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From: abe@mace.cc.purdue.edu (Vic Abell)
Newsgroups: comp.sys.next
Subject: loginwindow applications and pipes
Message-ID: <1797@mace.cc.purdue.edu>
Date: 22 Feb 89 16:28:56 GMT
Organization: Purdue University
Lines: 11

I've been conducting some experiments with processes that are begun right
after login by loginwindow and before the Workspace manger (they're started
by using "dwrite loginwindow Workspace <program path>").  I've learned a trick
about the standard I/O file descriptors that is worth passing on: processes
launched from loginwindow have only a stdin, and neither a stdout nor a stderr.

So, if your application is using a pipe to some other application - e. g., to
/etc/disk - you can't use the usual pipe/dup2/close techniques, because you
may accidentally close one of the pipe descriptors that you need.  First you
should open /dev/null and dup2 it to stdout and sterr, then use pipe, dup2
and close in their normal order.