Introduction to Mercurial

Barcamp Scotland 2008
Introduction to Mercurial
How to improve your source control.

Tane Piper
digitalspaghetti@gmail.com

http://digitalspaghetti.me.uk
http://twitter.com/tanepiper

February 2nd, 2008

Tane Piper digitalspaghetti@gmail.com Introduction to Mercurial

Introduction

What Is Covered?
A (Short) History of Source Control


Introduction

What Is Covered?
Distributed Source Control


Introduction

What Is Covered?
Mercurial itself


Introduction

What Is Covered?
Mercurial itself
How to import your project


Introduction

What Is Covered?
Mercurial itself
How to import your project
Download from http://tinyurl.com/2spv4h


A (Short) History of Source Control I

SCCS (Source Code Control System)
Marc Rochkind wrote at Bell Labs, in the early 1970s.



SCCS operated on individual ﬁles and every author had access
to a shared workspace on a single system.



SCCS operated on individual files and every author had access
to a shared workspace on a single system.
It was common for people to lock files, and later forget to
unlock them, preventing anyone else from modifying those
files without the help of an administrator.


A (Short) History of Source Control II

Dick Grune developed CVS (Concurrent Versions System).



CVS let developers work simultaneously and somewhat
independently in their own personal workspaces.



CVS let developers work simultaneously and somewhat
independently in their own personal workspaces.
They had to merge their edits prior to committing changes to
the central repository.


A (Short) History of Source Control III

In 2001 Jim Blandy and Karl Fogel developed Subversion.



Subversion, does not stray from CVS’s centralised
client/server model.



Added features such as multi-ﬁle atomic commits and better
namespace management.



At the same time Graydon Hoare was working on Monotone.



At the same time Graydon Hoare was working on Monotone.
Featured cryptographic hashes as identiﬁers, and has an
integral notion of ”trust” for code from diﬀerent sources.


Distributed Version Control

What is Distributed Version Control?


Distributed Version Control (DVCS)

Both git and Mercurial were announced in April 2005 to
replace the withdrawal of free BitKeeper VC software, which
was used to control the Linux kernel.



git developed by Linus Torvalds to manage the Linux kernel.



git developed by Linus Torvalds to manage the Linux kernel.
Mercurial was also developed for kernel, but git won out.


An Example of the DVCS Model

Figure: An example of the Mercurial distributed model.


Simple description of the DVCS model

No repository is king - no ”central” repository except for one
agreed in a social fashion.



Can be thought of as ”the bittorrent of the DVCS world”,
compaired to CVS/SVN model which is akin to a FTP.



Cloning repositories locally allows for more experimentation.



Cloning repositories locally allows for more experimentation.
As simple to set up as typing ’hg init’.


Mercurial Itself

Excellent support on Windows / Unix / MacOSX


Mercurial Itself

Tools such as TortoiseHG for Windows, QCT, Push Me Pull
You, etc make usage easy.


Mercurial Itself

Functionality can be added through an extension API with
hooks (e.g. pre and post commit).


Mercurial Itself

Doesn’t pollute the namespace - keeps everything in one
’.hg’ directory.


Mercurial Itself

Doesn’t pollute the namespace - keeps everything in one
’.hg’ directory.
Provides it’s own web interface - hgweb (hgwebdir for a
collection of repositories).


Mercurial Commands I

’hg init <name>’ - This initialises the local repository. You
can do this command within the root folder too.



’hg add’ - This will add any ﬁles within the directory
structure to the local repository.



’hg commit’ - This will commit any changes to your local
repository.



’hg commit’ - This will commit any changes to your local
repository.
’hg push’ - This will push any changes to your repository.


Mercurial Commands II

’hg pull’ - This will pull the content to your local
repository from the remote repository set in the conﬁg ﬁle.



’hg update’ - Updates and merges pulls to local repository
where no heads are created (i.e. if you have made no local
changes since your last pull).



’hg merge’ - This will merge any heads created by
pushing/pulling from repositories.



’hg merge’ - This will merge any heads created by
pushing/pulling from repositories.
’hg log’ - View a list of changesets.


How Mercurial Changesets Work

Figure: A example of linear changesets. This is very common in
repositories from one developer and once branch.


Simultaneous Local Changesets

Figure: Two local repositories with diﬀerent changeset histories.


Results of pulling a changeset into your local repository.

Figure: Pulling a remote repository’s tip into your local repository creates
2 heads. These need to be merged before you can continue.


Results of merging heads.

Figure: Merging the two heads together creates a new head. This can
now be pushed or pulled to other repositories and merged with other
heads.


Thank you for listning.

Check out more about Mercurial at http://tinyurl.com/3xphcz



SHAMELESS PLUG - Follow the progress of Mercurial
Frontend at http://digitalspaghetti.me.uk



Comments welcome at digitalspaghetti@gmail.com



Comments welcome at digitalspaghetti@gmail.com
You can download these slides from
http://hg.digitalspaghetti.me.uk/hgtalk


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