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Tutorial10: Shell Scripting - Part 1

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→‎INVESTIGATION 4: CONTROL FLOW STATEMENTS

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER'''). [[Image:if-1.png|thumb|right|200px|Output of a shell script using the '''if''' control-flow statement.]]

# Issue the following Linux command to add execute permissions for your shell script: chmod u+x if-1.bash

# Run your shell script by issuing: ./if-1.bash Confirm that the output indicated a correct result.

# Use a text editor like vi or nano to create the text file called '''if-2.bash''' (eg. vi if-2.bash) If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule.

# Enter the following lines in your shell script: #!/bin/bash read -p "Enter the first number: " num1 read -p "Enter the second number: " num2 if [ $num1 -gt $num2 ] then    echo "The first number is greater than the second number." fi

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER'''). [[Image:if-2.png|thumb|right|320px|Output of a shell script using the '''read''' command '''if''' control-flow statement.]]

# Issue the following Linux command to add execute permissions for your shell script: chmod u+x if-2.bash

# Run your shell script by issuing: ./if-2.bash Confirm that the output indicated a correct result. What happens when you enter a first number that is less than or equal to the second number? Let's use an '''if-else''' statement to provide an appropriate alternative if the condition is FALSE.

# Use a text editor like vi or nano to create the text file called '''if-3.bash''' (eg. vi if-3.bash)

# Enter the following lines in your shell script: #!/bin/bash read -p "Enter the first number: " num1 read -p "Enter the second number: " num2 if [ $num1 -gt $num2 ] then    echo "The first number is greater than the second number." else    echo "The first number is less than or equal to the second number." fi

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER'''). [[Image:if-3.png|thumb|right|330px|Output of a shell script using the '''if-else''' control-flow statement.]]

# Issue the following Linux command to add execute permissions for your shell script: chmod u+x if-3.bash

# Run your shell script by issuing: ./if-3.bash What do you notice? Try running the script several times with numbers different and equal to each other to confirm that the shell script works correctly. Let's learn how to use a '''loop''' with shell scripting. In this tutorial, we will only focus on one simple use with the '''for''' loop.

# Use a text editor like vi or nano to create the text file called '''for-1.bash''' (eg. vi for-1.bash)

# Enter the following lines in your shell script: #!/bin/bash echo for x in 5 4 3 2 1 do    echo $x done echo "blast-off!" echo

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER'''). [[Image:for-1.png|thumb|right|125px|Output of a shell script using the '''for''' loop with a '''list'''.]]

# Issue the following Linux command to add execute permissions for your shell script: chmod u+x for-1.bash

# Run your shell script by issuing: ./for-1.bash

# Use a text editor like vi or nano to create the text file called '''for-2.bash''' (eg. vi for-2.bash)

# Enter the following lines in your shell script: #!/bin/bash echo for x do    echo $x done echo "blast-off!" echo

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').

# Issue the following Linux command to add execute permissions for your shell script: chmod u+x for-2.bash [[Image:for-2.png|thumb|right|175px|Output of a shell script using the '''for''' loop without a '''list'''.]]

# Run your shell script by issuing: ./for-2.bash 10 9 8 7 6 5 4 3 2 1 How does this differ from the previous shell script? You will learn in a couple of weeks more examples of using loop statements. Let's run a '''checking-script''' to confirm that both your '''for-1.bash''' and '''for-2.bash''' Bash shell scripts exist, have execute permissions, and when run, produce the same OUTPUT as required in this tutorial's instructions.

# Issue the following Linux command to run a checking script: bash /home/murray.saul/myscripts/week10-check-4 | more If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

# After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 3''', '''sections 2 and 3''' labelled '''Interactive Shell Environment''' and '''Introduction To Scripting (phone)'''.

Msaul

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Tutorial10: Shell Scripting - Part 1

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