Top 24 Shell Script Interview Questions Every Engineer Should Master

Shell scripting is a fundamental skill for Linux operations, and interviewers often test candidates with a range of practical questions.

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

A shell script is a text file that contains one or more commands. System administrators frequently combine multiple commands into a single script to automate routine tasks.

Q2: What is the default login shell and how can you change a user's login shell?

In Linux, /bin/bash is the default login shell assigned when a user is created. You can change a user's shell with the chsh command.

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

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

Shell scripts support two kinds of variables:

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

User-defined variables (accessed with $VARIABLE_NAME)

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

Two common methods:

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

&> # e.g., ls /usr/share/doc &> out.txt

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

Basic syntax:

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

Q6: What does the "$?" variable indicate?

It holds the exit status of the previously executed command; 0 means success, any non‑zero value indicates failure.

root@localhost:~# ls /usr/bin/shar /usr/bin/shar root@localhost:~# echo $? 0

root@localhost:~# ls /usr/bin/share ls: cannot access /usr/bin/share: No such file or directory root@localhost:~# echo $? 2

Q7: How do you compare two numbers in a shell script?

Use test operators such as -gt inside an if statement.

#!/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?

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

Q9: What does the continue command do?

It 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 do you make a script executable?

# chmod a+x myscript.sh

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

It is the shebang line that tells the system to execute the script using /bin/bash.

Q14: What is the syntax of a for loop?

for variable in list do command1 command2 ... done

Q15: How can you debug a shell script?

Use the -x option ( sh -x myscript.sh) or the -nv option ( sh -nv myscript.sh).

Q16: How do you compare strings in a shell script?

Use the test command (or [ ]) to compare strings character by character.

Q17: What special variables does the Bourne shell (bash) provide?

Examples include: $0 – script name $1 – first argument

… up to

$9

$#

– number of arguments $* – all arguments as a single word

Q18: How do you test files in a shell script?

Use the test command with flags such as: -d filename – true if it exists and is a directory -e filename – true if it exists -f filename – true if it exists and is a regular file -r filename – true if readable -s filename – true if not empty -w filename – true if writable -x filename – true if executable

Q19: How do you write comments in a shell script?

#!/bin/bash # This is a comment echo "I am logged in as $USER"

Q20: How can a script read input from the terminal?

# 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

Q21: How do you unset a variable or its value?

# unset <variable_name>

Q22: How can you perform arithmetic operations?

Two methods:

Using expr (e.g., expr 5 + 2)

Using the $[ expression ] syntax (e.g., test=$[16 + 4])

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

do { commands } while (condition)

Q24: How do you define a function in a shell script?

function_name() { commands; }

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