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Tutorial10: Shell Scripting - Part 1

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=INVESTIGATION 1: CREATING A SHELL SCRIPT=

'''ATTENTION''': Depending on your ULI101 instructor, you may be required to complete this tutorial for '''marks''' in this course. Please refer to your instructor's course notes and lecture notes regarding evaluation for this course. The due date for successfully completing this tutorial (i.e. '''tutorial 10''') is by '''Friday by midnight''' next week (i.e. '''Week 10'''). If your instructor has NOT assigned marks for completing this tutorial, you can perform it for '''practice'''.

In this investigation, you will learn how to create and run a '''Bash Shell script'''.

# Issue the following linux command to '''add''' execute permissions for your shell script: chmod u+x hello

# Issue the following to run your shell script: ./hello Did your shell script run? '''ATTENTION:''' Students might get FRUSTRATED when performing their '''assignment 3''' when their Bash shell scripts have errors. One major cause is the the OUTPUT of their Bash shell script when run does not '''EXACTLY match''' the required output for the '''correct''' Bash shell script. This requires that you CAREFULLY '''read''' the requirements of your Bash shell script and create it to the EXACT specifications

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/myscripts~~~uli101/week10-check-1

# 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 learn to create and run shell scripts that use '''variables''', '''positional''' and '''special parameters'''. You will also learn how to add a '''she-bang line''' at the top of a shell script to force it to run in a specified shell. Proceed to the next investigation.

# Exit your Matrix session, and log back into your Matrix session.

# Re-run the '''hello.bash''' shell script by just using the name. What did you notice? The setting of the '''PATH''' environment variable only worked in the current session only. If you exit the current Matrix session, then the recently changed settings for environment variables will be lost. You will in a future tutorial how to set environment variables in '''start-up''' files. '''ATTENTION:''' Students might get FRUSTRATED when performing their '''assignment 3''' when their Bash shell scripts have errors. One major cause is the the OUTPUT of their Bash shell script when run does not '''EXACTLY match''' the required output for the '''correct''' Bash shell script. This requires that you CAREFULLY '''read''' the requirements of your Bash shell script and create it to the EXACT specifications.

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/myscripts~~~uli101/week10-check-2 | more If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed. Unlike '''Environment variables''' that are used to set the environment of the shell or shell scripts, '''User-created''' variables are "customized" that the user can set or allow a user to set the variables' values. Let's create a Bash shell script that contain '''user-created variables'''.

# Use a text editor to create a Bash shell script called '''user-variables.bash'''

# Add the following lines to the beginning of the ''user-variables.bash'' file: #!/bin/bash read -p "Enter your Full Name: " name read -p "Enter your age (in years): " age echo "Hello $name - You are $age years old"

# 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 to run a checking script: ~~bash /home/murray.saul/myscripts~~~uli101/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.

# 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'''

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/myscripts~~~uli101/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)'''.

# Write a Bash shell script that clears the screen and displays the text Hello World on the screen. What '''permissions''' are required to run this Bash shell script? What are the different methods that you can run this Bash shell script from the command line?

# Write a Bash shell script that clears the screen, prompts the user for their '''full name''' and then prompts the user for their '''age''', then clears the screen again and welcomes the user by their name and tells them their age. What '''comments''' would you add to the above script’s contents to properly document this Bash shell script to be understood for those users that would read / edit this Bash shell script’s contents?

# Write a Bash shell script that will first set the value of a read-only variable called '''dogFactor''' to '''7'''. The script will then clear the screen and prompt the user to enter the age of a dog in human years (which will be stored into a variable called '''humanYears'''). The script will store in a variable called '''dogYears''' the value of ''humanYears x dogFactor''~~ ~~ The script will then clear the screen a second time and then display the age of the dog in ''“dog years”''. # Write a Bash shell script that will clear the screen and then display all '''arguments ''' that were entered after your Bash shell script when it was run. Also have the Bash shell script display the '''number of arguments ''' that were entered after your Bash shell script.

'''PART B: WALK-THRUS'''

</pre>

:WRITE ROUGH WORK AND OUTPUT FROM ISSUING:

:'''./walkthru1.bash'''

:ROUGH WORK:

:OUTPUT:

</pre>

:WRITE ROUGH WORK AND OUTPUT FROM ISSUING:

:'''./walkthru2.bash apple orange banana'''

:ROUGH WORK:

:OUTPUT:

:'''Walkthru #3:'''

:'''cat walkthru2.bash'''

<pre>

#!/usr/bin/bash

for x in 1 2 3 4 5

do

if [ $((x % 2)) -eq 0 ]

then

echo "this"

else

echo "that"

fi

done

</pre>

:WRITE ROUGH WORK AND OUTPUT FROM ISSUING:

:'''./walkthru3.bash apple orange banana'''

:ROUGH WORK:

:OUTPUT:

[[Category:ULI101]]

Msaul

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