Command line basics
(This is based on what the command line tutorial in the Boston Python Workshop.)
Many of the tools of open source development are primarily used via the command line. Let's get some practice with navigating the computer from the command line.
Open Source Communication Tools
The slides I use for this talk can be found here. These are modified from a version graciously provided by Jessica McKellar. There are substantial notes in the ODP file which can be viewed by going to the "Notes" tab.
- Slides 1-7 (#7 is titled 'Version Control')
- Version Control Demo
- Slide 8 (#8 is titled 'Sharing changes: diff and patch')
- Diff and Patch Demo
- Slides 9-11 (#11 is titled 'Issue Trackers')
- Issue Tracker Demo
- Slide 12 (#12 is titled 'IRC')
- IRC Demo
- Slides 13-19
Version Control Demo
(This talk is assuming you are speaking at Wellesley College. You're probably not going to be speaking at Wellesley, so you'll need to make a handful of changes!)
(FIXME: Go through this, and change the exercises so they start by having us make some edit to the page.)
- In open source software, people use version control to keep track of files as they change. To give you a sense of what this is for, how many of you have worked on group programming projects? (A few hands raise up.)
- How did you keep track of different people working on different files?
- Some people will say they emailed around different copies of files.
- Others may say that they had people all working in person and talking about changes.
- How well did that work out?
- Attendees will typically chuckle.
- So, yeah, one common way to do that is to email around copies of a file you're working on. A different way is to use what's called version control, where there is a system for tracking different versions of a file. The most popular tools let every contributor keep a copy of the project on their own computer, making whatever changes they want, and eventually synchronizing with the rest of the team.
- To talk about version control, I want to show you how version control works for purely text documents. So let's look at the Wikipedia page for Wellesley College.
- (Navigate web browser to http://en.wikipedia.org/wiki/Wellesley_College )
- So one of the great things about Wikipedia is that the system keeps every track of every version of every article. The wiki system is a version control system, too. If you click on the "Edit" tab, you can see the built in way to edit every article. Let's take a look at the history tab here. (click history tab)
- (find yourself at http://en.wikipedia.org/w/index.php?title=Wellesley_College&action=history ; zoom in so it's large enough for people to see; make it really enormous)
- So here, you can see a little heading for every version of the page, including (mouse over the date) the time and date of that version, who saved that version, and a brief summary of what the changes are. Here, the most recent version says +73 -- that means that 73 characters were added in that revision.
- One standard feature of version control tools is to be able to see each version of the file. On Wikipedia, you can do that by clicking on the date.
- (click on the most recent edit, taking you to e.g. http://en.wikipedia.org/w/index.php?title=Wellesley_College&oldid=559029901 )
- You can see the box at the top that says, "This is the current revision of the page." The real thing going on here is that we're using an identifier for the page that will never change, even if the page gets edited, because we're looking at the particular revision.
- Let's hit back, and take a look at an older version that has an edit summary. In this case, we see they say they added a note about New Zealand. When we click the date (Click the date)... and load the page, we can see visually that the page seems to have a note about New Zealand. But we don't know just from looking at this version of the page if maybe they made other changes.
- You folks already saw diffs, and like most version control tools, Wikipedia lets you see a diff between the two pages. It's line-based, like a lot of tools used in programming. Let's click back... (back to http://en.wikipedia.org/w/index.php?title=Wellesley_College&action=history ) and instead of clicking on the date, we'll select this revision as the first item selected, and the one right after it as the one we want to diff against. When we click "Compare selected revisions", it takes us to a page like http://en.wikipedia.org/w/index.php?title=Wellesley_College&diff=558216275&oldid=556114296
- On that page, you can see the one + line: the addition of this link to a different school in New Zealand. In particular, this shows us that there are no changes other than the particular one about the new link.
- Whew. That was a lot. Are there any questions? I'm happy to go over and review anything here. (Take questions from the whole group, since probably someone else has the same question as any individual person who asks.)
- So that's the very basics of what version control is. In open source projects, probably the most popular version control tool is called git. It's a command line program, and during the laptop setup process you already installed it hopefully. A lot of projects tracked with git also use Github, which is a website for browsing these git repositories. One fun git repository that's hosted on Github is this one,
- (go to https://github.com/bundestag/gesetze)
- which is the law of Germany. It's a good example of a version control project, tracked in git, where not everyone is allowed to edit the repository. But we can click around on their Github site and see all the commits.
- Again, one difference here is that Wikipedia is the encyclopedia that anyone can edit. For Wikipedia, that means that as soon as we edit a page, it's automatically live. For open source software projects, or the German legal system, there's often a review process -- you can use version control to prepare a diff and share it, and if the maintainer likes it, they merge it into the main project.
- (Click "Commits" -- https://github.com/bundestag/gesetze/commits/master )
- Another difference is that in git, revisions are called commits. They track not just changes to one file, but the entire state of the project at that time. So when you click "Browse code" at the most recent commit, it takes you to e.g. https://github.com/bundestag/gesetze/tree/ee428461b034de54f1cdcab524d2808486383677 which shows you the entire project.
- Usually you are just interested in the difference between this commit and the previous commit, so Github makes that easy: you just click on this short hexadecimal number, and it shows you a diff.
- One more difference is how the version numbers are encoded. In git, the revision number is a checksum of all the important information about the commit: the name and email address of the person who made the change, plus the contents of the files that are part of the commit, plus a timestamp of when the commit was made, plus a few other bits of data. In some systems, the version numbers are just numbers that increase over time. With git, since every person uses their own computer and can make commits whenever they want, the commit IDs can't collide, so they're computed based on the content.
- So, in a nutshell, those are the key notions behind version control, and git. Now's a great time for questions! After the questions, we'll take some time to work through a training mission to give you hands on experience in git and how projects use it.
- (Put on projector: https://openhatch.org/missions/git)
- This is the URL for an interactive teaching tool to show you how open source communities use git, and that helps you get used to using it on your own computer. We'll have teaching assistants walking around hoping to help you.
- If you finish that, work through this second URL:
- (put on projector: http://try.github.io/ ) but we really encourage you to work through the training mission first.
Diff and Patch Demo
This demo uses the files in this repository.
I have a To Do List! But maybe it needs editing. First, I'll make a copy to edit:
cp ToDoList new_ToDoList
Then I'll open it up and make changes to it. (Side note: make sure to explain which editor you're using and give options for those following along - emacs, vim, nano, or a GUI.)
How do I view the differences between the two?
diff -u ToDoList new_ToDoList
That's just printed to the command line, though. How do I store it in a file?
diff -u ToDoList new_ToDoList > changes.diff
I open up the file and see it contains the same stuff as was printed out before. Okay, now how do I apply these changes to the original list?
patch -p0 ToDoList < changes.diff
Note that the argument given to the patch is the file I want to modify, not the file that already has the changes.
People often ask - what does the argument "-u" given to diff mean, or the argument -p0 given to "patch"?
-p[x] is an argument which allows the user to specify how much of the given file's path needs to be matched. -p0 gives the entire file name unmodified. The documentation has a bit more info.
Issue Tracker Demo
Pick a few random issue trackers, ideally ones which use different platforms, such as:
Information to look for:
- tags like "bite size"
Log into IRC and join the #openhatch channel.
Forgot to install? Go here.
- how your name is highlighted if someone uses it
- how to do /me
- how to send messages to individual users
- different servers vs different channels (#openhatch on other servers might be empty)
- how to make a new channel, if asked
Introduction to the Command Line (as needed)
Need to extract relevant tutorial bits from: https://openhatch.org/wiki/Boston_Python_Workshop_7/Friday
Introduction to Version Control
The purpose of this demo is to get students more experience, hands-on, in a social environment, submitting pull requests to a project on Github. The content of the pull requests is not the point; instead, the idea is to focus on the social/personal concept that this is how projects often want changes submitted, and the technical side of getting practice with the tools. Students have already been through a basic tutorial on git; the idea is to cement this knowledge.
Typically, this takes the following form.
Before the session, an instructor creates a sample repository where it is safe to merge pull requests from students. This could be a personal project of theirs or a fork of someone else's project through which they create a sandbox to accept students' work where it is okay to eventually erase those changes.
The instructor begins by explaining the project in question, and showing how to find the project's Github page.
They then use the Github website to point to a particular file that can accept simple, text-based edits, typically a file like README. They then navigate to a terminal and demonstrate how to create a pull request by demonstrating all the following steps:
- They "fork" the project into their personal Github account. (In most cases, instructors are demonstrating a personal project; in this case, it would be wise for the instructor to create a dummy Github account to be the person submitting the pull request. This also avoids some trouble where Github accounts that are part of "organizations" see a slightly different fork UI than accounts that aren't.)
- They explain the key concept about forking: This copies all the history of the project into a space they are permitted to modify.
- They "clone" the repository onto their own computers.
- They make a change on their own computer, and run 'git add' on the change. Then they use 'git commit -m' to commit the change. The change is can be as simple as adding their name to a README file. It can also be silly.
- Then they 'git push' the change, which updates their master branch on Github.
- Then they visit their fork on the Github website and notice that their fork has their personal work on it.
- Then they click around in the Github UI to submit a pull request.
- Then they visit the upstream project, and show what the pull request looks like. They typically do not click "Merge" because it might create conflicts for student submissions.
- Then they tell students to submit changes, encouraging them to raise their hand if they need any help.
- The instructor sticks around at the front of the room, showing the upstream project's "List of pull requests" page, which typically automatically refreshes as students' work rolls in. Typically, seeing the student submissions makes for a lot of fun in the classroom. We often have to ask, "Hey, who is susanna112" (for example) and see a student raise their hand.
NOTE: We would do well to have a cheat sheet for students for the commands they use. Typically, students are supposed to follow along with the instructor by typing in analogous commands, with TAs roaming to help students as they run into issues. (For example, one student once ran into an issue where the Git version we recommend on Mac OS X would segfault in libcurl if using the HTTPS access method. Switching to SSH-based worked around the issue, but then she was behind.) We haved typically worked around this by having someone type the corresponding commands into IRC.
Also NOTE: It is important that the instructor suggest students use the HTTP(S) access method for Github; otherwise, students who do not have SSH keys set up will spend time on that, which is beside the point.
Some students may have trouble following along, and it is essential that TAs work to identify students who are not progressing well by walking around and looking at laptop screens to find students who seem stuck.
Ethics and History of Free Software
Typically this takes 20-30 minutes and takes place right before the Career panel.
The inspiration for the career panel comes partly from a past event, namely the first one (at Penn). After the main lecturer (Asheesh) gave a history tour in the lecture, students did Q&A with him and one other staffer. The main lecturer and the other staffer had similar but different opinions, which helped.
To deliver an equivalent lecture to what was given at at UMD or Wellesley College, follow the link to the full Ethics history talk.
- Join our general mailing list.
- Join the alumni mailing list.
- Hang out with us on IRC.
- Training missions?
- Bug list?
- Programs like GSoC and GNOME outreach.
Release goal: Ready for teachers, Wed June 19
In time for http://opensourcebridge.org/sessions/1066 , in order of highest priority to lowest priority:
Shauna: Write a section on event logistics(see OSCTC_logistics) Asheesh: Take intro to command line tutorial from BPW and make it part of this page Asheesh: Write up intro to version control tutorial, based on the current outline of using Wikipedia as a demo, but with more writing clearly about what to say and how to introduce the git version control demo
- Asheesh, probably: Prepare a solid plan for a nice looking version of this page (aka a "frame" to help people navigate the materials)
- Maybe not doable by Jun 19, but nice: (Asheesh or Shauna) Improve the Github demo by adding screenshots and stating more clearly what to say out loud
- Maybe not doable by Jun 19, but nice: Revisit the intro to FLOSS