path: root/Version_Control/vcs4/vcs4.rst

================================
Version Control using Hg  Part 4
================================

.. Prerequisites
.. -------------

.. Version Control using Hg, Part 1, 2, 3


.. Author : Primal Pappachan
   Internal Reviewer : Kiran Isukapatla
   Date: Feb 20, 2012

======
Script
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.. L1

*{{{ Show the first slide containing title, name of the production team along
with the logo of MHRD}}}*

.. R1

Hello friends and welcome to the fourth part of tutorial on 'Version Control with hg'.

.. L2

*{{{Show the slide 'Prerequisite'}}}*

.. R2

Please make sure that you have gone through the following tutorials before you
continue on this tutorial.

.. L3

*{{{Show the slide containing the objectives}}}*

.. R3

At the end of this tutorial you will be able to
 #. Clone existing repositories 
 #. Share your repositories with peers
 #. use 'version control' for collaborating with your peers

.. L4

*{{{Show the slide 'Cloning Repositories'}}}*

.. R4

When motivating the use of version control systems, we spoke a lot about
collaboration and sharing our changes with our peers. Let us now see how we can
share a project with our peers and collaborate with them.

For this purpose, let us create a 'central repository' and a copy of 'our repository',
which is different from the one in which we are working. The 'clone' command is
used to clone or replicate an existing repository.

.. L5

``$ hg clone book book-repo``

.. R5

The syntax of the 'clone' command is -- hg clone SOURCE [DEST], where DEST is an
 optional argument, represented in brackets. The 'clone' command can
be used to replicate already existing repositories, either on your own machine
or on a remote machine. Since, hg maintains a copy
of the full repository with every copy of the repository, the two copies that
we have are exactly equivalent.

In this example 'book-repo' shall be our central repository being shared with
peers.

.. L6

*{{{Show the slide 'Sharing Repositories'}}}*

.. R6

A mercurial repository can be shared in multiple ways.  Mercurial comes inbuilt with a tiny server
that can be used to share your repository over the network. To start sharing
the repository, we go to the repository and say 'hg serve'.

.. L7

``$cd book-repo``

``$hg serve``

.. R7

This will start serving the repository on the network on the port 8000. 

.. L8

Open the url http://localhost:8000 in browser.

.. R8

Now if your friend 'John' wishes to clone the repository, he uses:

.. L9

``$ hg clone http://my-ip-address:8000 book-john``

.. R9


By this process, we share a central repository and work on our local copies. It
doesn't make much sense to allow anybody to make changes to a public
repository by default. To allow this, we need to make few changes to the settings of the
repository. To set the write permissions, we add the following lines
in .hg/hgrc

.. L10

``[web]``

``push_ssl=False``

``allow_push=*``

.. R10 

This will allow anybody to push to the repository. Now, John can push 
his changes which will then appear in the central repository.

.. L11


*{{{Show the slide 'Sharing Changes'}}}*

.. R11

Use 'hg push' to push your commits (changesets) to the central repository. The
changes made by John will appear in the central repository.

.. L12

``$ hg push``

.. R12

Let's now see how to get the changes from central repository.

.. L13

*{{{Show the slide 'Pulling Changes'}}}*

.. R13

Before pulling the changes, we may use the command 'hg incoming'. This shows the
changes that have been made to the repository, after our last pull and the
changesets that will be coming into our repository, after we do a pull.

.. L14

``$ hg incoming``

.. R14

If you wish to pull those changes shown by 'hg incoming', we use the 'hg pull' command.

.. L15

``$ hg pull``

.. R15

These changes do not affect our working directory. To see this, we could use
the 'hg parent' command.

.. L16

``$ hg parent``

.. R16

After pulling the changes, the parent will still be the last commit, and the
changes are still not in the working directory.

.. L17

*{{{Show the slide 'Pulling Changes 2'}}}*

.. R17

To get these changes, we do the update as suggested by hg.

.. L18

``$ hg update``

.. R18

The update command updates the parent to the latest changes that we have 
just pulled from the remote repository.
 
 #. Updates to the tip if no revision is specified
 #. Tip is the most recently added changeset
 #. Can specify revision number to update to

You can try

.. L19

``$ hg up -r1``

.. R19

'hg tip' shows the tip of the repository

.. L20

``$ hg tip``

.. R20

Let see what happens when two users make simultaneous changes to the same file,
by editing different (or) same parts of the file.

.. L21

*{{{Show the slide 'Simultaneous Changes'}}}*

.. R21

With simultaneous changes, following things happen
 #. The logs of both repositories will be different
 #. The repositories have diverged
 #. 'hg push' fails, in such a scenario


Don't take the advice given by mercurial. Using the -f would be disastrous. We
will leave out a discussion on that, for this course.

.. L22

*{{{Show the slide 'Merging'}}}*

.. R22

The new changes that have been pushed to the 
repository after the last pull, has to be pulled and merged. So
use following commands in order

.. L24

``$ hg pull``

``$ hg merge``

.. R24

We have now pulled the changes from the central repository and merged them with
the changes in our repository. As hg warns you, do not forget to commit. 

.. L25

``$ hg commit``

.. R25

Now, the changes can be pushed to the central repository. We could also check
the changes before pushing them, using the 'hg outgoing' 
command.

.. L26

*{{{Show the slide 'Outgoing Changes'}}}*

.. L26

``$ hg outgoing``

``$ hg push``

.. R26

The changes have now been successfully pushed! Let us look at the 'web interface'
of the repository, to see that the changes have actually taken place.

.. L27

Show the 'Change graph' in the browser.

.. R27

What will happen if we edit the same portion of the file, at the same time?
How would merge work? This will be the last thing that we are going to see in
this part of the spoken tutorial. 

.. L28

*{{{Show the slide 'Simultaneous Conflicting Changes'}}}*

.. R28

Let's say both of us edit the same part of the same file.
 #. hg push fails
 #. So we first do hg pull
 #. followed by hg merge


.. L29

``$ hg commit``

``$ hg push``

``$ hg pull``

``$ hg merge``

.. R29

What happens now actually depends on how Mercurial is configured and the
programs available in your machine. You will either get a diff view with 3
panes or merge will insert markers in your file at the points where the
conflicts occur.

If you get a 3 pane view, the first pane is the actual file, where you make
changes, to resolve the conflicts. The second pane shows the changes that you
made, to the file. The last pane shows the changes that you pulled from the
original repository. Once you are satisfied with the changes, save and quit.

Once you are done, you need to tell mercurial that you have resolved the
conflicts manually.

.. L30

``$ hg resolve -m filename``

.. R30

You will now need to commit your changes, just like the simple merge.

.. L31

``$ hg commit -m "Merge heads."``

``$ hg push``

.. R31

We could look at the graph of the changes, in our web interface, which makes
clear how the merging has occurred. 

.. L32

Show the change graph in browser.

.. R32 

Here's an advice on the Work-flow to be followed.

.. L33

*{{{Show the slide 'Advice: Work-flow}}}*


.. R33

That brings us to the end of this tutorial on Mercurial. What we have covered
is nothing close to all the features of Mercurial. We've only scratched the
surface, but let's hope that this will get you started and you will be able to
organize your work and projects, better.

.. L34

*{{{Show the 'summary' slide'}}}*

.. R35

In this tutorial, we have learnt to, 

#. Clone repositories, using 'hg clone',
#. Serve our repositories via http using 'hg serve',
#. push changes to a repository using 'hg push',
#. check the changesets in a repository after last pull, using 'hg incoming',
#. pull changes from a repository using 'hg pull' ,
#. update the working directory, using 'hg update',
#. merge two heads, using 'hg merge',
#. and resolve conflicts using 'hg resolve'.

.. L36

*{{{Show the slide 'Evaluation'}}}*

.. R36

Here are some self assessment questions for you to solve
 #. Mention the easiest way to get started on sharing your repository by 
    providing a web interface.
 #. Suppose Melissa made some changes to files in the central repository. Would 
    Joey's local repository be automatically updated with these changes after he
    has executed 'hg pull' command?
 #. What are the commands involved in the process of merging changes? 
   
.. L37

*{{{ Show Solution of self assessment questions on slide }}}*

.. R37

And the answers,

 #. hg serve
 #. No, Joey has to execute 'hg update' to apply the pulled 
    changes to his repository.
 #. hg pull, hg merge, hg commit -m "Merged Remote changes"

.. L38

*{{{Show the slide 'Additional Reading'}}}*

.. R38

It is strongly recommended that you to go through the following topics, once
you are comfortable with using Mercurial on a day-to-day basis.

 #. .hgignore
 #. hg rollback
 #. hg bisect
 #. hg backout


.. L39

{{{ Show the Thank you slide }}}

.. R39

Hope you have enjoyed this tutorial and found it useful. 

Thank you!