mjhjmtu

we want to capture the disk device that belong to the OS ( Linux )

since each linux machine have list of disks that are not the OS , we want to capture the disk that belong to the OS

so by fdisk we can see that boot is on sda1

# sfdisk -l | grep Linux
/dev/sda1 * 0+ 63- 64- 512000 83 Linux
/dev/sda2 63+ 19581- 19518- 156773376 8e Linux LVM

so according to that I created the following command , in order to capture the disk that belong to the OS ( linux )

# OS_DISK=` sfdisk -l | grep Linux | awk '$2 == "*" print $1' | sed s'/// /g' | awk 'print $2' | sed 's/[0-9]*//g' `

# echo $OS_DISK 
 sda

seems the command do the Job

but Ifeel that this cli is too long and little clumsy

1. I find the simplest command to identify the operating system disk
   to be df /. 
   Unfortunately, it produces a lot of output
   (by which I mean a header line and many fields),
   so you would still need to do some filtering
   to get just the device name.


2. 
   

   You're right; your command is overly long and somewhat clumsy. 
   awk is a very powerful program; you rarely need
   to combine it with grep and/or sed,
   and having multiple awk commands in the same pipeline
   is almost never necessary. 
   Your pipeline can be replaced with

   
   

   sfdisk -l | awk '/Linux/ && $2 == "*" gsub("[0-9]", "", $1); split($1, a, "/"); print a[3]; '

   
   OK, it's only about a dozen characters shorter,
   but it's one command instead of five.
   
   

   P.S. sed 's/[0-9]*//g' is a slightly dangerous command. 
   Because of the g,
   it doesn't really make sense to have the * also. 
   To see what I mean, try sed 's/[0-9]*/X/g' with various inputs,
   and compare to s/[0-9]/X/g and s/[0-9]+/X/g.

   
   


3. 
   OS_DISK=` command ` can be changed
   to OS_DISK=$(command),
   and the second form (with the parentheses) is preferred.

Commands fdisk and sfdisk are included in package util-linux.
In the same package there is also findmnt command, that you can use like bellow:

findmnt / -no SOURCE
/dev/sda6