Linux commands: diff

By Flavio Copes

Learn how the Linux diff command compares two files or directories line by line, with -y for a side-by-side view and -u for the unified format Git uses.

diff is a handy command. Suppose you have 2 files, which contain almost the same information, but you can’t find the difference between the two.

diff will process the files and will tell you what’s the difference.

Suppose you have 2 files: dogs.txt and moredogs.txt. The difference is that moredogs.txt contains one more dog name:

diff dogs.txt moredogs.txt will tell you the second file has one more line, line 3 with the line Vanille:

If you invert the order of the files, it will tell you that the second file is missing line 3, whose content is Vanille:

Using the -y option will compare the 2 files line by line:

The -u option however will be more familiar to you, because that’s the same used by the Git version control system to display differences between versions:

Comparing directories works in the same way. You must use the -r option to compare recursively (going into subdirectories):

In case you’re interested in which files differ, rather than the content, use the r and q options:

There are many more options you can explore in the man page running man diff:

The diff command works on Linux, macOS, WSL, and anywhere you have a UNIX environment

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