2.1 Command Line Basics - Part 2

Question 1

What is a variable in bash?

Answer 1

Variables are pieces of storage for data.

Once set, a variable’s value can be accessed at a later time by calling the variable’s name

ex:

$PATH

Question 2

What are the two types of variables?

Answer 2

1. Local - which are available to the current shell processes only.
2. Environmental - which are available in both a specific shell session and in sub processes spawned from that shell session.

Programs can access environmental variables only. Environmental variables are in capital letters (e.g. PATH. USER, DATE)

Question 3

True or False: Variables persist through the closure of a shell session.

Answer 3

False - All variables and their contents are lost.

Most shells provide configuration files that contain variables which are set whenever a new shell is started.

Question 4

How do you set a local variable in bash?

Answer 4

By using the “=” operator

ex:

greeting=hello
echo greeting
hello

Question 5

Which command removes a variable in bash?

Answer 5

unset

ex:

greeting=hello
echo $greeting
hello
unset greeting
echo $greeting
[nothing gets printed]

Question 6

Which command creates an ‘environmental variable’?

Answer 6

export

ex:

export greeting=hello

(NOTE: You can use export as a command at the same time you assign the greeting variable)

Question 7

Explain the “PATH” variable in bash and why it’s important

Answer 7

The PATH variable is an environmental variable that stores a list of directories, separated by a colon, that contains executable programs eligible as commands from the Linux shell.

Any programs you want to execute within the shell must be contained within the PATH variable

Question 8

What command would you use to append a new directory to the PATH variable?

Answer 8

PATH=$PATH:new_directory

The “=” operator assigns the value to the PATH variable. The “:” operator is needed to append (instead of replacing) the existing PATH variable.

ex:

echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:
PATH=$PATH:/home/user/bin
echo $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/home/user/bin