Lecture 1

Question 1

How many namespaces do operating systems like Windows and Unix have?

Answer 1

Windows can have many. i.e. C:\, D:\, etc.
Unix has 1. /

Question 2

What is a path name?

Answer 2

A description of where a file can be found.
In Unix example: dir1/dir2/dir3/file.c

Question 3

What are some special directories in the Unix root?

Answer 3

/bin
/sbin
/lib
/usr
/etc
/home
/boot
/dev
/opt
/var
/tmp
/proc

Question 4

/bin directory.

Answer 4

Where most executables or binaries are found. Things like gcc or vim. Essential for operation of the system itself.

Question 5

Home directory shorthand.

Answer 5

~/
Know this well.

Question 6

/sbin directory.

Answer 6

System binaries that should only be executed by the root (admin) user.

Question 7

/lib directory.

Answer 7

Libraries.

Question 8

/usr directory.

Answer 8

User binaries, libraries, etc. Meant for the end-user and not required for the system itself.

Question 9

/etc directory.

Answer 9

Editable Text Configurations. Where configuration files are found.

Question 10

/home directory.

Answer 10

User home (or personal) directories found here.

Question 11

/boot directory.

Answer 11

Files needed to boot the system like the operating system kernel.

Question 12

/dev directory.

Answer 12

Device files. Allows interface with I/O devices.

Question 13

/opt directory.

Answer 13

Optional software located here. Rarely used.

Question 14

/var directory.

Answer 14

Variable files that change as the system operates. Like log files.

Question 15

/tmp directory.

Answer 15

Temporary files not persistent between system reboots.

Question 16

/proc directory.

Answer 16

An imaginary directory created by the kernel to keep track of a currently running process.

Question 17

Change directory command.

Answer 17

cd

Question 18

How to go to home directory?

Answer 18

~

Question 19

What does BASH stand for?

Answer 19

Bourne Again Shell.

Question 20

General format of commands.

Answer 20

command [arg1] [arg2] … [argn] RETURN

Question 21

Two ways to get help on a command through BASH.

Answer 21

command –help
or man command

Question 22

What command is EOF?

Answer 22

ctrl+d

Question 23

Output redirection.

Answer 23

> overwrites
> appends
command [arguments] > filename

Question 24

Input redirection

Answer 24

<
command [arguments] < filename

Question 25

Pipelines (review).

Answer 25

One or more commands separated by |
Connects standard output of the command preceding the pipe symbol to standard input of the following.
command_a [arguments] | command_b [arguments]

Question 26

echo command

Answer 26

Takes input and puts it in output.

Question 27

tr command

Answer 27

tr string1 string2
It then looks for characters that match string1 and finds the corresponding in string2.

Example:
tr abc xyz
a
x
abab
xyxy

Question 28

printf command

Answer 28

Different than C function.
Can be used in pipelines to pass input.

Question 29

What is BASH scripting?

Answer 29

One or more shell commands in a text file.
Running a BASH script makes it run the commands one by one.

Everything a BASH script can do can be done in the command line, and vice versa.

This includes variables and control structures.

Question 30

First line of a BASH script.

Answer 30

!/bin/bash

Question 31

How to write comments in BASH script?

Answer 31

comment goes here

Question 32

Variables in BASH.

Answer 32

They are strings.
name=value
or
let name=value
Leave no spaces around ‘=’

Question 33

Variable reassignment in BASH.

Answer 33

Use let.
Example:
let x=x+1

Question 34

Accessing command line arguments.

Answer 34

$1 gives first positional argument (‘arg1’).

Question 35

Using if-else in BASH.

Answer 35

if test-command
then
commands
fi

or

if test-command
then
commands
else
commands
fi

Question 36

test-command in BASH

Answer 36

Example:
[ $variable conditional-operator value ]
Such as [ $1 == “apple”]
Checks if arg1 passed to the command is “apple”.

Question 37

Conditional operators in BASH

Answer 37

== equality
!= not equality
< if string1 sorts before string2 lexicographically
> opposite of <

Also,

arg1 OP arg2
If OP is one of -eq, -ne, -lt, -le, -gt, -ge, they act as equal to, not equal to, less than, and so on

Question 38

How to chain if-else statements in BASH?

Answer 38

if test-command
then
commands
elif test command
then
commands
…
else
commands
fi

Question 39

! pneumonic to remember BASH scripts.

Answer 39

!, shabang

#!/bin/bash

Question 40

While loops in BASH.

Answer 40

while test-command
do
commands
done

Question 41

How to make a bash scipt?

Answer 41

vim myscript.sh
(.sh or .bash by convention)
convert to executable by using
chmod +x myscript.sh
run using
./myscript.sh