Lect18 - Advanced Bash

Question 1

What is Bash?

Answer 1

Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been distributed widely as the default login shell for most Linux distributions and Apple’s macOS (formerly OS X). A version is also available for Windows 10

Question 2

What are environment variables?

Answer 2

Bash stores a number of variables that control the way it operates. Some are system default. Many can be set by the user to adjust the operating environment. These can be displayed with the env command.

Question 3

How can you display shell variables?

Answer 3

# echo $USER

or

# echo $LANG

Question 4

How can you assign value to custom variable?

Answer 4

# fruit=apple

then

# echo $fruit

the variable is available ONLY in the current shell.

Question 5

How can you make variable globally available?

Answer 5

# export fruit=apple

Question 6

How can you substitute the output of a command for a variable

Answer 6

md5 = $(md5sum MyEvid.raw)

Question 7

Show basic usage of a for loop?

Answer 7

$ for item in list

do

action on $item

done

Question 8

Run a command for any txt file found?

Answer 8

for x in $(find . -name ‘*.txt’)

do

file $x

done

Question 9

How can you execute multiple commands without interrupt?

Answer 9

echo 1; echo 2; echo 3;

Question 10

How can you execute multiple commands, but only if preceding command is successful?

Answer 10

echo 1 && echo 2 && echo 3

dd if=/dev/sdh of=sdh.raw && md5sum sdh.raw

Question 11

You want to view all pictures in a directory without having to use a separate command for each?

Answer 11

for pic in ./*
do
xv $pic
done