Path: utzoo!mnetor!uunet!husc6!m2c!jjmhome!cloud9!bob
From: bob@cloud9.UUCP (Bob Toxen)
Newsgroups: comp.unix.wizards
Subject: Re: Redirect Output in the Middle of a Program??
Message-ID: <342@cloud9.UUCP>
Date: 29 Apr 88 22:10:27 GMT
References: <13085@brl-adm.ARPA> <3571@gryphon.CTS.COM> <2841@cvl.umd.edu> <11257@mimsy.UUCP>
Organization: Stratus Computer, Inc., Marlboro, MA
Lines: 18
Summary: Use close/open for the shell game

In article <11257@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
> In article <62@denali.UUCP> karish@denali.UUCP writes:
> >... The user's program can catch the SIGHUP.  This handler can use
> >fopen() to open outfiles, and freopen() to reassign the output streams.
> This is quite dangerous.
> In-Real-Life: Chris Torek uunet!mimsy!chris
(Edited to satisfy inews.)

The safe way is to do a close and then an open on the desired file
descriptors.  This will work even while executing stdio code.
System calls are internally consistent (except in some non-native
UNIXes).  If you want to be ultra-safe, have your interrupt ignore
signals before doing this and then restore them afterwards.
-- 

Bob Toxen	{ucbvax!ihnp4,harvard,cloud9!es}!anvil!cavu!bob
Stratus Computer, Marlboro, MA
Pilot to Copilot: What's a mountain goat doing way up here in a cloud bank?