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Tutorial10: Shell Scripting - Part 1

18 bytes added, 15:38, 16 March 2021

→‎INVESTIGATION 4: CONTROL FLOW STATEMENTS

# Copy and paste the following (correct) '''test''' command: [ $number1 -gt $number2 ]

# Issue a command to view the value of the '''exit status''' of the previously issued '''test''' command. You should notice that is works properly. Now that we have learned how to test conditions, let's learn about '''control-flow''' statements. '''LOGIC STATEMENTS''' are used to create '''different paths''' or directions that the shell script will take based on the result of the '''test condition'''. In this tutorial,we will only focus on the '''if''' and '''if-else''' logic statements.

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

# Enter the following lines in your shell script: #!/bin/bash num1=5 num2=10 if [ $num1 -lt $num2 ] then    echo "num1 is less than num2" fi

# 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 indicates 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)

# 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 and the '''if''' control-flow statement.]]

# Run your shell script by issuing: ./if-2.bash When prompted, make certain that the '''first number''' is greater than the '''second number'''. What happens?

# Run the ./if-2.bash Bash shell script again. When prompted, make certain that the '''first number''' is less than or equal to the '''second number'''. What happens? Let's use an '''if-else''' statement to provide an '''alternative''' if the first number is less than or equal to the second number.

# 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 [[Image:if-3.png|thumb|right|330px|Output of a shell script using the '''if-else''' control-flow statement.]]

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

# 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'''

Msaul

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Tutorial10: Shell Scripting - Part 1

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