Topic 7 - Unix Shell Environments

Question 1

HOME

Answer 1

the full path name of your home directory

Question 2

SHELL

Answer 2

the name of your login shell

Question 3

PWD

Answer 3

the full path of the current working directory

Question 4

USER

Answer 4

the user name of the logged in user

Question 5

TERM

Answer 5

the kind of terminal the user is using

Question 6

DISPLAY

Answer 6

which X server to display on

Question 7

PATH

Answer 7

the directories the shell should search to find a command

Question 8

HOST

Answer 8

the name of e the computer you are using

Question 9

REMOTEHOST

Answer 9

the name of the host logged-in from

Question 10

MANPATH

Answer 10

the directories the man command should search to find man pages

Question 11

Shell variable names can be made up of:

Answer 11

Alphabetical characters
Digits
Underscores

Question 12

Shell variable names cannot begin with:

Answer 12

a digit

Question 13

Shell variables can store either:

Answer 13

string of characters, or NULL

Question 14

Shell variables can be accessed by putting a ____ in front of ____

Answer 14

putting a $ in front of their names. e.g., echo $HOME

Question 15

Are variable names case-sensitive?

Answer 15

yes

Question 16

What are the two kinds of shell variables?

Answer 16

Environmental variables (GLOBAL) & Regular Variables (LOCAL)

Question 17

Define environmental variables

Answer 17

Affecting the current shell and the programs invoked from the shell.

Question 18

Define regular variables

Answer 18

Affecting the current shell, but not the programs invoked from the shell

Question 19

Which type of shells define their shell variables in each of the following:

• .profile
• .cshrc and .login

Answer 19

.profile = Bourne-Style shells

.cshrc and .login = C-Style shells

Question 20

C-Style Shells: How do you set a variable?

Answer 20

set varname=varvalue

Question 21

C-Style Shells: Clearing a regular (local) variable?

Answer 21

unset varname

Question 22

C-Style Shells: How do you set environment variables?

Answer 22

setenv EnvironemntVarialbe EnvironemntValue No “=” sign here!

Question 23

C-Style Shells: How do you clear environment variables?

Answer 23

unsetenv EnvironemntVariable

Question 24

C-Style Shells: How do you list all environment shell variables?
Regular shell variables?

Answer 24

1) “printing” or “env”

2) “set” without any arguments

Question 25

Bourne-Style Shells: How do you set a regular (local) variable?

Answer 25

varname=varvalue (there is no “set” here - also, no spaces before / after “=” !!!)

Question 26

Bourne-Style Shells: How do you clear regular (local) variable?

Answer 26

unset varname (same as C-Style Shell)

Question 27

Bourne-Style Shells: How do you set an environmental variable?

Answer 27

Same as local variable (EnvironmentVariable = EnviromentValue)
Then, use “export EnvironmentVariable”

Question 28

Bourne-Style Shells: How do you clear an environmental variable?

Answer 28

unset EnvironmentVaraible (only ‘unset’ - same as regular variables)

Question 29

Bourne-Style Shells: How do list all local variables? Environmental variables?

Answer 29

“set” - lists ALL existing local AND enviro variables

“print env or just env” will list ONLY enviro (exported) shell variables

Question 30

Once a variable is exported, the only way to stop the export effect is to _____

Answer 30

“unset” the variable

Question 31

The shell searches in each directory of $Path how?

Answer 31

In left to right order and executers the first version.

Question 32

What does “which” cmd do?

Answer 32

locates a unix command and displays its pathname or alias

Question 33

What does .login do?

Answer 33

Runs once when you log in: contains one-time things like terminal setup

Question 34

What does .cshrc do?

Answer 34

Runs before the execution of any [t]csh process: Sets lots of variables, e.g., PATH, MANPATH etc.

Question 35

In C-Style shells, what does “history” cmd do?

Answer 35

Displays the command history list with line numbers

Question 36

List the ways to rerun a command line in the history:

Answer 36

1) !! - reruns last command
2) !str - returns the latest command beginning with str
3) !n - where n is a number; reruns command number n in the history list

Question 37

The variable savehist determines:

Answer 37

How much history to be saved in the file name histfile for your next session;

Question 38

Where are savehist and hostile variables likely to be set?

Answer 38

In C-Style shells: in your .cshrc file. Example:
set history=24
set savehist=10
set histfile=$home/.history.$HOSTTYPE

Question 39

What is the “alias” cmd syntax?

Answer 39

alias alias-name real-command

Question 40

Can you put your aliases in your .cshrc file?

Answer 40

Yes

Question 41

Can you display the alias of a command using the which command?

Answer 41

Yes.

Question 42

What does the alias command without any arguments do?

Answer 42

Lists ALL existing aliases.

Question 43

How do you delete alias(s)?

Answer 43

Using the “unalias” cmd: unalias alias-anem

Question 44

C-Style shells has command and filename completion where you can let the shell complete a long command name - how do you use this feature?

Answer 44

Type a prefix of a command (only the first few letters), then hit the TAB key: the shell will fill in the rest for you, if possible. Same with filenames.