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Comparing Files

We can compare the data of two files by using the following commands:

  1. cmp
  2. diff
  3. sdiff
  4. vidiff
  5. comm

1. cmp Command:

It compares files byte by byte.

cmp file1.txt file2.txt

If the content is the same, there will be no output.
If the content is different, it provides information about only the first difference, including the byte number and line number.

$ cmp a.txt c.txt
a.txt c.txt differ: byte 7, line 2

Note: The cmp command only shows the first difference and not all differences.

2. diff Command:

It shows all differences in the content.

diff file1.txt file2.txt

If the content is the same, there will be no output.
If the content is different, it will show all differences.

$ diff a.txt b.txt
$ diff a.txt c.txt
2,3c2,3
< Bunny
< Chinny
---
> bunny
b

For the diff command, we can use the following options:

  • -q: Shows a message when files are different.
  • -s: Shows a message when files are the same (identical).
  • -y: Shows a comparison line by line (parallel comparison).
$ diff -q a.txt c.txt
Files a.txt and c.txt differ

$ diff -s a.txt b.txt
Files a.txt and b.txt are identical

$ diff -y a.txt c.txt
Sunny  Sunny
Bunny  | bunny
Chinny | chinny
Vinny  Vinny
Pinny  Pinny

If we want to suppress common lines, we should use the --suppress-common-lines option with the -y option.

$ diff -y --suppress-common-lines a.txt c.txt
Bunny  | bunny
Chinny | chinny

3 sdiff Command:

We can use the sdiff command for side-by-side comparison (parallel comparison).

$ sdiff a.txt b.txt
Sunny  Sunny
Bunny  Bunny
Chinny Chinny
Vinny  Vinny
Pinny  Pinny

$ sdiff a.txt c.txt
Sunny  Sunny
Bunny  | bunny
Chinny | chinny
Vinny  Vinny
Pinny  Pinny

Note: The sdiff command and the diff command with the -y option are the same.

4 vimdiff Command:

  • It will highlight differences directly in vim.
  • To use this command, we need to install vim using the following command:
sudo apt install vim
  • To compare files:
vimdiff a.txt b.txt
  • Key commands in vimdiff:
    • ctrl+w+w: Switch to the next window.
    • :q: Close the current window.
    • :qa: Close all windows.
    • :qa!: Forcefully close all windows.

5 comm Command:

Using the comm command, we can compare the data of two files.
The result is displayed in 3 columns:

  • Column 1: Data present only in file1.txt but not in file2.txt.
  • Column 2: Data present only in file2.txt but not in file1.txt.
  • Column 3: Common data present in both files.
comm file1.txt file2.txt

For example:

$ comm a.txt c.txt
Sunny
bunny
Bunny
chinny
Chinny
Vinny
Pinny

With the comm command, we can use the following options:

  • -1: Do not display column 1.
  • -2: Do not display column 2.
  • -3: Do not display column 3.
  • -12: Do not display both columns 1 and 2.

Note: These comparison commands—cmp, diff, sdiff, vimdiff, comm—can be used to compare files across different builds, making them highly versatile.

"Comparison is the thief of joy." – Theodore Roosevelt. However, when it comes to comparing files, it's a necessary skill!