Machine lab and all that

• Three of you will have a lab machine.
• Get yourself a personal machine
• Have one of your favourite Unices on it (GNU/Linux or *BSD)

Prerequisites

• One of vim or emacs (my preference)
• Basic usage of computers, command prompts etc.
• Know about man pages and google.

General Advice for being a hacker.

• Use terminals for interaction
• Use applications like tmux and screen

Git and Bitbucket, what are they?

• Git is a Distributed Version controller
• Helps you keep track of a changing set of files.
• Bitbucket hosts git (and mercurial) repositories.

Bitbucket accounts

• You must create an account (visit http://bitbucket.org)
• Get Academic accounts (just use cse.ac.in id)
• Has a lot of nice features like unlimited private repo.

Goodies on bitbucket

• Source of slides, code examples etc
• Course wiki
• Issue tracker for issues and discussion.
• Assignments should be in private repos there.

What is git?

• It is a Distributed version control system (DVCS)
• Written by Linus Torvalds and is used by the Linux Kernel
• Very popular.
• You can host stuff on sites like bitbucket and github.

Name and Email

$ git config --global user.name "James Bond"
$ git config --global user.email '007@mi6.uk'

Start giting

• Initialising

$ cd /your/project/dir
$ git init

• Clone

$ git clone https://your-bitbucket-userid@bitbucket.org/ppk-teach/tools.git

$ git clone git@bitbucket.org:ppk-teach/tools

Every repository is first class

• There are no "centralised store"
• Changes/patches are pushed or pulled into repositories

Some Git terminologies.

Repository

• Stuff that has been kept track of
• History commit messages etc

Working copy

• The latest stuff.
• Can contain modifications to stuff in repository
• Some untracked files.

Working copy to repository

• Stage stuff: new untracked file or modification of tracked file.
• Commit: Added the staged stuff to the repo

In command line.

$ git add README.md  # This stages the file for commit
$ git commit # This will start an editor to record commit message'
$ git commit -m 'Added a readme'
             # -m sets the one line commit message
             # no editor is started.
$ git commit -a README.md -m 'added a readme'
$ hack hack hack
$ git commit -am 'more detailed install process in readme'
           # Added all the modifications to tracked files and commit

Exercise

Which is the editor started for commit? How can one set it?

Branches.

$ git branch      # See branches
* master          # Only one branch master and you are on it

$ git branch topic   # Create a topic branch
$ git checkout topic # Move to topic branch
$ git branch
  master
* topic
$ do stuff on topic
$ git checkout master # move back to master
$ git merge topic     # merge the changes to topic

$ git push  # Send our changes to upstream
$ git fetch # get changes but do not merge
$ git pull  # fetch and merge.

Remote repositories.

• What if you want to work with multiple repositories.
• You can define remote repositories.

Example workflow.

$ cd code/git/raaz
$ git remote -v
  abhijaju        https://github.com/abhijaju/raaz.git (fetch)
  abhijaju        https://github.com/abhijaju/raaz.git (push)
  build   ppk@ppk.cse.iitk.ac.in:code/git/raaz (fetch)
  build   ppk@ppk.cse.iitk.ac.in:code/git/raaz (push)
  ...
  origin  git@github.com:piyush-kurur/raaz.git (fetch)
  origin  git@github.com:piyush-kurur/raaz.git (push)
  ...
  upstream        git@github.com:raaz-crypto/raaz.git (fetch)
  upstream        git@github.com:raaz-crypto/raaz.git (push)

$ git fetch abhijaju/master      # Bring abhimanyu's changes
$ git checkout abhijaju/master   # See his snapshot.
# review the changes
$ git checkout master            # Back to master
$ git merge abhijaju/master      # Looks good so merge.
$ git push origin                # Send it to my fork on github
$ git push upstream              # Send changes to upstream
                                 # Yeah I am the king here.

Summary

• Start with init or clone
• add new files with add or stage them
• hack, push, fetch,
• branch, mergez.

More information

• Comprehensive Documentation http://git-scm.com/documentation
• Millions of tutorials on web.

Some tools I use

• tig - a git changes browser.
• magit - An emacs mode for working with git.
• gitk - a graphical git browser that I rarely use.

SSH without passwords

• Use public key authentication
• Multiple users without sharing passwords
• Multiple hosts with the same public key

SSH key generation

$ ssh-keygen
$ ls $HOME/.ssh/
...
id_rsa      # Private key (keep it safe)
id_rsa.pub  # public key  (upload on bitbucket)

More details on my blog on key based access