Date: Fri, 15 Jun 2012 20:23:27 +0200 (CEST) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-stable@FreeBSD.ORG, wblock@wonkity.com Subject: Re: devd problem with 9-stable Message-ID: <201206151823.q5FINRFT084093@lurza.secnetix.de> In-Reply-To: <alpine.BSF.2.00.1206151053360.26334@wonkity.com>
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Warren Block wrote:
> Well, it did work with an attach event. Progress: the event is seen
> with a notify event. However, something is not right with the execution
> of backticks in the action string:
>
> notify 20 {
> match "subsystem" "DEVICE";
> match "type" "ATTACH";
> match "cdev" "ugen[0-9]+.[0-9]+";
> match "vendor" "0x04b8";
> match "product" "0x010a";
> action "devnum=`echo $cdev | sed -e 's/^ugen//'` && \
> echo $devnum > /tmp/example && \
> echo $cdev >> /tmp/example";
> };
>
> When the event is seen:
> Executing 'devnum=`echo ugen0.6 | sed -e 's/^ugen//'` && echo devnum: > /tmp/example && echo cdev: ugen0.6 >> /tmp/example'
>
> $devnum never gets a value, the contents of /tmp/example are:
> devnum:
> cdev: ugen0.6
>
> Trying $() instead of backticks makes it worse:
> Executing 'devnum=$(echo $cdev | sed -e 's/^ugen//') && echo devnum: $devnum > /tmp/example && echo cdev: $cdev >> /tmp/example'
Unfortunately, the manual page does not explain how the action
strings are parsed exactly. I guess the problem is not the
backticks but the fact that the parser tries to expand $devnum
as a devd variable, so the shell never sees it. This also
explains why using $() makes things worse.
You can try to prepend a backslash, i.e. echo \$devnum. This
isn't documented, but then again, using backslashes to continue
strings that span multiple lines isn't documented either.
In case the sed command still doesn't work, alternatively you
can use shell substring processing instead (this is also more
efficient because the shell doesn't have to create a pipe and
fork a sed process):
action "devnum=$cdev; devnum=\${devnum##ugen}; echo \$devnum > /tmp/foo"
Or even:
action "devnum=$cdev; echo \${devnum##ugen} > /tmp/foo"
Best regards
Oliver
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