How do I get an array of currently attached (but not formatted/mounted) hard drives sorted by size (but without the sizing data in the array)

I wanted a way to script the mounting of hard drives to a specific mount point. After some browsing, I found: https://gist.github.com/trentmswanson/9c22bb71182e982bd36f

This was for MS Azure and did not cover specific hard drives types in the AWS Infrastructure. It used sdf in needed nvm. I made those changes and the result worked. I have an array that holds the mount points:

# Custom Mount Points for first 2 HDDs
typeset -A MountPoint
MountPoint[1]="/FileMakerData"
MountPoint[2]="/FileMakerData/Backups"

and a line that tries to read "this" HDD size and mount it appropriately:

# Tests the size of volume to test for the proper disk size
DiskSize=$(sudo fdisk -s ${DISK})

# Calculates the number of GB and resets the variable as that number
let DiskSize=DiskSize/1048576

echo "$DiskSize"
# Uses the disk size to determine disk type. 
# Assumes that the Backup drive will never be less than 50 GB and Data will never start GT 50 GB
if [ "$DiskSize" -lt 50 ]; 
then DiskType="Data"
elif ["$DiskSize" -ge 50 ];
then DiskType="Backup"
fi

A function then gets the mount point from the array based on the value.

get_next_mountpoint() {
    DeviceType=${1}
    if ( test "$DeviceType" == "Data" ); then echo "${MountPoint[1]}"
    elif ( test "$DeviceType" == "Backup" ); then echo "${MountPoint[2]}"
    else
        # Echos blank so the script will know to exit loop
        echo ""
    fi
}

There is a lot more to the script. The issue with this process, though, is that the HDD to be mounted to /FileMakerData must be created/mounted first.

When I mount /FileMakerData/Backups then mount /FileMakerData I get a single directory in /FileMakerData that is labeled "lost+found". It makes sense that this happens since I am suddenly changing the middle of the directory structure. But, I cannot figure out a way to list the Hard Drives by increasing size so that when the script gets an arbitrary order from the folders (Because AWS mounted them backward) I can still mount the correct size drive to the correct folder in the correct order.

My current code is:

# An set of disks to ignore from partitioning and formatting; Use pipe to seperate (may act as OR in this case)
BLACKLIST="/dev/nvme0"

# Gets a list of disks filters out the listed ones then searches for others
DEVS=($(ls -1 /dev/nvme*|egrep -v "${BLACKLIST}"|egrep "[0-9]n[0-9]$"))

I found: https://linuxhint.com/list_disks_ubuntu/ But it does not tell me how to get them in a simple array and I cannot also sort by size with this command.

I tried:

ls -1 /dev/nvme*|egrep -v "${BLACKLIST}"|egrep "[0-9]n[0-9]$" | sort

and

ls -1 /dev/nvme*|egrep -v "${BLACKLIST}"|egrep "[0-9]n[0-9]$" | sort -r

but (as expected) this does not sort on size. It sorts on the HDD name that is passed:

/dev/nvme1n1
/dev/nvme2n1 

and

/dev/nvme2n1
/dev/nvme1n1

Respectively. That is exactly what I want, just sorted by size, not name.

Other googling has not turned up much useful help for extracting the size and sorting the main value by size. I am running an Ubuntu 18.04 minimal install as this is a web server. I have access to df and fdisk and I am trying to install many more packages but will consider it if it should prove to be significantly easier.

I don't really understand what you are trying to do (or why), but you could consider using lsblk with its --json output format specifier, piping the result to jq where you can implement custom filtering / sorting.

For example:

$ lsblk -b --json | jq -r '
    .blockdevices[] | select(.name == "sda") |
    [ .children[] | select(.mountpoint == null and .name != "sda4") ] | sort_by(.size) | .[].name
'
sda1
sda2

I think you want systemd.mount for this. Adding x-systemd.requires-mounts-for= to your fstab entry creates a transient mount unit:

# fstab(5):
/dev/loop1 /opt/mnt      ext4 noauto 0 0  
/dev/loop2 /opt/mnt/data ext4 noauto,x-systemd.requires-mounts-for=/opt/mnt 0 0

which you can start and stop as a systemd.unit:

systemctl start opt-mnt-data.mount

this will mount the filesystem in a certain order.