Question

CIT 371 Lab 12: shell scripting

Start VMware, your VM and log in as Student. cd to your home directory and create a subdirectory called scripts. cd to that directory. You can use gedit or some other editor but you need to get used to vi, so I strongly recommend that you use vi. Remember before running any new script that you will need to modify its permissions to be executable. Use either 745 or 755.

1. Create a script called script1 with the following. Match the syntax precisely. Pay close attention to the use of the back tick marks on line 4. This is the character right above the tab key on your keyboard.

#!/bin/bash

echo You are $USER

echo Your home directory is $HOME

echo Your home directory consists of `du –sH ~`

Run the script by typing ./script1 <enter>. Alter your script so that the output of each echo statement is redirected to the file info.txt. How did you do this?

2. Create the following script, named script2 and run it.

#!/bin/bash

echo What is your name?

read NAME

echo What is your username?

read USERNAME

echo Hello $NAME, your home directory contents and size:

Complete this script by adding instructions to output this user’s home directory contents (using ls) assuming that the user’s home directory will be /home/$USERNAME as well as using the du statement from script1 to output the disk usage of the user’s home directory. When done, add this script to your answer file.

3. Rewrite the script from #2 so that the NAME and USERNAME are supplied to the script as parameters, removing the first four instructions (the first two echo and the two read statements). Save and test your script. When done, add this script to your answer file.

4. Write the following script, calling the file script

#!/bin/bash

if [ $# -ne 2 ]; then echo Illegal input

elif [ $1 –gt $2 ]; then echo $1 is greater

else echo $2 is greater

fi

Save and run the script providing it no parameters, two parameters of 5 and 10, two parameters of 10 and 5, and two parameters of 5 and 5. What does [ $# -ne 2 ] mean? Do we need this in the script?

5. Modify the script from #4 so that it will also output a message if the two parameters are the same. For instance, it might output “5 equals 5”. When done, include the modified script as the answer to this step.

6. Write the following script calling it script

#!/bin/bash

read –p “Enter the number you seek   ” NUM

for VALUE in $@; do

     if [ $VALUE –eq $NUM ]; then COUNT=$((COUNT+1)); fi

done

echo $NUM appeared $COUNT times

Run script5 passing it the list of numbers 5 10 6 12 5 18 10 4 19 21 5 12 18 22 and when prompted, input 5. Rerun the script inputting 18 instead. Rerun the script inputting 23 instead. What outputs did you get for each input?

7. Rewrite the script from #6 to input two inputs from the user, instead of just NUM, and count the number of parameters that are equal to or in between the two. For instance, if the user inputs 12 and 20, we would have 5 matches (12, 18, 19, 12, 18). Assume the first input is less than the second (that is, you do not need to worry about the user inputting 20 and then 12). Add this revised script to your answers file.

8. Write a script which receives a list of parameters and iterates through them using a for loop similar to what you wrote in #6. In this case, the for loop requires two if statements (or an if-then-else) to locate the smallest and the largest values of the inputs. Output both values. Assume the list of parameters contains at least one number. As an example, if the list of parameters was 5 10 6 12 5 18 10 4 19 21 5 12 18 22, it will output that 4 is the smallest and 22 is the largest. When done, add this script to your answer file.

Shut down your VM, exit VMware and submit your lab report.

Answer 1

Script 1
***********

bash script1.sh > info.txt

Script 2
**********

#!/bin/bash
echo "What is your name?"
read NAME

echo "What is your username?"
read USERNAME

echo "Hello $NAME, your home directory contents and size: `ls`"
echo
echo "size: `du -sH /home/$USERNAME`"

Modified

#!/bin/bash

echo "Hello $1, your home directory contents and size: `ls`"
echo
echo "size: `du -sH /home/$2`"

Script 3
**********

#!/bin/bash

if [ $# -ne 2 ]
then
   echo "Illegal input"
elif [ $1 -gt $2 ]
then
   echo "$1 is greater"
else
   echo "$2 is greater"
fi

What does [ $# -ne 2 ] mean

This means if there must be 2 arguments if not then condition will be false

Script 4
*********

#!/bin/bash

if [ $# -ne 2 ]
then
   echo "Illegal input"
elif [ $1 -gt $2 ]
then
   echo "$1 is greater"
elif [ $1 -eq $2 ]
then
   echo "$1 equals $2"
else
   echo "$2 is greater"
fi

Script 5
************

#!/bin/bash

read -p "Enter the 1st number " NUM1
read -p "Enter the 2nd number " NUM2

for VALUE in $@;
do
if [ $VALUE -ge $NUM1 ] && [ $VALUE -le $NUM2 ]
then
    COUNT=$((COUNT+1))
fi
done
echo
echo "$NUM appeared $COUNT times"

#!/bin/bash
echo "enter size of an array"
read n
#taking input from user
for((i=0;i<n;i++))
do
echo " enter $((i+1)) number"
read nos[$i]
done
#printing the entered number
echo "number entered are"
for((i=0;i<n;i++))
do
echo ${nos[$i]}
done
#main loop
small=${nos[0]}
greatest=${nos[0]}
for((i=0;i<n;i++))
do
#logic for smallest number
if [ ${nos[$i]} -lt $small ]; then
small=${nos[$i]}
#logic for greatest number
elif [ ${nos[$i]} -gt $greatest ]; then
greatest=${nos[$i]}
fi
done
#printing smallest and greatest number
echo "smallest number in an array is $small"
echo "greatest number in an array is $greatest"

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