Week 10: Shell Environments / Programming / Makefiles

Question 1

The shell environment consists of a set of _____ with _____

Answer 1

Variables with values

Question 2

Shell variables are used by putting _ in front of their names

Answer 2

$ in front of their names:

$HOME

Question 3

The two kinds of shell variables are:

Answer 3

Environment variables: available in the current shell and the programs invoked by the shell

Regular shell variables: not available by programs invoked in this shell

Question 4

In bash, REGULAR variables are defined by:

Answer 4

varname=varvalue

Question 5

In bash, environment variables are called

Answer 5

“exported variables”

Question 6

Environment variables are defined by:

Answer 6

MYENVVAR=”env var”
export MYENVVAR

or

export MYENVVAR=”env var”

Question 7

To clear an environment variable, simply use…

Answer 7

unset

ex: unset varname;

Question 8

In csh and tcsh to create REGULAR variables, use…
To delete them….

Answer 8

set

ex: set VARNAME=”var”

unset

ex: unset VARNAME

Question 9

In csh and tcsh to create environment variables, use

Answer 9

setenv WITH NO EQUALS SIGN

ex: setenv VARNAME “var”

unsetenv

ex: unsetenv VARNAME

Question 10

What do the following shell variables mean:

SHELL
PATH
LANG
USER
HOME
TERM
DISPLAY
HOSTNAME

Answer 10

SHELL: the name of the shell being used

PATH: where to find executables to execute

LANG: the locale you are using

USER: the user name of the user logged in

HOME: the user’s home directory

TERM: the kind of terminal the user is using

DISPLAY: where X program windows are shown

HOSTNAME: the name of the host logged on to

Question 11

In UNIX, single quotes do what

Answer 11

Stop the expansion of a variable:

echo “Welcome $HOME”
Welcome /home/Connor

echo ‘Welcome $HOME’
Welcome $HOME

Question 12

In UNIX, backwards quotes do what

Answer 12

Replace the variable with what is returned from the execution of the command

Question 13

Unix automatically searches for executables in…

Answer 13

Whatever is specified by the variable PATH

Question 14

In Unix, do executables automatically execute from the current durectory?

Answer 14

NO

use: ./ to specify the current directory using the .

Question 15

If there are multiple versions of a command, Unix executes them in the order of …

Answer 15

Left to right

Question 16

How does the alias command work, syntax?

Answer 16

alias alias-name=’real-command’

Where alias-name is one word and real-command can be separated by spaces

Question 17

A shell script is basically

Answer 17

A UNIX file with shell commands in it

Question 18

Why write shell scripts?

Answer 18

To automate difficult processes
and to avoid repetition

Question 19

In order to run a shell script, you must first

Answer 19

chmod the files in order to make them executable

chmod u+x myencrypt mydecrypt

Question 20

The syntax of a for loop in bash is:

Answer 20

for var in value1 value2 …
do
command_set
done

Question 22

The syntax of an if statement in bash is

Answer 22

if

then

…

fi

Question 23

An if, elif script looks like…

Answer 23

Question 24

Semicolons in scripts are used to…

Answer 24

Seperate statements on the same line:

if grep “UNIX” myfile; then echo “Got it”; fi

Question 25

A colon in shell scripts are meant for…

Answer 25

nothing, they do nothing

Question 26

What is the syntax of the test command?

Answer 26

test -(file type) file

test –f file does file exist and is a regular file?

test -d file does file exist and is a directory?

test –x file does file exist and is executable?

test –s file does file exist and is longer than 0 bytes?

Question 27

What does “test -d” do?

Answer 27

Does the file exist and is it a directory?

Question 28

What does “test -r” do?

Answer 28

Does the file exist and is it a regular file?

Question 29

What does “test -x” do?

Answer 29

Does the file exist and is it an executable?

Question 30

What does test -s do?

Answer 30

Does the file exist and is it longer than 0 bytes?

Question 31

What are the three types of string tests?

Answer 31

test -z

• Test whether or not the string has 0 characters in it

test str1 = str2

• Is str1 equal to str2

test str != str2

• Not equal?

Question 32

What are the following options for integer tests?

-eq, -ne, -lt, -le, -gt, -ge

Answer 32

-eq, -ne, -lt, -le, -gt, -ge

equal, not equal, less than, less than or equal to, greater than, greater than or equal to

Question 33

In shell scripts, how many command line arguments can be taken?

Answer 33

$1 up to $9

Question 34

In unix shell commands, the shift command…

Answer 34

Shifts all the command arguments to the left

Question 35

In shell scripts, the read command…

Answer 35

Reads iput from the terminal:

read var1 var2 var3

Action: reads a line of input from standard input

Assign first word to var1, second word to var2, …

The last variable gets any excess words on the line.

Question 36

In shell scripts, the case syntax is in the form of…

Answer 36