Week 5 - The UNIX Shell

Question 1

What is a shell?

Answer 1

a program that runs operating system commands

Question 2

What happens when you open the shell?

Answer 2

a user-level process is started

Question 3

How does the shell create a child process?

Answer 3

by calling fork

Question 4

what does the child process invoke?

Answer 4

the loader, via execve

Question 5

What 3 open files does each process begin with?

Answer 5

standard input, output and error

Question 6

STDIN_FILENO = ?

Answer 6

0

Question 7

STDOUT_FILENO = ?

Answer 7

1

Question 8

STDERR_FILENO = ?

Answer 8

2

Question 9

Whats the chmod command format?

Answer 9

chmod [who] operator [permissions] filename

Question 10

how do you check the value of a single variable?

Answer 10

echo $VARNAME

Question 11

how do you set the value of a variable?

Answer 11

export VARNAME=x

Question 12

what does * mean in pattern matching?

Answer 12

matches any string (including null)

Question 13

what does ? mean in pattern matching?

Answer 13

matches any one character

Question 14

what does […] mean in pattern matching?

Answer 14

matches any characters enclosed in the brackets

Question 15

what does [!…] mean in pattern matching?

Answer 15

matches any characters other than the ones in the brackets

Question 16

what is the format for a grep command?

Answer 16

grep “[a,b]” input.txt

Question 17

what is a shell script?

Answer 17

a file holding a program built with shell commands

Question 18

what is $#?

Answer 18

the n umber of parameters passed to the script

Question 19

what is $0?

Answer 19

the script name

Question 20

what is $1?

Answer 20

first parameter

Question 21

what is $2?

Answer 21

second parameter

Question 22

what is $@?

Answer 22

all parameters

Question 23

what is $? ?

Answer 23

the exit value of the last command