diff

The 'diff' command line tool is used to compare the contents of two files or directories and display the differences between them. It shows which lines or files are added, modified, or removed.

Here are some key aspects of the 'diff' command:

1. Syntax: The basic syntax of 'diff' is as follows: 'diff [options] file1 file2'. It takes two file arguments as input and compares them.

2. Output: The output of 'diff' shows the differences between the two files with specific markings. Lines starting with '<' indicate lines present only in file1, while lines starting with '>' denote lines present only in file2. Lines starting with '---' and '+++' signify the context or file name. Lines starting with '!' represent differences within changed lines.

3. Directories: 'diff' can also be used to compare directories. In this case, the tool compares the files within the directories and highlights any differences it finds.

4. Options: 'diff' provides various options to customize the output and behavior. Some commonly used options include '-c' (context output), '-u' (unified output), '-r' (recursive comparison of directories), and '-q' (brief output indicating only whether files differ or not).

5. Patching: 'diff' output can be used to create "patches". By redirecting the output to a file using the '>' operator, the differences can be saved as a patch file. The patch file can then be applied to another version of the file using 'patch' command.

Overall, the 'diff' command line tool is an essential utility for comparing files and directories, enabling users to identify and understand the differences between versions.