Daily Dev Log: Find Lines in One File but Not in Another

We can use comm to find lines in one file but not in another file

# fine lines only in file-a
comm -23 file-a file-b

From comm --help,

-2 suppress column 2 (lines unique to FILE2)

-3 suppress column 3 (lines that appear in both files)

So to find lines exist in both file-a and file-b.

comm -12 file-a file-b

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