Fix #518 for 07-find

_episodes/07-find.md

@@ -504,6 +504,11 @@ about them."
 > 2. `grep -E "of" haiku.txt`
 > 3. `grep -w "of" haiku.txt`
 > 4. `grep -i "of" haiku.txt`
+>
+> > ## Solution
+> > The correct answer is 3, because the `-w` flag looks only for whole-word matches.
+> > The other options will all match "of" when part of another word.
+> {: .solution}
 {: .challenge}
 
 > ## `find` Pipeline Reading Comprehension
@@ -514,20 +519,39 @@ about them."
 > wc -l $(find . -name '*.dat') | sort -n
 > ~~~
 > {: .bash}
+>
+> > ## Solution
+> > 1. Find all files with a `.dat` extension in the current directory
+> > 2. Count the number of lines each of these files contains
+> > 3. Sort the output from step 2. numerically
+> {: .solution}
 {: .challenge}
 
 > ## Matching and Subtracting
 >
 > The `-v` flag to `grep` inverts pattern matching, so that only lines
 > which do *not* match the pattern are printed. Given that, which of
 > the following commands will find all files in `/data` whose names
-> end in `ose.dat` (e.g., `sucrose.dat` or `maltose.dat`), but do
-> *not* contain the word `temp`?
+> end in `s.txt` (e.g., `animals.txt` or `planets.txt`), but do
+> *not* contain the word `net`?
+> Once you have thought about your answer, you can test the commands in the `data-shell`
+> directory.
 >
-> 1.  `find /data -name '*.dat' | grep ose | grep -v temp`
-> 2.  `find /data -name ose.dat | grep -v temp`
-> 3.  `grep -v "temp" $(find /data -name '*ose.dat')`
+> 1.  `find /data -name '*s.txt' | grep -v net`
+> 2.  `find /data -name *s.txt | grep -v net`
+> 3.  `grep -v "temp" $(find /data -name '*s.txt')`
 > 4.  None of the above.
+>
+> > ## Solution
+> > The correct answer is 1. Putting the match expression in quotes prevents the shell
+> > expanding it, so it gets passed to the `find` command.
+> >
+> > Option 2 is incorrect because the shell expands `*s.txt` instead of passing the wildcard
+> > expression to `find`.
+> >
+> > Option 3 is incorrect because it searches the contents of the files for lines which
+> > do not match "temp", rather than searching the file names.
+> {: .solution}
 {: .challenge}
 
 > ## Tracking a Species
@@ -544,15 +568,14 @@ about them."
 > ~~~
 > {: .source}
 >
-> She wants to write a shell script that takes a directory and a species 
-> as command-line parameters and return one file called `species.txt` 
-> containing a list of dates and the number of that species seen on that date,
-> such as this file for rabbits:
+> She wants to write a shell script that takes a species as the first command-line argument 
+> and a directory as the second argument. The script should return one file called `species.txt` 
+> containing a list of dates and the number of that species seen on each date.
+> For example using the data shown above, `rabbits.txt` would contain:
 > 
 > ~~~
 > 2013-11-05,22
 > 2013-11-06,19
-> 2013-11-07,18
 > ~~~
 > {: .source}
 >
@@ -571,6 +594,23 @@ about them."
 >
 > Hint: use `man grep` to look for how to grep text recursively in a directory
 > and `man cut` to select more than one field in a line.
+>
+> An example of such a file is provided in `data-shell/data/animal-counts/animals.txt`
+>
+> > ## Solution
+> >
+> > ```
+> > grep -w $1 -r $2 | cut -d : -f 2 | cut -d , -f 1,3  > $1.txt
+> > ```
+> > {: .source}
+> >
+> > You would call the script above like this:
+> >
+> > ```
+> > $ bash count-species.sh bear .
+> > ```
+> > {: .bash}
+> {: .solution}
 {: .challenge}
 
 > ## Little Women
@@ -579,13 +619,42 @@ about them."
 > Louisa May Alcott, are in an argument.  Of the four sisters in the
 > book, Jo, Meg, Beth, and Amy, your friend thinks that Jo was the
 > most mentioned.  You, however, are certain it was Amy.  Luckily, you
-> have a file `LittleWomen.txt` containing the full text of the novel.
+> have a file `LittleWomen.txt` containing the full text of the novel
+> (`data-shell/writing/data/LittleWomen.txt`).
 > Using a `for` loop, how would you tabulate the number of times each
 > of the four sisters is mentioned?
 >
 > Hint: one solution might employ
 > the commands `grep` and `wc` and a `|`, while another might utilize
 > `grep` options.
+> There is often more than one way to solve a programming task, so a
+> particular solution is usually chosen based on a combination of
+> yielding the correct result, elegance, readability, and speed.
+>
+> > ## Solutions
+> > ```
+> > for sis in Jo Meg Beth Amy
+> > do
+> > 	echo $sis:
+> >	grep -ow $sis littlewomen.txt | wc -l
+> > done
+> > ```
+> > {: .source}
+> >
+> > Alternative, slightly inferior solution:
+> > ```
+> > for sis in Jo Meg Beth Amy
+> > do
+> > 	echo $sis:
+> >	grep -ocw $sis LittleWomen.txt
+> > done
+> > ```
+> > {: .source}
+> >
+> > This solution is inferior because `grep -c` only reports the number of lines matched.
+> > The total number of matches reported by this method will be lower if there is more
+> > than one match per line.
+> {: .solution}
 {: .challenge}
 
 > ## Finding Files With Different Properties
@@ -600,10 +669,12 @@ about them."
 >
 > Hint 2: The value for `-mtime` will need to be negative---why?
 >
-> Solution: Assuming that Nelle’s home is our working directory we type:
->
-> ~~~
-> $ find ./ -type f -mtime -1 -user ahmed
-> ~~~
-> {: .bash}
+> > ## Solution
+> > Assuming that Nelle’s home is our working directory we type:
+> >
+> > ~~~
+> > $ find ./ -type f -mtime -1 -user ahmed
+> > ~~~
+> > {: .bash}
+> {: .solution}
 {: .challenge}

data-shell/data/animal-counts/animals.txt

@@ -0,0 +1,8 @@
+2012-11-05,deer,5
+2012-11-05,rabbit,22
+2012-11-05,raccoon,7
+2012-11-06,rabbit,19
+2012-11-06,deer,2
+2012-11-06,fox,4
+2012-11-07,rabbit,16
+2012-11-07,bear,1