Shell Scripting & Linux Interview Questions for DevOps Engineers | Bash Zero to Hero | #devops

Name: Shell Scripting & Linux Interview Questions for DevOps Engineers | Bash Zero to Hero | #devops
Uploaded: 2022-12-06T14:44:55.000Z
Duration: 1 h 14 min 34 s

Shell Scripting Interview Questions

Introduction to Shell Scripting Series

Abhishek introduces the third episode of his shell scripting series, focusing on interview questions.

He emphasizes the importance of watching previous videos covering basic and intermediate shell scripting concepts before tackling interview questions.

The video will cover 20 commonly asked shell scripting interview questions gathered from various sources and personal experiences.

Commonly Asked Questions in Interviews

Question 1: List Common Shell Commands

Interviewers often start by assessing candidates' understanding of shell scripting through common commands used daily.

Candidates should mention frequently used commands like ls, cp, mv, mkdir, touch, and grep.

It's advised to avoid mentioning advanced debugging commands unless relevant, as they are not typically used in day-to-day operations.

Question 2: Write a Simple Shell Script to List All Processes

This question tests practical knowledge; candidates can use the command ps -ef to list all processes running on a machine.

If asked for specific information like process IDs, candidates should explain how to filter output using tools like awk.

The explanation includes identifying fields in the output and using field separators effectively with commands.

Advanced Log Handling

Writing Scripts for Remote Logs

Abhishek discusses writing scripts that can print errors from remote logs stored in cloud services like Google Storage or S3 buckets.

How to Use Curl and Grep for Log File Analysis

Introduction to Curl and Grep

The discussion begins with the use of the curl command to retrieve output from a remote file, emphasizing that instead of fetching the entire content, one can filter specific error messages.

Filtering Output with Grep

An example is provided using curl google.com, illustrating how to obtain specific lines such as an error message or a hyperlink reference (href).

By piping (|) the output of curl into the grep command, users can isolate desired information, like error messages.

Practical Application with Log Files

A dummy log file is referenced from a Git repository for practice purposes. It contains various log types including info logs and trace logs.

To extract only trace logs from this large file, one can use curl followed by the URL and pipe it into grep with appropriate keywords.

Command Combination Explained

The combination of commands—curl, pipe (|), and grep—is highlighted as essential for efficient data retrieval in interviews or practical scenarios.

Each command has its significance:

Curl retrieves the full log file,

Grep filters out unwanted sections,

Pipe connects these commands allowing seamless data flow.

Importance of Pipe Command

Without using a pipe, executing both commands results in receiving the entire log file rather than filtered outputs. This demonstrates how critical pipes are for effective command execution.

Creating Shell Scripts for Number Filtering

Overview of Script Requirements

The task involves writing a shell script that prints numbers divisible by three and five but not fifteen. This combines multiple common programming interview questions into one exercise.

Understanding Divisibility Conditions

The question is broken down into three parts:

Numbers must be divisible by 3,

Numbers must be divisible by 5,

Numbers should not be divisible by 15.

Example Breakdown

Using numbers from 1 to 15 as an example:

Divisible by three: 3, 6, 9, 12, 15

Divisible by five: 5, 10, 15

How to Write a Shell Script for Divisibility

Understanding the Problem

The task is to write a shell script that prints numbers divisible by 3 and 5 but not by 15. The interviewer should clarify the range of numbers (e.g., from 1 to 100).

Setting Up the Script

Begin by creating a shell script file named sample_script.sh. Use a shebang (#!/bin/bash) at the top of the script.

Include metadata in your script, such as author information and purpose, although this part is skipped for brevity.

Breaking Down the Logic

Explain your approach clearly to the interviewer: identify conditions for divisibility by 3 and 5 while ensuring it’s not divisible by 15.

Clarify that you will check if numbers are divisible by both 3 and 5, while also confirming they are not multiples of 15.

Writing Conditions in the Script

Start with an if statement to check if a number is divisible by either condition using logical operators.

Implement two if conditions: one for checking divisibility by 3 and another for divisibility by 5. Use an or operator between them.

Finalizing Conditions

Add an additional condition using an and operator to ensure that numbers are not divisible by 15.

Combine these conditions logically: use && for "not divisible" checks alongside existing conditions.

Defining the Range

Use a for loop to define your range (1 to 100). This loop will iterate through each number within this specified range.

Executing and Testing the Script

Change permissions on your script using chmod +x sample_script.sh, then execute it.

How to Write a Shell Script for Counting Characters

Writing Scripts for Character Counting

The speaker encourages practicing writing scripts for various tasks, such as counting even and odd numbers or multiples of different integers. This practice helps improve scripting skills.

A specific example is given: counting the occurrences of the letter 's' in the word "Mississippi." The choice of this word is due to its complexity and common usage in interviews.

The expected output for "Mississippi" is 4 (for four 's' characters), while for "Singapore," it would be 1. This illustrates how to approach character counting in strings.

Basic Structure of a Shell Script

The script begins with a shebang (#!/bin/bash), which indicates that it should be run in a Bash shell. Starting with basic commands is emphasized during interviews.

It's important to communicate that you are using simple methods first before suggesting more efficient approaches, especially when discussing shell commands rather than programming complexities.

Using Commands Effectively

To count occurrences, define the target word (e.g., x="mississippi"). Use the grep command with options like -o to filter only instances of 's'.

The command structure involves piping output from grep into wc -l, which counts lines. This method effectively counts how many times 's' appears by treating each occurrence as a line.

Debugging Shell Scripts

To debug shell scripts, use set -x at the beginning of your script. This enables debugging mode, allowing you to trace execution step-by-step.

Understanding Cron Jobs

A cron job automates tasks at scheduled times (e.g., sending reports daily at 6 PM). It eliminates manual execution by setting up automated scripts through cron scheduling.

How to Use Vim and Understand Links in Linux

Using Vim in Read-Only Mode

To open a file in read-only mode, use the command vim -R filename, which prevents any modifications to the file.

Understanding Soft Links vs. Hard Links

In Linux, there are two types of links: soft links (symbolic links) and hard links. It's essential to understand their differences for effective file management.

When you create a file, it is saved on disk memory. If you want multiple references to this file without duplicating its content, hard links can be used instead of copying files with the cp command.

A hard link creates a mirror copy of the original file; if the original is deleted, the hard link remains intact, preserving access to the data.

Soft links point to another file's location; if the target (e.g., Python 3 executable) is deleted, accessing the soft link will fail since both reference the same memory address.

Soft links are useful for creating aliases or shortcuts (e.g., linking python to python3) but do not provide data redundancy like hard links do.

Break vs. Continue Statements in Loops

The break statement terminates loop execution immediately when a specified condition is met, while continue skips the current iteration and proceeds with the next one.

The concept of "continue" can be understood as skipping certain iterations based on conditions (e.g., ignoring multiples of 15).

For example, if searching through numbers from 1 to N and finding a specific number (like 5), using break allows immediate termination once found rather than continuing through all iterations.

In practical scenarios such as searching for a student's name in a list, using break allows stopping further processing once that name is encountered.

Disadvantages of Shell Scripting

Shell Scripting and Interview Preparation

Understanding Shell Scripting

When preparing for a Python interview, it's important to discuss real-time use cases of shell scripting. Highlight practical disadvantages such as the lack of static typing, which allows undeclared variables without compiler complaints.

Discuss different types of loops in shell scripting: for, while, and do while. Each loop serves specific purposes, and candidates should be prepared to explain their use cases.

Emphasize that understanding the purpose of each loop is crucial. This knowledge is commonly tested in interviews, so candidates should familiarize themselves with various loop types.

Typing in Programming Languages

Modern programming languages like Go are statically typed, requiring variable type definitions upfront. In contrast, languages like Python and shell scripting are dynamically typed.

In dynamic typing (e.g., shell), variables can change types without prior declaration. For instance, assigning an integer to a string variable won't raise errors until execution time.

Networking Tools for Troubleshooting

One recommended tool for network troubleshooting is traceroute. It helps identify slow network paths by showing the number of hops from your device to a destination (e.g., google.com).

The command provides insights into each hop's response time, helping diagnose where delays occur in the network path.

Another useful command is tracepath, which functions similarly but does not require root privileges. It's effective for identifying network issues without elevated permissions.

Managing System Logs

When asked about managing large log files generated daily by applications, mention using the logrotate command. This tool efficiently handles log file rotation based on defined criteria (e.g., daily rotation).

Explain that using logrotate prevents disk space issues caused by accumulating logs over time. Candidates should understand how to configure it according to application needs.

Sorting Data Efficiently

Shell Scripting and Log Management

Overview of Log File Management

The speaker discusses the process of compressing log files, mentioning various formats such as gzip, zip, and tar for creating compressed versions.

A recommendation is made to delete log files after a specified duration (30 days), emphasizing the importance of managing storage effectively.

The speaker highlights common commands related to shell scripting that are often encountered in interviews, indicating their relevance in practical applications.

Engagement with Audience

Viewers are encouraged to ask questions in the comment section, with the speaker committing to respond to each inquiry received on their videos.

A call-to-action is made for viewers to like and subscribe to the channel, promoting community engagement and support for future content.