comm is a command-line utility used in Unix-based operating systems, including Mac OS X, to compare two sorted text files line by line. The comm command displays the lines that are unique to each file, as well as the lines that are common to both files.
To use comm, open the Terminal application and navigate to the directory where the two text files that you want to compare are located. Then, use the following command:
comm file1 file2
Replace "file1" and "file2" with the names of the two text files that you want to compare. The comm command will display three columns of output: the first column contains the lines that are unique to "file1", the second column contains the lines that are unique to "file2", and the third column contains the lines that are common to both files.
By default, comm ignores leading whitespace on each line. You can use the -t option to include leading whitespace in the comparison. You can also use the -1 and -2 options to suppress the first and second columns of output, respectively.
For example, if you want to compare two text files named "example1.txt" and "example2.txt", you would use the following command:
comm example1.txt example2.txt
After running this command, the comm command will display the lines that are unique to each file, as well as the lines that are common to both files.