Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!stan!dce
From: dce@Solbourne.COM (David Elliott)
Newsgroups: comp.unix.questions
Subject: Re: Help with strings in Bourne shell
Message-ID: <870@marvin.Solbourne.COM>
Date: 25 Apr 89 14:16:06 GMT
References: <10166@orstcs.CS.ORST.EDU> <1493@vsedev.VSE.COM>
Reply-To: dce@Solbourne.com (David Elliott)
Distribution: usa
Organization: Solbourne Computer Inc., Longmont, Colorado
Lines: 38

In article <1493@vsedev.VSE.COM> logan@vsedev.VSE.COM (James Logan III) writes:
>BTW, you can also read from a specific file by redirecting the
>input to the read command like this:
>
>	INPUTFILE="some_file";
>
>	while read DEFINITION <$INPUTFILE; do
>		echo "$DEFINITION";
>		.
>		.
>		.
>	done;

Watch out for this one.  It's very important to note that in the
"standard" shells (those that come with most commercial UNIXes),
the redirection causes a subshell to be spawned to run the loop.

The result is that any variables set inside the loop will not
have the same values when the loop is exited.  So, if the input
data are used to set variables to be used later in the program,
this won't work.

A typical trick is

	exec 3<&0 0<"$INPUTFILE"
	while read DEFINITION
	do
		echo "$DEFINITION"
	done
	exec 0<&3

The first exec makes fd 3 a duplicate of fd 0 (stdin), and
redirects stdin.  The second exec changes fd 0 back to what
it was.

-- 
David Elliott		dce@Solbourne.COM
			...!{boulder,nbires,sun}!stan!dce