How to enumerate USB block devices (USB memory sticks and HDDs)

There is also a method of How to enumerate USB block devices (USB memory and HDD) (Part 2).

Method

ls /sys/block/ -1 | \
  xargs -I{} echo /sys/block/{} | \
  xargs readlink | \
  grep usb | sed -e 's!.*/\([a-z]\+\)!\1!'

Commentary

Block device enumeration

You can enumerate block devices on linux by enumerating the following / sys/block /.
Each item is a symbolic link.
For usb devices, the symbolic link path contains the string usb.

ls /sys/block/ -l
Total 0
lrwxrwxrwx 1 root root 0 December 27 19:08 loop0 -> ../devices/virtual/block/loop0
lrwxrwxrwx 1 root root 0 December 27 19:08 loop1 -> ../devices/virtual/block/loop1
lrwxrwxrwx 1 root root 0 December 27 19:08 loop10 -> ../devices/virtual/block/loop10
lrwxrwxrwx 1 root root 0 December 27 19:08 loop2 -> ../devices/virtual/block/loop2
lrwxrwxrwx 1 root root 0 December 27 19:08 loop3 -> ../devices/virtual/block/loop3
lrwxrwxrwx 1 root root 0 December 27 19:08 loop4 -> ../devices/virtual/block/loop4
lrwxrwxrwx 1 root root 0 December 27 19:08 loop5 -> ../devices/virtual/block/loop5
lrwxrwxrwx 1 root root 0 December 27 19:08 loop6 -> ../devices/virtual/block/loop6
lrwxrwxrwx 1 root root 0 December 27 19:08 loop7 -> ../devices/virtual/block/loop7
lrwxrwxrwx 1 root root 0 December 27 19:08 loop8 -> ../devices/virtual/block/loop8
lrwxrwxrwx 1 root root 0 December 27 19:08 loop9 -> ../devices/virtual/block/loop9
lrwxrwxrwx 1 root root 0 December 27 19:08 sda -> ../devices/pci0000:00/0000:00:17.0/ata1/host0/target0:0:0/0:0:0:0/block/sda
lrwxrwxrwx 1 root root 0 December 27 19:19 sdb -> ../devices/pci0000:00/0000:00:14.0/usb1/1-2/1-2:1.0/host3/target3:0:0/3:0:0:0/block/sdb
lrwxrwxrwx 1 root root 0 December 27 19:08 sr0 -> ../devices/pci0000:00/0000:00:17.0/ata2/host1/target1:0:0/1:0:0:0/block/sr0
t

Enumerate USB block devices

Pass the output of ls/sys/block/-1 to xargs, and then use readlink to enumerate the entities of the symbolic link.

$ ls /sys/block/ -1 | xargs -I{} echo /sys/block/{} | xargs readlink | grep usb
../devices/pci0000:00/0000:00:14.0/usb1/1-2/1-2:1.0/host3/target3:0:0/3:0:0:0/block/sdb

Extract the part of the USB block device

The last sdb part of ... block/sdb by using a regular expression like sed -e's!. */\ ([Az] \ + \)! \ 1!' Is extracted.

Finally, you can extract the part of the device file (such as sdb) with the following command.

ls /sys/block/ -1 | \
  xargs -I{} echo /sys/block/{} | \
  xargs readlink | \
  grep usb | sed -e 's!.*/\([a-z]\+\)!\1!'

You can output in the format / dev/sdb with the following command.

ls /sys/block/ -1 | \
  xargs -I{} echo /sys/block/{} | \
  xargs readlink | \
  grep usb | sed -e 's!.*/\([a-z]\+\)!\1!' | \
  xargs -I{} echo /dev/{}

Reference information

Block device size

You can get the sector size of the block device of / dev/sdb with the following command.

$ cat /sys/block/sdb/size 
15646720

You can get the size of the entire block device in bytes by multiplying the value of / sys/block/sdb/size by 512.