Description
Description
This project aims to familiarize you with the Unix system call interface and the shell by
letting you implement several features in a shell, called seashell, using C/C++. A shell is
a program that provides interface to the operating system by gathering input from the user
and executing programs based on that input. Once executed, the seashell will read both
system and user-defined commands from the user. The projects has six parts:
Part I
(20 points)
• Use the skeleton program provided as a starting point for your implementation. The
skeleton program reads the next command line, parses and separates it into distinct
arguments using blanks as delimiters. You will implement the action that needs to be
taken based on the command and its arguments entered in seashell. Feel free to modify
the command line prompt and parser as you wish.
• Read ”Project 1- Unix Shell” at the end of Chapter 3 in the book starting from P12
(10th edition). That will be useful.
• Use execv() system call (instead of execvp()) to execute common Linux programs (e.g.
ls, mkdir, cp, mv, date, gcc) and user programs by the child process. The difference is
that execvp() will automatically resolve the path when finding binaries, whereas for
execv() your program should search the path for the command invoked, and execute
accordingly.
Part II
(10 points) shortdir: In this part, you will implement a new command, shortdir, to associate short names with the current directory. The purpose is to reach the directory (change
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Part III COMP 304 – seashell – Your Custom Shell ( Spring 2021): Project 1 DESCRIPTION
to the directory) with a short name instead of typing the whole path. For instance, we
associate the name matlab with the directory /usr/local/MATLAB/R2018b/ and use it to
change to that directory by using the name matlab. You will also implement supportive
options for the shortdir as follows:
• shortdir set name: associates name with the current directory. Overwrites an existing
association.
• shortdir jump name: changes to the directory associated with name.
• shortdir del name: deletes the name-directory association.
• shortdir clear: deletes all the name-directory associations.
• shortdir list: lists all the name-directory associations.
Note that this command lives across shell sessions; when a new shell session is started, it
should remember the associations from the previous sessions. Refer to Listing 1 for sample
usage of shortdir.
Listing 1: Setting alias for a directory using shortdir
1 seashell> pwd
2 /usr/local/MATLAB/R2018b
3 seashell> shortdir set matlab
4 matlab is set as an alias for /usr/local/MATLAB/R2018b/
5 …
6 seashell> shortdir jump matlab
7 seashell> pwd
8 /usr/local/MATLAB/R2018b
Part III
(10 points) highlight: In this part, you will implement the highlight command that takes a
word-color pair and a text file as an input. For each instance of the word appearing in the
text file, the command prints the line where the word appears and highlights the word with
that color. The colors can be one of the r (red), g (green) or b (blue) colors. The word check
is not case-sensitive. The command syntax and its sample usage are as shown below:
seashell> highlight
seashell> highlight language r file.txt
The programming language used for this code is C.
The first three letters of English language are A B and C.
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Part IV COMP 304 – seashell – Your Custom Shell ( Spring 2021): Project 1 DESCRIPTION
Part IV
(15 points) In this part of the project, you will implement a new seashell command, goodMorning:
• This command will take a time and a music file as arguments and set an alarm to wake
you up by playing the music using rhythmbox. In order to implement goodMorning,
you may want to use the crontab command.
Listing 2: Sample usage of goodMorning command
1 seashell> goodMorning 7.15 /home/musics/muse.mp3
Before implementing the new command inside seashell, you should get familiar with
crontab (if you decide to use crontab) and rhythmbox on a regular shell.
More info about rhythmbox:
http://manpages.ubuntu.com/manpages/hardy/man1/rhythmbox-client.1.html
More info about crontab:
http://www.computerhope.com/unix/ucrontab.htm
Part V
(20 points) In this part, you will implement the kdiff utility to compare two files in given
paths. Sample usage of kdiff to compare two files is given in Listing 3. The utility will
operate in two modes:
• −a: the utility reads the input files (file1.txt and file2.txt) as text files and compares
them line-by-line. If the two files are different, the utility first prints the differing lines
from each file and then prints the count of differing lines as shown in Listing 3. The
utility checks for file extensions and if they are not .txt, flags an error. If the two files
are identical, it displays the message ”The two files are identical”.
• −b: the utility reads the input files as binary files and compares them byte-by-byte. If
the two files are different, the utility prints the message ”The two files are different in
xyz bytes”, where xyz is the number of bytes different between the files. The utility
accepts files with any extension in this case. If the files are identical, the message saying
”The two files are identical” is displayed. Refer to Listing 3 for the sample output.
If the user does not provide either −a or −b, −a is assumed by default.
Note: You are not allowed to use existing file comparison tools (such as diff) to compare
the files. We expect you to use C/C++ file I/O operations to complete this task. You
may use the existing tools to verify your output.
Listing 3: kdiff utility sample output
1 seashell> kidff -a file1.txt file2.txt
2 The two text files are identical
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Part VI COMP 304 – seashell – Your Custom Shell ( Spring 2021): Project 1 DESCRIPTION
4 seashell> kdiff -a file1.txt file2.txt
5 file1.txt:Line 23: A quick brown fox jumps over the lazy dog
6 file2.txt:Line 23: A swift squirrel climbs the tree
7 file1.txt:Line 41: Corona cases today = 1200
8 file2.txt:Line 41: Corona cases today = 689
9 2 different lines found
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11 seashell> kdiff -a file.txt file2.txt
12 The two files are identical
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14 seashell> kdiff -b file1.bin file2.bin
15 The two files are identical
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17 seashell> kdiff -b file1.bin file21.bin
18 The two files are different in 8213 bytes
Part VI
(10 points) In this final part, you will implement a command of your choice in seashell.
Come with a new, non-trivial command and implement it inside seashell. Creativity will be
rewarded and selected commands will be shared with your peers in the class. It is possible
that command you come up with is already implemented in Unix. That should not stop you
from implementing your own but do not simply execute the existing Unix version of it.
Deliverables
You are required to submit the followings packed in a zip file (named your-username(s).zip)
to the blackboard :
• .c source code file that implements the seashell shell. Please comment your implementation.
• any supplementary files for your implementations (e.g., Makefile)
• a short REPORT file briefly describing your implementation, particularly the new command you invented in Part V. You may include your snapshots in your report.
• Do not submit any executable files (a.out) or object files (.o) to blackboard. Do not
submit the file for the song you use in Part-III.
• You are required to implement the project on a Unix-based virtual machine or Linux
distribution.
• (15 points) Finally there will be project demos after the deadline. Demos account for 15
points towards your grade. We expect that both team members have equally contributed
to the project and are competent to answer questions on any part of the implementation.
TA will direct questions to any members of the team thus team members may receive
different grades based on their demo performance.
GOOD LUCK.
Student Name: Page 4 of 4
