Temporary root Nexus 5 in adb shell to access a /data folder I want to backup a data/data/com.package.name folder but the app manifest is set to backup=false. 

To access the folder I want to temporary root the phone in the ADB shell and then access the folder to copy my files. There's no need for me to make root persistent.

The nexus runs on Android 5.0.1. Is there a way to get access to my data without installing a custom recovery, and others?
There is a way (or there was) to boot your device and access to it as root using ADB. First, you have to boot your device into the bootloader.


Turn it off. Press and hold Volume Down and press power.

You need to find and download boot insecure image (boot.img) and boot your phone using that image
fastboot boot boot.img


Now you should be able to access your device as root and copy your files
adb shell


will give you root access to it
To put a file into it do:

adb push file /phone/folder/



Be careful since an old boot insecure image in Android 5.0 or above can mess up with your phone. In my case an old image ruined my sensors and WiFi, and the only way I could fix it was by erasing the user data.