Using sed on Bash Command

Question

I'm trying to get a list of devices on my linux box from normal bash commands in a script. I've used the following however it isn't working. Ideally, I'd like to get all sd* and nvme devices into an array. This is what I have tried:

lsblk --nodeps | sed -n '/sd\.*/p'
lsblk --nodeps | sed '/(sd | nv)\.*/p'
lsblk --nodeps | sed -n 's/^([a-z0-9]+?).*/\1/'
lsblk --nodeps | sed -n '/^.*?/p'
lsblk --nodeps | sed '/^(.+?)\s*/p'
lsblk --nodeps | sed '/^(s.+?|n.+?)?)\s*/p'

This is the starting syntax:

$ lsblk --nodeps
NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda       8:0    0 119.2G  0 disk
sdb       8:16   1  57.8G  0 disk
nvme0n1 259:0    0 232.9G  0 disk

So I want to regex for sd* and nvme, without the trailing spaces.

Any insight appreciated how I can get drives into an array.

You realize you can get a list of block devices from /dev? You don't need lsblk for the job at all. — Charles Duffy
– Charles Duffy, Commented Jun 25, 2022 at 22:46
shopt -s nullglob; cd /dev; disks=( sd* nvme* ) and there you are, you get an array named disks with, in your case, three entries. — Charles Duffy
– Charles Duffy, Commented Jun 25, 2022 at 22:47
Or, to get easy-to-parse output from lsblk, you can do something like readarray -t disks < <(lsblk -nr --output NAME | egrep '^(sd|nvme)'). No reason to fight to parse a table when you can just ask for a format that's easier-to-parse than a table. — Charles Duffy
– Charles Duffy, Commented Jun 25, 2022 at 22:50
...eh, going to migrate the above two comments into an answer. — Charles Duffy
– Charles Duffy, Commented Jun 25, 2022 at 22:51
I was under the impression that sed could parse and return items. — Rich_F
– Rich_F, Commented Jun 25, 2022 at 22:53

Charles Duffy · Accepted Answer · 2022-06-25 23:11:35Z

1

Making `lsblk` Output Easier To Parse

lsblk can be told to suppress a header line, and to emit only the specific pieces of data you care about -- in this case, device names.

If you have a listing with nothing but device names, grep is the easiest tool to use to parse them; but to add an additional rule (in this case, discarding partitions), awk comes into play.

Thus:

readarray -t disks < <(lsblk -dnr --output NAME | grep '^(sd|nvme)')

Filtering `/dev/disk/by-id` Yourself

For the stubborn, to show that it can be done:

shopt -s nullglob extglob
declare -A results=( )
devices=( /dev/disk/by-id/!(*-part*) )
for device in "${devices[@]}"; do
  target=$(readlink -f "$device")
  results[${target#/dev/}]=1
done
disks=( "${!results[@]}" )
declare -p disks # print the resulting array

edited Jun 25, 2022 at 23:11

answered Jun 25, 2022 at 22:55

Charles Duffy

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9 Comments

Rich_F Over a year ago

``` [Sat Jun 25 19:00:26 rich@server1 /dev] declare -p disks declare -a disks='([0]="nvme0" [1]="nvme0n1" [2]="sda" [3]="sda1" [4]="sda2" [5]="sdb" [6]="sdb1" [7]="sdb2")' [Sat Jun 25 19:00:26 rich@server1 /dev] echo $disks nvme0 ```

Charles Duffy Over a year ago

echo "${disks[@]}" to print all elements of the array -- when you echo $disks it prints only ${disks[0]}. (That's true for all arrays in bash; if you're accustomed to different behavior, you aren't really using arrays).

Rich_F Over a year ago

nvme0 nvme0n1 sda sda1 sda2 sdb sdb1 sdb2 Still has partitions.

Charles Duffy Over a year ago

Fair 'nuff. One could do more magic to distinguish dependent devices (devfs and sysfs let you do everything lsblk does yourself -- they're where it gets its data), but it's work.

Rich_F Over a year ago

The nvme drives not showing up, as the partitions have convoluted endings. declare -a disks='([0]="sda" [1]="sdb")'

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Making `lsblk` Output Easier To Parse

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