Lab assignment 1: Unix/Linux Commands and Basic Shell Programming

COEN 177L: Operating Systems Lab
Lab assignment 1: Unix/Linux Commands and Basic Shell Programming
Objectives
1. To learn Unix/ Linux
2. To use command – line programs
3. To develop sample shell programs
Guidelines
Good knowledge in Unix/Linux based C programming is required for all labs. You are highly encouraged to use
command line tools in developing, compiling, and running your programs. You may use editors like vi or gedit and
gcc compiler. This lab is designed to teach you basics of the Linux technical environment, including tools,
commands, and shell scripts.
Please pay attention to your coding style and good programming practices, if your program is not worth
documenting, it probably isn't worth running.1
 Please follow the GNU coding standards available on:
https://www.gnu.org/prep/standards/html_node/Writing-C.html.
Unix/ Linux
Linux is a Unix-like operating system, following the design principles of Unix monolithic kernel in process control,
cpu scheduling, memory management, file systems, networking, and access to the peripherals. Please read
details on https://en.wikipedia.org/wiki/Linux.
Unix/ Linux has a culture of distinctive art and powerful design philosophy since its inception in 1969. Software
technologies come and go but Unix/ Linux remained dominant and continued to evolve on a wide variety of
machines ranging from supercomputers and PCs to handheld devices and embedded networking hardware. C
language is ubiquitous and a central technology of Unix/ Linux. It is very hard to imagine developing applications
at the core system level without C. The POSIX, Portable Operating System Standard, the Unix API (Application
Programming Interface) is used to write truly portable software that can run across a heterogeneous mix of
computers. TCP/IP (which you will learn in this class) and Unix represent the core technologies of the Internet.
For more details, see 2
.
Please install Linux on your laptop computer, either as a bare operating system or as a virtual machine. For
details, please check https://www.linux.com. If you are using Mac OS, you can use Linux commands in a terminal
window, including vi and gcc compiler.
Command-line programs (utilities)
The use of command-line programs is a tradition in Unix\Linux. Commands are executable programs that can run
with variety of arguments (options). Command-line options are single letters preceded by a single hyphen,
including:
-a: all, -b: buffer, -c: command, -d: debug, -e: execute, -f: file, -l: list, -o: output, -u: user
Some of the basic commands are:
- ls: lists all files and directories (try with options: -a, -al)
- cat: displays file content (try cat file1 file2 > file3)
- mv: moves a file to a new location (try mv file1 file2)
1
Jonathan Nagler, "Coding Style and Good Computing Practices”, PS: Political Science and Politics, Volume 28, Issue 3, 1995, pp. 488-492.
2
Eric S. Raymond, The Art of Unix Programming, Pearson, 2004
COEN 177L – Lab assignment 1 1/5
- rm: deletes a file
- cp: copy file
- cmp: compares two files
- man: gives help information on a command
- history: gives a list of past commands
- clear: clear the terminal
- mkdir: creates a new directory
- cd: changes directory
- rmdir: deletes a directory
- chmod: changes the access mode of the specified files to the specified mode
- chown: changes the owner of the specified files to the specified userid
- echo: writes arguments to the standard output (try echo ‘Hello World’ > myfile)
- df: shows disk usage
- apt -get: install and update packages
- mail -s ‘subject’ -c ‘cc-address’ -b ‘bcc-address’ ‘to-address’ < filename: sends email with attachment
- chown/ chmod: change ownership/ permission of file or directory
- date: show the current date and time
- ps: displays active processes
- kill: kills process
- sh: bourne shell – command interpreter (good to learn about shell programming)
- grep: searches for pattern in files
- Ctrl+c: halts current command
- Ctrl+z: stops current command and resumes with foreground
- Ctrl+d (exit): logout of current session
- man: displays the manual page of the specified command
- echo: prints on the screen
For more commands, please refer to Linux command quick reference3
.
Shell programming (aka scripting)
A shell program (aka script) is a text file (typically has .sh extension, but not required) that contains standard Unix
and shell commands. It allows you to execute a series of commands in a shell program simply by running the
shell program rather than typing all commands. Shell programs are interpreted not compiled. They are used to
automate system administration tasks. In a shell program, you can use
1. comments,
2. variables,
3. conditional commands,
4. repeated actions of commands, and
5. functions.
Bourne Shell (bsh or sh) is used for this lab. Other Shells are C-Shell – csh, Korn Shell, Born Again Shell – BASH,
Thomas C-Shell – tcsh.
1. Comments: Use the # character to signify comments. Anything after a # character until the end of the line is
considered a comment and is ignored by the shell.
3
 https://www.oreilly.com/openbook/debian/book/appe_01.html
COEN 177L – Lab assignment 1 2/5
2. Variables: Use letters, numbers, and the underscore to define variable names is a shell program. The assigned
values to variables are stored internally as strings. To use a variable, precede the name with $. The shell provides
the following pre-defined shell variables that may be used to pass parameters to a shell script.
$0 the name of the shell program
$1 thru$9 the first thru to ninth parameters
$# the number of parameters
$* all parameters passed represented as a single word with individual parameters separated
$@ all the parameters passed with each parameter as a separate word
$? hold the exit status of the previous command
$$ the process id of the current process
PATH the value of the PATH environment variable
HOME the full path name of your home directory
USER your user name
PWD the current directory path
3. Conditional commands: Use if keyword for a conditional statement in either of the following arrangements:
if expression
then
 command-list
fi
if expression
then
 command-list
elsif expression
 command-list2
fi
if expression
then
 command-list1
else
 command-list2
fi
case keyword can also be used to execute one of several lists of statements depending on the value of a
variable.
 Expressions (Boolean):
- Relational operators:
-eq, -ne, -gt, -ge, -lt, -le
- File operators:
-f file True if file exists and is not a directory
-d file True if file exists and is a directory
-s file True if file exists and has a size > 0
- String operators:
-z string True if the length of string is zero
-n string True if the length of string is nonzero
s1 = s2 True if s1 and s2 are the same
s1 != s2 True if s1 and s2 are different
s1 True if s1 is not the null string
- Compound comparison:
-a And
-o Or
! Not
COEN 177L – Lab assignment 1 3/5
The other type of conditional command supported by the shell is the case command. The case command allows
the user to compare a single value against multiple values and when a match is found execute the associated
command list.
4. Repeated actions of commands: The Bourne shell provides three repeated action commands: for, while, and
until as follows:
for variable in word1 word2 word3 ... wordn
do
 command-list
done
while command
do
 command-list
done
until command
do
 command-list
done
5. Functions: shell functions are generally defined in a file as:
name () { add (){
commands; e.g. echo $[$1 + $2]
 } }
Important notes:
- Shell programming is not good in numerical computation, but use can still use some mathematical
expressions by using the keyword expr, e.g. i=‘expr $i+1’ or you may close expressions in brackets, e.g.
i=$[i+1]
- Use #!/bin/sh as the first line of a shell program to define the path of the command interpreter.
- Use chmod +x <program_name> to make a shell program executable, then run either using sh
<program_name>, or ./<program_name>
- Shell metacharacters are:
'...' takes without interpreting contents
“...” takes after processing $, `...` and \
\ escape, for example \c takes character c
`...` runs enclosed command and replace with output
Sample shell program
Demonstrate each of the following steps to the TA to get a grade on this part of the lab assignment
Step 1. Write the following shell program using vi, emacs, or an editor of your choice
#Sample shell programs for Lab assignment
#!/bin/sh
echo Executing $0
echo $(/bin/ls | wc -l) files
wc -l $(/bin/ls)
echo "HOME="$HOME
echo "USER="$USER
echo "PATH="$PATH
echo "PWD="$PWD
echo "\$\$"=$$
COEN 177L – Lab assignment 1 4/5
user=`whoami`
numusers=`who | wc -l`
echo "Hi $user! There are $numusers users logged on."
if [ $user = "salagtash" ]
then
 echo "Now you can proceed!"
else
 echo "Check who logged in!"
 exit 1
fi
response="Yes"
while [ $response != "No" ]
do
 echo "Enter height of rectangle: "
 read height
 echo "Enter width of rectangle: "
 read width
 area=`expr $height \* $width`
 echo "The area of the rectangle is $area"
 echo "Would you like to repeat for another rectangle [Yes/No]?"
 read response
done
Step 2. Run the shell program by typing sh <YourProgram.sh>. When it runs without errors or warnings, write
down your observations in detail and make a copy of the source file.
Step 3. Rewrite the program in Step 1. so that you compute also the area of a circle, then demonstrate steps 1
– 3 to the TA.
When your program runs without errors or warnings, make a copy of the source file
Requirements to complete the lab
1. Show the TA correct execution of the shell programs.
2. Submit your answers to questions, observations, and notes as .txt file and upload to Camino
3. Submit the source code for all your programs as .sh file(s) and upload to Camino.
Be sure to retain copies of your .sh and .txt files. You will want these for study purposes and to resolve any
grading questions (should they arise)
Please start each program/ text with a descriptive block that includes minimally the following information:
# Name: <your name>
# Date: <date> (the day you have lab)
# Title: Lab1 – task
# Description: This program computes … <you should
# complete an appropriate description here.>
COEN 177L – Lab assignment 1 5/5