bash Assign Result Query to Variable

Question

The situation, where I have unknown number of volume groups and their names with unknown number of disks assigned to them. Example :

pvs -o pv_name,vg_name
  PV         VG
  /dev/vdd   appvg01
  /dev/vdb   appvg01
  /dev/vdf3  vg00
  /dev/vdh   testvg

 vgs --noheadings | awk '{print $1}'| while read line ; do echo $line;vgs --noheadings -o pv_name $line; done
appvg01
  /dev/vdd
  /dev/vdb
testvg
  /dev/vdh
vg00
  /dev/vdf3

At the final stage I'd like to mirror each volume with new disk that I'll add manually :

for i in `/sbin/lvs| /bin/awk '{if ($2 ~ /appvg01/) print $1}'`; do
  /sbin/lvconvert -b -m0 appvg01/$i /dev/vde
done

but, I don't know what volume name should I correlate with, as it might be any other name. what is the best approach for this structure.

Thanks

...beyond that, though, I really don't understand the question. What do you mean by "correlate"? Why do you need to know a name? Etc. — Charles Duffy
– Charles Duffy, Commented Jul 22, 2014 at 18:31

Charles Duffy · Accepted Answer · 2014-07-22 18:33:24Z

2

The correct data structure to store this kind of information in bash is associative arrays:

declare -A pvs
{
  read # skip the header
  while read -r pv vg; do
     pvs[$pv]=$vg
  done
} < <(pvs -o pv_name,vg_name)

Thereafter, you can iterate and do lookups:

for pv in "${!pvs[@]}"; do
  vg="${pvs[$pv]}"
  echo "vg $vg is backed by pv $pv"
done

answered Jul 22, 2014 at 18:33

Charles Duffy

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3 Comments

user1607856 Over a year ago

Hi Charles, thanks for the quick response. sorry, if I didn't was clear enough. I need to know a name of volume to be able to use this name whenever I mirror it. At the end of the procedure I have to un-mirror mirrored volume and I need to know the name again: for i in /sbin/lvs| /bin/awk '{if ($2 ~ /appvg01/) print $1}'; do /bin/nice -n 19 /usr/bin/ionice -c 3 /sbin/lvconvert -b -m1 --corelog appvg01/$i $NewDisks; done for i in /sbin/lvs| /bin/awk '{if ($2 ~ /appvg01/) print $1}'; do /sbin/lvconvert -b -m0 appvg01/$i $OldDisks; done

Charles Duffy Over a year ago

...well, I've showed you how to do an associative array lookup; store what you want in an associative array (in other languages, this might be called a map or hashmap), and thereafter getting back to the name should be a straightforward exercise.

Charles Duffy Over a year ago

@user1607856, ...if you want a better answer than that, questions where it's easy to tell if an answer is correct are going to get much less handwavey responses. See sscce.org, or stackoverflow.com/help/mcve -- build a reproducer that doesn't require LVM, and it'll be easier to help you here.

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