BASH Shell Scripting – Part II
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This document discusses Bash shell scripting and provides examples of scripts using while and until loops. The scripts print numbers in different orders, check if a file exists, read user input with the read command, and print the input back to the user. The objective is to learn how to write and run shell scripts using conditions and user input.
![EE-332 Operating System
Department of Electrical Engineering | The University of Faisalabad
Zeeshan Iqbal BEE-FA18-022 (Computer)
Experiment # 5
Title:
• BASH Shell Scripting – Part II
Objective:
• To learn how write and run shell scripts.
Information:
While statement syntax: Until statement syntax:
while condition_is_true
do
execute commands
done
example
while [ $num -gt 100 ]
do
sleep 5
done
until false
do
execute commands
done
COMMANDS:
1. Numbers in reverse order
This Command is used to write script to print numbers as 5,4,3,2,1 using while loop.
#!/bin/bash
# Linux Shell Scripting Tutorial
#
i=5
while test $i != 0
do
echo "$i"
let i=i-1](https://image.slidesharecdn.com/lab5-210227052100/85/BASH-Shell-Scripting-Part-II-1-320.jpg)
![EE-332 Operating System
Department of Electrical Engineering | The University of Faisalabad
Zeeshan Iqbal BEE-FA18-022 (Computer)
Output:
2. Numbers in order
This command is used to write script to print numbers as 0 … 9 using while loop.
#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 10 ]; do
echo The counter is $COUNTER
let COUNTER=COUNTER+1
done
Output:](https://image.slidesharecdn.com/lab5-210227052100/85/BASH-Shell-Scripting-Part-II-2-320.jpg)
![EE-332 Operating System
Department of Electrical Engineering | The University of Faisalabad
Zeeshan Iqbal BEE-FA18-022 (Computer)
3. Numbers in reverse order
This command is used to write script to print numbers as 20 … 10 using until loop.
#!/bin/bash
COUNTER=20
until [ $COUNTER -lt 10 ]; do
echo COUNTER $COUNTER
let COUNTER-=1
done
Output:
4. Check is a file exists or not
This command is used to determine whether given file exist or not, file name is
supplied as command line argument, also check for sufficient number of command line
argument.
#!/bin/bash
# Linux Shell Scripting
if [ $# -ne 1 ]
then](https://image.slidesharecdn.com/lab5-210227052100/85/BASH-Shell-Scripting-Part-II-3-320.jpg)
![EE-332 Operating System
Department of Electrical Engineering | The University of Faisalabad
Zeeshan Iqbal BEE-FA18-022 (Computer)
echo "Usage - $0 file-name"
exit 1
fi
if [ -f $1 ]
then
echo "$1 file exists"
else
echo "Sorry, $1 file does not exist"
fi
Output:
5. Reading user input with read
This command is used to write a shell script to read the name of the user from keyboard
and print it back to screen. Use read command.
#!/bin/bash
echo Please, enter your name
read NAME
echo "Hi $NAME!"
Output:](https://image.slidesharecdn.com/lab5-210227052100/85/BASH-Shell-Scripting-Part-II-4-320.jpg)
BASH Shell Scripting – Part II
- 1. EE-332 Operating System Department of Electrical Engineering | The University of Faisalabad Zeeshan Iqbal BEE-FA18-022 (Computer) Experiment # 5 Title: • BASH Shell Scripting – Part II Objective: • To learn how write and run shell scripts. Information: While statement syntax: Until statement syntax: while condition_is_true do execute commands done example while [ $num -gt 100 ] do sleep 5 done until false do execute commands done COMMANDS: 1. Numbers in reverse order This Command is used to write script to print numbers as 5,4,3,2,1 using while loop. #!/bin/bash # Linux Shell Scripting Tutorial # i=5 while test $i != 0 do echo "$i" let i=i-1
- 2. EE-332 Operating System Department of Electrical Engineering | The University of Faisalabad Zeeshan Iqbal BEE-FA18-022 (Computer) Output: 2. Numbers in order This command is used to write script to print numbers as 0 … 9 using while loop. #!/bin/bash COUNTER=0 while [ $COUNTER -lt 10 ]; do echo The counter is $COUNTER let COUNTER=COUNTER+1 done Output:
- 3. EE-332 Operating System Department of Electrical Engineering | The University of Faisalabad Zeeshan Iqbal BEE-FA18-022 (Computer) 3. Numbers in reverse order This command is used to write script to print numbers as 20 … 10 using until loop. #!/bin/bash COUNTER=20 until [ $COUNTER -lt 10 ]; do echo COUNTER $COUNTER let COUNTER-=1 done Output: 4. Check is a file exists or not This command is used to determine whether given file exist or not, file name is supplied as command line argument, also check for sufficient number of command line argument. #!/bin/bash # Linux Shell Scripting if [ $# -ne 1 ] then
- 4. EE-332 Operating System Department of Electrical Engineering | The University of Faisalabad Zeeshan Iqbal BEE-FA18-022 (Computer) echo "Usage - $0 file-name" exit 1 fi if [ -f $1 ] then echo "$1 file exists" else echo "Sorry, $1 file does not exist" fi Output: 5. Reading user input with read This command is used to write a shell script to read the name of the user from keyboard and print it back to screen. Use read command. #!/bin/bash echo Please, enter your name read NAME echo "Hi $NAME!" Output:
- 5. EE-332 Operating System Department of Electrical Engineering | The University of Faisalabad Zeeshan Iqbal BEE-FA18-022 (Computer) 6. Reading user input with read This command is used to write a shell script to read the name (first and last names) of the user from keyboard and print it back to screen. Use read command. #!/bin/bash echo Please, enter your firstname and lastname read FN LN echo "Hi! $LN, $FN !" Output: