Is `dpkg --contents` unable to handle SIGPIPE?

Question

I noticed a weird antipattern in some CI scripts I've taken over, which basically boils down to this code checking whether a particular file is present in a package:

dpkg --contents some.deb > contents.txt
grep --quiet foo contents.txt

I tried the obvious refactor of dpkg --contents some.deb | grep --quiet foo, but I keep getting this error:

dpkg-deb: error: tar subprocess was killed by signal (Broken pipe)

From some more investigation, this is definitely a timing issue. If I use a regex which matches early in the input stream I get the error, but if I use a regex which specifically matches a late line it succeeds.

The most obvious conclusion is that dpkg (or possibly tar) does something wrong with SIGPIPE. Is this a known issue?

Platform:

# lsb_release --all
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:    18.04
Codename:   bionic
# dpkg --version
Debian 'dpkg' package management program version 1.19.0.5 (amd64).
This is free software; see the GNU General Public License version 2 or
later for copying conditions. There is NO warranty.
# tar --version
tar (GNU tar) 1.29
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by John Gilmore and Jay Fenlason.

Answer 1

dpkg用于tar列出包内容。当tarcan\xe2\x80\x99t 处理完整的存档时，表示发生错误，并且 \xe2\x80\x99dpkg是报告的内容。这两个命令都认为无法完成任务是一个错误，并采取相应的行动。

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您可以通过确保grep在退出之前读取其所有输入来避免这种情况：

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| grep foo > /dev/null\n

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（而不是-q，一旦匹配就退出）。

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