How to compare two files in Linux

There are various tools provided in various linux flavors to compare two text files, but there are few common ways of doing this i as below.

1. Using "diff" command.
    It compare two files line by line and list out the differences.

    Syntax: diff [options] file1 file 2
 
     Options: options can be used to change behavior of command scope
                    -b Instruct the system to ignore extra spaces and tabs.
                    -w Ignore all white spaces
                    -i Ignore any case differences
                    -E Ignore changes due to tab expansion.
                    -c useful in comparing tow code files and points ! to indicate difference,- for less and +                             for  more
                    <for more options refer manual>
 
     Example:
   

                 file1:

                         1

                         2

                         3

                         4

                         5

                         6

                         7

                         8

                         9

                 file2:

                        1

                        2

                        3

                        7

                        8

                        9

                       10

                       11

                       16

     
            $ diff file1 file2

                4,6d3

                < 4

                < 5

                < 6

               9a7,9

                > 10

                > 11

                > 16

The output is produced in ED line editor format, which suggest what changes to file will make it same as other file being compared. in above example 4,6d3 means delete 3 lines from 4-6 in first file and 9a7,9 means append at 9th position line 7-9 from second file.

Note: diff can be used to compare files in two different directory.

2. Using "vimdiff" or "vim -d" text editor functionality
    this tool will display the difference in file in vertical column and highlighting the difference.

    Syntax: vimdiff file1 file2

    Example: vimdiff 1 2 or vim -d 1 2

   
3. Using "comm" command
     This command will compare the files and will display the difference in  3 column.

    Syntax: comm [-123i] file1 file2
                  -1 to display difference in 1st file compared to 2nd file
                  -2 to display difference in 2nd file compared to 1st file.
                  -3 to display matching lines.
                  -i to do case sensitive comparison.

     Example: comm 1 2

                                           1

                                           2

                                           3

4

5

6

                                           7

                                           8

                                           9

                  10

                  11

                  16