Bash; creating arrays which names are computed from other variables [duplicate] - arrays

Question

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Assign to a bash array variable indirectly, by dynamically constructed variable name
(1 answer)
Closed 5 years ago.
My goal is to create a list of partitions for each block device listed in /sys/block;
#!/bin/bash
block_devices_list=($(ls /sys/block))
partition_list=($(cat /proc/partitions | awk '{print $4}'))
unset partition_list[0]
for block_device in ${block_devices_list[#]}; do
for partition in ${partition_list[#]}; do
partitions+=($(echo $partition | grep $block_device))
done
# Right here?
unset partitions
done
Every time the outside 'for loop' completes it's cycle it ends up with an array of partitions for a particular block device. At that point I would like to transfer that data to a separate array, dynamically named after the device it belongs to (like 'partitions_sda' for example).
I have read a few questions/answers about 'dynamic' variable names, 'associative' arrays and whatnot but don't seem to be able to figure this out. Any help much appreciated.

Answer 1

As a best-practices example (for bash 4.3 or newer):
#!/bin/bash
for blockdev in /sys/block/*; do
devname=${blockdev##*/} # remove leading path elements
devname=${devname//-/_} # rename dashes in device name to underscores
declare -a "partitions_${devname}=()" # define an empty array
declare -n _current_partitions="partitions_$devname" # define a nameref
for part in "$blockdev"/*/dev; do # iterate over partitions
[[ -e $part ]] || continue # skip if no matches
part=${part%/dev} # strip trailing /dev
_current_partitions+=( "${part##*/}" ) # add match via nameref
done
unset -n _current_partitions # clear the nameref
declare -p "partitions_$devname" # print our resulting array
done
For my local test VM, this emits:
declare -a partitions_dm_0=()
declare -a partitions_dm_1=()
declare -a partitions_sda=([0]="sda1" [1]="sda2")
declare -a partitions_sdb=()
declare -a partitions_sr0=()
...which is correct, as sda is the only partitioned device.
The basic mechanism here is the nameref: declare -n name1=name2 will allow one to refer to the variable name2 under the name name1, including updates or assignments, until unset -n name1 is performed.

Answer 2

Not sure I understood what you are trying to do but this is an example that you can, maybe, start with:
#!/bin/bash
list1=(a b c)
list2=(j k l)
for x in ${list1[#]}; do
for y in ${list2[#]}; do
tmplist+=(${x}${y})
done
cmd="declare -a list_${x}=(${tmplist[#]})"
eval $cmd
unset tmplist
done
echo "list_a: ${list_a[#]}"
echo "list_b: ${list_b[#]}"
echo "list_c: ${list_c[#]}"
It shows how to create arrays which names are computed from other variables, how to unset a temporary array...

Answer 3

I would create two types of arrays. One for containing disk names, then different arrays for each disk for storing partition specific information.
#!/usr/bin/env bash
while read -r l; do
t="${l#* }"
if [[ $t == "disk" ]]; then
# disks list contains all the disk names
disks+="${l% *} "
elif [[ $t == "part" ]]; then
# for each disk 'XXX', a separate partitions array 'parts_XXX' is created
[[ $l =~ [^a-z0-9]*([a-z]*)([0-9]*)\ ]] && d="${BASH_REMATCH[1]}" && p="${BASH_REMATCH[2]}"
eval parts_$d+=\"my-value=\$d\$p \" # append to partitians array
else
echo "unknown type $t in $l"
exit 1
fi
done <<< $(lsblk -n --output=NAME,TYPE | tr -s ' ')
# arrays are created. now iterate them
for i in ${disks[#]}; do
echo "iterating partitions of disk: $i"
# following is the name of the current disks partitions array
var=parts_$i[#]
# iterate partitians array of the current disk
for j in ${!var}; do
echo ">> $j"
done
done