Chapter 19. An Introduction to Bash Shell Scripting

Question 1

What is the effect if a script does not start with a shebang?

Answer 1

The script will be interpreted by the same shell as the parent shell.

Question 2

How can you check if a variable VAR has no value?

Answer 2

test -z $VAR or [ -z $VAR ] can be used to check whether a variable VAR has no value.

Question 3

What would you use in a script to count the number of arguments that have been used?

Answer 3

Use $# to count the number of arguments that have been used.

Question 4

What would you use to refer to all arguments that have been used when starting the script?

Answer 4

Use $@ to refer to all arguments that have been used when starting the script.

Question 5

How do you process user input in a script?

Answer 5

Use “read SOMEVAR” to process user input in a script.

Question 6

What is the simplest way to test whether a file exists and execute the command echo “file does not exist” if it does not?

Answer 6

”[ -f filename ] || echo file does not exist” determines whether the file exists and, if not, executes the specified command.

Question 7

Which test would you perform to find out if an item is a file or a directory?

Answer 7

[ -e filename ] can be used to determine whether an item is a file or a directory.

Question 8

Which construction would you use to evaluate a range of items?

Answer 8

A for statement is typically used to evaluate a range of items.

Question 9

How do you close an elif statement in a script?

Answer 9

You do not; it is a part of the if statement that is closed with fi.

Question 10

In a case statement, you evaluate a range of items. For each of these items you execute one or more commands. What do you need to use after the last command to close the specific item?

Answer 10

Using ;; after the last command closes the specific item.