Diff`ing Files with Difftastic

What is Difftastic?

Difftasic is a CLI tool that allows you to compare files based on their syntax rather than rely on line-by-line matching.

For example, this means that if you had the following files, Difftastic would not detect any differences.

$ cat vlans_1.json
{ "vlans": [100, 200, 300] } 

$ cat vlans_2.json 
{
  "vlans": [
    100,
    200,
    300
  ]
}

$ difft vlans_1.json vlans_2.json
vlans_2.json --- JSON
No syntactic changes.

Some other features that Difftastic provides are:

• Support for 40+ programming languages
• Support for all the major structured text formats (inc JSON, YAML, XML, etc.)
• Ability to perform diffs recursively across directories.
• Language detection based on file extension.

Install

Since Difftastic is Rust-based, we must ensure the Rust package manager – cargo – is installed. Then, we perform the required installation. Like so:

# Install the Rust package manager
# sudo apt install cargo

# Install difftastic
cargo install --locked difftastic

Example

Here's a quick example of using Difftastic against 2 JSON files that contain the output of show ip ospf neighbors from a Cisco Nexus device.

$ difft pre/sh_ip_ospf_neighbor.json post/sh_ip_ospf_neighbor.json
...

Here's an example of the output:

There are a few things to mention here:

• The format of the file is autodetected.
• The default display is side-by-side
• The exit code of 0 will be returned regardless.

Therefore a few other options we can also use are:

• --display inline to display the output in a single column.
• --exit-code to return a return code of 1 should there be a difference in files.

In addition, should you have multiple files in 2 folders with the same name, we can use: difft folder1 folder2 to have Difftastic recurse and diff the various files across each of the folders.

Closing Comments

If you need a quick way to diff different files based on syntax, then Difftasitc is an excellent choice for a tool to add to your automation toolbox, as it's quick and easy to use, plus it provides support for many different languages.

On the other hand:

• if you are looking to compare text-based files, then a tool such as difflib may be better suited.
• if you want the results from diffing structured based formats such as JSON, back also as structured data then a tool such as jsondiff may be a better choice.