Top 20 Shell Script Interview Questions and Answers Every Linux Engineer Should Know

Although Python is now common in operations, many companies still ask Linux cloud engineers about shell scripts , which help automate many tasks.

Q:1 What is a shell script and is it necessary?

A shell script is a text file containing one or more commands, allowing system administrators to bundle multiple commands into a single file for routine tasks.

Q:2 What is the default login shell and how to change a user’s login shell?

The default login shell in Linux is /bin/bash. Use the chsh command to change it, e.g.:

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

Q:3 What types of variables can be used in shell scripts?

Two types: system-defined variables (usually uppercase, viewable with set) and user-defined variables (accessed with $variable).

Q:4 How to redirect both standard output and error to the same location?

Method 1: 2>&1 # e.g., ls /usr/share/doc > out.txt 2>&1 Method 2: &> # e.g., ls /usr/share/doc &> out.txt Q:5 How to nest "if" statements in a shell script?

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

Q:6 What is the purpose of the $? variable?

It holds the exit status of the last command; 0 means success, non‑zero indicates failure.

# ls /usr/bin/shar
/usr/bin/shar
# echo $?
0

Q:7 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

Q:8 What does the break command do?

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

Q:9 What does the continue command do?

It skips the remainder of the current loop iteration and proceeds with the next iteration.

Q:10 What is the syntax of the case statement?

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

Q:11 What is the syntax of a while loop?

while [ condition ]
do
    # commands
 done

Q:12 How to make a script executable? # chmod a+x myscript.sh Q:13 What is the purpose of #!/bin/bash ?

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

Q:14 What is the syntax of a for loop?

for variable in list
 do
    # commands
 done

Q:15 How to debug a shell script?

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

Q:16 How to compare strings in a shell script?

Use the test command or [ ] with string operators.

Q:17 What special variables exist in Bourne shell (bash)?

$0   script name
$1   first argument
$2   second argument
...   
$#   number of arguments
$*   all arguments as a single word

Q:18 How to test files in a shell script?

Test   Usage
-d file   true if file exists and is a directory
-e file   true if file exists
-f file   true if file exists and is a regular file
-r file   true if file is readable
-s file   true if file is not empty
-w file   true if file is writable
-x file   true if file is executable

Q:19 How to write comments in a shell script?

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

Q:20 How to read input from the terminal in a shell script?

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

Q:21 How to unset a variable or its value? # unset <variable_name> Q:22 How to perform arithmetic operations?

Method 1: using expr: # expr 5 + 2 Method 2: using $[ expression ]: test=$[16 + 4] Q:23 What is the basic format of a do‑while loop?

do {
    # commands
} while (condition)

Q:24 How to define a function in a shell script?

diskusage () { df -h; }
# or
function func_name() { 
    # commands
    return int
}