Lisp session. For example:
clisp > FOO
If we follow the specification and attach *terminal-io* to UNIX
stdin/stdout file descriptors and leave all the other streams
bound to *terminal-io*, output from *debug-io* will also be
redirected to the file, not to the terminal. If we attach
*terminal-io* to /dev/tty and leave the other streams bound to
*terminal-out*, then UNIX redirection doesn't work.
Our proposed solution is to attach *terminal-io* to /dev/tty,
then attach *standard-in* to UNIX stdin and *standard-out* to
UNIX stdout (not to *terminal-io*). All the other io streams
remain bound to *terminal-io*.
This permits the user to redirect stdin and stdout, and output
from *debug-io*, etc., still appears on the terminal. Although
this does not abide by the standard, it is useful enough that we
propose it as a UNIX-specific addition.
Anne Jane Gray
Gould CSD, Urbana, IL.