Shell Scripting Interview Questions and Answers

1️⃣ List Some Commonly Used Shell Commands

Some frequently used shell commands include:

• ls – List files and directories

• cd – Change directory

• pwd – Print working directory

• mkdir – Create a new directory

• rm – Remove files or directories

• cp – Copy files or directories

• mv – Move or rename files

• cat – Display file contents

• echo – Print text to the terminal

• grep – Search for patterns in a file

• chmod – Change file permissions

• chown – Change file ownership

• ps – Display currently running processes

• kill – Terminate processes

2️⃣ Write a Shell Script to List All Processes

You can use the ps command to list processes:

bashCopyEdit#!/bin/bash

# Display all running processes
ps -f

# Print only the second column (process IDs)
ps -ef | awk '{print $2}'

3️⃣ Write a Script to Print Only Errors from a Remote Log

You can fetch a remote log file using curl and filter errors using grep:

bashCopyEditcurl -s <log_url> | grep "ERROR"

• curl fetches the log file

• grep "ERROR" filters out only the error messages

4️⃣ Write a Shell Script to Print Numbers Divisible by 3 & 5 but Not 15

bashCopyEdit#!/bin/bash

for i in {1..100}; do
    if { [ $((i % 3)) -eq 0 ] || [ $((i % 5)) -eq 0 ]; } && [ $((i % 15)) -ne 0 ]; then
        echo $i
    fi
done

• The script loops from 1 to 100.

• It checks if a number is divisible by 3 or 5 but not 15.

5️⃣ Write a Script to Count the Number of ‘S’ in "Mississippi"

bashCopyEdit#!/bin/bash

x="mississippi"
echo "$x" | grep -o "s" | wc -l

• grep -o "s" extracts all occurrences of "s".

• wc -l counts the occurrences.

6️⃣ How Do You Debug a Shell Script?

Use the set -x command to enable debugging:

bashCopyEditset -x  # Enable debugging

To disable debugging:

bashCopyEditset +x  # Disable debugging

7️⃣ What is Crontab in Linux? Example Usage?

Crontab is a scheduler that allows you to run scripts at specific times.

Example: Schedule a script to run daily at 6 PM:

bashCopyEditcrontab -e

Add the following line:

bashCopyEdit0 18 * * * /path/to/script.sh

This executes script.sh every day at 6 PM.

8️⃣ How Do You Open a File in Read-Only Mode?

Use the following command:

bashCopyEditvim -R filename.sh

• -R opens the file in read-only mode.

9️⃣ Difference Between Soft Link and Hard Link

Example Use Case:

• Soft Links: Used for pointing to configuration files, e.g., /usr/bin/python → /usr/bin/python3.

• Hard Links: Used to create backup copies of files without duplication.

🔟 break and continue Statements in Loops

• break: Exits the loop immediately.

• continue: Skips the current iteration and moves to the next.

Example:

bashCopyEdit#!/bin/bash

for i in {1..10}; do
    if [ $i -eq 5 ]; then
        break  # Stops the loop at 5
    fi
    echo "Number: $i"
done

bashCopyEdit#!/bin/bash

for i in {1..10}; do
    if [ $i -eq 5 ]; then
        continue  # Skips number 5
    fi
    echo "Number: $i"
done

1️⃣1️⃣ Disadvantages of Shell Scripting

• Slow execution: Shell scripts are slower than compiled programs.

• Limited debugging tools: Hard to trace errors compared to languages like Python.

• Portability issues: Some commands behave differently on different shells (Bash, Zsh, etc.).

• Security risks: Improperly written scripts may expose security vulnerabilities.

---

1️⃣2️⃣ Types of Loops in Shell Scripting

• For loop → Used when the number of iterations is known

• While loop → Runs while a condition is true

• Until loop → Runs until a condition becomes true

Example of a for loop:

bashCopyEditfor i in {1..5}; do
    echo "Iteration: $i"
done

1️⃣3️⃣ Is Bash Dynamically or Statically Typed? Why?

• Bash is dynamically typed because variables do not require explicit data types.

• Example:

    bashCopyEditx=5  # Integer
    x="hello"  # Now it's a string
  

  Unlike statically typed languages (C, Java), Bash does not enforce type checking.

---

1️⃣4️⃣ Explain a Network Troubleshooting Utility

One of the most common utilities is traceroute, which tracks the path packets take to a destination.

bashCopyEdittraceroute google.com

• Helps identify network latency and packet loss.

---

1️⃣5️⃣ How to Sort a List of Names in a File?

bashCopyEditsort names.txt

• Sorts names alphabetically.

• Use -r for reverse sorting:

    bashCopyEditsort -r names.txt
  

---

1️⃣6️⃣ How to Manage Large System Log Files?

1️⃣ Rotate logs automatically using logrotate:

bashCopyEditsudo nano /etc/logrotate.d/custom_log

Add:

luaCopyEdit/var/log/myapp.log {
    weekly
    rotate 4
    compress
    missingok
    notifempty
}

• Rotates logs weekly and keeps last 4 copies.

• Compresses old logs to save space.

2️⃣ Manually clear logs:

bashCopyEdit> /var/log/syslog

• This clears the log file without deleting it.

---

🚀 Conclusion

Shell scripting is an essential skill for Linux administrators, DevOps engineers, and AWS Cloud Engineers. Understanding these interview questions will help you tackle real-world challenges in automation and system administration.