Comparing files line by line can be done with a tool named diff. There are a lot of different options provided by diff. We will look at the most popular and useful features in this tutorial.
Syntax
diff
has simple syntax. There are options that we will look later and files to be compared.
diff [OPTION] FILES
Compare Two Files
In this example, we will compare two files line by line
$ diff file1 file2
If there is no output after diff operation this means that there is no difference between files.
In this output, we see that one line is different. > means the second file has one extra line
- 3a4 means after line 3 line 4 is added
We change file and compare again with the same command
file1
This is line 1 We can resume Extra file Change the station
file2
This is line 1 We can resume Change the station Forth line
$ diff file1 file2

- 3d2 Lines 3 in the file1 need to be deleted in order to match line 2 in the file2
- 4a4 From file2 delete line 4 to match first file line 4
View Verbose Diff
We can list all lines of two files with which lines will add or deleted both files to match each other.
$ diff -c file1 file2

Unified Mode
In a unified view, only one file is shown with related changes like delete or add. It is simpler than verbose mode to review.
$ diff -u file1 file2
