how to transfer a file from within system partition on android to desktop background

I'm developing an app that downloads files to the device.. some of these files are acting out and to trouble shoot I want to actually transfer these files to my (mac) desktop and go through them.

So this is what I did: 


i rooted my device
i know exactly where my file is:

$adb shell
$su
cd /data/user/0/com.app.name.dev/files/34234/
ls


here i get the file name.. let's say it's called
file_name.txt

the problem is when i go to my desktop and do something like


adb -s $device_id pull /data/user/0/com.app.name.dev/files/34234/file_name.txt


i get the error message 


remote object '/data/user/0/com.app.name.dev/files/34234/file_name.txt' does not exist


when i know it does! 


I also tried using scp from within the android shell command.. but scp doesn't exist there
i tried running adb root and got

adbd cannot run as root in production builds



any help?
it turns out that i simply should use the cp command from within my root android shell.. and copy it to /mnt/sdcard.. the rest is obvious after that