Exercise 1

Due: 5:00 p.m. EST, Friday 23 September 2005.

Weight: 5% of course grade.

Question 1

Follow the instructions given to you by your instructor to check out a copy of the Subversion repository you'll be using in this course. Unless otherwise noted, the exercises below assume that you have done this, and that your working copy is in a directory called course. You will submit all of your exercises in this course by checking files into your repository.

Question 2

Create a file course/ex01/bio.txt (where course is the root of your working copy of your Subversion repository), and write a short biography of yourself (100 words or so) of the kind used in academic journals, conference proceedings, etc. Commit this file to your repository. Remember to provide a meaningful comment when committing the file!

Question 3

What's the difference between mv and svn mv? Put the answer in a file called course/ex01/mv.txt and commit your changes.

Once you have committed your changes, type svn log in your course directory. If you didn't know what you'd just done, would you be able to figure it out from the log messages? If not, why not?

Question 4

Add another line or two to course/ex01/bio.txt and commit those changes. Then, use svn merge to restore the original contents of your biography (course/ex01/bio.txt), and commit the result. When you are done, bio.txt should look the way it did at the end of the first part of the previous exercise.) Note: the purpose of this exercise is to teach you how to go back in time to get old versions of files&emdash;while it would be simpler in this case just to edit bio.txt, you can't (reliably) do that when you've made larger changes, to multiple files, over a longer period of time.

Question 5

Suppose you want to remove all files whose names (not including their extensions) are of length 3, start with the letter a, and have .txt as extension. What command would you use? For example, if the directory contains three files a.txt, abc.txt, and abcd.txt, the command should remove abc.txt , but not the other two files.

Submit your answer in course/ex01/q05.txt in your Subversion repository.

Question 6

What does the command cd ~ do? What about cd ~gvwilson?

Submit your answer in course/ex01/q06.txt in your Subversion repository.

Question 7

What's the difference between the commands cd HOME and cd $HOME?

Submit your answer in course/ex01/q07.txt in your Subversion repository.

Question 8

Suppose you have written a program called analyze. What command or commands could you use to display the first ten lines of its output? What would you use to display lines 50-100? To send lines 50-100 to a file called tmp.txt?

Submit your answer in course/ex01/q08.txt in your Subversion repository.

Question 9

The command ls data > tmp.txt writes a listing of the data directory's contents into tmp.txt. Anything that was in the file before the command was run is overwritten. What command could you use to append the listing to tmp.txt instead?

Submit your answer in course/ex01/q09.txt in your Subversion repository.

Question 10

What do the commands pushd, popd, and dirs do? Where do their names come from?

Submit your answer in course/ex01/q10.txt in your Subversion repository.

Solutions

Question 3

mv is a Unix command, which you can apply to any file or directory to change its name (or location). svn mv is a sub-command of Subversion, and you can only apply it to something that's under version control. It renames (or moves) a file or directory, but Subversion keeps track of where the new file or directory came from. Note that svn mv only acts on your working copy; you have to use svn commit in order to push that change into the repository.

Question 5

rm a??.txt.

Question 6

cd ~ "moves" you (i.e., changes your current working directory) to your home directory. cd ~gvwilson attempts to change working directory to gvwilson's home directory. If you don't have permission to be there, the operation fails.

Question 7

cd HOME attempts to move to a directory called HOME directly below the current directory. cd $HOME moves you to your home directory, because $HOME is a reference to the environment variable HOME, whose values is always the absolute path to your home directory.

Question 8

The commands are:

analyze | head -10
analyze | head -100 | tail -51
analyze | head -100 | tail -51 > tmp.txt

Question 9

Use ls data >> tmp.txt. Note the double greater-than sign: this means "append", instead of "redirect".

Question 10

pushd pushes the current working directory onto a stack of directories, and changes your current directory to dir. popd takes the top directory from the directory stack, and moves you there. Thus:

pushd /tmp
...do something...
popd

moves you to the /tmp directory, where you do some work, and then takes you back to wherever you were before. dirs print out the current directory stack. The leftmost directory is the top of stack.

Results