How to find non-existing terms based on the list?
If the list is in text file (list.txt), this can be achieved by grep comparision.

First, extract the list of terms from the database by drush:

$ drush sqlq "SELECT name FROM taxonomy_term_data -- WHERE vid = 1" &gt; my_list.txt


Then compare the two lists:

$ grep -Fxv -f my_list.txt list.txt


This will print all the term names which doesn't exist in my_list.txt file.

This solution is based on: Is there a tool to get the lines in one file that are not in another?.