CS 497C - Homework 6 - Name:_________________

    DUE: Monday, November 26 (in class)

    Please show all work on a separate sheet attached to this sheet.
    (50 points - 5 points for each problem) + (10 bonus points)

    1. How do you find out the PID of your login shell?
       Which is the process that listens on every terminal for a login
       request?
       What is the role of th swap area in the control of processes?

  Ans: 1) Use echo $$
       2) The getty process.
       3) The swap are is a special file system that contains the process 
          image when it is no longer running. The kernel recalls the image
          from the swap area when it's time for it to run again.

    2. First create a directory foo and then fill up a shell script with
       three commands shown below. What happens when you execute this script 
       and why?

       mkdir foo; cd foo; pwd

  Ans: 1) This is what happens after executing the script:
          mkdir: cannot create directory `foo': File exists
          /usr/users/User22/chang/lecture/cs497c/homework/foo
          The script run is a sub-shell. First, it fails to create the 
          directory foo because the directory foo already exists. Then
          it changes to the directory foo and shows the current directory.
       2) Because changes made by the child process are not available in 
          the parent, the original directory is restored after the
          completion of the script.

    3. If this pipeline is run from a shell script, who will be the parent 
       and grandparent of all these processes?

       nl foo | sort -nr | cut -f2-

  Ans: The sub-shell used to run the script will be the parent, and the
       login shell will be the grandparent. 

    4. What is the difference between a process run with & and one run
       with nohup?

  Ans: A process run with nohup continues to run even after the user has
       logged out. When run with only an &, the background process is
       terminated on logging out. However, this doesn't happen in the C shell
       and bash.

    5. How are the signal numbers 2 and 9 generated? What are their names 
       and how do they differ in function?

  Ans: The interrupt key generates signal 2, the SIGINT signal. It may or not 
       may not terminate a program. The SIGKILL signal having the number 9 
       terminates a process unconditionally. It is generated by using the
       name or number with the kill command; it cannot be generated by 
       pressing a key.

    6. Frame regular expressions to match lines containing (i) jefferies
       jeffery jeffeys (ii) hitchen hitchin hitching (iii) Heard herd
       Hird (iv) dix dicks dickson dixon (v) Mcgee mcghee magee.

  Ans: (i) jeffe*r*[iy]e*s* (ii) hitch[ei]ng* (iii) [Hh][ei]a*rd
       (iv) di[xc]k*s*o*n* (v) [Mm][ac]gh*ee

    7. Use command substitution with grep to list the names of the persons 
       from emp.lst who has birthday today.
       
  Ans: Use grep `date "+%m/%d"` emp.lst | cut -d\| -f2. The date command 
       extracts the month and day in mm/dd format.

    8. Find out the occurrences of three consecutive and identical word
       characters (like aaa or bbb) using (i) grep and (ii) sed. 
      
  Ans: Use the tagged regular expression:
       (i) grep '\([a-zA-Z0-9_]\)\1\1' foo 
       (ii) sed -n '/\([a-zA-Z0-9_]\)\1\1/p' foo

    9. Locate lines that are less than 100 characters in length using
       (i) grep and (ii) sed.

  Ans: (i) grep -v ".\{100,\}" foo (ii) sed "/.\{100,\}/d" foo

   10. What is wrong with this command? How do you correct it?

       sed 's/compute/calculated/g
       s/computer/host/g' foo

  Ans: The first s command converts the compute in computer to calculate as 
       well, leaving nothing for the second s commadn to act on. Reverse the
       instructions:

       sed 's/computer/host/g
            s/compute/calculated/g' foo

   11. Write a command sequence to find out the number of occurrences of
       the word "encryption" in a file. (Note: A word may occur more than
       once in a line.)

  Ans: sed 's/encryption/&\
       /g' foo | grep -c encryption

   12. Invert the names in short list on Page 275 and place a comma after the 
       last name (i.e. last name, first name). The result should look like
       as below: 

       2233|harris, charles |g.m.     |sales     |12/12/52| 90000
       9876|johnson, bill   |director |production|03/12/50|130000
       5678|dylan, robert   |d.g.m.   |marketing |04/19/43| 85000
       2365|woodcock, john  |director |personnel |05/11/47|120000
       5423|wood, barry     |chairman |admin     |08/30/56|160000

       Use as few commands as possible.

  Ans: cut -d\| -f1 shortlist > temp1
       cut -d\| -f2 shortlist > temp2
       cut -d\| -f3- shortlist > temp3

       Now, cut the two components of the name from the name field, but
       offset the first name by one space:

       awk -F' ' '{printf "%s, %s|%s\n", $2, $1, length($0)}' temp2 > temp2a
       awk -F'|' '{printf "%-*s\n", $2, $1}' temp2a > temp2

       Paste the two names using the comma as delimiter before pasting
       back all sections:

       paste -d'|' temp[1-3]