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From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: csh reading from stdin
Message-ID: <7370@star.cs.vu.nl>
Date: 23 Aug 90 15:24:25 GMT
References: <glenn.651406891@bilby>
Sender: news@cs.vu.nl
Reply-To: maart@cs.vu.nl (Maarten Litmaath)
Organization: VU Dept. of Computer Science, Amsterdam, The Netherlands
Lines: 23

In article <glenn.651406891@bilby>,
	glenn@wacsvax.uwa.oz (Glenn Huxtable) writes:
)...
)[SunOS 4.0.3]
)
)	set line=$<
)	# decide which filter
)	(echo $line ; cat) | $FILTER
)
)this resulted in two copies of the first line.

1) The bug is in `cat': it reads the file using mmap(2), blindly assuming
   you want to start reading at byte offset 0.  :-(
   Probably fixed in SunOS 4.1.
   You can't mmap() a pipe, so things work correctly if stdin is a pipe,
   as cat must use read(2) in that case.

2) Your scheme depends on csh reading the line 1 byte at a time (normally
   file IO is _block-buffered_); though your implicit assumption appears
   to be correct indeed, the manual doesn't guarantee it.  :-(
--
        "[Your C code] seems about as portable as the Rock of Gibraltar."
                                 (Wayne Throop)