OT: posix sh problem

[Teske, Devin]

On Apr 4, 2013, at 5:32 AM, Mark Felder wrote:

> Hi all,
> 
> Hopefully someone here is much more clever than I am. I've run out of ideas on how to cleanly convert this chunk of ksh to posix sh.

/me takes the challenge (and shame on some of the current responses; this is trivial in sh and there's actually nothing wrong with the OPs code -- it works)


> This is from a BB/Hobbit/Xymon monitoring script for ZFS. I'd really like to have this working cleanly on FreeBSD without requiring any funky shells or using any temporary files.
> 

Cool! After I help you fix whatever the issue is, I'd be interested in this a little more. ZFS monitoring would be nice.


> The following is supposed to be able to loop through the output of multiple zpools reading one line at a time and each line item is set as a variable:
> 
> 
> /sbin/zpool list -H | while read name size used avail cap dedup health altroot
> do
>  # do interesting things here
> done
> 
> Unfortunately you can't pipe through read in posix sh.

Wait, you can't? Then I've been doing something wrong all these years…

#!/bin/sh
printf "line1\nline2\n" | while read line
do
	echo "line=[$line]"
done

===

dteske at scribe9.vicor.com ~ $ sh bar
line=[line1]
line=[line2]

===

Just a side note, on my "zpool list -H" on my 8.1-R system doesn't provide the "dedup" column, so your mileage may vary (you may have to adjust the script to account for that on systems like mine).

Aside from that, I took your script as-is, copy/paste and it worked fine on 8.1-RELEASE-p6:

dteske at oos0a.lbxrich.vicor.com ~ $ cat bar
#!/bin/sh
/sbin/zpool list -H | while read name size used avail cap dedup health altroot
do
 echo $name
done
dteske at oos0a.lbxrich.vicor.com ~ $ sh bar
NEC1-RAID6-ARRAY1
NEC1-RAID6-ARRAY2
NEC1-RAID6-ARRAY3



> You also can't use process substitution: while read var1 var1 < <(/sbin/zpool list -H)
> 

I'll admit that one's unsupported.


> Any ideas are greatly appreciated. I know there's a python-based script floating on github but I cant guarantee every server will have python on it…
> 

Stick to /bin/sh if you can (like you say, portability and potability in using base utilities).



> Source of script is here: http://en.wikibooks.org/wiki/System_Monitoring_with_Xymon/Other_Docs/HOWTO#Hobbit_Client_and_ZFS_monitoring

The only things I saw that needed changing to go from ksh to /bin/sh were:

	if [ … == … ]; then

Needs to be

	if [ … = … ]; then

And optionally, a style nit would be to convert back-tick pairs into nestable $(…) syntax. For example, change:

	cap=`…`

to instead:

	cap=$(…)

Oh and of course, the HTML should go away since you're making a command-line tool and not a BB/Hobbit/Xymon module.
-- 
Devin

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