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Re: libedit: patch to fix unexpected behavior on Linux
In article <1296077811.3348.479.camel@clint-MacBookPro>,
Clint Byrum <clint%ubuntu.com@localhost> wrote:
>Hi there, I have been debugging this libedit issue for a little while
>now, and I think I've got it.
>With GNU readline, using_history() doesn't actually take over the
>terminal (it barely does anything actually). However, with libedit, it
>does. This means that any program that runs using_history() as part of
>its initialization, will take over the tty attached to stdin
>The issue with this is that sometimes you are running with stdout
>directed to a pipe or file, and do not want/can't use editing. In fact,
>it shouldn't be enabled.
>This is made apparent when on Ubuntu Linux, you install the php package,
>which has libedit linked in, and run
>php | less
>This leads to not being able to use the arrow keys in less, because php
>grabs the controlling terminal. If PHP is built with readline, this
>For whatever reason, NetBSD does not suffer from this problem. I
>narrowed it down to a difference in the way tcsetattr(,TCSADRAIN) is
>handled. in libedit/tty.c, tty_setup() calls this (via the tty_setty
>macro), which on NetBSD, simply flushes and moves on. On Linux however,
>linux takes this as a signal to grab the fd as a controlling terminal
>and hold on to it.
>So this problem probably isn't apparent on NetBSD, but it definitely
>affects all Linux users of libedit.
>I propose this patch be applied to libedit, which will disable tty
>handling if the output is not a tty.
>This is also tracked in Ubuntu here:
>Your time and feedback on this matter is greatly appreciated!
Yes, I think it makes sense not to enable editing if stdout is not a tty
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