Software Carpentry

Version 1135 (2006-06-25 18:03:00)

License

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Copyright © 2005-06 Python Software Foundation

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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Introduction

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Introduction

Self Assessment

The State of Play

Meeting Standards

The Grass Isn't That Much Greener

Hidden in Plain Sight

The Times They Are A-Changin'

This Course

Setting Up

A Note on Tool Choice

Contributing

Recommended Reading

Typographic Conventions

Summary

Exercises

Exercise 2.1:

What is the largest software project you have ever worked on? How well did it meet its original objectives? What is the most important thing you learned from it?

Exercise 2.2:

Write a point-form list of the programming tools you use on a regular basis. When and how did you learn each one? How proficient do you think you are with each? Compared to whom?

Exercise 2.3:

Suppose you have been given one week to write a program to translate old-style configuration files to a new syntax. Write a point-form description of how you would go about it.

Exercise 2.4:

Rewrite the following fragment of code to make it more readable. Don't worry about the fact that you don't know the language it's written in; feel free to use any functions or language features you're familiar with from other languages.

i = open('oldconfig.cnf', 'r');
ll = i.readlines();
for j in 0..len(ll) {
    if len(j) > 0 {
        if not defined(r) r = new list;
        r.append(j);
    }
}
sort(r);
print 'longest line is', r[0];

Exercise 2.5:

What are the errors in the function shown below? Don't worry about the lack of variable declarations: this language doesn't need them. Note that, like C and Java, this language uses 0 as the first index for lists.

# Calculate a running sum of a list of numbers.
# If the input values are [1, 2, 3], the final values are [1, 3, 6].

def running_sum(values) {
    i = 1;
    while (i < len(values)) {
        values[i] = values[i] + values[i-1];
    }
}

Exercise 2.6:

A sub-contractor in Euphoristan has just written a function that takes two lists of phone numbers (represented as strings), and returns all those in the first list that are not in the second. You only have a few minutes to test it before she goes off-line for the weekend; what are the first half-dozen test cases you would try?

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Shell Basics

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Introduction

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The Shell

The Shell is Not the Operating Sytsem

The File System

Paths

Navigating the File System

Execution Cycle

Providing Options

Creating Files and Directories

Looking at Files

Basic Tools

Summary

Exercises

Exercise 3.1:

Suppose ls shows you this:

Makefile    biography.txt   data    enrolment.txt   programs    thesis

What argument(s) will make it print the names in reverse, like this:

thesis  programs    enrolment.txt   data    biography.txt   Makefile

Exercise 3.2:

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

Exercise 3.3:

What command will show you the first 10 lines of a file? The first 25? The last 12?

Exercise 3.4:

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

Exercise 3.5:

How would you send the file earth.txt to the default printer? How would you check it made it (other than wandering over to the printer and standing there)?

Exercise 3.6:

The instructor wants you to use a hitherto unknown command for manipulating files. How would you get help on this command?

Exercise 3.7:

diff finds and displays the differences between two text files. For example, if you modify earth.txt to create a new file earth2.txt that contains:

Name: Earth
Period: 365.26 days
Inclination: 0.00 degrees
Eccentricity: 0.02
Satellites: 1

you can then compare the two files like this:

$ diff earth.txt earth2.txt
3c3
< Inclination: 0.00
---
> Inclination: 0.00 degrees
4a5
> Satellites: 1

(The rather cryptic header "3c3" means that line 3 of the first file must be changed to get line 3 of the second; "4a5" means that a line is being added after line 4 of the original file.)

What flag(s) should you give diff to tell it to ignore changes that just insert or delete blank lines? What if you want to ignore changes in case (i.e., treat lowercase and uppercase letters as the same)?

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More Shell

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Introduction

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Wildcards

Redirecting Input and Output

Redirection Examples

Pipes

Environment Variables

Setting Environment Variables

Configuration

How the Shell Finds Programs

Common Search Path Entries

Cygwin on Windows

File Ownership and Permissions

Directory Permissions

Changing Permissions

Ownership and Permission: Windows

More Advanced Tools

Summary

Exercises

Exercise 4.1:

-rwxr-xr-x   1 aturing   cambridge  69 Jul 12 09:17 mars.txt
-rwxr-xr-x   1 ghopper   usnavy     71 Jul 12 09:15 venus.txt

According to the listing of the data directory above, who can read the file earth.txt? Who can write it (i.e., change its contents or delete it)? When was earth.txt last changed? What command would you run to allow everyone to edit or delete the file?

Exercise 4.2:

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.

Exercise 4.3:

You're worried your data files can be read by your nemesis, Dr. Evil. How would you check whether or not he can, and if necessary change permissions so only you can read or write the files?

Exercise 4.4:

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

Exercise 4.5:

Suppose you want to list the names of all the text files in the data directory that contain the word "carpentry". What command or commands could you use?

Exercise 4.6:

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?

Exercise 4.7:

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?

Exercise 4.8:

What command(s) would you use to find out how many subdirectories there are in the lectures directory?

Exercise 4.9:

What does rm *.ch? What about rm *.[ch]?

Exercise 4.10:

What command(s) could you use to find out how many instances of a program are running on your computer at once? For example, if you are on Windows, what would you do to find out how many instances of svchost.exe are running? On Unix, what would you do to find out how many instances of bash are running?

Exercise 4.11:

A colleague asks for your data files. How would you archive them to send as one file? How could you compress them?

Exercise 4.12:

You have changed a text file on your home PC, and mailed it to the university terminal. What steps can you take to see what changes you may have made, compared with a master copy in your home directory?

Exercise 4.13:

How would you change your password?

Exercise 4.14:

grep is one of the more useful tools in the toolbox. It finds lines in files that match a pattern and prints them out. For example, assume the files earth.txt and venus.txt contain lines like this:

Name: Earth
Period: 365.26 days
Inclination: 0.00
Eccentricity: 0.02

grep can extract lines containing the text "Period" from all the files:

$ grep Period *.txt
earth.txt:Period: 365.26 days
venus.txt:Period: 224.70 days

Search strings can use regular expressions, which will be discussed in a Regular Expressions. grep takes many options as well; for example, grep -c /bin/bash /etc/passwd reports how many lines in /etc/passwd (the Unix password file) that contain the string /bin/bash, which in turn tells me how many users are using bash as their shell.

Suppose all you wanted was a list of the files that contained lines matching a pattern, rather than the matches themselves—what flag or flags would you give to grep? What if you wanted the line numbers of matching lines?

Exercise 4.15:

Suppose you wanted ls to sort its output by filename extension, i.e., to list all .cmd files before all .exe files, and all .exe's before all .txt files. What command or commands would you use?

Exercise 4.16:

What does the alias command do? When would you use it?

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Version Control

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Introduction

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Problem #1: Collaboration

Solution: Version Control

Problem #2: Undoing Changes

Solution: Version Control (Again)

Which Version Control System?

Basic Use

How To Do It

Resolving Conflicts

Example of Resolving

Example of Resolving (continued)

Example of Resolving (continued)

Starvation

Binary Files

Reverting

Rolling Back

Creating and Checking Out

Subversion Command Reference

Reading Subversion Output

Summary

Exercises

Exercise 5.1:

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.

Exercise 5.2:

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!

Exercise 5.3:

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?

Exercise 5.4:

In this exercise, you'll simulate the actions of two people editing a single file. To do that, you'll need to check out a second copy of your repository. One way to do this is to use a separate computer (e.g., your laptop, your home computer, or a machine in the lab). Another is to make a temporary directory, and check out a second copy of your repository there. Please make sure that the second copy isn't inside the first, or vice versa—Subversion will become very confused.

Let's call the two working copies Blue and Green. Do the following:

a) Create Blue/ex01/planets.txt, and add the following lines:

Mercury
Venus
Earth
Mars
Jupiter
Saturn

Commit the file.

b) Update the Green repository. (You should get a copy of planets.txt.)

c) Change Blue/ex01/planets.txt so that it reads:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn

Commit the changes.

d) Edit Green/ex01/planets.txt so that its contents are as shown below. Do not do svn update before editing this file, as that will spoil the exercise.

Mercury 0
Venus 0
Earth 1
Mars 2
Jupiter 16 (and counting)
Saturn 14 (and counting)

e) Now, in Green, do svn update. Subversion should tell you that there are conflicts in planets.txt. Resolve the conflicts so that the file contains:

1. Mercury 0
2. Venus 0
3. Earth 1
4. Mars 2
5. Jupiter 16
6. Saturn 14

Commit the changes.

f) Update the Blue repository, and check that planets.txt now has the same content as it has in the Green repository.

Exercise 5.5:

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—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.

Exercise 5.6:

Subversion allows users to set properties on files and directories using svn propset, and to inspect their values using svn propget. Describe three properties you might want to change on a file or directory, and how you might use them in your current project.

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Automated Builds

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Introduction

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Automate, Automate, Automate

Make

Our Example

Hello, Make

Terminology

Multiple Targets

Phony Targets

Dependencies

Updating Dependencies

Conventions

Automatic Variables

Automatic Variables Example

Pattern Rules