300+ TOP Linux Shell Scripting Interview Questions and Answers

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Q1. What Is The Default Login Shell And How To Change Default Login Shell For A Specific User?

In Linux like Operating system “/bin/bash” is the default login shell which is assigned while user creation. We can change default shell using the “chsh” command.

Example is shown below:

# chsh -s

# chsh linuxtechi -s /bin/sh

Q2. How To Put Comments In Your Shell Script?

Comments are the messages to yourself and for other users that describe what a script is supposed to do and how its works. To put comments in your script, start each comment line with a hash sign (#).

Example is shown below:

#!/bin/bash

# This is a command

echo “I am logged in as $USER”

Q3. How To Compare Numbers In Linux Shell Scripting?

Test command is used to compare numbers in if-then statement.

Example is shown below:

#! /bin/bash

x=10

y=20

if [ $x -gt $y ]

then

echo “x is greater than y”

else

echo “y is greater than x”

fi

Q4. What Is The Use Of Break Command?

The break command is a simple way to escape out of a loop in progress. We can use the break command to exit out from any loop, including while and until loops.

Q5. How To Test Files In A Shell Script?

Test command is used to perform different test on the files. Basic test are listed below:

Test: Usage

  • -d file_name: Returns true if the file exists and is a directory.
  • -e file_name: Returns true if the file exists.
  • -f file_name: Returns true if the file exists and is a regular file.
  • -r file_name: Returns true if the file exists and have read permissions.
  • -s file_name: Returns true if the file exists and is not empty.
  • -w file_name: Returns true if the file exists and have write permissions.
  • –x file_name: Returns true if the file exists and have execute permissions.

Q6. What Is The Syntax Of For Loop In Shell Script?

Basic Syntax of for loop is given below:

for variables in list_of_items

do

command1

command2

….

last_command

done

Q7. Basic Syntax Of Do-while Statement?

The do-while statement is similar to the while statement but performs the statements before checking the condition statement.

The following is the format for the do-while statement:

do

{

statements

} while (condition)

Q8. How To Make A Shell Script Executable?

Using the chmod command we can make a shell script executable.

Example is shown below :

# chmod a+x myscript.sh

Q9. How To Debug A Shell Script?

A shell script can be debug if we execute the script with ‘-x’ option ( sh -x myscript.sh). Another way to debug a shell script is by using ‘-nv’ option (sh -nv myscript.sh).

Q10. How To Use Bc (bash Calculator) In A Shell Script?

Use the below Syntax to use bc in shell script.

Variable=`echo “options; expression” | bc`.

Q11. What Are The Special Variables Set By Bourne Shell For Command Line Arguments?

The following table lists the special variables set by the Bourne shell for command line arguments.

Special Variables: Holds

  • $0: Name of the Script from the command line
  • $1: First Command-line argument
  • $2: Second Command-line argument
  • …..
  • …….
  • $9: Ninth Command line argument
  • $#: Number of Command line arguments
  • $*: All Command-line arguments, separated with spaces

Q12. How Compare The Strings In Shell Script?

Test command is used to compare the text strings. The test command compares text strings by comparing each character in each string.

Q13. What Is Shell Script And Why It Is Required?

A Shell Script is a text file that contains one or more commands. As a system administrator we often need to issue number of commands to accomplish the task, we can add these all commands together in a text file (Shell Script) to complete daily routine task.

Q14. How To Perform Arithmetic Operation?

There are two ways to perform arithmetic operations:

  1. Using expr command (# expr 5 + 2).
  2. Using a dollar sign and square brackets ( $[ operation ] ) Example : test=$[16 + 4] ; test=$[16 + 4].

Q15. How To Redirect Both Standard Output And Standard Error To The Same Location?

There two methods to redirect std output and std error to the same location:

Method:1 2>&1 (# ls /usr/share/doc > out.txt 2>&1 )

Method:2 &> (# ls /usr/share/doc &> out.txt )

Q16. How To Get Input From The Terminal For Shell Script?

‘read’ command reads in data from the terminal (using keyboard). The read command takes in whatever the user types and places the text into the variable you name.

Example is shown below:

# vi /tmp/test.sh

#!/bin/bash

echo ‘Please enter your name’

read name

echo “My Name is $name”

# ./test.sh

Please enter your name

LinuxTechi

My Name is LinuxTechi

Q17. What Is The Basic Syntax Of While Loop In Shell Scripting?

Like the for loop, the while loop repeats its block of commands a number of times. Unlike the for loop, however, the while loop iterates until its while condition is no longer true.

The basic syntax is :

while [ test_condition ]

do

commands…

done

Q18. How To Define Functions In Shell Scripting?

A function is simply a block of of code with a name. When we give a name to a block of code, we can then call that name in our script, and that block will be executed.

Example is shown below:$ disk usage () { df -h ; }

Q19. What Are The Different Type Of Variables Used In A Shell Script?

In a shell script we can use two types of variables:

  • System defined variables
  • User defined variables

System defined variables are defined or created by Operating System (Linux) itself. These variables are generally defined in Capital Letters and can be viewed by “set” command.

User defined variables are created or defined by system users and the values of variables can be viewed by using the command “echo $”.

Q20. How To Unset Or De-assign Variables?

‘unset’ command is used to de-assign or unset a variable.

Syntax is shown below:

# unset

Q21. What Is The Use Of Continue Command In Shell Scripting?

The continue command is identical to break command except it causes the present iteration of the loop to exit, instead of the entire loop. Continue command is useful in some scenarios where error has occurred but we still want to execute the next commands of the loop.