Creating a bash script that logs the output of 'watch lsusb' into an empty file

Question

I have an embedded Linux system (running Ubuntu 10) on a microprocessor that has an onboard USB hub (specifically a BeagleBone Black).

I made a simple bash script that's supposed to run a command, watch lsusb; and as that runs, my program needs to dump the output my command generates into a text or JSON file (ideally on a USB stick, called usb0 for the sake of the example).

So far, this is what I have:

#!/bin/bash
#DATE=$(date +'%F %H:%M:%S')
DIR=/home/ubuntu/lsusb_logs
CMD='watch lsusb'
$CMD > $DIR

This runs until I stop it, which is fine. But when I go to look at my now created lsusb_logs file, all the data appears to be either encoded or needs to be formatted because its not at all like the original format a single lsusb or even watch lsusb outputs.

The purpose of this script is to gather historical data of the peripherals on the USB hub state over a 24 hour period in an environment chamber (climate stress testing).

Any advice or insight is helpful, thanks.

Answer 1

watch is going to print some non-readable characters because it needs to clear the screen every time it runs the command. You could however just run the command in an infinite while loop with some delay:

while true; do
    lsusb >> lsusb_logs
    sleep 1 # 1 second delay
done

Answer 2

Instead of looping through the same repetitive command indefinitely, you can take another approach.

You can utilize udev to monitor for plugged or unplugged USB devices, and execute a script at that time.

Example, create 2 scripts:

vi /bin/device_added.sh
vi /bin/device_removed.sh

which will log to a log file the ACTION (added or removed),

and make those executable:

chmod +x /bin/device_added.sh
chmod +x /bin/device_removed.sh

then create a udev rule that will contain the triggers on when a device change is detected:

vi /etc/udev/rules.d/80-test.rules

which will contain for example:

SUBSYSTEM=="usb", ACTION=="add", ENV{DEVTYPE}=="usb_device",  RUN+="/bin/device_added.sh"
SUBSYSTEM=="usb", ACTION=="remove", ENV{DEVTYPE}=="usb_device", RUN+="/bin/device_removed.sh"

This way with your 2 scripts log only upon change, and not all the time..