Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!vsi!friedl
From: friedl@vsi.COM (Stephen J. Friedl)
Newsgroups: comp.unix.questions
Subject: Re: Help with strings in Bourne shell
Summary: A common Bourne shell mistake
Message-ID: <1107@vsi.COM>
Date: 26 Apr 89 14:44:09 GMT
References: <10166@orstcs.CS.ORST.EDU> <1493@vsedev.VSE.COM>
Distribution: usa
Organization: V-Systems, Inc. -- Santa Ana, CA
Lines: 43

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:
> 
> 	while read DEFINITION < inputfile; do
> 		echo "$DEFINITION";
> 		# other stuff
> 	done;

This is a common mistake.  The redirection applies to only the
read command, and every time the while hits the read, the input
file is opened anew and the same first line is read over and
over (and the while never terminates).  Try:

	while read line < /etc/passwd ; do
		echo $line
	done

and you'll learn your encrypted root password quite well.

The {Bou,Ko}rn shells support piping and redirection into and
out of control flow, so things like:

	while read foo ; do
		stuff here
	done < inputfile
or
	while condition ; do
		stuff here
	done > outputfile
or
	grep stuff file | while read line ; do .... ; done

all do things that make sense.

     Steve

-- 
Stephen J. Friedl / V-Systems, Inc. / Santa Ana, CA / +1 714 545 6442 
3B2-kind-of-guy   / friedl@vsi.com  / {attmail, uunet, etc}!vsi!friedl

As long as Bush is in office, you'll never see Nancy Reagan in *my* .sig.