</section>
- <section id="s:rollback">
+<section id="s:rollback">
+ <h2>Recovering Old Versions</h2>
- <h2>Recovering Old Versions</h2>
-
- <div class="understand" id="u:rollback">
- <h3>Understand:</h3>
- <ul>
- <li>How to undo changes to a working copy.</li>
- <li>How to recover old versions of files.</li>
- <li>What a branch is.</li>
- </ul>
- </div>
+ <div class="understand">
+ <h3>Learning Objectives:</h3>
+ <ul>
+ <li>Discard changes made to a working copy.</li>
+ <li>Recover an old version of a file.</li>
+ <li>Explain what branches are and when they are used.</li>
+ </ul>
+ </div>
- Now that we have seen how to merge files and resolve conflicts,
- we can look at how to use version control as an "infinite undo".
- Suppose that when Wolfman starts work late one night,
- his copy of <code>explore</code> is in sync with the head at revision 12.
- He decides to edit the file <code>moons.txt</code>;
- unfortunately, he forgot that there was a full moon,
- so his changes don't make a lot of sense:
- </p>
+ <p>
+ Now that we have seen how to merge files and resolve conflicts,
+ we can look at how to use version control as an "infinite undo".
+ Suppose that when Wolfman starts work late one night,
+ his copy of <code>explore</code> is in sync with the head at revision 12.
+ He decides to edit the file <code>moons.txt</code>;
+ unfortunately, he forgot that there was a full moon,
+ so his changes don't make a lot of sense:
+ </p>
<pre src="svn/poetry.txt">
Just one moon can make me growl
...
</pre>
- When he's back in human form the next day,
- he wants to undo his changes.
- Without version control, his choices would be grim:
- he could try to edit them back into their original state by hand
- (which for some reason hardly ever seems to work),
- or ask his colleagues to send him their copies of the files
- (which is almost as embarrassing as chasing the neighbor's cat when in wolf form).
- </p>
+ <p>
+ When he's back in human form the next day,
+ he wants to undo his changes.
+ Without version control, his choices would be grim:
+ he could try to edit them back into their original state by hand
+ (which for some reason hardly ever seems to work),
+ or ask his colleagues to send him their copies of the files
+ (which is almost as embarrassing as chasing the neighbor's cat when in wolf form).
+ </p>
- Since he's using Subversion, though,
- and hasn't committed his work to the repository,
-
all he has to do is <a href="glossary.html#revert">revert</a> his local changes.
- <code>svn revert</code> simply throws away local changes to files
- and puts things back the way they were before those changes were made.
- This is a purely local operation:
- since Subversion stores the history of the project inside every working copy,
- Wolfman doesn't need to be connected to the network to do this.
- </p>
+ <p>
+ Since he's using Subversion, though,
+ and hasn't committed his work to the repository,
+ all he has to do is <a href="glossary.html#revert">revert</a> his local changes.
+ <code>svn revert</code> simply throws away local changes to files
+ and puts things back the way they were before those changes were made.
+ This is a purely local operation:
+ since Subversion stores the history of the project inside every working copy,
+ Wolfman doesn't need to be connected to the network to do this.
+ </p>
- To start,
- Wolfman uses <code>svn diff</code> <em>without</em> the <code>-r HEAD</code> flag
- to take a look at the differences between his file
- and the master copy in the repository.
- Since he doesn't want to keep his changes,
- his next command is <code>svn revert moons.txt</code>.
- </p>
+ <p>
+ To start,
+ Wolfman uses <code>svn diff</code> <em>without</em> the <code>-r HEAD</code> flag
+ to take a look at the differences between his file
+ and the master copy in the repository.
+ Since he doesn't want to keep his changes,
+ his next command is <code>svn revert moons.txt</code>.
+ </p>
<pre>
$ <span class="in">cd jupiter</span>
<span class="out">Reverted moons.txt</span>
</pre>
- What if someone <em>has</em> committed their changes,
- but still wants to undo them?
- For example,
- suppose Dracula decides that the numbers in <code>moons.txt</code> would look better with commas.
- He edits the file to put them in:
- </p>
+ <p>
+ What if someone <em>has</em> committed their changes,
+ but still wants to undo them?
+ For example,
+ suppose Dracula decides that the numbers in <code>moons.txt</code> would look better with commas.
+ He edits the file to put them in:
+ </p>
<pre src="svn/moons_commas.txt">
Name Orbital Radius Orbital Period Mass Radius
Elara 11<span class="highlight">,</span>740 259.6528 0.008 40.0
</pre>
- then commits his changes to create revision 13.
- A little while later,
- the Mummy sees the change and orders Dracula to put things back the way they were.
- What should Dracula do?
- </p>
+ <p class="continue">
+ then commits his changes to create revision 13.
+ A little while later,
+ the Mummy sees the change and orders Dracula to put things back the way they were.
+ What should Dracula do?
+ </p>
- We can draw the sequence of events leading up to revision 13
- as shown in <a href="#f:before_undoing">Fixture XXX</a>:
- </p>
+ <p>
+ We can draw the sequence of events leading up to revision 13
+ as shown in <a href="#f:before_undoing">Fixture 12</a>:
+ </p>
- <figure id="f:before_undoing">
- <img src="svn/before_undoing.png" alt="Before Undoing" />
- </figure>
+ <figure id="f:before_undoing">
+ <img src="svn/before_undoing.png" alt="Before Undoing" />
+ <figcaption>Figure 12: Before Undoing</figcaption>
+ </figure>
- Dracula wants to erase revision 13 from the repository,
- but he can't actually do that:
- once a change is in the repository,
- it's there forever.
- What he can do instead is merge the old revision with the current revision
- to create a new revision
- (<a href="#f:merging_history">Fixture XXX</a>).
- </p>
+ <p class="continue">
+ Dracula wants to erase revision 13 from the repository,
+ but he can't actually do that:
+ once a change is in the repository,
+ it's there forever.
+ What he can do instead is merge the old revision with the current revision
+ to create a new revision
+ (<a href="#f:merging_history">Fixture 13</a>).
+ </p>
- <figure id="f:merging_history">
- <img src="svn/merging_history.png" alt="Merging History" />
- </figure>
+ <figure id="f:merging_history">
+ <img src="svn/merging_history.png" alt="Merging History" />
+ <figcaption>Figure 13: Merging History</figcaption>
+ </figure>
- This is exactly like merging changes made by two different people;
- the only difference is that the "other person" is his past self.
- </p>
+ <p class="continue">
+ This is exactly like merging changes made by two different people;
+ the only difference is that the "other person" is his past self.
+ </p>
- To undo his commas,
- Dracula must merge revision 12 (the one before his change)
- with revision 13 (the current head revision)
- using <code>svn merge</code>:
- </p>
+ <p>
+ To undo his commas,
+ Dracula must merge revision 12 (the one before his change)
+ with revision 13 (the current head revision)
+ using <code>svn merge</code>:
+ </p>
<pre>
$ <span class="in">svn merge -r HEAD:12 moons.txt</span>
U moons.txt</span>
</pre>
- The <code>-r</code> flag specifies the range of revisions to merge:
- to undo the changes from revision 12 to revision 13,
- he uses either <code>13:12</code> or <code>HEAD:12</code>
- (since he is going backward in time from the most recent revision to revision 12).
-
This is called a <a href="glossary.html#reverse-merge">reverse</a> merge
- because he's going backward in time.
- </p>
+ <p class="continue">
+ The <code>-r</code> flag specifies the range of revisions to merge:
+ to undo the changes from revision 12 to revision 13,
+ he uses either <code>13:12</code> or <code>HEAD:12</code>
+ (since he is going backward in time from the most recent revision to revision 12).
+ This is called a <a href="glossary.html#reverse-merge">reverse</a> merge
+ because he's going backward in time.
+ </p>
- After he runs this command,
- he must run <code>svn commit</code> to save the changes to the repository.
- This creates a new revision, number 14,
- rather than erasing revision 13.
- That way,
- the changes he made to create revision 13 are still there
- if he can ever convince the Mummy that numbers should have commas.
- </p>
+ <p>
+ After he runs this command,
+ he must run <code>svn commit</code> to save the changes to the repository.
+ This creates a new revision, number 14,
+ rather than erasing revision 13.
+ That way,
+ the changes he made to create revision 13 are still there
+ if he can ever convince the Mummy that numbers should have commas.
+ </p>
- Merging can be used to recover older revisions of files,
- not just the most recent,
- and to recover many files or directories at a time.
- The most frequent use, though,
- is to manage parallel streams of development in large projects.
- This is outside the scope of this chapter,
- but the basic idea is simple.
- </p>
+ <p>
+ Merging can be used to recover older revisions of files,
+ not just the most recent,
+ and to recover many files or directories at a time.
+ The most frequent use, though,
+ is to manage parallel streams of development in large projects.
+ This is outside the scope of this chapter,
+ but the basic idea is simple.
+ </p>
- <p>
- Suppose that Universal Monsters has just released a new program for designing secret lairs.
- Dracula and Wolfman are supposed to start adding a few features
- that had to be left out of the first release because time ran short.
- At the same time,
- Frankenstein and the Mummy are doing technical support:
- their job is to fix any bugs that users find.
- All sorts of things could go wrong if both teams tried to work on the same code at the same time.
- For example,
- if Frankenstein fixed a bug and sent a new copy of the program to a user in Greenland,
- it would be all too easy for him to accidentally include
- the half-completed shark tank control feature that Wolfman was working on.
- </p>
+ <p>
+ Suppose that Universal Missions has just released a new program
+ for designing interplanetary voyages.
+ Dracula and Wolfman are supposed to add some features
+ that were left out of the first release because time ran short.
+ At the same time,
+ Frankenstein and the Mummy are doing technical support:
+ their job is to fix any bugs that users find.
+ </p>
- <p>
- The usual way to handle this situation is
- to create a <a href="glossary.html#branch">branch</a>
- in the repository for each major sub-project
- (<a href="#f:branch_merge">Figure XXX</a>).
- While Wolfman and Dracula work on
- the <a href="glossary.html#main-line">main line</a>,
- Frankenstein and the Mummy create a branch,
- which is just another copy of the repository's files and directories
- that is also under version control.
- They can work in their branch without disturbing Wolfman and Dracula and vice versa:
- </p>
+ <p>
+ All sorts of things could go wrong
+ if both teams tried to work on the same code at the same time.
+ In particular,
+ Dracula and Wolfman might want to make large changes
+ to the structure of the code
+ in order to make it easier to add new features,
+ while Frankenstein and the Mummy want to make as few changes as possible
+ so as not to introduce new bugs while fixing old ones.
+ </p>
- <figure id="f:branch_merge">
- <img src="svn/branch_merge.png" alt="Branching and Merging" />
- </figure>
+ <p>
+ The usual way to handle this situation is
+ to create a <a href="glossary.html#branch">branch</a>
+ in the repository for each major sub-project
+ (<a href="#f:branch_merge">Figure 14</a>).
+ While Wolfman and Dracula work on
+ the <a href="glossary.html#main-line">main line</a>,
+ Frankenstein and the Mummy create a branch,
+ which is just another copy of the repository's files and directories
+ that is also under version control.
+ They can work in their branch without disturbing Wolfman and Dracula and vice versa:
+ </p>
- <p>
- Branches in version control repositories are often described as "parallel universes".
- Each branch starts off as a clone of the project at some moment in time
- (typically each time the software is released,
- or whenever work starts on a major new feature).
- Changes made to a branch only affect that branch,
- just as changes made to the files in one directory don't affect files in other directories.
- However,
- the branch and the main line are both stored in the same repository,
- so their revision numbers are always in step.
- </p>
+ <figure id="f:branch_merge">
+ <img src="svn/branch_merge.png" alt="Branching and Merging" />
+ <figcaption>Figure 14: Branching and Merging</figcaption>
+ </figure>
- <p>
- If someone decides that a bug fix in one branch should also be made in another,
- all they have to do is merge the files in question.
- This is exactly like merging an old version of a file with the current one,
- but instead of going backward in time,
- the change is brought sideways from one branch to another.
- </p>
+ <p>
+ Branches in version control repositories are often described as "parallel universes".
+ Each branch starts off as a clone of the project at some moment in time
+ (typically each time the software is released,
+ or whenever work starts on a major new feature).
+ Changes made to a branch only affect that branch,
+ just as changes made to the files in one directory don't affect files in other directories.
+ However,
+ the branch and the main line are both stored in the same repository,
+ so their revision numbers are always in step.
+ </p>
- <p>
- Branching helps projects scale up by letting sub-teams work independently,
- but too many branches can cause as many problems as they solve.
- Karl Fogel's excellent book
- <a href="bib.html#fogel-producing-oss"><cite>Producing Open Source Software</cite></a>,
- and Laura Wingerd and Christopher Seiwald's paper
- "<a href="bib.html#wingerd-seiwald-scm">High-level Best Practices in Software Configuration Management</a>",
- talk about branches in much more detail.
- Projects usually don't need to do this until they have a dozen or more developers,
- or until several versions of their software are in simultaneous use,
- but using branches is a key part of switching from software carpentry to software engineering.
- </p>
+ <p>
+ If someone decides that a bug fix in one branch should also be made in another,
+ all they have to do is merge the files in question.
+ This is exactly like merging an old version of a file with the current one,
+ but instead of going backward in time,
+ the change is brought sideways from one branch to another.
+ </p>
- <div class="keypoints" id="k:rollback">
- <h3>Summary</h3>
- <ul>
- <li>Old versions of files can be recovered by merging their old state with their current state.</li>
- <li>Recovering an old version of a file does not erase the intervening changes.</li>
- <li>Use branches to support parallel independent development.</li>
- <li><code>svn merge</code> merges two revisions of a file.</li>
- <li><code>svn revert</code> undoes local changes to files.</li>
- </ul>
- </div>
+ <p>
+ Branching helps projects scale up by letting sub-teams work independently,
+ but too many branches can cause as many problems as they solve.
+ Karl Fogel's excellent book
+ <a href="bib.html#fogel-producing-oss"><cite>Producing Open Source Software</cite></a>,
+ and Laura Wingerd and Christopher Seiwald's paper
+ "<a href="bib.html#wingerd-seiwald-scm">High-level Best Practices in Software Configuration Management</a>",
+ talk about branches in much more detail.
+ Projects usually don't need to do this until they have a dozen or more developers,
+ or until several versions of their software are in simultaneous use,
+ but using branches is a key part of switching from software carpentry to software engineering.
+ </p>
- </section>
+ <div class="keypoints">
+ <h3>Summary</h3>
+ <ul>
+ <li>Old versions of files can be recovered by merging their old state with their current state.</li>
+ <li>Recovering an old version of a file does not erase the intervening changes.</li>
+ <li>Use branches to support parallel independent development.</li>
+ <li><code>svn merge</code> merges two revisions of a file.</li>
+ <li><code>svn revert</code> undoes local changes to files.</li>
+ </ul>
+ </div>
+
+ <div class="challenges">
+ <h3>Challenges</h3>
+
+ <p class="fixme">write some</p>
+ </div>
+
+</section>
<section id="s:setup">
projects / swc-version-control-svn.git / blobdiff