diff - compare files line by line

The diff command in Linux is a utility used to compare files line by line and display the differences between them. It is a powerful tool for identifying changes made to files over time, or for comparing two versions of a file to see what has been modified. Here's a detailed explanation of how to use the diff command and some of its options:

1. Basic Usage: The basic syntax of the diff command is diff [OPTION]... FILES, where FILES can be the names of the two files you want to compare. The command will compare these files line by line and output the differences.13

2. Line Numbers: The output of the diff command includes line numbers corresponding to the lines where differences are found in the first file, followed by a special symbol indicating the type of difference (such as a line unique to that file, or a line that has been changed). This makes it easy to see exactly where and how the files differ.2

3. Case-Insensitive Comparison: If you want to compare the files without considering case differences in the file contents, you can use the -i or --ignore-case option. This is useful when the files are expected to have differences in capitalization but are otherwise the same.1

4. Ignoring File Name Case: There are also options to ignore case when comparing file names, such as --ignore-file-name-case and --no-ignore-file-name-case, which can be important in case-insensitive file systems.1

5. Context and Unified Mode: The diff command can display differences in different modes. The context mode provides a few lines of context around the differences, while the unified mode shows the changes in a more readable format that includes a wider context.2

6. Quiet Mode: If you want the diff command to be quiet and only report when the files are different, you can use the -q or --quiet option.5

7. Normal Output: The --normal option outputs a normal diff, which is the default behavior if no other output option is specified.5

8. Identical Files: There is an option to report when the files are identical, which can be useful for verifying that two files are the same.6

In conclusion, the diff command is a versatile tool for comparing files line by line in Linux. It offers various options to customize the output and make it easier to understand the differences between files.7