How to compare 2 files in linux?

Question

linux

Hello! How to use bash to compare 2 files and show only the line that is missing in the second file?
I do diff -ui file1 ..file2 | grep строка, and the output
is + line - line
,
although the "line" is in both files, only in different places. Please help with a solution.

Answer 1

show only the line that is missing in the second file

comm -23 <(sort file1.txt) <(sort file2.txt)