Comparing text files: how to display lines that are in the first, but not in the second?

Question

bash

Hello! There are two text files. Contain filenames (one per line, not repeated). The order may vary.
How to find lines that are only in the first file, but not in the second (the position in the file does not matter)

Answer 1

$ grep -f 2.txt -v 1.txt

spoiler

3
4

$ cat 1.txt

spoiler

1
2
3
4
5

$ cat 2.txt

spoiler

1
2
5
6
7