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Date:   Mon, 11 May 2020 16:28:42 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Masami Hiramatsu' <mhiramat@kernel.org>,
        Shuah Khan <shuah@kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        Li Philip <philip.li@intel.com>,
        Liu Yiding <yidingx.liu@intel.com>,
        Xiao Yang <yangx.jy@cn.fujitsu.com>,
        Andreas Schwab <schwab@linux-m68k.org>
Subject: Re: [PATCH v2] selftests/ftrace: Use printf for backslash included
 command
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On Mon, 11 May 2020 14:59:20 +0000
David Laight <David.Laight@ACULAB.COM> wrote:

> > >      echo "Test command: $command"
> > >      echo > error_log
> > > -    (! echo "$command" >> "$3" ) 2> /dev/null
> > > +    (! printf "%s" "$command" >> "$3" ) 2> /dev/null  
> 
> WTF is the (! for ??
> The (...) is a subshell.
> And ! inverts the exit status.
> Neither is needed at all.

This is done because the scripts are run with '-e' and will exit the script
on any error.

This particular test is examining errors in the error log. The command
being written into $3 is going to fail, and return an exit code. The
"(! ..)" is needed, otherwise that failure will exit out the script.

-- Steve