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From: Eli Schwartz <eschwartz@archlinux.org>
Newsgroups: gnu.bash.bug
Subject: Re: command "cat /etc/localtime" breaks output on tty-terminal
Date: Sun, 23 Jun 2019 13:00:28 -0400
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Approved: bug-bash@gnu.org
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References: <20190623123102.fa9221e067faed8874ea7fc2@gmx.de> <CANaoh6++Y25Ug+TKww3+WvbvOer8=jpGLLZohwWUyjvoBRFUrQ@mail.gmail.com> <20190623141810.d3ba78fb13821008b401f45f@gmx.de> <f9de320d-caee-1544-abf4-ac1bdaff515a@archlinux.org>
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From: Eli Schwartz <eschwartz@archlinux.org>
To: bug-bash@gnu.org
Message-ID: <f9de320d-caee-1544-abf4-ac1bdaff515a@archlinux.org>
Subject: Re: command "cat /etc/localtime" breaks output on tty-terminal
References: <20190623123102.fa9221e067faed8874ea7fc2@gmx.de>
 <CANaoh6++Y25Ug+TKww3+WvbvOer8=jpGLLZohwWUyjvoBRFUrQ@mail.gmail.com>
 <20190623141810.d3ba78fb13821008b401f45f@gmx.de>
In-Reply-To: <20190623141810.d3ba78fb13821008b401f45f@gmx.de>

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On 6/23/19 8:18 AM, bitfreak25 wrote:
> On Sun, 23 Jun 2019 06:04:29 -0500
> Dennis Williamson <dennistwilliamson@gmail.com> wrote:
>=20
>> On Sun, Jun 23, 2019, 5:31 AM bitfreak25 <bitfreak25@gmx.de> wrote:
>>
>>> OS: Arch Linux 5.1.12-arch1-1-ARCH (tty1)
>>> Bash-Version: 5.0.7(1)-release
>>> localization: de_DE.UTF-8 UTF-8
>>> keymap: de-latin1-nodeadkeys
>>>
>>> Description:
>>> The command "cat /etc/localtime" was called in a tty-terminal. After =
that
>>> some characters will be printed incorrectly (mostly "cyrillic" chars
>>> instead of the correct ones). The typed chars seems to be handled cor=
rectly
>>> (e.g. calling "exit") but the output is broken at this point. This
>>> behaviour is reproducible on my other PC with Debian Stable (Bash-Ver=
sion
>>> in Debian: 4.4-5), so it seems to be a old bug. Changing to another t=
ty or
>>> rebooting the OS will fix this behaviour until the command is called =
again.
>>>
>>> Kind regards,
>>> bitfreak
>>>
>>>
>>
>>
>> /etc/localtime is symlinked to a file that contains time zone data. If=
 you
>> enter the command
>>
>> file -L /etc/localtime
>>
>> you'll see that that's the case. It contains data that's not meant to =
be
>> displayed including control characters which cause the effect you obse=
rved.
>> If you cat any so-called binary file such as this you are likely to se=
e the
>> same kind of thing happen. Entering the
>>
>> reset
>>
>> command in the affected terminal will correct the problem after it occ=
urs.
>=20
> I kind of thought that this could be the reason. It also happens with
> "cat /dev/urandom" which is stopped by [STRG] + [C].
>=20
> It seems to be a very small bug thats only breaks the output with an
> unusual command and there are already 3 workarounds. But in my opinion
> it should be fixed some time as it isn't the correct behaviour like
> doing it with a gui-terminal e.g. xfce4-terminal.

All GUI terminals in my experience display the correct behavior. The
correct behavior is to:
- faithfully emit the output you requested
- thereby emit control characters which the terminal cannot properly
  parse
- break terminal output in some cases, depending on the control
  characters in question

Some programs, unlike cat, try to protect you from this effect. See for
example,

$ curl file:///etc/localtime
Warning: Binary output can mess up your terminal. Use "--output -" to tel=
l
Warning: curl to output it to your terminal anyway, or consider "--output=

Warning: <FILE>" to save to a file.

--=20
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User


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