University of Windsor : System Programming Winter Midterm 01-1h20mn. Instructor: Dr. A. Habed

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1 University of Windsor : System Programming Winter Midterm 01-1h20mn. Instructor: Dr. A. Habed Solution Last name: First name: Student #: NONE NONE NONE Read this first Make sure your paper contains 10 pages (including this one). Write your name and student # before you start. Check the Appendix page 10 for some useful commands/modifiers you have used in the lab. Answer each question in the space provided to it in this document. Documents allowed: textbook and unmarked lecture slides only. Marking scheme is out of

2 Question 1 25 marks Definition: an IP address is expressed as four integer numbers between 0 and 255 shown separated by periods. For example, is the IP address of our school s sol server. Write a C-shell script isvalidip with the following synopsis: isvalid <string> where <string> is a string given in the command-line argument. Your script must check whether its command-line argument is a valid IP address or not. Any command-line argument that does not satisfy the above definition of an IP address must be identified as an invalid IP address. The output displayed by your script must be of the same format as the output in the examples below. Examples: when executing the following command at the shell prompt: isvalidip your script must display on the terminal window: is a valid IP address when executing the command isvalidip your script must display on the terminal window: is not a valid IP address 2

3 Question 1: your answer #!/bin/csh # Script that checks of argument is a valid IP # Each component is treated separately for clarity # a loop can be used instead set ipaddress = $1 set d4 = $ipaddress:e if ($d4 == "" echo $d4 tr -d"[:digit:]"!= "" $d4 > 255) then echo "$1 is not a valid IP address" exit(1) set d = $ipaddress:r set d3 = $d:e if ($d3 == "" echo $d3 tr -d "[:digit:]"!= "" $d3 > 255) then echo "$1 is not a valid IP address" exit(1) set d = $d:r set d2 = $d:e if ($d2 == "" echo $d2 tr -d "[:digit:]"!= "" $d2 > 255) then echo "$1 is not a valid IP address" exit(1) set d1 = $d:r if ($d1 == "" echo $d1 tr -d "[:digit:]"!= "" $d1 >255) then echo "$1 is not a valid IP address" exit(1) echo $1 is a valid IP address 3

4 Question 2 25 marks Write a C-shell script with the following synopsis: myls <direcory> <size> where <directory> is a string that refers to the absolute or relative path of a directory and size refers to an integer number. Your script must list all regular files (excluding hidden files and directories) stored in the directory <directory> with a size greater than the value <size>. The output displayed by your script must be of the same format as the output of myls in the example below. Example: For example, listing the files in the directory /global/stu2/adlane/source with the shell s command ls -l: ls -l /global/stu2/adlane/source displays the list of all files in that directory in addition to additional information such as read-write-execute permissions, the owner of each file...etc.: 1 adlane Feb 12 03:50 binary.c 1 adlane Feb 12 03:50 test0.c 1 adlane Feb 12 03:50 test1.c 1 adlane Feb 12 03:50 test2.c 1 adlane Feb 12 03:50 test3.c 1 adlane Feb 12 03:50 test4.c 1 adlane Feb 12 03:50 test5.c Note that the 5th column of the above list contains the size (in bytes) of each file. Now running at the prompt: myls /global/stu2/adlane/source 250 should display: binary.c test2.c whose respective sizes are greater than 250 bytes. 4

5 Question 2: your answer #!/bin/csh cd $1 set files = ls foreach file ($files) if (-f $file) then set d = ls -l $file if ($d[5] > $2)then echo $file end 5

6 Question 3 25 marks Write a C-shell script with the following synopsis: groupinfo <username> where <username> is a string that refers to the user-name (or login-name) of a system user. Your script must list all the groups to which the user belongs and their corresponding group IDs. The output displayed by your script must be of the same format as the output in the example below. Example: For example, on luna, running at the prompt: groupinfo steve displays steve belongs to the group named staff with group ID 10 steve belongs to the group named sysadmin with group ID 14 steve belongs to the group named www with group ID 20 steve belongs to the group named dba with group ID 22 steve belongs to the group named pc2 with group ID 23 steve belongs to the group named acm with group ID 70 steve belongs to the group named srsnetc with group ID 72 steve belongs to the group named cs140 with group ID 1021 steve belongs to the group named anything with group ID

7 Question 3: your answer #!/bin/csh # Display information about the groups to which # the user (argument) belongs set groups = cat /etc/group grep $1 foreach group ($groups) set info = echo $group tr "[:]" "[ ]" echo $1 belongs to the group named $info[1] with group ID $info[2] end 7

8 Question 4 25 marks When you receive an on sol or luna, the message is appended to a file carrying your user-name and stored in the directory /var/mail/. For example, when the user adlane receives a new , it is appended to the file /var/mail/adlane. When a message is deleted or moved to a folder, it is removed from that file. Write a C-shell script with the following synopsis: checkmail <seconds> that checks every <seconds> number of seconds whether the user running the script has received a new message, deleted or moved a message. When a new message is received, checkmail must display the message: You have received a new mail When a message is deleted or moved, checkmail must display the message: One or more s have been deleted or moved from your mailbox 8

9 Question 4: your answer #!/bin/csh set d = ls -l /var/mail/$user set size = $d[5] while(1) set d = ls -l /var/mail/$user if ($size < $d[5])then echo You have received a new mail else if ($size > $d[5])then echo One or more s have been deleted echo or moved from your mailbox set size = $d[5] sleep $1 end 9

10 Appendix The following are some useful commands/modifiers that you have used in your labs and that might be useful to solve one or more questions in this test. The following filenames modifiers (:h,:r,:e,:t) allow access to various portions of the value of a variable. E.g. set filename = /global/stu2/adlane/unix/test1.tex echo $filename:h #produces /global/stu2/adlane/unix echo $filename:r #produces /global/stu2/adlane/unix/test1 echo $filename:e #produces tex echo $filename:t #produces test1.tex The tr command: The tr utility copies the standard input to the standard output with substitution or deletion of selected characters. For example: tr "[a]" "[b]" replaces each occurrence of a in the standard input by the letter b in the standard output (without changing the other characters). Also, in order to delete all occurrences of the character a in the standard input, we use tr -d "[a]". tr refers to classes of characters. Digits are referred to as [: digit :] (also [0 9]), [: lower :] refers to lower-case alphabet letters (also [a z]) and [: upper :] (also [A Z]) are capital letters. 10