Version Control with Mercurial

Version control is the lab notebook of the digital world: it’s what professionals use to keep track of what they’ve done and to collaborate with other people. Every large software development project relies on it, and most programmers use it for their small jobs as well. And it isn’t just for software: books (like this one), papers, small data sets, and anything that changes over time or needs to be shared can and should be stored in a version control system.

Version control is better than mailing files back and forth because:

  • Nothing that is committed to version control is ever lost. This means it can be used like the “undo” feature in an editor, and since all old versions of files are saved it’s always possible to go back in time to see exactly who wrote what on a particular day, or what version of a program was used to generate a particular set of results.
  • It keeps a record of who made what changes when, so that if people have questions later on they know who to ask.
  • It’s hard (but not impossible) to accidentally overlook or overwrite someone’s changes: the version control system automatically notifies users whenever there’s a conflict between one person’s work and another’s.

This lesson shows how to use a popular open source version control system called Mercurial (also known as hg). It is widely used, both because it’s easy to set up and because of a hosting site called Bitbucket. No matter which version control system you use, the most important thing to learn is not the details of their more obscure commands, but the workflow that they encourage.


Students should understand how to interact with the Unix shell (e.g., how to change their working directory) before beginning this lesson.

Getting ready

You are ready to go.


  1. A Better Kind of Backup
  2. Collaborating
  3. Conflicts
  4. Open Science

Other Resources