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Tutorial10: Shell Scripting - Part 1

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→‎INVESTIGATION 4: CONTROL FLOW STATEMENTS

# To generate a '''test error''', copy and paste the following '''test''' command: [$number1 -gt $number2] The reason for the error was that you need '''spaces''' between the '''square brackets''' and the '''test condition'''.

# 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~~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 statement.

# 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-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 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. '''~~Loop Statements~~LOOP STATEMENTS''' [[Image:loop-1.png|thumb|right|210px|Example of using the '''for''' looping control-flow statement.]]''A loop statement is a series of steps or sequence of statements executed repeatedly zero or more times satisfying the given condition is satisfied.'' Reference: https://www.chegg.com/homework-help/definitions/loop-statement-3

# 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

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Tutorial10: Shell Scripting - Part 1

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