MCQ - Shell Pipes and Filters

Mar 12, 2015 • Konrad Förstner

Multiple choice questions with diagnotic answers

Both of my multiple choise questions are building on the lessons about Shell Pipes and Filters.

Question 1

Which of the following combination of shell commands will return the output Welcome. (If you not familiar with the commands: echo will give a string to the standard output; tr will replace one string by another one, sort return sorted lines; tail will give the last lines of a given input (-n specifies the number of lines)).

  1. echo "Welcome to the shell" | tr " " "\n" | sort | tail -n 1
  2. echo "Welcome to the shell" ; tr " " "\n" ; sort ; tail -n 1
  3. echo "Welcome to the shell" > tr " " "\n" > sort > tail -n 1
  4. echo "Welcome to the shell" < tr " " "\n" < sort < tail -n 1

Question 2

Let us assume we have the plain text file fruits.txt with the following 12 lines of content:


What will be the outcome of the following commands.

cat fruits.txt | head | wc -l

  1. Nothing as head and wc do not have any input files
  2. 12
  3. 10
  4. 10 10 77

What can the different answer tell us about misconception of the student?

  1. The student does not know how Unix shell pipes work. I.e. that the output of one command that is given to the standard output is used by the next command connected by | as standard input.
  2. The student is not aware that head will show per default only the first 10 lines of a file.
  3. The correct answer
  4. The student is not aware the impact of the parameter -l of the command wc.