Errata for Everyday Scripting with Ruby

#27045: Hi

I am trying to find a site/forum dedicated to the excercises in this book. A place where people can talk about their solutions and discuss the questions.

I"m even willing to setup a site for this, but can't find a way to contact the author to discuss.

I can be reached at: theopensourceguy _aatt_ gmail _ddoott_ com

(I'm no Ruby expert and yet I feel this is a perfect way to become one)--John Bateman

#26983: Instead of suggesting WinZip as a zip program for Windows (shareware), I recommend suggesting the open source zip program from SourceForge called 7-Zip (7-zip.org).--Steve Kim

#30621: For us real neophytes, it would be helpful if the text said "open your text editor" when applicable, at least for the first few chapters until it becomes ingrained. The first instance would be under 3.7 on page 25. The book does a good job warning about the difference between typing at the prompt and at irb, but the idea that there is a third "typing venue" is rather glossed over.--jkm

#28149: ref. exercise 3.9.2.
When you say a file is unchanged you usually mean the contents of the file remain the same. Thus I'd recommend changing problem 3 to read: "and (the trickiest one) how many files are in both the new and the old inventories."--Colin Godfrey

#26967: "I encourage you to play around with these methods."

Possibly confusing for those new to programming, because I don't think the term "method" has been introduced yet at this point in the book, or if it has, not recently or memorably. My suggestion is to introduce or reintroduce the "method" here.--Eeby

#26984: For technical readers, Ruby treats all lower-cased "names" as variables and capitalized "names" as constants.

The reason why the interpreter is complaining on changing values for MyShip is because it's a constant (note: capitalized name). Constants are meant to be initialized with a value and left alone. It is good practice to use lowercased alphanumeric words for variables and capitalized alphanumeric words for constants.--Steve Kim

#26882: When looking at the source for inventory.rb, it appears that it will work on Windows and MACOSX because their file systems are case preserving but case insensitive. It is not possible to have two or more files in the same directory whose names differ only by the case of the letters. UNIX based systems other than MACOSX have file systems that are case sensitive. It is possible to have two file names that differ only in case. I think there should be at least a footnote mentioning that it is possible for the inventory.rb program to mis-report the file names which would cause the array subtraction to get erronious results. Or perhaps you should have a UNIX version of inventory.rb that does not invoke downcase on the file name.--Kim Shrier

#26885: I am somewhat confused by the intent of adding downcase to differences.rb since inventory.rb has already downcase'd all the file names. And once again, I think that you should mention that this "improvement" which works on Windows and MACOSX does not work on UNIX.--Kim Shrier

#29180: You say that subversion is not required to work on this project...yet you will get different results than the book and you won't be sure if what you did was right or wrong. Why not just put the svn output in a text file so everyone can play?--Mike

#26886: In the test template in figure 7.3, you use the letter X to stand for something to be replaced and it occurs three times. My first thought when I saw that is that the letter X would be replaced by the same string in all three places. I know that you mention in the discussion that X is just a placeholder to indicate where you would want to substitute your own text, but, maybe it would be better to use a different letter in each place, like X, Y, and Z. --Kim Shrier

#26891: In bullet item number 4, you state that test methods start with "test_". Another requirement is that the method must have no parameters or that all parameters must be optional. If that is not the case, the unit test code will raise an invalid_test exception.--Kim Shrier

#28386: As others have noted, the svn repository has not been updated in quite a while, making this a boring script to test.

I would make the suggestion that you have people hard-code the start date to Time.local(2006, 7, 11), since that's a time when meaningful changes had been made.

Of course, this means that your suggested fix for Exercise 1 is invalid. I would recommend:

def header (inTime)
endTime = Time.local(inTime.split('-')[0], inTime.split('-')[1], inTime.split('-')[2])
endTime += 60 * 60 * 24 * 28
"Changes between #{inTime} and #{svn_date(endTime)}"
end

--a sharp old jewel

#28320: There don't seem to have been any changes in the churn-demo subversion repertory recently, so when running churn.rb all the subsystems show zero asterisks and a count of zero. maybe you could cron some changes for us?--Damian leGassick

#26892: In the box that talks about "What to Test", you mention testing the case where the value to be rounded is 3.5. When dividing an integer by 5, it is impossible to have a result that ends in .5. The only way to get a value that ends in .5 is to pass a floating point number into asterisks_for. This seems to me to not be a good example to talk about testing rounding.--Kim Shrier

#30025: In these code examples, the line

svn log #{timespan} #{root}/#{subsystem}

appears to be surrounded by single-quotes. But they are actually back-ticks. If someone (like me) is following along with the printed examples & uses the single-quotes the script won't work.

Looking at the downloadable code revealed the problem. But the presence of back-tics should be obvious looking at the printed code in the book as well.--Ian

#28360: "We know that this line's change count starts at character 14."
A number other than 14 would be better as (when counting spaces) this could be confused with the right-justification amount for the subsystem name.
An output pasted from churn would be something like
" ui2**(13)" - i.e 11 spaces before ui2.
Given any real churn output, the first irb example on the page will always yield => 16 when applied to it.--Damian leGassick

#28362: irb might not indent as shown here. if not, within an irb session, type:

conf.auto_indent_mode = true

or (better) add this line to your ~/.irbrc file

IRB.conf[:AUTO_INDENT] = true

see [TH01], p.190--Damian leGassick

#29707: The irb example about mid-page suggests text.scan(/Customer.*also/)

Surprise! Amazon now capitalizes 'Also'.

I suggest adding 'i' after the regexp.
text.scan(/Customer.*also/i)--Kevin Corbett

#27866: In the solution to Exercise 9, one of the class files referenced is formatter.rb. With the Ruby one-click installer v1.8.5-21, another formatter.rb is installed automatically on the path, making it so that calling a different file formatter.rb results in the code not working. In the one-click-installer v1.8.6-25, this is no longer a problem and the file can be named formatter.rb again. It might be good to add a footnote or something indicating this.--Andy Tinkham