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Tutorial12: Shell Scripting - Part 2

12 bytes added, 10:51, 21 March 2021

→‎INVESTIGATION 2: ADDITIONAL LOOPING STATEMENTS

# '''Add execute permissions''' for this shell script and '''run Bash shell script''' What do you notice? Does the output for this shell script differ from '''for-4.bash'''? Why? We now want to introduce you to the use of '''error-checking'''.

# Use the '''more''' command to view the previously-created Bash shell script '''~/if-5.bash''' (eg. more ~/if-5.bash) Take a few moments to re-familiarize yourself with this shell script

# Run your shell script by issuing: ~/if-5.bash When prompted, enter a '''letter''' instead of a ''number''. What happens? Let's edit the '''for-5.bash''' shell script to perform '''error-checking''' to force the user to enter a numeric value between '''0 ''' and '''100'''. '''NOTE:''' The '''while''' statement can be used with the '''test''' command (or a simple linux command or a linux pipeline command) for error checking. In our case, we will use a pipeline command with extended regular expressions. In order to loop while the result is TRUE (not FALSE), you can use the negation symbol (!) to set the test condition to the opposite.

# Use a text editor like vi or nano to edit the text file called '''~/if-5.bash''' (eg. vi ~/if-5.bash)

# Add the following lines in your shell script IMMEDIATELY AFTER the read statement to prompt the user for a mark: while ! echo $mark | egrep "^[0-9]{1,}$" > /dev/null 2> /dev/null do    read -p "Not a valid number. Enter a mark (0-100): " mark done

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