Top 24 Shell Scripting Interview Questions Every Linux Engineer Should Know

Shell Scripting Interview Q&A

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

A shell script is a plain‑text file containing one or more commands that can be executed sequentially, allowing system administrators 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 the chsh command to change it, e.g.:

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

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

System‑defined variables (usually uppercase, viewable with set)

User‑defined variables (accessed with $VAR_NAME)

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

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

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

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

if [ condition ]
then
    command1
    command2
else
    if [ condition ]
    then
        command1
        command2
    else
        command1
        command2
    fi
fi

Q6: What does the $? variable represent?

$?

holds the exit status of the most recently executed command; 0 means success, any non‑zero 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 remainder of the current loop iteration and proceeds with the next iteration.

Q10: What is the syntax of a case statement?

case variable in
    value1)
        command1
        command2
        ;;
    value2)
        command1
        command2
        ;;
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 run the script using the /bin/bash interpreter.

Q14: What is the syntax of a for loop?

for variable in list
do
    command1
    command2
    …
    last_command
 done

Q15: How to debug a shell script?

Run the script with sh -x myscript.sh for trace output, or use sh -nv myscript.sh to check syntax without execution.

Q16: How to compare strings?

Use the test command (or [ … ]) with string operators such as = and !=.

Q17: Common special variables in Bourne shell (bash)

$0

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

Q18: How to test file attributes with test ?

-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 non‑empty -w file – true if writable -x file – true if executable

Q19: How to write comments in a 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?

Method 1 – expr: # expr 5 + 2 Method 2 – arithmetic expansion:

result=$[16 + 4]

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

do {
    commands
} while (condition)

Q24: How to define a function?

myfunc () {
    df -h
}

These questions and answers provide a solid foundation for anyone preparing for Linux shell scripting interviews.