EECS2031-LAB 7 Solved

Part I  Unix Utilities/commands 
The purpose of this lab exercise is for you to get some hands-on experience on using some fundamental Unix utilities (commands). After this lab, you are expected to be able to accomplish lots tasks using command line utilities, without resorting to your GUI based utilities such as File Manager. Command line execution is faster than GUI based utilities in general. Also in some systems GUI tools are not available at all and thus using command line utilities is your only option. We covered in class the following basic utilities/commands:  man, pwd,  ls, cd,  mkdir,  rmdir, cat, more, head,  tail, cp, mv,  rm, wc, chmod, chgrp, grep/egrep.  We also discussed how to use pipe to use one utility’s output as the input of another utility. In the next class we will also cover  uniq, sort, cmp/diff, cut, find etc.   

You can get the specifications of each utility by using utility  man.  E.g.,  man chmod or even better,   man 1 chmod 

Go through the following 110 (small) practices. Write down your answers (with question #) besides the questions.   

Note: Each question should be solved with only one entry of utility (e.g., cp file1 file2) or a pipeline of utilities (e.g., cat file1  | sort | wc). 

 

0.      Login to your home directory, change to Bourne (again) shell by issuing sh or bash.The prompt should change from % to $. Now create a working directory for this lab, and navigate to the working directory.

1.      There is a file named xxx in directory /eecs/dept/course/2018-19/W/2031Z/    Copy this file to your current working directory, using one entry of utility (command).

2.      Check that the file is copied here.

$ ls xxx xxx $ 

3.      There are two files named  xFile2 and xFile3 in directory /eecs/dept/course/2018-19/W/2031Z/   Copy these two files to your current working directory using one entry of utility. Assume these two files are the only files whose names begin with 'xFile'.  Hint:  so you can use xFile* or File? to match these two files. (If you don’t understand  * and  ?, look for page 10 of the Guided Lab Tour for CSE1020). Note, don’t confuse that with * and  ? that are used in (extended) regular expression. . 

4.      Verify that the 2 files are copied successfully to the current directory.

$ ls xFile* xFile2  xFile3  

$ ls 

xxx xFile2  xFile3  

5.      Rename file xxx to xFile1

6.      Verify that the renaming is successful.

One (professional) way to verify if an execution of a utility is successful is to examine the exit code (return value) of the executed process, which is stored in a system variable $?.   Issue echo $?   You should see 0, which means successful (this is opposite to C where 0 means false).  

Also verify by listing files  

$ your_command xFile1 xFile2 xFile3  

7.      (1) Create a sub-directory named 2019 under your current working directory. (2)Then still in the current working directory, create a subdirectory lab7a under 2019.  

8.      Verify that the two directories are created successfully, by recursively listing directory 2019 and its contents.

$ ls -R 2019 2019: lab7a 

    

   2019/lab7a: 

9.      Still in current working directory, (1) remove lab7a using rmdir and (2) then remove 2019 using rmdir

10.  Verify 9. by trying to list directory 2019. Should get ls: cannot access 2019: No such file or directory 11. (1) Create (again)  subdirectories 2019 and 2019/lab7a under the current working directory, using   mkdir 

2019/lab7a. What do you get?

(2) Check the exit code of execution. You should get 1, which means unsuccessful (note that 1 means true in C).

12.  (1) Fix the problem in 11.  

(2)  Check the exit value of execution. You should get 0, which means successful

(3)  confirm by recursively listing directory 2019 and its contents, you should see same results as in 8.

13.  Move xFile1 into subdirectory lab7a (with same name)

14.  Then move all the other 2 files (together) into lab7a (using one entry of utility)

15.  Verify that the creation and moving (12-14) were successful, by recursively listing directory 2019 and its contents..   

$ ls -l -R 2019 

./2019: total 4 

drwx------ 2 yourname ugrad 4096 Jul  5 15:12 lab7a 

 

Note that on each line, the first character –  means this entry is a regular file,  d  means this entry is a directory. 
./2019/lab7a: 

total 12 

-rwx------ 1 yourname ugrad 145 Mar  25 15:11 xFile1 

-rwx------ 1 yourname ugrad 145 Mar  25 15:11 xFile2 -rwx------ 1 yourname ugrad  87 Mar  25 15:11 xFile3 

16.  (1) Navigate to 2019 and (2) list the files of lab7a.

$ ls -l lab7a total 12 

-rwx------ 1 yourname ugrad 145 Mar  25 15:11 xFile1 -rwx------ 1 yourname ugrad 145 Mar  25 15:11 xFile2 -rwx------ 1 yourname ugrad  87 Mar  25 15:11 xFile3  

17.  Then list the information of lab7a itself

$ your-command drwx------ 2 yourname ugrad 48 Mar  25 15:12 lab7a 

 

18.  Copy directory lab7a to a new directory named lab7b  (using one utility).

19.  Verify that lab7b is created and the two directory are identical

$ ls -l * lab7a: total 12 

-rwx------ 1 yourname ugrad  145 Mar  25 23:32 xFile1 -rwx------ 1 yourname ugrad  145 Mar  25 23:50 xFile2 -rwx------ 1 yourname ugrad  87  Mar  25 23:50 xFile3 

 lab7b: total 12 

-rwx------ 1 yourname ugrad  145 Mar  25 23:32 xFile1 

-rwx------ 1 yourname ugrad  145 Mar  25 23:32 xFile2 

-rwx------ 1 yourname ugrad  87  Mar  25 23:32 xFile3 

20.  Remove the whole directory lab7a using rmdir. What happened?   

21.  Examine the exit code of the above execution, you should get 1, which means something wrong happened.

22.  Remove the whole directory lab7a using a more effective utility.

23.  (1) Verify the exit code of above execution, you should get 0 now

(2) Verify by trying to list lab7a

$ ls lab7a ls: cannot access lab7a: No such file or directory

24.  Move xFile1, which is in subdirectory lab7b, to current (parent) directory, using relative pathname.   

25.  Verify that the above move was successful. Instead of listing the files, let’s verify by searching for the files.

$ find . –name "xFile*"  or  find . –name "xFile?"   

./lab7b/xFile2 

./lab7b/xFile3 

./xFile1  

26.  Change the name of directory lab7b to lab7working

27.  Navigate to directory lab7working 28. Verify that you are in lab7working

$ your-command 

/cs/home/your_account/…/2019/lab7working 

29.  Move xFile1 (which is in the parent directory) into the current directory using relative pathname.

30.  Verify that the move was successful by listing all the files currently in lab7working

$ ls -l total 12 

-rwx------ 1 yourname ugrad  145 Mar 25 16:58 xFile1 

-rwx------ 1 yourname ugrad  145 Mar 25 16:58 xFile2 

-rwx------ 1 yourname ugrad  87  Mar 25 16:58 xFile3 

31.  Display on stdout the contents of file xFile1     

32.  Display on stdout the contents of the three files with one entry  (Try  more xFile1 xFile2 xFile3 or more xFile?  Use space bar to proceed.)

33.  Check how many lines xFile1 contains. You should get 5.

34.  Display (only) the first two line of xFile1  

35.  Display the last 3 lines of xFile2  

36.  (1) Confirm that xFile1 and xFile2 are identical now, using a utility, which should return silently (Hint:  cmp or diff).   (2) Then examine the exit code, you should get 0.  

37.  (1) Confirm that xFile1 and xFile2 are identical, using another utility, which should return silently (diff or cmp).  (2) Examine the exit code, you should get 0.   

38.  (1) Show that xFile2 and xFile3 are not identical, using diff utility, which will not be silent this time. Try to understand the message but don’t spend too much time on it.  (2) Examine the exit code, you should get 1.

39.  (1) Show that xFile2 and xFile3 are not identical, using cmp utility, which will not be silent this time. Try to understand the message but don’t spend too much time on it.  (2) Examine the exit code, you should get 1.

FYI: these two utilities are used by some professors to do automated grading of your lab or labtest :

       gcc yourCode.c  

a.out > yourOutputFile   

cmp yourOutputFile professorsOutputFile 

A student gets 0 if the last command does not return silently. That means, student gets 0 even if the student’s output contains an extra white space. L 
40.  (1) Concatenate the contents of the three files into a new file xFile123, in the order of xFile1,xFile2 and xFile3.  Hint: use cat and redirection >.   

(2) After that, show on stdout the content of xFile123.

$ more xFile123 

John Smith  1222 26 Apr 1956 

Tony Jones  2152 20 Mar 1950 John Duncan 2    20 Jan 1966 

Larry Jones 3223 20 Dec 1946 Lisa Sue    1222 4  Jul 1980 

John Smith  1222 26 Apr 1956 Tony Jones  2152 20 Mar 1950 

John Duncan 2    20 Jan 1966 Larry Jones 3223 20 Dec 1946 

Lisa Sue    1222 4  Jul 1980 John Smith  1222 26 Apr 1956 John Duncan 2    20 Jan 1966 Larry Jones 3223 20 Dec 1946 

 

41. Sort lines in file xFile123 so identical lines are adjacent now

$ your_command 

John Duncan 2    20 Jan 1966 John Duncan 2    20 Jan 1966 

John Duncan 2    20 Jan 1966 John Smith  1222 26 Apr 1956 

John Smith  1222 26 Apr 1956 John Smith  1222 26 Apr 1956 

Larry Jones 3223 20 Dec 1946 Larry Jones 3223 20 Dec 1946 

Larry Jones 3223 20 Dec 1946 

Lisa Sue    1222 4  Jul 1980 Lisa Sue    1222 4  Jul 1980 

Tony Jones  2152 20 Mar 1950 

Tony Jones  2152 20 Mar 1950 

42.      Show on the stdout the content of xFile123, with duplicate lines removed/merged Hint: utility uniq will do the job

$ your_command 

John Duncan 2    20 Jan 1966 John Smith  1222 26 Apr 1956 

Larry Jones 3223 20 Dec 1946 Lisa Sue    1222 4  Jul 1980 

Tony Jones  2152 20 Mar 1950  

43.      Remove the identical lines and save the result into a file xFile123compact.  Hint: Just redirect the output of 42 using  redirection >   

44.      Show on the stdout the content of xFile123compact. You should get same output as in question 42.

45.      Issue chmod 775 xFile1, and then examine the resulting permission mode of the file. What do you get? You should get  -rwxrwxr-x  Can you understand what we are doing here? 

46.      Now issue chmod 777 xFile1, and then examine the resulting permission mode of the file. What do you get?  

You should get -rwxrwxrwx   Can you understand what we are doing here? 

47.      Change the permission of xFile123compact using octal numbers so that the permission becomes  

-rwxr--r--  1 yourname ugrad 140 Mar 25 17:23 xFile123compact 

48.      Change the permission of xFile123compact by giving group an execute permission. You should get the following result:  -rwxr-xr--  1 yourname ugrad 145 Mar 25 17:23 xFile123compact 

 

49.      Change the permission of xFile123compact by giving group a write permission, and remove read permission of the others of the file. You should issue chmod only once. You should get the following result:  

-rwxrwx---  1 yourname ugrad 145 Mar 25 17:23 xFile123compact 

50.      Change the permission of xFile123compact by removing write permission from group, and giving write and execute permission to others. You should issue chmod only once.  You should get the following result:  

–rwxr-x-wx  1 yourname ugrad 145 Mar 25 17:23 xFile123compact

 

51.      Change the permission of xFile123 by adding the read permission to user, group and others (although they may already have one). You should issue chmod only once. You should get the following result:  

–rw-r--r--  1 yourname ugrad 145 Mar 25 31 17:23 xFile123compact  

52.      Modify xFile1 by adding a new line at the end of the file. This can be done by  echo "this is a xxx new line" >> xFile1   or cat >> xFile1      and then enter "this is a xxx new line",  followed by Ctrl-D.

       

      Question 54-57 should be done without using sort.  Utility ls can do sorting itself.

53.      List the files in the current directory, sorted by the modification time.  xFile1 should be the first file in the list and other files are also sorted according to the modification time.

$ your_command total 20 

-rwxrwxrwx 1 yourname ugrad 166 Mar  25 14:20 xFile1 

-r-xr-x--x 1 yourname ugrad 145 Mar  25 14:12 xFile123compact 

-rw-r--r-- 1 yourname ugrad 377 Mar  25 14:11 xFile123 

…… 

54.      List the files, sorted by the modification time, in reverse order. xFile1 should become the last file in the list.

55.      List the files, sorted by the size of the files. xFile123 should be the first file in the list and other files are also sorted according to the sizes.

$ your_command total 20 -rw-r--r-- 1 yourname ugrad 377 Jul  6 13:35 xFile123 

-rwxrwxrwx 1 yourname ugrad 168 Jul  6 13:42 xFile1 

-r-xr-x--x 1 yourname ugrad 145 Jul  6 13:37 xFile123compact 

-rwx------ 1 yourname ugrad 145 Jul  6 13:27 xFile2 

-rwx------ 1 yourname ugrad 87  Jul  6 13:27 xFile3 

56.      List the files, sorted by the size of the files, in reverse order.

57.      Try to get the type of the file xFile123compact  (Hint: use file utility) xFile123compact: ASCII text 

58.      Try to get the type of one of your c source files.

hello.c: ASCII C program text 

59.      Try to get the type of one of your a.out files.

a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, …… not stripped  

60.      Recall that utility who lists the people who are currently logging on to the EECS server.  Get how many people are currently log on to EECS server

61.      Sort the list of people who are currently logging on.

62.      Sort the list of people who currently logging on, based on the logon date (the 3rd column), in chronological order.

63.      Get the information of the first three people who logged on the system. Hint:  pipe the result of 62 to utility head     

64.      Sort xFile123compact according to the numerical value of the 3rd field

$ sort -k3 xFile123compact   

John Smith  1222 26 Apr 1956 Lisa Sue    1222 4  Jul 1980 Tony Jones  2152 20 Mar 1950 

John Duncan 2    20 Jan 1966 

Larry Jones 3223 20 Dec 1946 

65.      The above result is incorrect (why?).  Fix the problem by using the utility more effectively.

$ your-command    

John Duncan 2    20 Jan 1966 John Smith  1222 26 Apr 1956 

Lisa Sue    1222 4  Jul 1980 Tony Jones  2152 20 Mar 1950 Larry Jones 3223 20 Dec 1946 

 

66.      Sort xFile123compact according to the numerical value of the 3rd field, in reverse order  

Larry Jones 3223 20 Dec 1946 Tony Jones  2152 20 Mar 1950 Lisa Sue    1222 4  Jul 1980 John Smith  1222 26 Apr 1956 

John Duncan 2    20 Jan 1966   

67.      [For your information] In the previous two exercises, John Smith and Lisa Sue, who have the same 3rd field value, did not get further sorted according to the 4th field.  The following command sort xFile123compact according to the numerical value of the 3rd field, and then based on this, further sort according to the 4th field.

$ sort –n –k3 -k4 xFile123compact 

John Duncan 2    20 Jan 1966 

Lisa Sue    1222 4  Jul 1980 

John Smith  1222 26 Apr 1956 Tony Jones  2152 20 Mar 1950 

Larry Jones 3223 20 Dec 1946  

 

68.      Sort xFile123compact according to the year (the last field)

Larry Jones 3223 20 Dec 1946 

Tony Jones  2152 20 Mar 1950 John Smith  1222 26 Apr 1956 

John Duncan 2    20 Jan 1966 

Lisa Sue    1222 4  Jul 1980  

 

69.      Sort xFile123compact according to the year (the last field), in reverse order.

Lisa Sue    1222 4  Jul 1980 John Duncan 2    20 Jan 1966 

John Smith  1222 26 Apr 1956 

Tony Jones  2152 20 Mar 1950 Larry Jones 3223 20 Dec 1946 

 

70.      Sort xFile123compact according to the 5th field (month) 

$ sort -k 5 xFile123compact  

John Smith  1222 26 Apr 1956 Larry Jones 3223 20 Dec 1946 

John Duncan 2    20 Jan 1966 Lisa Sue    1222 4  Jul 1980 Tony Jones  2152 20 Mar 1950 

 

71.      In the previous question, month field is not sorted correctly (why?). Fix by using the utility more effectively.

$ your_command 

John Duncan 2    20 Jan 1966 Tony Jones  2152 20 Mar 1950 

John Smith  1222 26 Apr 1956 Lisa Sue    1222 4  Jul 1980 Larry Jones 3223 20 Dec 1946 

   The following exercises involve searching matches in files.  (Use  egrep or grep –E , which guarantee to accept          the extended  regular expression)  and make sure you are in sh or bash.

72.      (1) Use grep or egrep to get the people who are logging on using yorku.ca network.  (2) Then reverse the result, showing who logon using non yorku.ca network (so you can see clearly who is logon from the department and who is logon from outside, e.g., from home.  Occasionally I use this trick to check if the professors I want to drop by is currently in the office – you’d better hold off going if he is currently logged on from non-York network such as bell or rogers :)

73.      Display records of people in file xFile123compact who has a field value 2 in the record.   

$ egrep 2 xFile123compact  

        John Duncan 2    20 Jan 1966 

        John Smith  1222 26 Apr 1956 

        Larry Jones 3223 20 Dec 1946         Lisa Sue    1222 4  Jul 1980 

        Tony Jones  2152 20 Mar 1950 

74.      The above result is not desirable. Use the utility effectively so that only John Duncan 2   20 Jan 1966 is displayed. Hint: do a ‘whole word’ match.

75.      Display the records of people in file xFile123compact who were born in 1950s. Hint: from the perspective of regular expression, a person’s year field is 195. where . represent any single character.

$ egrep  

John Smith 1222 26 Apr 1956 

Tony Jones 2152 20 Mar 1950 

76.      Get the number of peoples in xFile123compact who were born in 1950s. You should get  2.

        

77.      The EECS department maintains the records of all the students, staff and faculty members in a file /etc/passwd, one person per line.  Issue a command to see the content of the file.  

For such a long file, cat is not a good choice.

 

78.      Issue a utility to find out how many people are in the list. You should get about 3656.

79.      Find out the number of people with name Wang in the file /etc/passwd. You should get about 43.

 

 

The (modified) class list of our class can be found at /eecs/dept/course/2018-19/W/2031Z/classlist. Each line of the file contains one student information, where the first column is the EECS login id.

80.      Get the number of students currently enrolled in the course.  You should get 145. You can use the file directly (by giving the pathname), or, copy the file to your current directory.   

81.      Retrieve your record from the class list.  

82.      Get the number of students whose family name is Wang. You should get 0

  

83.      Get the number of students whose family name is Zhang. You should get 2.

 

84.      Confirm 83 by retrieving the record of students whose family name is Zhang. You should see two lines.

 

85.      Get the number of students whose family name is Leung. You should get 2.

 

86.      Confirm 85 by retrieving the record of students whose family name is Leung. You should see two lines.

 

87.      Get the number of students whose family name is Chen or Chan. You should get 2.  

Hint, from the perspective of regular expression, Ch[ae]n  or  "Chan | Chen" will do the trick.   

 

88.      Confirm 87 by retrieving the record of students whose family name is Chen or Chan. You should see two lines.

 

89.      Look for the students whose eecs login id (in the first column of the file) starts with cse.    

$ egrep cse classlist 

cse*****        dshwet**        *********       Dixit, Shweta cse*****        pavi***         *********       Kugarajah, Pavithra cse*****        pbst***         *********       Thabet, Pierre yuying          cse****         *********       Yu, Ying 

90.      The above result is not desirable. Use this utility more effectively, so the last line is filtered out.

$ your command 

cse*****        dshwet**        *********       Dixit, Shweta cse*****        pavi***         *********       Kugarajah, Pavithra cse*****        pbst***         *********       Thabet, Pierre 

91.      cut is a utility that can extract columns of a text file. By default cut assumes that the columns are separated by tab.  (We can also specify other delimiters such as space or comma).  To specify the columns to extract, use -f.

Issue cut -f 1  classlist       Observe that the only eecs user info (the first column) is displayed.

Issue cut -f 4  classlist       Observe that the only names (the 4th column) is displayed.

Issue cut -f 1-3 classlist   Observe that columns 1 to 3 are displayed.

Issue cut -f 1,4  classlist   Observe that the first and the 4th column are displayed.  

There is a file lyrics in directory /eecs/dept/course/2018-19/W/2031Z. Find the lines in lyrics  that:

92.      Contains the

 #So turn off the light, 1980 

 Say all your prayers and then, 

   Beautiful mermaids will swim through the sea, And you will be swimming there too. sea 1980 I got there by chance. 

93.      contains the as a whole word           

 #So turn off the light, 1980 

Beautiful mermaids will swim through the sea,

94.      contains digits                      

#So turn off the light, 1980 

Oh you sleepy young 1970 heads dream of wonderful things, sea 1980 I got there by chance. 

95.      contains 1980

  #So turn off the light, 1980 sea 1980 I got there by chance. 

96.      end with 1980

 #So turn off the light, 1980 

97.      contains  sea

  Beautiful mermaids will swim through the sea, sea 1980 I got there by chance. 

98.      begins with sea

 sea 1980 I got there by chance. 

99.      contains one (any) character followed by nd

 Say all your prayers and then, 

  Oh you sleepy young 1970 heads dream of wonderful things, And you will be swimming there too. 

100.   contains one (any) character followed by nd, but as a whole world only (so wonderful does not match)

 Say all your prayers and then, 

 And you will be swimming there too. 

101.  begins with one (any) character followed by nd      

 And you will be swimming there too. 

102.  contains letter A or B or C or D

 Beautiful mermaids will swim through the sea, And you will be swimming there too. 

103.  begins with a capital letter

Well you know it's your bedtime, 

Say all your prayers and then, 

Oh you sleepy young 1970 heads dream of wonderful things, 

Beautiful mermaids will swim through the sea, And you will be swimming there too. 

104.  ends with a and one other character.        

 Beautiful mermaids will swim through the sea, 

105.  contains a character that is either a or b or c, followed by nd     

 Say all your prayers and then, 

106.  contains a character that is not a nor b nor c,  followed by nd

  Oh you sleepy young 1970 heads dream of wonderful things, And you will be swimming there too.

 

107.  Go back to the parent directory

cd .. 

108.  Issue utility

find  .  -name "xFile?"  What do you get?

109.  Now issue the utility  

 find  .  -name "xFile*"  What do you get?

 

110.  Now issue   

find  .  -name "xFile*"  -exec mv {}  {}.Lab7 \; What we intend to do here?   

List directory lab7working and examine what happens to the files in lab7working?

 

Note: for solutions using grep/egrep  

•       you can use egrep  or grep -E 

•       all the unquoted search patterns can be quoted 

e.g.,  egrep the lyrics  is same as egrep "the" lyrics   or egrep 'the' lyrics         egrep ^.nd lyrics is same as egrep "^.nd" lyrics  or egrep '^.nd' lyrics  

Actually it is a good habit to always quote search patterns    
 

 

Part II  Common shell functionalities and corresponding meta-characters
In the last lecture we discussed some functionalities that are common among the different shells, and their associated meta-characters. In part I above we have experienced some of them, for example, Pipes |, Filename substitution (wildcards) * ? [], Redirections < > >>. Here you will practice some more functionalities, including Command substitution ` `, Variable substitution $, Conditional sequence && ||,  and Quotes ''  and " ".  

111.    Filename substitution (Wild-cards * ? []). Navigate to your working directory.

• 
Issue   ls *          
Observe that all files in the directory are listed  
• 
Issue   ls xFile*.Lab7 
Observe that all files whose name begins with xFile are listed  
• 
Issue   ls xFile?.Lab7 
Observe that files xFile1.Lab7, xFile2.Lab7, xFile3.Lab7 (but not   
                                                   xFile123.Lab7 and xFile123compact.Lab7) are listed (why?) 

•       Issue   ls xFile??? .Lab7 Observe that only file xFile123.Lab7 is listed (why?)  


 

112.    Command substitution `` 

•       Issue a single command to output current date and time. Something like  

Hello, now is Sat Mar 30 18:08:44 EDT 2019. Have a good day!

•       Issue a single command to output  There are 145 students in EECS2031Z. where 145 comes from the result of a command that reads from file classlist.

•       Issue a single command to output  There are 2 students in EECS2031Z  with family name Zhang where 2 comes from the result of a command that reads from file classlist.

•       Issue a single command to output  There are 3 students in EECS2031Z  whose eecs username begins with cse where 3 comes from the result of a command that reads from file classlist.

 

113.    Conditional sequence && ||.  1) For a series of commands separated by “&&” tokens,  the next command is executed only if the previous command returns an exit code of 0. Which means ‘successful’.   2) For a series of commands separated by “||” tokens, the next command is executed only if the previous command returns a non-zero exit code, which means ‘unsuccessful’.

•       Issue egrep -w Wang classlist  and then echo $? to examine the exit code 1 which means ‘unsuccessful’ (no matching found).

•       Issue egrep -w Zhang classlist , and then echo $? to examine the exit code 0 which means matching found.

•       Issue egrep -w Wang classlist && echo HELLO, observe that HELLO is not printed (why?).

•       Issue egrep -w Zhang classlist && echo HELLO, observe that HELLO is printed (why?).

•       Issue egrep -w Wang classlist || echo HELLO, observe that HELLO is printed (why?).

•       Issue egrep -w Zhang classlist || echo HELLO, observe that HELLO is not printed (why?).

 

114.    There are often times when you want to inhibit the shell’s filename-substitution (wild-card) * ? [], variablesubstitution $, and/or command-substitution ` ` mechanisms.  The shell’s quoting system allows you to do just that. The way that it works is: 1) Single quotes ('   ') inhibits both wildcard substitution, variable substitution, and command substitution.   2) Double quotes("  ") inhibits wildcard substitution only.  

 

•       Issue courseN=2031Z; (no space around =)   This assign variable courseN with value 2031Z

Then issue echo   3  * 4  = 12,  course name is $courseN – today’s date is `date`  Observe that both filename-substitution (wildcard) *, variable-substitution $n, and command-substitution `date` are interpreted.  Among them the wildcard-substitution is interpreted as ‘any file name’.

•       Then issue echo  ' 3  * 4  = 12,  course name is $courseN – today’s date is `date` '   

Observe that interpretation of filename-substitution (wildcard) * is inhibited. Interpretation of variablesubstitution $n and command substitution `date` are also inhibited, due to the fact that single quote ' ' inhibited the interpretation of both the three substitutions.  

•       Finally, issue  echo  " 3  * 4  = 12,  course name is $courseN – today’s date is `date` " Observe that interpretation of * is inhibited. Interpretation of variable-substitution $n and `date` are not inhibited, due to the fact that double quote " " inhibits the interpretation of filename-substitution (wildcard) * only.