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Tutorial10: Shell Scripting - Part 1

33 bytes added, 09:26, 11 March 2021

→‎INVESTIGATION 3: COMMAND SUBSTITUTION / MATH OPERATIONS

# Confirm that you are located in your '''home''' directory in your Matrix account.

# To demonstrate the need for the '''( )''' construct, issue the following Linux command from the shell: echo "1 + 2" What did you notice? # Issue the following Linux commands (using the ''math construct''): echo "$((1 + 2))" What did you notice? The '''$''' in front of the construct '''expands''' the result of the calculation. # Issue the following Linux commands demonstrating other types of math calculations: echo "$((2 - 3))" echo "$((2 * 3))" echo "$((2 / 3))" echo "$((2 ** 3))" '''NOTE:''' You may notice that '''dividing''' '''2''' by '''3''' shows a '''zero''' result. To perform decimal calculations would require the use the '''awk''' or '''bc''' Linux commands (we will '''NOT''' cover that method to work with decimal numbers in this course). You can use the ''math construct'' with variables as well. # Issue the following Linux commands demonstrating using the ''math construct'' with variables: num1=34 num2=12 echo "$((num1 * num2))" What did you notice? You can create variables and assign them values in the ''math construct'' as well. # Issue the following Linux commands demonstrating using the math construct with variables: num1=5 num2=3 ((result = num1 ** num2)) echo "The result is: $result"

# Use a text editor to create a Bash shell script called '''dog-years.bash'''

# Add the following lines to the beginning of this file: #!/bin/bash echo dogFactor=7 read -p "Please enter your age (in years): " humanYears ((dogYears = humanYears * dogFactor)) echo "You age in dog-years is: $dogYears" echo

# Issue the '''chmod''' command to add execute permissions for the user for the '''dog-years.bash''' file.

# Issue the following to run the user-variables.bash Bash shell script: ./dog-years.bash Enter your age to see what happens.

# Issue the following ~~Linux command~~ to run a checking script: bash /home/murray.saul/myscripts/week10-check-3 | more If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

:In the next investigation, you will use '''control-flow statements''' to allow your shell scripts to perform differently under different situations.

Msaul

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Tutorial10: Shell Scripting - Part 1

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