Operational Linux OS Shell Interview Questions & Answers:

1. To redefine a variable, it can be removed from the list of variables by using the command:
a) unset
b) delete
c) remove
d) clear

a) unset

2. What is the output of this program?

#!/bin/bash
san_var=10
echo "the value of "san_var" is $san_var"
exit 0
a) the value of "san_var" is 10
b) the value of is 10
c) the value of san_var is $san_var
d) the value of "san_var" is $san_var

a) the value of "san_var" is 10
Output:
root@ubuntu:/home/google# ./test.sh
the value of "san_var" is 10
root@ubuntu:/home/google#

3. What is the output of this program?

#!/bin/bash
san_var=hello
readonly san_var
san_var=hi
echo $san_var
exit 0
a) hello
b) hi
c) nothing will print
d) none of the mentioned

a) hello
Explanation:
After the execution of the 'readonly' command, shell will not provide the permission to overwrite the value stored in variable 'san_var'.
Output:
root@ubuntu:/home/google# ./test.sh
./test.sh: line 4: san_var: readonly variable
hello
root@ubuntu:/home/google#

4. What is the output of this program?

#!/bin/bash
var[1]=san_1
var[2]=san_2
var[3]=san_3
echo ${var[*]}
exit 0
a) san_1
b) san_2
c) san_3
d) san_1 san_2 san_3

d) san_1 san_2 san_3
Explanation:
All items of an array can be accessed by using ${[*]} or ${[@]}.
Output:
root@ubuntu:/home/google# ./test.sh
san_1 san_2 san_3
root@ubuntu:/home/google#

5. What is the output of this program?

#!/bin/bash
var1=10
$var1=20
echo $var1
exit 0
a) program will print 10
b) program will generate a warning message
c) program will print 20
d) both (a) and (b)

d) both (a) and (b)
Explanation:
The doller sign ($) is used to access a variable's value, not to define it.
Output:
root@ubuntu:/home/google# ./test.sh
./test.sh: line 3: 10=20: command not found
10
root@ubuntu:/home/google#

6. What is the output of this program?

#!/bin/bash
san_var="google"
echo "$san_var"
echo '$san_var'
echo '"$san_var"'
echo "'$san_var'"
echo $san_var
exit 0
a) google
$san_var
"$san_var"
'google'
$san_var
b) google
google
"google"
'google'
google
c) program will generate an error message
d) program will print nothing

a) google
$san_var
"$san_var"
'google'
$san_var

Explanation:
Using double quotes does not affect the substitution of the variable, while single quotes and backslash do.
Output:
root@ubuntu:/home/google# ./test.sh
google
$san_var
"$san_var"
'google'
$san_var
root@ubuntu:/home/google#

7. In the shell, by default, all variables are considered and stored as:
a) string
b) integer
c) character
f) float

a) string

8. Which one of the following is not a valid shell variable?
a) _san
b) san_2
c) _san_2
d) 2_san

d) 2_san
Explanation:
The shell variable can contain only letters(a to z or A to Z), numbers(0 to 9), or a underscore character(_) and a variable can not start with a number.

9. Which one of the following statement is true about variables in shell?
a) variables do not require declaration before assigning value to them
b) variables are case sensitive
c) to extract the contents of a variable, we have to provide the variable a preceding $
d) all of the mentioned

d) all of the mentioned

10. Which command reads user input from the terminal and assign this value to a variable name?
a) read
b) get
c) declare
d) set

a) read