__bionic_open_tzdata_path: ANDROID_DATA not set!

When running commands like date or ls -l I always get a multiple repetition of the following lines to the standard error: __bionic_open_tzdata_path: ANDROID_DATA not set! __bionic_open_tzdata_path: ANDROID_ROOT not set! I used to consider it acceptable, until I created a script running date in a loop, causing an awful endless stream of the same repeated lines. I couldn't find any documentation about it, yet the problem seems to be common. Any idea how to fix this? Thanks in advance