GNU bug report logs - #24276
head without pipline is not reading complete STDIN, resulting in unwilling and unexpected command execution

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Sebastian <sebastian <at> ifyouwantblood.de>
To: bug-coreutils <at> gnu.org
Subject: head without pipline is not reading complete STDIN, resulting in
 unwilling and unexpected command execution
Date: Sat, 20 Aug 2016 23:01:07 +0200

hi,

while comparing my rewrite in google go of coreutils i noticed that head without pipeline
is not reading complete STDIN:

> head -c 2

enter:

> asdf

press return

this results in printing "as" and execution of the df command. thats highly unexpected and 
probably a good example for a variant of WYSINWYC (What you see is not what you copy)*.
someone might even come up with a not harmful looking code, that is harmful (heredoc?).

> head --version
> head (GNU coreutils) 8.25

> bash --version
> GNU bash, version 4.3.46(1)-release (x86_64-suse-linux-gnu)

> uname -o
> GNU/Linux

> printfile /etc/os-release
> NAME=openSUSE
> VERSION="Tumbleweed"
> VERSION_ID="20160811"
> PRETTY_NAME="openSUSE Tumbleweed (20160811) (x86_64)"
> ID=opensuse
> ANSI_COLOR="0;32"
> CPE_NAME="cpe:/o:opensuse:opensuse:20160811"
> BUG_REPORT_URL="https://bugs.opensuse.org"
> HOME_URL="https://www.opensuse.org/"

* http://www.ush.it/team/ascii/hack-tricks_253C_CCC2008/wysinwyc/what_you_see_is_not_what_you_copy.txt

-- 
Sebastian Kratz
@ProhtMeyhet

Message #10 received at 24276-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Sebastian <sebastian <at> ifyouwantblood.de>, 24276-done <at> debbugs.gnu.org
Subject: Re: bug#24276: head without pipline is not reading complete STDIN,
 resulting in unwilling and unexpected command execution
Date: Sat, 20 Aug 2016 17:12:36 -0700

This is not a bug. It's quite OK for 'head' to read just as much input as is 
required, and to not bother to read the rest of input. In fact, POSIX requires 
this behavior if standard input is a seekable file. See:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html

and look for "seekable input".

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