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From: chawley@sundiver.esd.sgi.com (Christopher J. Hawley)
Newsgroups: comp.unix.questions,comp.unix.shell
Subject: Re: Help bourne shell problem on sun and bsd
Keywords: builtin, redirection, loop, bourne shell
Message-ID: <1991Jun7.004435.16257@odin.corp.sgi.com>
Date: 7 Jun 91 00:44:35 GMT
References: <3089@cod.NOSC.MIL>
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    In article <3089@cod.NOSC.MIL>, medin@cod.nosc.mil (Ted Medin) writes:

|>  When using the bourne shell:
|> 
|> pwd > temp
|> read dir < temp
|> 
|>  Just hangs until you type something on the keyboard when using bsd 4.3.
|> However on a sun machine it works fine, the variable dir gets the current
|> working directory.
|>  Is "read" keyboard input only or ?????

    From The UNIX Programming Environment, Kernighan & Pike, pp. 159-160:
	 --------------------------------

	  " read  can only read from the standard input; it can't even
	be redirected.  None of the shell built-in commands (as opposed
	to the control flow primitives like  for ) can be redirected
	with  >  or  < :

	[example omitted]

	  "This might be described as a bug in the shell, but it is a
	fact of life.  Fortunately, it can usually be circumvented by
	redirecting the loop surrounding the  read .  This is the key
	to our implementation of the  pick  command: "

	[example of shell command  pick  omitted]


So, in any environment (with the dubious exception of Sun's), you can say

		for foo in dummy
		do
		    read  dir
		done < temp

with the desired results.  Any of the control flow primitives can be used
to achieve the same effect...

		while : ; do read  dir; break; done < temp

is another way to get what you want.

    For the curious: what version of Sun software are you running which has
the  sh  behaviour you describe?

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