Question

Question 2

0/1 point (graded)

What happens when you remove a directory using the command rm -r?

You cannot remove a directory using the rm command.

You permanently remove the entire directory, including all files and subdirectories.

You move the entire directory to a trash folder, but it can be restored later.

You get a warning message asking if you want to proceed, then you delete the directory. incorrect

Answer

Incorrect:

Try again. Unix does not warn you before permanently deleting files.

Question 3

0/1 point (graded)

By default, the head command in Unix displays the first 10 lines of a specified file. You can change the number of lines using an argument that indicates the numeric value of the desired number of lines.

Which of the following commands displays only the first 6 lines of a manual for the ls command?

man ls -6 | head

head | man ls -6 incorrect

head -6 | man ls

man ls | head -6

Answer

Incorrect:

Try again. Your pipe is reversed. You need to call the manual for ls, then look at the first 6 lines of it using the head function.

You have used 1 of 2 attempts

Question 7

0/1 point (graded)

What does the command echo $HOME do?

Moves into to the home directory.

Makes the current directory the home directory.

Prints the path to the home directory.

Prints “$HOME” to the screen. incorrect

Answer

Incorrect:

Try again. Echo prints something to the screen, but it interprets $HOME as a shortcut for something longer.

Question 8

0/1 point (graded)

Many systems operate using the Unix shell and command language, bash. Each time you start using bash, it executes the commands contained in a “dot” file. Your “dot” file may be called something like “.bash_profile” or “.bash_rc”.

Which command will let you see your “dot” files?

ls -a

ls bash* incorrect

head *bash*

ls -l

Answer

Incorrect:

Try again. This use of ls command will not let you see your dot files. Remember, files that begin in “.” are hidden in Unix.

Question 9

0/1 point (graded)

Your colleague was editing his “dot” files when something went wrong. He first noticed there was an issue when he tried to execute the following line of code:

ls

He received the following error:

-bash: ls: command not found

What could have happened to cause this error?

He is trying to execute ls which is a bash command, but his system isn’t running bash as a shell.

The command ls doesn’t exist. He should be using the command ll.

He forgot to specify a file name to be listed. The command ls * should work. incorrect

He changed the information contained in $PATH. Now the system cannot find the executable file for ls.

Answer

Incorrect:

Try again. The ls command does not require that a file name be provided. Provided the system knows where to find the file to execute the ls command, it will list every visible file in the current directory.

Question 10

0/1 point (graded)

The bash profile in your home directory contains information that the bash shell runs each time you use it. You can customize the information in your bash profile to tell your system to do different things. For example, you can make an “alias”, which acts like a keyboard shortcut.

Which line of code, when added to your bash profile, will let you print “seetop” to view the name, size, and file type of the 10 most recently added visible files?

alias seetop=’ls -lt’

alias seetop=’ls -lt | head’

alias seetop=’ls -t | head’ incorrect

alias seetop=’head | ls -l’

Answer

Incorrect:

Try again. You want to see the size and file type too. This command will only show the name.

Question 1

0/1 point (graded)

Why might you want to create a report using R Markdown?

R Markdown has better spell-checking tools than other word processors.

R Markdown allows you to automatically add figures to the final document.

R Markdown final reports have smaller file sizes than Word documents.

R Markdown documents look identical to the final report. incorrect

Answer

Incorrect:

Try again. The final report looks different than the working R Markdown document. For example, plots called in the R Markdown document do not show up until the final report is compiled.

You have used 1 of 2 attempts Some problems have options such as save, reset, hints, or show answer. These options follow the Submit button.

Incorrect (0/1 point)

Question 2

0/1 point (graded)

You have a vector of student heights called heights. You want to generate a histogram of these heights in a final report, but you don’t want the code to show up in the final report. You want to name the R chunk “histogram” so that you can easily find the chunk later.

Which of the following R chunks does everything you want it to do?

```{r, histogram, message=FALSE}

hist(heights)

```

incorrect

```{r histogram, warning=FALSE}

hist(heights)

```

```{r, echo=FALSE}

hist(heights)

```

```{r histogram, echo=FALSE}

hist(heights)

```

Answer

Incorrect:

Try again. message=FALSE and the similar warning=FALSE stop R from printing non-code text, but the code will still be echoed.

You have used 1 of 2 attempts Some problems have options such as save, reset, hints, or show answer. These options follow the Submit button.

Incorrect (0/1 point)

Question 5

0/1 point (graded)

```{r, echo=F}

n <- nrow(mtcars)

```

Here `r n` cars are compared

What will be the output for the above Rmarkdown file?

The only output is the text: Here 32 cars are compared.

Since we have echo=F, the code chunk is not evaluated, therefore we will have both the code and the text: Here `r n` cars are compared. incorrect

The code will be displayed as well as Here 32 cars are compared.

R cannot comprehend the value of n, we will get an error.

You have used 1 of 2 attempts Some problems have options such as save, reset, hints, or show answer. These options follow the Submit button.

Answer 1

Answer 2
*********
You permanently remove the entire directory, including all files and subdirectories.

Answer 3
*********
man ls -6 | head

Answer 7
**********
Prints the path to the home directory.

Answer 8
*********
ls -a

Answer 9
*********
He changed the information contained in $PATH. Now the system cannot find the executable file for ls.

We are allowed to do only 4 exercise out of any given.

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