The //**diff**// command in Linux and Unix-like systems is used to compare the contents of two files and display the differences. It can be used to compare files on the file system, or the output of two commands.

Here is the basic syntax for the **diff** command:

<code>
diff [options] file1 file2
file1 is the name of the first file you want to compare
file2 is the name of the second file you want to compare</code>


Here are some examples of the **diff** command in action:

1. To compare the contents of two files called "file1.txt" and "file2.txt"
<code>
$ diff file1.txt file2.txt</code>

2. To compare the contents of two common subdirectories recursively
<code>
$ diff -r dir1 dir2</code>
Note: The **-r** option is used to compare directories recursively.


3. To ignore changes in white spaces while comparing
<code>
$ diff -b file1.txt file2.txt</code>
Note: The **-b** option is used to ignore changes in trailing blanks (spaces and tabs) while comparing

4. To show the line numbers in the output
<code>
$ diff -n file1.txt file2.txt</code>
Note: The **-n** option is used to show the line numbers in the output.

The **diff** command is useful for identifying the differences between two files or the output of two commands. It can be used to compare files on the file system, or the output of two commands. It can also be used to compare two versions of the same file, or to compare the changes made in a file after editing it. The output of the **diff** command shows the lines that are different between the two files, including the line numbers where the differences occur. This can be useful for identifying and resolving conflicts when working on collaborative projects or for keeping track of changes made to a file.