Unix Assignment 1. Explain the difference between && and ||. 2. What command can

Question

Unix Assignment

1. Explain the difference between && and ||.

2. What command can be used to take the place of several nested if statements in a bash shell script

3. What command ends every do loop in a while…do statement? What command ends an until…do statement?

4. Write a script that checks the user’s home directory for a file named hw5file. Assuming it’s present, append the file with, “Today’s date is mm/dd/yy”. If you can’t locate the file hw5file, then create it and store, “This is username on computer_name making my first entry.”

Explanation / Answer

1. && is AND operator. This operator is used when we want some statements to be executed only when all the required conditions are satisfied. So even if one conditions fails, the statements will not be executed if we use && operator.

|| is OR operator. This operator is used when we want some statements to be executed if at least one of the conditions is statisfied. So if we use || operator, then even if many conditions fail, but if there is at least one condition that is satisfied, statements will be executed.

2. Nested if statements can be replaced by case statements. For example:

#!/bin/bash

# case example

case $1 in

apple)

echo apple

;;

orange)

echo orange

;;

banana)

echo banana

;;

*)

echo unknown

;;

esac

3. Both while...do and until...do statements end with the command "done".

Syntax of do...while loop is:

while
do
   statement 1
   statement 2
   statement 3
   ...
   statement n
done

And syntax for until...do loop is:

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