Top 24 Shell Script Interview Questions & Answers Every Linux Engineer Should Know

Shell scripting is a fundamental skill for Linux and cloud engineers, and interviewers often test candidates on it. Below are 24 common interview questions with concise answers and code examples.

Q1: What is a shell script and is it necessary?

A shell script is a text file containing one or more commands. It allows system administrators to bundle multiple commands into a single file to automate routine tasks.

Q2: What is the default login shell and how to change a user’s login shell?

The default login shell on most Linux systems is /bin/bash. Use chsh to change it:

# chsh <username> -s <new_shell>
# chsh linuxtechi -s /bin/sh

Q3: What types of variables can be used in shell scripts?

Two types of variables are used:

System-defined variables (usually uppercase, viewable with set).

User-defined variables (accessed with $variable_name).

Q4: How to redirect both standard output and error output to the same location?

Two methods:

# ls /usr/share/doc > out.txt 2>&1

# ls /usr/share/doc > out.txt

Q5: How to nest "if" statements in a shell script?

if [ condition ]
then
    # commands
else
    if [ condition ]
    then
        # commands
    else
        # commands
    fi
fi

Q6: What is the purpose of the "$?" variable?

"$?" holds the exit status of the previous command; 0 means success, any other value indicates failure.

Q7: How to compare two numbers in a shell script?

#!/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

Q8: What does the break command do?

break

exits the innermost loop (e.g., while or until).

Q9: What does the continue command do?

continue

skips the current iteration of a loop and proceeds with the next one, useful for handling errors without aborting the whole loop.

Q10: What is the syntax of a case statement?

case variable in
    value1)
        # commands
        ;;
    value2)
        # commands
        ;;
    *)
        # default commands
        ;;
esac

Q11: What is the syntax of a while loop?

while [ condition ]
do
    # commands
 done

Q12: How to make a script executable?

# chmod a+x myscript.sh

Q13: What is the purpose of "#!/bin/bash"?

This is the shebang line; it tells the system to execute the script using /bin/bash.

Q14: What is the syntax of a for loop?

for variable in list
 do
    # commands
 done

Q15: How to debug a shell script?

Run the script with sh -x myscript.sh or sh -nv myscript.sh to trace execution.

Q16: How to compare strings in a shell script?

Use the test command or [ "${str1}" = "${str2}" ] syntax.

Q17: What are some special variables in Bourne shell (bash)?

$0

– script name $1 … $9 – positional parameters $# – number of arguments $* – all arguments as a single word

Q18: How to test files in a shell script?

-d file

– true if directory -e file – true if exists -f file – true if regular file -r file – true if readable -s file – true if not empty -w file – true if writable -x file – true if executable

Q19: How to write comments in a shell script?

# This is a comment

Q20: How to read input from the terminal?

#!/bin/bash
echo "Please enter your name"
read name
echo "My Name is $name"

Q21: How to unset a variable?

# unset <variable_name>

Q22: How to perform arithmetic operations?

Two methods:

# expr 5 + 2

result=$[16 + 4]

Q23: What is the basic format of a do‑while loop?

do {
    # commands
} while (condition)

Q24: How to define a function in a shell script?

myfunc() {
    df -h
}