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From: wtho@cgcha.UUCP (Tom Hofmann)
Newsgroups: comp.unix.questions
Subject: Shell escapes within piped programs
Message-ID: <510@cgcha.UUCP>
Date: Tue, 18-Aug-87 11:45:17 EDT
Article-I.D.: cgcha.510
Posted: Tue Aug 18 11:45:17 1987
Date-Received: Thu, 20-Aug-87 04:23:23 EDT
Organization: CIBA-GEIGY AG, FO/WIRZ/WRZ, CH-4002 Basel, Switzerland
Lines: 29
Keywords: shell pipe

I've just had a strange experience with shell escapes within
piped programs.  E.g. I called

	   ls | more

and typed

	   !mail <address>

at the "more" prompt.  But instead of being prompted for "Subject:"
and entering text (as I expected), the rest of the listing to be
displayed was mailed to <address>, and the "more" prompt returned.
The reason, as I think, is that standard input of "more" is not
the terminal but the pipe, and therefore the standard input of the
invoked program is that pipe as well.  Therefore "mail" reads from
the pipe and not from the terminal.  I tried it both on a SUN and
a CADMUS and got the same (strange) result.  I made another test
using "pg" (System V) instead of "more", and this time I got the
expected behavior on both machines.

My question:  Shouldn't shell escapes redirect the input (and output)
to the terminal?

Tom Hofmann
CIBA-GEIGY AG
Scientific Computer Center
P.O. Box				Tel.  +41 61 372059
CH-4002 Basel
Switzerland				uucp: ...!mcvax!cgcha!wtho