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Message-ID: <4FE23FDE.9070506@redhat.com>
Date: Wed, 20 Jun 2012 15:25:50 -0600
From: Eric Blake <eblake AT redhat DOT com>
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Subject: Re: piping input to executable reading from /dev/tty?
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On 06/20/2012 03:20 PM, Dan B. wrote:
> Eric Blake wrote:
>> On 06/20/2012 10:33 AM, Dan B. wrote:
>>> Is there any way to redirect /dev/tty similarly to how stdin can be
>>> redirected (e.g., like "echo ... | someexecutable")?
>>
>> Yes; use 'expect'.
>>
>>> Does Cygwin (or Unix/Linux, for that matter) have any equivalent way
>>> of redirecting /dev/tty?
>>>
>>> Can /dev/tty be redirected at all?  (I would guess that something
>>> could be done with pseudoterminals, but I know very little about
>>> them.)
>>
>> Yes, 'expect' is the command line tool that lets you script around
>> programs that expect to be run interactively, but where you want to
>> script the input that your program will see.
>=20
> Does expect use only redirection of file descriptors, or can it also
> redirect references to /dev/tty?

expect uses pseudoterminals so that the stdin of the child process is
also its /dev/tty (remember, /dev/tty is a magic name that resolves to
the current controlling terminal, and that a pseutoterminal can be a
controlling terminal).  Therefore, anything that normally requires you
to interactively type something because the child process opened
/dev/tty can be run under expect, where opening /dev/tty in the child
will now be asking expect for the input, and expect then hands it the
information that you wrote into your expect script.  This is not
cygwin-specific, so you may get better support by looking for help on
using 'expect'.

--=20

Eric Blake   eblake AT redhat DOT com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org




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