9 and 11-Jan CSCI 4152/6509 Natural Language Processing Lab 1: FCS Computing Environment, SVN Tutorial. FCS Computing Environment, SVN Tutorial

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1 Lecture 1 p.1 Faculty of Computer Science, Dalhousie University CSCI 4152/6509 Natural Language Processing Lab 1: FCS Computing Environment, SVN Tutorial 9 and 11-Jan-2019 Lab Instructor: Dijana Kosmajac, Afsan Gujarati, and Yuhan Fu Location: Goldberg CS Building Time: 12:35 13:25 Notes copyright: Mike McAllister, Vlado Keselj, Magdalena Jankowska FCS Computing Environment, SVN Tutorial Slide notes: Lab Overview An objective: Make sure that all students are familiar with their CSID and how to login to the bluenose server Refresh your memory about Linux Command-Line Interface Introduction to your SVN repository for the course Introduction to Perl (just hello world for now) Note 1: Replace CSID with your FCS CS user id (a.k.a., CSID) Note 2: If you do not know your CSID, lookup at: An objective of this lab it to make sure that all students are familiar with the basic FCS (Faculty of Computer Science, Dalhousie University) computing environment. This means that you should know your CSID. This is a separate Computer Science user id, in addition to the the Dalhousie ID and Banner number. Among other things, the CSID is needed when logging in into the Computer Science servers and when using the SVN repository. Step 1: Logging in to server bluenose You can choose Windows, Mac or Linux environment in some labs Windows: you will use PuTTY program On Mac: open a Terminal and type: ssh CSID@bluenose.cs.dal.ca (instead of CSID use your CS userid ) On Linux: similarly to Mac, you open the terminal and type the same command: ssh CSID@bluenose.cs.dal.ca Your first step is to login into the bluenose server. You can use a lab computer or your own laptop. Some labs have a choice of using Windows or Mac environment; in some labs you may only use Windows. You can use any of them. You may have a chance to use a Linux computer, and it is very convenient for this lab as well. On Mac: In Mac OS environment, you can click on the search image in the upper right corner and type Terminal to find the Terminal application. Another way to find the Terminal application is to look into the Mac applications folder. Once you open the terminal, you can login to the bluenose server by typing: ssh CSID@bluenose.cs.dal.ca January 18, 2019, CSCI 4152/ prof6509/

2 Lecture 1 p.2 CSCI 4152/6509 where CSID is your CS userid. On Linux: In a Linux environment, you should, similarly to Mac, open a terminal and type: ssh CSID@bluenose.cs.dal.ca where CSID is your CS userid. On Windows: If you use a Windows environment, you will need to use a program named PuTTY to login to the bluenose.cs.dal.ca server. The PuTTY program has already been installed in the lab machines. You can also install it on any other machine since it is freely available at sgtatham/putty Running PuTTY If you use Windows, then one option is to use PuTTY to login to the bluenose server Double-click the PuTTY icon, and the following window should appear: You should fill in the basic information: bluenose.cs.dal.ca for the Host Name. Make sure that the port number is 22; i.e., Connection type is SSH. You click Open and the login process should start. You are likely to receive a warning about an unknown host key. Normally, this is something that you should be careful about and try to make sure that the offered fingerprint matches the fingerprint of the server, but in a relatively secure network you can accept this connection. Once accepted, the host key is stored with PuTTY and this warning should not appear again. Review of Some Linux Commands We will now briefly review some Linux command-line commands that you can use on the bluenose server. If you already know Linux or other type of Unix-like system, you should be familiar with the following commands and you can quickly try them out. Otherwise, these commands are a good start into learning more about basics of using a Linux file system.

3 CSCI 4152/6509 Lecture 1 p.3 Step 2: pwd. Immediately after login, your current directory will be a directory known as your home directory. The program that you are communicating with in a terminal after logging in is called shell (known also as command line in some operating systems). Our current directory is associated with our currently executing shell. To print our current working directory we can use the command pwd. Enter the command: pwd to show the path name of your current working directory. It is a good idea to frequently use this command to verify that your current working directory is the one you think it is, or to find out what is your current working directory. If you are not familiar with the Unix (Linux) command line, you should read about it: there are a lot of resources on the web. A useful way to learn more about a command is to use command man. For example, if you type: man pwd you can read about the command pwd. The command man stands for manual pages. You can exit the man pwd command by pressing the key q. Step 3: mkdir, ls, chmod. Depending on which course number you registered for (CSCI4152 or CSCI6509) you should create a directory named csci4152 or csci6509. To use an example, we will show the commands with the 6509 number, but you should use the appropriate number. First you can create a directory for the course work using the following command: mkdir csci6509 or mkdir csci4152 depending on the course number. Enter the command: ls to display the files (including subdirectories) in your working directory. Do you see the name of the directory you just created? Now, enter the command: chmod go-rx csci6509 or chmod go-rx csci4152 This command will prevent other users from entering and seeing the content of this directory. Step 4: lab1 directory. Enter the command: cd csci6509 or cd csci4152 to change your current working directory to to the directory you created in the previous step. Use the pwd command to verify that you performed this task successfully. Create a directory with the name lab1 in your current working directory, and change the current working directory to the directory lab1. Verify that you have performed these tasks successfully. If you type the command pwd it should display the following path: /users/cs/csid/csci4152/lab1 or /users/cs/csid/csci6509/lab1 The part /users/cs/ may vary in case that there are some changes on the server, but the part CSID/csci6509/lab1 (or CSID/csci4152/lab1 ) should be exactly as shown. Step 5: Prepare hello.pl in emacs. Now we are going to write a simple Perl program and run it. This will be a simple Hello world! program, which prints a line saying Hello world!. The first step is to write the source code.

4 Lecture 1 p.4 CSCI 4152/6509 We can use emacs editor for this task. If you are more comfortable with some other editor, you can use it. For example, the editors pico and nano are user-friendly, but less suitable for serious programming as they are less powerful in terms of functionality. The editors vi and vim are quite powerful, but with possibly a bit steeper learning curve. In this course, we will provide most help with emacs. A file with filename filename is opened in the editor emacs using command emacs filename or in the editor pico using the command pico filename. If you are not familiar with emacs, it should be relatively easy to start using it. A few basic instructions will be explained below, and there are many resources on the Internet that can be used. One available resource on the Internet is the following tutorial. It is very useful, although somewhat long: You can start reading it and stop once you are comfortable using emacs to edit a small program. Another way that you can learn Emacs is to simply type emacs in your PuTTY terminal. This will start the editor, with an initial splash screen explaining basic commands. You can also notice in the splash screen that by pressing C-h t ; i.e,., Control-h and then t, you can start a tutorial, and this is also a way to learn emacs. The emacs documentation uses notation C-x for Ctrl-x, i.e., Control-x key. Additional special way for pressing keys is M-x, which stands for Meta-x. Some keyboards have a special Meta key which is used, but more commonly this is obtained by pressing the Alt key and x in the same time, or by pressing Esc and x one after another (not in the same time!). Here are the most important emacs commands: to start editing a (possibly new) file in emacs: type in the terminal emacs filename where filename is the name of the file to exit emacs: type C-x C-c sequence (remember, this means Control-x Control-c). to save the current file: type C-x C-s Now, we can go back to editing the Perl program, which we will call hello.pl and which should print string Hello world! on a line by itself. You can start by typing: emacs hello.pl in the shell command line. Now, in the emacs window, type in the following program: #!/usr/bin/perl print "Hello world!\n"; After finishing the program, you can exit emacs using C-x C-c. You will need to confirm that you want to save the file by pressing y on the emacs question Save file.... If you want to save the file without exiting, use C-x C-s. Also, if you do not see font highlighting, you may want to try enabling that by typing M-x global-font-lock-mode (remember, M-x is produced with key combination Alt+x or Esc x one after another). This can be set as default by adding the following line to the emacs initialization file.emacs in your home directory: (global-font-lock-mode 1) Step 6: Running a Perl program. Exit emacs and enter: perl hello.pl to run you program. The program should produce one line of output: Hello world!. To run the program in this way, we did not even need the first line of the program (#!/usr/bin/perl); but this line is important in the second way to run the program, as follows. First, we change the file permissions allowing the user to execute the program:

5 CSCI 4152/6509 Lecture 1 p.5 chmod u+x hello.pl Then, we run the program in the following way:./hello.pl We will now go through an SVN tutorial. The SVN system will be used for assignment submission. SVN Tutorial: Source Control with SVN (Perl Version) In this tutorial, you will learn or refresh your knowledge about SVN. Performing these steps will be graded as a part of an assignment SVN will be used for assignment submission It is possible that not all students have the course SVN repository. In that case, let the instructor know. You will be able to finish the tutorial next week. This tutorial is slightly modified version of the SVN tutorial Source Control with SVN prepared by Michael McAllister for CSCI Source Control with SVN In the second part of this lab you will familiarize yourself with the Subversion (or SVN) source control system. While many people interact with SVN using a GUI interface (often part of their development IDE), we can access SVN with command line parameters on bluenose. All development companies use some form of source control, so becoming familiar with the basic notions of source control is useful. You won t be a master of source control after this lab, but you will have at least seen some of the basic concepts and commands. Subversion is relatively popular (as far as free software goes). A more recent source control system is called git while Perforce and ClearCase are two popular commercial offerings. Older source control systems include SCCS, RCS, and CVS (in case you hear about them). You will learn or refresh your knowledge about how to: 1. checkout projects in SVN 2. add a subproject (subdirectory) to SVN 3. add, delete files in SVN; and commit your changes 4. change files in SVN, and merge changes from different copies 5. resolve conflicts that may result from parallel changes 6. revert changes and retrieve older versions of the files Repository and Working Copy SVN uses remote directory system called repository to store files and history of their changes You can review changes and retrieve older versions Files can be shared among users and SVN can be used for collaborative work SVN uses notion of working copy of the files We send (or commit) files to the repository when we are happy with their state For example, we generally do not commit program unless they can be compiled A Couple Notes Replace CSID with your CS user id (a.k.a., CSID) Important Security Note: Each time that you enter an SVN command in this lab, you will be asked for your bluenose password. Enter it. When asked if you want to store the password, answer no each time, since the password is not stored safely currently.

6 Lecture 1 p.6 CSCI 4152/6509 If you are sure that you know what you are doing, you may temporarily say yes to make SVN use easier, but then make sure that only you have access permissions to the the directory./subversion, and it is a good idea to delete the whole directory after each session. Step 7: Set-up for the SVN Tutorial 1. If you are not logged in into bluenose, login now. You need to be logged in in two different windows (If you use putty on windows, open putty twice and login to bluenose both times. If you use a terminal on mac or linux, open two terminals and ssh to bluenose from each of them.) Call one window your primary window and the other window your secondary window. The lab will be working in two different directories, so you can have each window open to a different directory to avoid changing directories all the time. 2. In the primary window, change directory to csci4152/lab1 or csci6509/lab1, whichever is your course number using the command: cd /csci6509/lab1 or cd /csci4152/lab1 make directory primary with command: mkdir primary and change directory to it: cd primary 3. Similarly, in the secondary window, change directory to csci4152 or csci6509, whichever is your course number using the command: cd /csci6509/lab1 or cd /csci4152/lab1 make directory secondary with command: mkdir secondary and change directory to it: cd secondary In summary, if you use the command pwd it should show the following directory in the primary window: /csci6509/lab1/primary or /csci4152/lab1/primary and the following directory in the secondary window: /csci6509/lab1/secondary or /csci4152/lab1/secondary The part will be replaced with a common directory for all student home directories, so the only important part to compare is the end part. As mentioned previously, whenever CSID appears in the commands, you should include your own CS userid, which is also your bluenose username. Concepts of Repository and Working Copy SVN helps you manage a remote directory system where you can store files. That directory system is called a repository. The repository keeps a history of all the changes that are made to its files so that you can review how the files changed and retrieve previous versions of your files. Repositories are often shared among people as a way for all the people to get access to the same set of files. SVN uses the notion of a working copy of the repository. So, when you put files into the SVN repository, you don t edit the files directly there. Instead, you retrieve a working copy of the files, modify your working copy, and then send (or commit) the files back to the SVN repository when you are satisfied with their state. So, you generally just commit files from your working copy to the SVN repository once the files are in some kind of stable (though possibly incomplete) state. For example, when using a repository to store programs, you generally do not commit files until they compile, at the least. In most cases, you will just commit the program files after they pass your unit tests.

7 CSCI 4152/6509 Lecture 1 p.7 Step 8: Checkout and Adding a Directory Our first step is to create a subproject for this lab in your repository. 1. Checkout. In your primary window, retrieve a working copy of the whole NLP course directory of yours using SVN s checkout command. The repository is located on a separate machine, called svn.cs.dal.ca, that you cannot log into. You interact with svn.cs.dal.ca through the svn command on bluenose. In the following command, replace CSID with your own bluenose username: svn checkout Note: If this command does not work, a possible reason is that you registered only recently in the course and your SVN directory for the course has not been set up. In that case, you should the course instructor with your name, CSID, and Banner number and this information will be used to set-up your directory. However, it will take probably a day or two until this is done. Only then you will be able to continue with this lab. Notice that the checkout command uses a web address, so you can get to the machine from anywhere on the Internet. Also notice that the start of the web address is https and not http. You now have a directory called CSID in your primary window that has the entire contents of your NLP course repository (which is nothing so far). Make this CSID directory your working directory in your primary window using command cd CSID. 2. List all files (visible and hidden) in the CSID directory ls -a While there are no visible files, SVN created a hidden subdirectory called.svn. This directory contains all the SVN state for the directory, including the location of your repository. While you are in this directory, you don t need to specify the repository name anymore since SVN will get that information from the.svn subdirectory. 3. Adding directory. Create a subdirectory in your primary window called svnlab. This will be our new subproject to add to SVN. mkdir svnlab We will now add this directory to the SVN repository with the SVN add command: svn add svnlab You should see the output line A svnlab where SVN is telling you that svnlab will be added (the A ) when you next commit your changes to SVN. The svnlab subdirectory is not in your repository yet. It is just ready to go. Step 9: Commit Command To create the svnlab subdirectory in your repository, you must commit the add command using the SVN commit command: svn commit -m "Creating a project for my SVN lab" And you should see back Adding svnlab Committed revision 2. The part revision 2. will probably show a different (higher) number of revision. This number is increased every time a commit is made to the repository. This particular repository is shared among students in the class, where anyone making a commit will increase this number, so the number will keep increasing.

8 Lecture 1 p.8 CSCI 4152/6509 This subdirectory is now available in your repository with the web address Open this address with your browser to check that the directory has been submitted. You will need your CSID and password to login. The -m "xx" part of the command adds a message to the repository to explain what you are doing. When you or other people review your repository later, the log messages will be used to find out what changed, in a high-level view, in the code. All commit commands require a log message. If you forget to include the -m part then SVN will start your default editor to ask you for a log message. Step 10: Adding Files 10.a: Adding files: Make the svnlab directory your working directory in the primary window. Copy the following program into a file called hello.pl: #!/usr/bin/perl print "Hello world!\n"; Create two more copies of this file as hello2.pl and tmp.pl: cp hello.pl hello2.pl cp hello.pl tmp.pl 10.b: We will now add two files to your repository, again with the SVN add command: svn add hello.pl hello2.pl with output A hello.pl A hello2.pl Notice that we can add any number of files at the same time to the repository. Are these files in the repository yet? No, since we haven t issued a commit command to send them from your working copy to your repository. We can compare the state of our working directory with the SVN repository with the SVN status command. In your primary window, enter svn status Your output should look like A hello.pl A hello2.pl? tmp.pl The A for the two sample files indicates that these files are waiting to be added to the repository. The? at tmp.pl indicates that SVN knows nothing about the tmp.pl file and will do nothing with the file. 10.c: Commit Files: Send the two files to SVN with the SVN commit command. svn commit -m "Adding the first version of my sample files." If you re-issue the SVN status command, you should now get as output? tmp.pl SVN does not report on hello.pl and hello2.pl since the copy in your working directory is now identical to what is in the repository. Step 11: Deleting Files 11.a: Delete files: Suppose now that we did not mean to add hello2.pl to the repository and want to remove it. While still in the primary window, we use the SVN delete command: svn delete hello2.pl that outputs D hello2.pl

9 CSCI 4152/6509 Lecture 1 p.9 The leading D indicates that the file is now set for deletion. Re-issue the SVN status command to get the output? tmp.pl D hello2.pl again, showing that SVN does not know about tmp.pl and is ready to delete hello2.pl. 11.b: The change doesn t happen until you commit it to the repository (one line): svn commit -m "File hello2.pl was added by mistake earlier. It was just a backup copy of hello.pl" While hello2.pl is no longer active in the SVN repository, we can still retrieve past copies of it later if we conclude that we shouldn t have deleted the file. Notice that the hello2.pl file is no longer in our working directory. Step 12: Checking out Second Copy 12: Checking out second copy: We will now start to work with two copies of your code. You might do this in real life if you are trying out two different solutions or if two different people were working on the same code. Activate your secondary window and make sure that you are in the directory:... /lab1/secondary You can check this using the command pwd and if you are not in the appropriate directory, you can go there using the command cd. In your secondary window, checkout a copy of just the svnlab code, remembering to replace the CSID part with your own bluenose username: svn checkout You should now have a svnlab directory in your secondary window with a hello.pl file in it. Make that svnlab directory your working directory in the secondary window. Notice that there is no hello2.pl file in this directory. We did the SVN delete command on the file, so we don t retrieve the file when we checkout fresh copies from the repository. By default, SVN returns the most recent copy of the code that is in the repository. Step 13: Changing Files 13.a In your primary window, edit your copy of hello.pl to become the following file: #!/usr/bin/perl for my $i (1..10) { print "Hello world!\n"; } Save the file and run: svn commit. Now, go to the secondary window and run svn update. You can verify that the updated file is there. 13.b: Modifying a file: In your primary window, edit your copy of hello.pl and change the for loop to iterate 15 times rather than 10 times. Once you exit your editor, issue the SVN status command again. You should have output that looks like? tmp.pl M hello.pl The M with hello.pl indicates that your working copy of the file has modifications that are not in the repository. 13.c: You can view the modifications with the SVN diff command: svn diff hello.pl The command will show you the lines where your version and the repository version of the file are different along with a few lines before and after the difference. Let s send this modification to the repository with the SVN commit command again

10 Lecture 1 p.10 CSCI 4152/6509 svn commit -m "Use a longer loop iteration" You should get a message to show that the change was sent to the repository. Re-issue the SVN diff command for the hello.pl file. Does it report any differences? Why? In your secondary window, look at the contents of hello.pl. It doesn t include the change that you just sent to the repository. This is because changes to the repository are not automatically sent to your working copy of the code so that this working copy remains stable for you. 13.d: Update. To retrieve this newer copy, issue the SVN update command to update the working copy svn update with output U hello.pl Updated to revision 16. The leading U means that there is a more recent copy of the code in the repository than what is in the working copy of the code. What happened to the number of iterations in hello.pl in the working copy? 13.e: Delete. What happens if we delete a file in a working copy? In the secondary window, delete the hello.pl file: rm hello.pl Confirm that the file is gone with the UNIX ls command. Executing the SVN status command will show you that the file hello.pl is missing by the! symbol in its output:! hello.pl Issue the SVN update command one more time. What happens to the contents of the working directory? 13.f: Parallel Changes. Let s now introduce changes in our two copies of hello.pl. In hello.pl of your primary window, add a print statement before the for loop: print "I am about to start the loop\n"; In hello.pl of your secondary window, add a printf statement just before the return statement: printf ("I have finished the loop\n"); Now each copy of your file has a different change to hello.pl. In each of the directories, use the SVN status command to confirm that the hello.pl file is different from what is in the repository (look for the leading M tag beside the file names). 13.g: Merging Changes. In your primary window, issue an SVN commit command to send the change to the repository. Don t forget to include a -m "xx" log message in the command. For example, you can use: svn commit -mprimary In your secondary window, try to commit the change to hello.pl, for example, using command: svn commit -msecondary The command will fail since someone (you) committed a change to hello.pl in the repository after the working copy in the secondary window was retrieved. To do the commit, you must first ensure that you have the most up-to-date version of the code from the repository. Use the SVN update command to get this copy svn update with output G hello.pl Updated to revision 17. The M tag on hello.pl from before has now changed to a G. The G indicates that your changes and those from the repository have been automatically merged in the file. SVN was able to merge the changes since the changes in the primary and secondary windows did not overlap. Edit the hello.pl file to confirm that it now has both changes. We are satisfied with this change, so re-issue the SVN commit command in the secondary window to send the update to the repository. Again, don t forget to include a comment for the commit command, for example: svn commit -m"merged changes" Bring both directories up to date. In both the primary and secondary windows, issue the SVN update command

11 CSCI 4152/6509 Lecture 1 p.11 svn update 13.h: Conflicting Changes. We will now see what happens if the separate changes conflict with one another. In your primary window, edit hello.pl, change the for loop to iterate 30 times, and commit the change to SVN. In your secondary window, edit hello.pl, change the for loop to iterate 5 times, and try to commit the change to SVN. Like the last time, the commit in your secondary window failed because your secondary window didn t have the most recent copy of the code. Again, like before, use the SVN update command to try and get the most recent version of code from the repository. Unlike last time, SVN isn t able to merge the two changes since they are on the same line. Instead, the update returns with the following message: Conflict discovered in hello.pl. Select: (p) postpone, (df) diff-full, (e) edit, (mc) mine-conflict, (tc) theirs-conflict, (s) show all options: SVN is giving you the opportunity to fix see the differences (df) or fix the problem (edit the file). If you choose to edit the file, SVN will show you the file in your default editor. Since we haven t defined that editor, let s select the postpone option. Enter p and let SVN continue with the update (if there were other files). In the secondary directory, SVN has now left several files. In addition to your hello.pl, it has the files hello.pl.mine, and two hello.pl files with an ending of.rx where the X is the version number of each file. hello.pl the hello.pl file with the diff information embedded for you to resolve hello.pl.mine your modified code hello.pl.r9 the original copy of the code that you modified in this working directory (revision 9) hello.pl.r11 the most recent version of the code in the repository (revision 11) At this point, you can either change hello.pl to merge both changes (still having the other versions around as a reference) or copy one of the other versions to overwrite hello.pl with what you want the final copy to be. 13.i: Examining Conflict. In the secondary window, re-issue the SVN status command. Rather than seeing that hello.pl is modified, you will now get the output C hello.pl where the leading C indicates that hello.pl has a conflict that you need to resolve before it is sent to the repository. Before fixing the conflict, we should find out what the changes were. A first step is often to look at the comments from the commit to find out why someone else changed the repository. Use the SVN log command in the secondary window to get the log of messages for a file: svn log hello.pl You will get output to show each of the versions of the file along with the commit messages. If the message on the last commit for hello.pl isn t giving you enough information, you can use the SVN diff command again to see where your file differs from what is in the repository svn diff hello.pl A part of the output is something like: +<<<<<<<.mine +for my $i (1..5) { +======= for my $i (1..30) { +>>>>>>>.r39 13.j: Resolving Conflict: Given this information, choose a fix to hello.pl (for the lab, it doesn t matter what the fix is). Usually, you can either: Edit hello.pl directly (delete extra lines, etc.) Choose our version: cp hello.pl.mine hello.pl Choose repository version: cp hello.pl.r39 hello.pl Choose original last updated version: cp hello.pl.r38 hello.pl In this case, we can simply choose: cp hello.pl.mine hello.pl

12 Lecture 1 p.12 CSCI 4152/6509 If you try to commit the file, SVN will still refuse since it doesn t know yet that you have resolved the conflict. To do so, issue SVN s resolved command on the file: svn resolved hello.pl After issuing this command, the hello.pl.mine, and hello.pl.rxfiles will be removed from your working directory. You can now issue the SVN commit command to send the changes to the repository. Step 14: Retrieving copies of previous work 14.a You sometimes make changes to a program that you later regret and want to undo. Many of you probably make a copy of a file once it is working and this undo step means copying that old file to overwrite your current file. We want to use a repository to automate that process better. Each time you reach a stable point in your development, it is worthwhile to do an SVN commit to put that stable point into your repository. Aside: If you are making changes in parallel as someone else is, it is useful to make frequent updates and commits. In your secondary window, edit hello.pl and introduce a compile error (like changing the reserved word print to pprint). Save the file to disk (but not to the repository). Suppose that you now want to undo that change and return to the last saved copy in the repository. Three options that you already know how to do are: use SVN checkout elsewhere to get a fresh copy of the repository and copy the hello.pl file from there delete hello.pl in the working directory and then use the SVN update command to have SVN notice that there is a new version of hello.pl in the repository and make a copy in your working directory use SVN diff to identify the changes that you made and manually change hello.pl to return it to its previous state Each of these involves a bit more work than is necessary. If you want the last version of the file, SVN has a command called revert to retrieve that copy: svn revert hello.pl After issuing the command, look at hello.pl again to notice that you now have the version of the file that precedes your latest editing. 14.b: Retrieving Older Versions: It is possible that you might want to retrieve a much older version of your file. You can use the -r option the update command. The -r lets you specify which revision of the file that you want. Try svn update -r 34 hello.pl You can use svn log hello.pl to find interesting revision numbers. What is the content of this hello.pl file? If you changed this earlier version of the file, SVN will not let you commit the change directly to the repository since it is based on an out-of-date version of the file. You would need to do an SVN update command to return to latest copy (inducing a conflict with the file) where you then need to resolve any conflicts with the latest version. 14.c: Retrieving by Timestamps: Sometimes you don t know the exact revision number that you want to retrieve, but you know when the directory was last stable. You can specify a time, rather than a revision number, in the SVN update command. Suppose that I knew that the file was stable on January 22th, 2014 at 1pm. I could issue the following command to retrieve the version of the file that existed in the repository at that time: svn update -r "{ :00:00}" Step 15: End of the Lab After finishing with commits, you can even delete primary and the secondary directory, since all required updates are submitted to the SVN. If you want, you can still keep them until Assignment 1 is marked, just

13 CSCI 4152/6509 Lecture 1 p.13 to be sure. To delete the directories, you will need to be in their parent directory, and use the command rm -r primary secondary End of the lab.