Find lines from a file which are not present in another file

unix text-files
Sudar picture Sudar · Jan 23, 2013 · Viewed 69.2k times · Source

I have two files (let's say a.txt and b.txt), both of which has a list of names. I have already run sort on both the files.

Now I want to find lines from a.txt which are not present in b.txt.

(I spent lot of time to find the answer for this question, so documenting it for future reference)

Answer

Sudar picture Sudar · Jan 23, 2013

The command you have to use is not diff but comm

comm -23 a.txt b.txt

By default, comm outputs 3 columns: left-only, right-only, both. The -1, -2 and -3 switches suppress these columns.

So, -23 hides the right-only and both columns, showing the lines that appear only in the first (left) file.

If you want to find lines that appear in both, you can use -12, which hides the left-only and right-only columns, leaving you with just the both column.

Related questions

Why should text files end with a newline?

I assume everyone here is familiar with the adage that all text files should end with a newline. I've known of this "rule" for years but I've always wondered — why?

Read More
Count number of blank lines in a file

In count (non-blank) lines-of-code in bash they explain how to count the number of non-empty lines. But is there a way to count the number of blank lines in a file? By blank line I also mean lines that have …

Read More
Organizing the output of my shell script into tables within the text file

I am working with a unix shell script that does genome construction then creates a phylogeny. Depending on the genome assembler you use, the final output (the phylogeny) may change. I wish to compare the effects of using various genome …

Read More