CS 497C - Quiz 3 - Name: ________________

Date: Friday, November 9 (in class)

Part 1: (48 points - 4 points for each problem)

(2) 1. Which one won't remove the file Wal*Mart?
       (1) rm 'Wal*Mart' (2) rm 'Wal\*Mart' (3) rm Wal*Mart (4) rm Wal\*Mart
(1) 2. Which one is not equivalent to wc < in > out?
       (1) < out wc > in (2) > out wc < in (3) wc > out < in (4) < in wc > out
(4) 3. Which command is used to break the output in two streams?
       (1) tar (2) tr (3) tail (4) tee
(3) 4. You want to concatenate two files, a and b, but also insert some text 
       in between from the terminal. How will you do this?
       (1) cat - a b > c (2) cat - a b > c (3) cat a - b > c (4) cat a b - > c 
(3) 5. How do you show lines 5 to 10 of the file {\tt foo}? 
       (1) tail +5 foo | head (2) tail +10 foo | head -5
       (3) head foo | tail +5 (4) head -5 foo | tail +10
(1) 6. How will you find out the lines common to two sorted files?
       (1) comm -12 foo1 foo2 (2) cmp -12 foo1 foo2
       (3) comm -23 foo1 foo2 (4) cmp -23 foo1 foo2
(2) 7. How do you know how many different users are logging into the system?
       (1) who | uniq | sort | wc -l (2) who | cut -d' ' | uniq | wc -l 
       (3) who | sort | uniq | wc -l (4) who | cut -d' ' | uniq -d | wc -l
(2) 8. How do you remove duplicate lines from the file foo using sort?
       (1) sort -d foo (2) sort -u foo (3) sort -n foo (4) sort -p foo
(1) 9. Which system variable is used to store the PID of the current shell?
       (1) $$ (2) $! (3) $% (4) %$
(4) 10. How do you find out the complete command line of a process run by 
        user romeo?
        (1) ps -a -u romeo (2) ps -d -u romeo 
        (3) ps -e -u romeo (4) ps -f -u romeo
(3) 11. Which one will you use to make sure that a process is killed?
        (1) kill -7 (2) kill -8 (3) kill -9 (4) kill -10
(4) 12. Which command can you use to schedule a job?
        (1) cal (2) schedule (3) set (4) at

Part 2: (52 points)

   1. What are three standard files in UNIX and what are their default 
      source? (6 points)

Ans: 1) Standard input - The default source is the keyboard.
     2) Standard output - The default destination is the terminal.
     3) Standard error - The default destination is the terminal.

   2. What is a filter? Where does a filter get its input from? (6 points)

Ans: 1) A filter is a command which uses both standard input and standard 
        output.
     2) It can accept input from (i) a file with < (ii) a pipeline using |. 
        Most filters accpet input from the keyboard as well.

   3. What is command substitution? Give an example. (6 points)

Ans: 1) The shell executes the command enclosed within a pair of back quotes 
        (``) and places the command text where it occurs with the output the 
        command generates.
     2) echo Today is `date`.

   4. Sort the file {\tt /etc/passwd} on GUID (primary) and UID (secondary) 
      so that the users with same GUID are placed together. Users with a 
      lower UID should be placed higher in the list. (5 points)

Ans: You require to do a numeric sort on the fourth and third fields:
     sort -t: -n +3 +0 +2 /etc/passwd
  or sort -t: -n +3 -4 +2 /etc/passwd
  or sort -t: -n +3 -4 +2 -3 /etc/passwd

   5. How will you find out the number of times the character ? occurs in 
      a file? (5 points)

Ans: Delete all characters except the ? and then make a character count with 
     wc: tr -cd '?' < foo | wc -c

   6. Consider the following text file shortlist:

   2233|charles harris  |g.m.     |sales     |12/12/52| 90000
   9876|bill johnson    |director |production|03/12/50|130000
   5678|robert dylan    |d.g.m.   |marketing |04/19/43| 85000
   2365|john woodcock   |director |personnel |05/11/47|120000

   Each line contains emp-id, name, designation, department, date of
   birth, and salary.

   Write the command to sort the file on the salary. (3 points)
   Write the command to find out the unique designations. (3 points)

Ans: 1) sort -t'|' -n +5 +0 shortlist
     or sort -t'|' -n +5 -6 shortlist
     or sort -t'|' -n +5 shortlist
     2) cut -d'|' -f3 shortlist | sort -u

   7. What are three distinct phases in the creation of a process? Explain 
      it. (6 points)

Ans: 1) Fork - A copy of the process that invokes it is created.
     2) Exec - The parent then overwrites the copy to create the child.
     3) Wait - The parent waits for the death of the child.

   8. What is a signal? What happens to a process when it receive a signal?
      (6 points)

Ans: 1) A signal is an interrupt generated by the shell or even another
        process in response to some error condition.
     2) When a process receives a signal, it has to do one of three
        things: (i) Do nothing. (ii) Ignore the signal. (iii) Trap the signal.

   9. What can you do with the job control facilities? (6 points)

Ans: 1) Put a job to the background (bg).
     2) Bring it back to the foreground (fg).
     3) List the active jobs (jobs).
     4) Suspend a foreground job ([Ctrl-z]).
     5) Kill a job (kill).