bin/152154: /bin/csh & /bin/tcsh improperly diddle termios flags

[Bruce Evans]

The following reply was made to PR bin/152154; it has been noted by GNATS.

From: Bruce Evans <brde at optusnet.com.au>
To: "Ronald F.Guilmette" <rfg at tristatelogic.com>
Cc: FreeBSD-gnats-submit at freebsd.org, freebsd-bugs at freebsd.org
Subject: Re: bin/152154: /bin/csh & /bin/tcsh improperly diddle termios flags
Date: Fri, 12 Nov 2010 20:34:52 +1100 (EST)

 On Thu, 11 Nov 2010, Ronald F.Guilmette wrote:
 
 >> Description:
 >
 > Apparently, /bin/csh (aka /bin/tcsh) is diddling termios flags, in particular
 > the ECHO flag, for no apparently good reason and without ever even having been
 > asked to do so.  The result is that the /usr/bin/script program, when invoked
 > with the -k option, will log every input character the user types in TWICE,
 > but only if the user has SHELL set in the environment to either /bin/csh or
 > to /bin/tcsh.  This behavior does not seem to occur when and if SHELL is set
 > to /bin/sh.
 
 /bin/sh now does this too.  bash does this too (in at least versions 1.14.7
 and 4.0.35).  I think the mode switch in the shell is an unavoidable
 consequence of line editing in the shell, and script is depending on the
 line editing being done in the kernel.  The old versions of /bin/sh that
 don't have the problem differ in not starting up in line editing mode.
 
 > P.S.  Strangely, when you run /usr/bin/script with SHELL set to /bin/tcsh
 > and when you then run a program from the tcsh command prompt, that program
 > will see a properly set group of termios bitflags, e.g. when and if it
 > calls tcgetattr().
 
 This also happens with at least bash, since bash is careful to virtualize
 the terminal state by context switching it to a different value only
 while in its line editor.
 
 I don't understand why clearing ECHO in line editing mode doubles the
 script -k output instead of suppressing it.
 
 Bruce