CSC3320 - Systems Programming - Homework# 1 - Solved

PART 1

Answer the following questions briefly. Provide clear and succinct reasoning. 

 

Points per question = 5

1. Tell  the  differences  between  Unix  and  Linux.  Then  please  list  some  operating systems (at least three) which belong to Unix but not Linux. 

2. What is the pipe mechanism in UNIX? And show one command using  pipe and explain how the pipe works in it? 

3. In a Linux system, you can issue the command ls / to check the sub directories under root.  Please describe the meanings of directory /bin,  /dev, /boot, /usr, /etc, /mnt, /sbin, /var separately. For  example, you can say that /bin contains binary executable files. 

4. What is the meaning of Multitask and Multi-user in a Unix system? 

5.  What does -rwxr-xr-x  mean in terms of permissions for a file? What is the exact unix command (with the octal representation) for changing the permissions to this setting? 

6.  In  class,  you  have  learned  the  meaning  of  read,  write  and  execute  permission for regular files. However, these permissions are also applied  to directories.  So  please  describe  the  meaning  of  read,  write,  and  execute permission for directory.

  Part II-a

 

Regular Expression 

Find  outcomes  for each  given  basic/extended  regular  expression  (maybe multiple correct answers) 

 

Points per question: 2.5

Example:

‘ab+a’ （extended regex） 

Answer: aba , abba ; Pattern : The matched string should begin and end with ‘a’  and ‘b’ occurs at least once between leading and ending ‘a’)
 

Note: 7) to 10) are basic regexes;  Note: 11) to 18) are extended regexes. 

7) ‘a[ab]*a’ 

8) ‘a(bc)?’ 

9) ‘.[ind]*’ 

10) ‘[a-z]+[a-z]’ 

11) ‘[a-z] (\+[a-z])+’ 

12) ‘a.[bc]+’ 

13) ‘a.[0-9]’ 

14) ‘[a-z]+[\.\?!]’ 

15) ‘[a-z]+[\.\?!]\s*[A-Z]’ 

16) ‘(very )+(cool )?(good|bad) weather’ 

17) ‘-?[0-9]+’ 

18) ‘-?[0-9]*\.?[0-9]*’ 

 

Part II-b

 

Regular Expression 

Write down the extended regular expression for following questions. E.g. Social security number in the format of 999-99-9999. Answer: [0-9]{3}-[0-9]{2}-[0-9]{4} 

 

Points per question: 5

 

19) Valid  URL  beginning  with  “http://” and  ending  with  ".edu" (e.g.  http://cs.gsu.edu, http://gsu.edu) 

20) Non-negative integers. (e.g. 0, +1, 3320) 

21) A valid absolute pathname in Unix (e.g. /home/ylong4, /test/try.c) 

22) Identifiers  which  can  be  between  1  and  10  characters  long,  must  start with a letter or an underscore. The following characters can  be letters or underscores or digits. (e.g. number, _name1, isOK). 

23) Phone number in any of the following format: 9999999999,999-999- 9999, (999)-999-9999. (Note: all of these formats should be matched  by a single regular expression) 

 

 

Part III

Programming

Points per question: 15

24. Create a file named homework_instructions.txt using VI editor and type in it all the submission instructions from page1 of this document. Save the file in a directory named homeworks that you would have created. Set the permissions for this file such that only you can edit the file while anybody can only read. Find and list (on the command prompt) all the statements that contain the word POINTS. Submit your answer as a description of what you did in a sequential manner (e.g. Step1 … Step 2… and so on..). Add a screenshot to your answer as a proof of evidence.