Executing scripts that read from most recent USB udev plugged in device - linux

Question

As of right now, I've got my udev setup to execute scripts when a USB flash drive is plugged in or removed, but I'm stuck trying to figure out if there is some way that I can execute a script to read a file from the most recent USB device plugged in.
I am using usbmount to automatically mount all of my flash drives, and they are mounted according to this scheme:
/dev/sdb1 15G 8.0K 15G 1% /media/usb0
/dev/sdc1 15G 8.0K 15G 1% /media/usb1
/dev/sdd1 15G 8.0K 15G 1% /media/usb2
/dev/sde1 15G 8.0K 15G 1% /media/usb3
So for example, when I plug in USB flash drive #5, it gets automounted to /media/usb4, then I would like to say execute 'cat /media/usb4/data.txt > /tmp/output.txt' and only that drive that was just plugged in. Ideally I would like this to work no matter the number assigned to /media/usbx, so that if I replug in device 2, it would execute the script just for that device and not the rest.
Any ideas of how this can be done through bash scripting preferably but open to other ideas.
Thank you for your time.
------------- EDIT
I figured out a way although it's definitely not the prettiest or maybe even the most reliable:
$ sudo tail -n2 /var/log/syslog
Oct 4 14:40:58 development usbmount[32250]: executing command: mount -tvfat -osync,noexec,nodev,noatime,nodiratime /dev/sda1 /media/usb0
Oct 4 14:40:58 development usbmount[32250]: executing command: run-parts /etc/usbmount/mount.d
$
OK, so now to cut that down to just the media mount point,
$ sudo tail -n2 /var/log/syslog |grep media | awk '{print $12}'
/media/usb0
$
With this assuming no other errors or anything filling the last two spots on the syslog, I can execute scripts using something like:
#!/bin/bash
device=`sudo tail -n2 /var/log/syslog |grep media | awk '{print $12}'`
cat $device/data.txt > /tmp/output.txt

Answer 1

The run-parts bit is a tip-off...you can create a file /etc/usbmount/mount.d/50_copydata
Something like this:
#!/bin/bash
set -u
[[ -f "${UM_MOUNTPOINT}/data.txt" ]] && cat "${UM_MOUNTPOINT}/data.txt" > /tmp/output.txt
usbmount will set $UM_MOUNTPOINT to i.e. /media/usb0. I use set -u to make sure it only executes if $UM_MOUNTPOINT is set.
I assume you are going to filter the data - if you are only going to cat the file you might as well use cp.
Remember to make the file executable:
chmod +x /etc/usbmount/mount.d/50_copydata
Unplug and re-plug your device(s) to test. Hope this helps!