Top 23 Shell Script Interview Questions and Answers Every Engineer Should Know

Shell scripting is a core skill for Linux system automation and is frequently tested in technical interviews.

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

A shell script is a text file containing one or more commands; it lets administrators bundle multiple commands into a single executable file to automate routine tasks.

Q2: What is the default login shell and how can it be changed for a specific user?

In most Linux distributions the default login shell is /bin/bash. The chsh command changes a user’s login shell, 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 output to the same location?

Two common methods:

Append 2>&1 to the command, e.g. ls /usr/share/doc > out.txt 2>&1 Use &> shorthand, e.g.

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

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

if [ condition ]
then
    # commands
    if [ inner_condition ]
    then
        # inner commands
    else
        # else inner
    fi
else
    # else outer
fi

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

$?

holds the exit status of the most recently executed command; 0 indicates success, any non‑zero value indicates failure.

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

Use test operators such as -gt, -lt, -eq inside an if statement:

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 $var in
    pattern1)
        # commands
        ;;
    pattern2)
        # commands
        ;;
    *)
        # default
        ;;
esac

Q11: What is the syntax of a while loop?

while [ condition ]
do
    # commands
    # ...
done

Q12: How to make a script executable?

Use chmod a+x script.sh to add execute permission.

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

The shebang tells the kernel to run the script with the /bin/bash interpreter.

Q14: What is the syntax of a for loop?

for var in list
do
    # commands
    # ...
done

Q15: How to debug a shell script?

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

Q16: How to compare strings in a shell script?

Use the test command or [ ] with operators like = and !=.

Q17: What special variables does Bash provide?

Examples include $0 (script name), $1 ‑ $9 (positional parameters), $# (argument count), and $* (all arguments as a single word).

Q18: How to test file properties?

test -d file   # true if directory
test -e file   # true if exists
test -f file   # true if regular file
test -r file   # true if readable
test -w file   # true if writable
test -x file   # true if executable

Q19: How to write comments in a shell script?

Any line beginning with # 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:

Using expr, e.g. expr 5 + 2 Using the $[ expression ] syntax, e.g.

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() {
    # commands
    return 0
}

Functions allow reusable code blocks that can be invoked by name.