temporary redirection under a Bourne-shell using "exec"

[Peter Jeffe 512.823.4091]

In article <906 at mwtech.UUCP> martin at mwtech.UUCP (Martin Weitzel) writes:
->exec 3<&1 >&-	# open File Descriptor 3 (stdout), and close stdout
->echo invisible	# shell stdout is closed, local stdout is FD 3
->exec 1<&3 3>&-	# reopen stdout (and close FD 3)
->echo hello
-
-I would rather change this as follows:
-
->exec 3>&1 >/dev/null
-
-[...] I would not CLOSE stdout (...>&-...) but
-REDIRECT it to /dev/null in the first exec.
-
-Maybe many programs don't care for error returns from their output
-operations, but *some* may do (and IMHO these are the ones written
-by the more careful programmers). Such a program may assume that a
-severe error occured if sending something to stdout returns an error
-and terminate in an unexpected way.

And perhaps a more important reason to leave stdout open (but redirected)
is that if a program does an open() it will probably pick up file descriptor
1 if stdout has been closed.  Then, anything it puts on stdout will get
munged in with what is going to the opened file.  Very messy...

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Peter Jeffe   ...uunet!cs.utexas.edu!ibmchs!auschs!sandino.austin.ibm.com!jeffe