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From:   Alexander Kapshuk <alexander.kapshuk@gmail.com>
Date:   Fri, 17 May 2019 12:25:10 +0300
Message-ID: <CAJ1xhMVaeQPoW1v91bcNOkw1FJOr7ddhDc-ir=3AiKRCSzCj=g@mail.gmail.com>
Subject: Re: [PATCH v2] kbuild: check uniqueness of module names
To:     Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        linux-kbuild@vger.kernel.org, Sam Ravnborg <sam@ravnborg.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        Jessica Yu <jeyu@kernel.org>,
        Lucas De Marchi <lucas.de.marchi@gmail.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Michael Schmitz <schmitzmic@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Kees Cook <keescook@chromium.org>,
        Michal Marek <michal.lkml@markovi.net>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Fri, May 17, 2019 at 11:58 AM Bernd Petrovitsch
<bernd@petrovitsch.priv.at> wrote:
>
> On 17/05/2019 10:16, Alexander Kapshuk wrote:
> [...]
> > The 'xargs' '-r' flag is a GNU extension.
> > If POSIX compliance is important here, the use of 'cat', 'xargs' and
> > 'basename' may be substituted with that of 'sed' to initialise
> > same_name_modules:
> > sed 's!.*/!!' modules.order modules.builtin | sort | uniq -d
>
> 's!' is TTBOMK also a GNU-extension:
> sed 's/.*\///' modules.order modules.builtin | sort | uniq -d

It isn't.
Here's an excerpt from the POSIX manpage for 'sed',
http://pubs.opengroup.org/onlinepubs/009695399/utilities/sed.html:
[2addr]s/BRE/replacement/flags
...  Any character other than backslash or <newline> can be used
instead of a slash to delimit the BRE and the replacement....

>
> > 'Sed' may also be used on its own in the 'for' loop instead of as part
> > of a pipeline along with 'grep' to generate the desired output:
> > sed '/\/'$m'/!d;s:^kernel/:  :' modules.order modules.builtin
>
> sed "/\/${m}/!d;s/^kernel\//  /" modules.order modules.builtin

The parameter expansion syntax is redundant here.
See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02:
The parameter name or symbol can be enclosed in braces, which are
optional except for positional parameters with more than one digit or
when parameter is a name and is followed by a character that could be
interpreted as part of the name.

Here's an alternative version using double quotes.
sed "/\/$m/!d;s:^kernel/:  :" modules.order modules.builtin

>
> MfG,
>         Bernd
> --
> Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
>                      LUGA : http://www.luga.at