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

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11. What is the output of this program?

#!/bin/sh
san_function1() {
a=5
echo "This is the first function"
san_function2
}
san_function2() {
echo "This is the second function"
san_function3
}
san_function3() {
echo "This is the third function"
}
san_function1
exit 0
a) This is the first function
This is the second function
This is the third function

b) This is the first function
This is the third function
This is the second function

c) This is the second function
This is the first function
This is the third function

d) This is the third function
This is the first function
This is the second function

a) This is the first function
This is the second function
This is the third function
Output:
root@ubuntu:/home/google# ./test.sh
This is the first function
This is the second function
This is the third function
root@ubuntu:/home/google#

12. What is the output of this program?

#!/bin/sh
echo "Just call the function"
san_function
san_function() {
echo "This is a function"
}
exit 0
a) only first string will print without any error
b) only second string will print without any error
c) both strings will print
d) none of the mentioned

d) none of the mentioned
Explanation:
Function must be defined prior to call. Hence only first string will print and program will generate an error also.
Output:
root@ubuntu:/home/globalguideline# ./test.sh
Just call the function
./test.sh: 3: san_function: not found
root@ubuntu:/home/globalguideline#

13. What is the output of this program?

#!/bin/bash
function san_function1 {
echo "This is first function"
}
san_function2() {
echo "This is second function"
}
san_function1
san_function2
exit 0
a) This is the first function
b) This is the second function
c) This is the first function
This is the second function
d) program will generate error because first function definition is not correct

c) This is the first function
This is the second function

14. What is the output of this program?

#!/bin/sh
var="google"
san_function() {
var="Linux"
echo $var
}
san_function
exit 0
a) google
b) Linux
c) command not found
d) none of the mentioned

b) Linux
Explanation:
If local variable name is same as the global variable, it overlays the variable, but only within the function.
Output:
root@ubuntu:/home/google# ./test.sh
Linux
root@ubuntu:/home/google#

15. What is the output of this program?

#!/bin/sh
san_function() {
echo "Welcome to the google"
printf "World of Linuxn"
}
unset -f san_function
san_function
exit 0
a) Welcome to the google
b) World of Linux
c) both (a) and (b)
d) nothing will print

d) nothing will print
Explanation:
Function definition was deleted before calling the function. command 'unset -f function_name' deletes the function definition.
Output:
root@ubuntu:/home/google# ./test.sh
./test.sh: 6: san_function: not found
root@ubuntu:/home/google#

16. Parameters can be passed to a function:
a) by using the parameter variables $1, $2, $3.
b) by using the environment variables
c) both (a) and (b)
d) none of the mentioned

a) by using the parameter variables $1, $2, $3.

17. What command would send the output of cmd1 to the input of cmd2?
a) cmd1 | cmd2
b) cmd1 || cmd2
c) cmd1 && cmd2
d) cmd1 ; cmd2
e) cmd1 cmd2

a) cmd1 | cmd2

18. Functions improves the shell's program-ability significantly, because:
a) when we invoke a function, it is already in the shell's memory, therefore a function runs faster than seperate scripts
b) function provides a piece of code for repetative tasks
c) both (a) and (b)
d) none of the mentioned

c) both (a) and (b)

19. The keyword 'local' is used:
a) to define a variable within a function for its local scope
b) to redefine any global variable
c) this is not a valid keyword
d) none of the mentioned

a) to define a variable within a function for its local scope

20. Which of the following command provides the list of the functions defined in the login session?
a) declare -f
b) declare -F
c) both (a) and (b)
d) none of the mentioned

c) both (a) and (b)
Explanation:
'declare -F' provides just the name of the functions and 'declare -f' provides their definitions also.

21. Which variable will display the list of the positional parameters?
a) $#
b) $*
c) $?
d) $$

b) $*

22. ? Specifies:
a) one or more character
b) zero or more charecter
c) one character
d) None of the above

c) one character

23. * Specifies:

a) one or more character
b) zero or more charecter
c) nothing
d) None of the above

b) zero or more charecter

24. When the return value of any function is not specified within the function, what function returns?
a) nothing
b) exit status of the last command executed
c) 0
d) none of the mentioned

b) exit status of the last command executed

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25. What is the output of the following command for bash shell:
echo linux $0

a) linux echo
b) linux linux
c) linux bash
d) linux

c) linux bash

26. Which of the following file set in the current directory are identified by the regular expression a?b*?
a) afcc, aabb
b) aabb, axbc
c) abbb, abxy
d) abcd, axbb

b) aabb, axbc

27. Which command can be used to test various file attributes:
a) if
b) file
c) test
d) type

c) test

28. The $ variables in a shell script context designates:
a) The runtime of the script
b) Number of command line arguments
c) PID of the shell running the script
d) The exit status of the shell script

c) PID of the shell running the script

29. Syntax to suppress the display of command error to monitor?
a) command > &2
b) command 2> &1
c) command 2> &2
d) command 2> /dev/null

d) command 2> /dev/null

30. Which variable contains last background job process id:
a) $*
b) $?
c) $$
d) $!

d) $!

31. Which variable is used to display number of arguments specified in command line:
a) $0
b) $#
c) $*
d) $?

b) $#

32. Executing cat /etc/password > /dev/sda as superuser will:
a) Write data into a regular file called /dev/sda
b) Write data to the physical device sda
c) Create a temporary file /dev/sda and write data to it
d) None of the above

b) Write data to the physical device sda

33. cat < file1 >> file2 | file3:
a) file1 content will be appended to file2 and finally stored in file3
b) file1 content will be appended to file2 and file3 will be ignored
c) file2 and file3 will have same content
d) syntax error

d) syntax error

34. Which of these is the correct method for appending "foo" in /tmp/bar file?
a) echo foo > /tmp/bar
b) echo foo >> /tmp/bar
c) echo foo | /tmp/var
d) /tmp/bar < echo foo

b) echo foo >> /tmp/bar

35. From where would the read statement read if the following statements were executed?
exec < file1
exec < file2
exec < file3
read line
a) It would read all the files
b) It would not read any files
c) It would read all the files in reverse order
d) It would read only file3

b) It would not read any files