DEV Community: Mohammad Ridowan Sikder

Git for DevOps: The Essential Guide to Version Control

Mohammad Ridowan Sikder — Sun, 19 Oct 2025 11:09:03 +0000

Welcome back to the No BS DevOps: Zero to One series. In our first post, we established the foundation with Linux and networking fundamentals. Now, we're diving into the next essential pillar for any DevOps engineer: version control with Git.

Core Git Workflow

Understanding the basic Git workflow is crucial:

Working Directory → git add → Staging Area → git commit → Local Repository → git push → Remote Repository

Why the Staging Area?

The staging area acts as a buffer between your working directory and commits. This allows you to:

Review changes before committing
Stage only specific files or parts of files
Create focused, logical commits

Essential Commands

# Check status of working directory and staging area
git status

# View commit history
git log
git log --oneline --graph  # Compact view with branch visualization

# Configure Git (do this once)
git config --list
git config --global user.name "Your Name"
git config --global user.email "your.email@example.com"

Repository Setup

Connecting Local to Remote

# Add remote repository
git remote add origin git@gitlab.com:username/repository.git

# Push and set upstream tracking
git push --set-upstream origin master

Branching Strategies

Feature vs Trunk-Based Development

Feature-Based (Traditional):

Create separate branches for each feature/bugfix
Merge back to main branch via pull requests
Good for larger teams, complex features

Trunk-Based (Modern DevOps):

Work directly on main branch or very short-lived branches
Frequent small commits
Enables faster CI/CD cycles
Requires good testing practices

Branch Operations

# Switch to existing branch
git checkout branch_name

# Create and switch to new branch
git checkout -b branch_name

# Push new branch to remote
git push --set-upstream origin branch_name

# Delete local branch after merge
git branch -d branch_name

Handling Changes and Conflicts

Pulling Changes

When someone else pushes changes:

# Standard pull (creates merge commit)
git pull

# Rebase pull (cleaner history, no merge commit)
git pull -r

Merge Conflicts

When Git can't automatically merge changes:

Git marks conflicted files
Manually edit files to resolve conflicts
Stage resolved files: git add conflicted_file
Continue rebase: git rebase --continue
Push changes: git push

Pull/Merge Requests

Essential for code review and collaboration:

Purpose: Request to merge one branch into another
Process: Create → Review → Approve → Merge
Benefits: Code review, discussion, quality control

Managing Files

.gitignore

Exclude files/directories from version control:

# Create .gitignore file
echo ".idea/" >> .gitignore
echo "*.log" >> .gitignore

# Remove already tracked files
git rm -r --cached .idea
git commit -m "Remove .idea from tracking"

Temporary Storage

# Temporarily store changes
git stash

# Retrieve stashed changes
git stash pop

Viewing History and Navigation

# View commit history with graph
git log --oneline --graph

# Go to specific commit (detached HEAD)
git checkout commit_hash

# Return to latest commit
git checkout branch_name

Undoing Changes

Local Changes (Use Carefully)

# Undo last commit, keep changes in working directory
git reset --soft HEAD~1

# Undo last commit, discard changes completely
git reset --hard HEAD~1

# Modify last commit (add changes or fix message)
git add .
git commit --amend

Remote Changes (When Working Alone)

# Remove commit from remote (dangerous!)
git reset --hard HEAD~1
git push --force

Safe Undoing (Team Environment)

# Create new commit that undoes previous commit
git revert commit_hash

Rule of Thumb: Use reset when working alone, use revert when working in a team.

Branch Merging

# Merge source_branch into current branch
git checkout target_branch
git merge source_branch

Key Takeaways for DevOps

Infrastructure as Code: Your Terraform files, Ansible playbooks, and Kubernetes manifests should live in Git
Automation Scripts: Python scripts, shell scripts, and other automation tools need version control
CI/CD Integration: Build systems need to interact with Git repositories
Collaboration: Even infrastructure changes need code review through pull requests
Rollback Capability: Git history allows you to rollback infrastructure changes safely

Best Practices

Write descriptive commit messages
Commit small, related changes together
Pull frequently to stay in sync
Don't push directly to main/master branch
Use meaningful branch names: feature/user-auth, bugfix/memory-leak
Set up proper .gitignore files for your projects
Use git pull -r to maintain clean history

Git Commands Cheat Sheet

Git Configuration

Command	Description
`git config --global user.name <name>`	Define the author name to be used for all commits by the current user
`git config --global user.email <email>`	Define the author email to be used for all commits by the current user
`git config --global alias.<alias-name> <git-command>`	Create shortcut for a Git command. E.g. alias glog "log --graph --oneline"
`git config --system core.editor <editor>`	Set text editor used by commands for all users on the machine
`git config --global --edit`	Open the global configuration file in a text editor for manual editing

Git Basics

Command	Description
`git init <directory>`	Create empty Git repo in specified directory. Run with no arguments to initialize the current directory as a git repository
`git clone <repo>`	Clone repo located at `<repo>` onto local machine. Original repo can be located on the local filesystem or on a remote machine via HTTP or SSH
`git add <directory>`	Stage all changes in `<directory>` for the next commit. Replace `<directory>` with a `<file>` to change a specific file
`git commit -m "<message>"`	Commit the staged snapshot, but instead of launching a text editor, use `<message>` as the commit message
`git status`	List which files are staged, unstaged, and untracked
`git log`	Display the entire commit history using the default format. For customization see additional options
`git diff`	Show unstaged changes between your index and working directory

Git Branches

Command	Description
`git branch`	List all of the branches in your repo. Add a `<branch>` argument to create a new branch with the name `<branch>`
`git checkout -b <branch>`	Create and check out a new branch named `<branch>`. Drop the -b flag to checkout an existing branch
`git merge <branch>`	Merge `<branch>` into the current branch

Git Log Options

Command	Description
`git log --limit=<limit>`	Limit number of commits by `<limit>`. E.g. "git log -5" will limit to 5 commits
`git log --oneline`	Condense each commit to a single line
`git log -p`	Display the full diff of each commit
`git log --stat`	Include which files were altered and the relative number of lines that were added or deleted from each of them
`git log --author="<pattern>"`	Search for commits by a particular author
`git log --grep="<pattern>"`	Search for commits with a commit message that matches `<pattern>`
`git log <since>..<until>`	Show commits that occur between `<since>` and `<until>`. Args can be a commit ID, branch name, HEAD, or any other kind of revision reference
`git log -- <file>`	Only display commits that have the specified file
`git log --graph --decorate`	--graph flag draws a text based graph of commits on left side of commit msgs. --decorate adds names of branches or tags of commits shown

Git Diff

Command	Description
`git diff HEAD`	Show difference between working directory and last commit
`git diff --cached`	Show difference between staged changes and last commit

Git Reset

Command	Description
`git reset`	Reset staging area to match most recent commit, but leave the working directory unchanged
`git reset --hard`	Reset staging area and working directory to match most recent commit and overwrites all changes in the working directory
`git reset <commit>`	Move the current branch tip backward to `<commit>`, reset the staging area to match, but leave the working directory alone
`git reset --hard <commit>`	Same as previous, but resets both the staging area & working directory to match. Deletes uncommitted changes, and all commits after `<commit>`

Git Rebase

Command	Description
`git rebase -i <base>`	Interactively rebase current branch onto `<base>`. Launches editor to enter commands for how each commit will be transferred to the new base

Git Pull

Command	Description
`git pull --rebase <remote>`	Fetch the remote's copy of current branch and rebases it into the local copy. Uses git rebase instead of merge to integrate the branches

Git Push

Command	Description
`git push <remote> --force`	Forces the git push even if it results in a non-fast-forward merge. Do not use the --force flag unless you're absolutely sure you know what you're doing
`git push <remote> --all`	Push all of your local branches to the specified remote
`git push <remote> --tags`	Tags aren't automatically pushed when you push a branch or use the --all flag. The --tags flag sends all of your local tags to the remote repo

Undoing Changes

Command	Description
`git revert <commit>`	Create new commit that undoes all of the changes made in `<commit>`, then apply it to the current branch
`git reset <file>`	Remove `<file>` from the staging area, but leave the working directory unchanged. This unstages a file without overwriting any changes
`git clean -n`	Shows which files would be removed from working directory. Use the -f flag in place of the -n flag to execute the clean

Rewriting Git History

Command	Description
`git commit --amend`	Replace the last commit with the staged changes and last commit combined. Use with nothing staged to edit the last commit's message
`git rebase <base>`	Rebase the current branch onto `<base>`. `<base>` can be a commit ID, branch name, a tag, or a relative reference to HEAD
`git reflog`	Show a log of changes to the local repository's HEAD. Add --relative-date flag to show date info or --all to show all refs

Remote Repositories

Command	Description
`git remote add <name> <url>`	Create a new connection to a remote repo. After adding a remote, you can use `<name>` as a shortcut for `<url>` in other commands
`git fetch <remote> <branch>`	Fetches a specific `<branch>` from the repo. Leave off `<branch>` to fetch all remote refs
`git pull <remote>`	Fetch the specified remote's copy of current branch and immediately merge it into the local copy
`git push <remote> <branch>`	Push the branch to `<remote>`, along with necessary commits and objects. Creates named branch in the remote repo if it doesn't exist

Linux Fundamentals for DevOps

Mohammad Ridowan Sikder — Mon, 13 Oct 2025 18:38:39 +0000

This is the start of a series where I'll share everything I'm learning about DevOps technologies. Understanding the basics of Linux is essential for anyone in DevOps, so this guide will serve as the foundation for all the upcoming posts.

Linux File System Structure

Understanding the Linux filesystem hierarchy is crucial for DevOps work. Here's the essential directory structure:

/
├── home/          # User home directories
├── root/          # Root user's home directory
├── bin/           # Essential system binaries
├── sbin/          # System administration binaries
├── lib/           # Shared libraries for system programs
├── usr/           # User programs and data
│   ├── bin/       # User binaries
│   ├── sbin/      # Non-essential system binaries
│   ├── lib/       # Libraries for user programs
│   └── local/     # Locally installed software
├── etc/           # Configuration files
├── opt/           # Optional/third-party software
├── tmp/           # Temporary files
├── boot/          # Boot loader files
├── dev/           # Device files
├── var/           # Variable data (logs, cache, etc.)
│   ├── log/       # System and application logs
│   └── cache/     # Application cache data
├── media/         # Removable media mount points
└── mnt/           # Temporary mount points

Why does /usr duplicate directories? Historical reasons. Originally, /usr was a separate partition for user data. Over time, it became a secondary hierarchy for non-essential programs.

Essential CLI Commands

Master these commands for efficient system navigation and administration:

System Information

# CPU information
lscpu

# Memory information
lsmem

# Complete system information
uname -a

# OS release information
cat /etc/os-release

Navigation and History

# Reverse search through command history
Ctrl+R

# Execute command by history number
!123

# List files recursively
ls -R

User Management

# Switch to specific user (with environment)
su - username

# Switch to root user
su -

# Add new user (interactive)
sudo adduser username

# Add new group
sudo addgroup groupname

Package Management

Ubuntu uses multiple package management systems:

APT (Advanced Package Tool)

# Search for packages
apt search packagename

# Install package
sudo apt install packagename

# Remove package
sudo apt remove packagename

# Package sources configuration
/etc/apt/sources.list

APT vs APT-GET: apt is newer, more user-friendly, and combines common apt-get and apt-cache functions.

Alternative Installation Methods

Ubuntu Software Center: GUI package manager
Snap packages: Universal Linux packages
PPA (Personal Package Archives): Third-party repositories

# Add PPA repository
sudo add-apt-repository ppa:repository-name

# Install snap package
sudo snap install packagename

Vim Text Editor

Essential for editing configuration files on servers:

Basic Operations

Command	Action
`i`	Enter insert mode
`Esc`	Exit insert mode
`:wq`	Save and quit
`:q!`	Quit without saving

Text Manipulation

Command	Action
`dd`	Delete current line
`d10d`	Delete 10 lines
`u`	Undo last change
`2u`	Undo last 2 changes

Navigation

Command	Action
`A`	Go to end of line (insert mode)
`0`	Go to beginning of line
`$`	Go to end of line
`10G`	Go to line 10

Search and Replace

/searchterm     # Search forward
n               # Next match
N               # Previous match

:%s/old/new     # Replace first occurrence in each line
:%s/old/new/g   # Replace all occurrences
:%s/old/new/gc  # Replace all with confirmation

User Accounts and Groups

User Types

Root user: System administrator (UID 0)
Regular users: Standard user accounts (UID 1000+)
Service users: System service accounts (UID < 1000)

User Management Commands

# View user information
cat /etc/passwd

# Change password
passwd username

# Add user to group
usermod -aG groupname username

# View user's groups
groups username

# Remove user from group
sudo gpasswd -d username groupname

Group Management

# View all groups
cat /etc/group

# Change user's primary group
usermod -g groupname username

# Add user to multiple groups
usermod username -G group1,group2

File Ownership and Permissions

Understanding Permissions

ls -l filename
# Output: -rwxrw-r-- owner group
#         │││││││││
#         │││└┴┴┴┴┴─ Others permissions (r--)
#         ││└┴┴─────── Group permissions (rw-)
#         │└────────── Owner permissions (rwx)
#         └─────────── File type (- for file, d for directory)

Changing Ownership

# Change owner and group
chown username:groupname filename

# Change only owner
chown username filename

# Change only group
chgrp groupname filename

Changing Permissions

Symbolic Method

chmod u+x filename    # Add execute for owner
chmod g-w filename    # Remove write for group
chmod o+r filename    # Add read for others
chmod a+x filename    # Add execute for all

Numeric Method

Permission	Value
Read (r)	4
Write (w)	2
Execute (x)	1

# rwx = 4+2+1 = 7
chmod 755 filename    # rwxr-xr-x
chmod 644 filename    # rw-r--r--

Pipes and Redirection

Standard Streams

stdin (0): Standard input
stdout (1): Standard output
stderr (2): Standard error

Common Operations

# Pipe output to less for pagination
history | less

# Search through command output
history | grep "sudo"

# Redirect output to file (overwrite)
history | grep sudo > commands.txt

# Redirect output to file (append)
history | grep sudo >> commands.txt

Less Navigation

Key	Action
`Space`	Next page
`b`	Previous page
`q`	Quit

Shell Scripting Basics

Script Structure

#!/bin/bash

# Variables
file_name=config.yaml
echo "Processing $file_name"

# Command substitution
config_files=$(ls config)

Conditional Statements

# Directory check
if [ -d "config" ]; then
    echo "Directory exists"
else
    echo "Creating directory"
    mkdir config
fi

# File check
if [ -f "config.yaml" ]; then
    echo "File exists"
fi

# Numeric comparisons: -eq, -ne, -gt, -ge, -lt, -le
if [ $num -eq 10 ]; then
    echo "Number is 10"
fi

# String comparisons
if [ "$var" == "string" ]; then
    echo "Strings match"
fi

Script Parameters and User Input

# Script parameters
first_param=$1
second_param=$2
all_params=$*
param_count=$#

# User input
read -p "Enter value: " user_input
echo "You entered: $user_input"

Loops

# For loop
for param in $*; do
    echo $param
done

# While loop
sum=0
while true; do
    read -p "Enter number (q to quit): " input
    if [ "$input" == "q" ]; then
        echo "Sum: $sum"
        break
    fi
    sum=$(($sum + $input))
done

Functions

# Simple function
function process_file() {
    echo "Processing $1"
    return 0
}

# Call function
process_file "config.yaml"
result=$?  # Get return value

Environment Variables

Viewing Variables

# List all environment variables
printenv | less

# View specific variable
printenv USER
echo $USER

# Search for variables
printenv | grep USER

Setting Variables

# Temporary (current session only)
export MY_VAR="value"

# Permanent (user-specific)
echo 'export MY_VAR="value"' >> ~/.bashrc
source ~/.bashrc

# System-wide
sudo echo 'MY_VAR="value"' >> /etc/environment

PATH Management

# Add directory to PATH
export PATH=$PATH:/custom/location

# Make permanent
echo 'export PATH=$PATH:/custom/location' >> ~/.bashrc

Networking Fundamentals

Network Components

LAN: Local Area Network (switch)
WAN: Wide Area Network (router/gateway)
Subnet: Network segment with same IP range
CIDR: Classless Inter-Domain Routing notation

IP Addressing

192.168.1.0/24
│          │
│          └─ Subnet mask (255.255.255.0)
└─ Network address

Network Services

NAT: Network Address Translation
DNS: Domain Name System
Firewall: Network security filtering
Port: Communication endpoint

Network Commands

# Network interface information
ifconfig
ip addr show

# Network connections
netstat -tulpn

# DNS lookup
nslookup domain.com

# Test connectivity
ping hostname

# Running processes
ps aux

SSH (Secure Shell)

Key-Based Authentication Setup

Generate key pair on client:

ssh-keygen -t rsa
# Creates ~/.ssh/id_rsa (private) and ~/.ssh/id_rsa.pub (public)

Copy public key to server:

# Method 1: Manual copy
cat ~/.ssh/id_rsa.pub
# Paste into ~/.ssh/authorized_keys on server

# Method 2: Using ssh-copy-id
ssh-copy-id username@hostname

SSH Usage

# Connect with password
ssh username@hostname

# Connect with specific key
ssh -i ~/.ssh/id_rsa username@hostname

# Copy files over SSH
scp localfile username@hostname:/remote/path
scp username@hostname:/remote/file ./local/path

SSH Security Best Practices

Use key-based authentication over passwords
Keep private keys secure (600 permissions)
Use strong passphrases for keys
Disable root SSH access in production

Introduction to MongoDB Aggregation Pipelines

Mohammad Ridowan Sikder — Wed, 22 Jan 2025 07:15:34 +0000

MongoDB aggregation pipelines provide a robust and versatile way to work with your data. They allow to transform, filter, and group information stored in collections seamlessly. By chaining together a series of stages, each performing a specific operation, we can manipulate the data and uncover valuable insights efficiently.

Schema Overview

Users Collection

{
  "_id": { "$oid": "678e6ac8ba2404dd3d61fe7e" },
  "index": 0,
  "name": "Aurelia Gonzales",
  "isActive": false,
  "registered": { "$date": "2015-02-11T04:22:39.000Z" },
  "age": 20,
  "gender": "female",
  "eyeColor": "green",
  "favoriteFruit": "banana",
  "company": {
    "title": "YURTURE",
    "email": "aureliagonzales@yurture.com",
    "phone": "+1 (940) 501-3963",
    "location": {
      "country": "USA",
      "address": "694 Hewes Street"
    }
  },
  "tags": ["enim", "id", "velit", "ad", "consequat"]
}

Authors Collection

{
  "_id": 100,
  "name": "F. Scott Fitzgerald",
  "birth_year": 1896
}

Books Collection

{
  "_id": 1,
  "title": "The Great Gatsby",
  "author_id": 100,
  "genre": "Classic"
}

Aggregation Examples

1. How Many Active Users Are There?

[
  { "$match": { "isActive": true } },
  { "$count": "activeUsers" }
]

Explanation:

$match: Filters documents to include only those where isActive is true.
$count: Counts the resulting documents and outputs the count as activeUsers.

2. Average Age of Users

[
  { "$group": { "_id": null, "avgAge": { "$avg": "$age" } } }
]

Explanation:

$group: Groups all documents together (_id: null) and calculates the average age using $avg.

3. Average Age of Males and Females

[
  { "$group": { "_id": "$gender", "avgAge": { "$avg": "$age" } } }
]

Explanation:

$group: Groups documents by gender and calculates the average age for each group.

4. Top 5 Most Common Fruits

[
  { "$group": { "_id": "$favoriteFruit", "users": { "$sum": 1 } } },
  { "$sort": { "users": -1 } },
  { "$limit": 5 }
]

Explanation:

$group: Groups documents by favoriteFruit and counts users for each fruit.
$sort: Sorts the fruits by user count in descending order.
$limit: Limits the result to the top 5 fruits.

5. Total Number of Males and Females

[
  { "$group": { "_id": "$gender", "users": { "$sum": 1 } } }
]

Explanation:

$group: Groups documents by gender and counts the number of users in each group.

6. Country with the Most Registered Users

[
  { "$group": { "_id": "$company.location.country", "users": { "$sum": 1 } } },
  { "$sort": { "users": -1 } },
  { "$limit": 1 }
]

Explanation:

$group: Groups documents by country and counts the number of users.
$sort: Sorts by user count in descending order.
$limit: Outputs the country with the highest user count.

7. List All Unique Eye Colors and Their Count

[
  { "$group": { "_id": "$eyeColor" } },
  { "$count": "uniqueEyeColors" }
]

Explanation:

$group: Groups documents by unique eyeColor values.
$count: Counts the unique eye colors.

8. Average Number of Tags per User

Using `$unwind`:

[
  { "$unwind": "$tags" },
  { "$group": { "_id": "$_id", "numberOfTags": { "$sum": 1 } } },
  { "$group": { "_id": null, "avgTags": { "$avg": "$numberOfTags" } } }
]

Explanation:

$unwind: Deconstructs the tags array, creating a document for each tag.
$group: First groups by user (_id) to count tags per user, then calculates the average tag count across all users.

Using `$addFields`:

[
  { "$addFields": { "numberOfTags": { "$size": "$tags" } } },
  { "$group": { "_id": null, "avgTags": { "$avg": "$numberOfTags" } } }
]

Explanation:

$addFields: Adds a field numberOfTags containing the size of the tags array for each user.
$group: Calculates the average of numberOfTags across all users.

9. Users with a Specific Tag

Users with the Tag `enim`:

[
  { "$match": { "tags": "enim" } },
  { "$count": "NumberOfUsers" }
]

Explanation:

$match: Filters users whose tags array contains enim.
$count: Counts these users.

Users Who Are Inactive and Have the Tag `velit`:

[
  { "$match": { "isActive": false, "tags": "velit" } },
  { "$project": { "name": 1, "age": 1 } }
]

Explanation:

$match: Filters users who are inactive and have velit in their tags array.
$project: Selects and outputs only the name and age fields.

10. Users with Phone Numbers Starting with "+1 (940)"

[
  { "$match": { "company.phone": { "$regex": "^\\+1 \\\(940\\)" } } },
  { "$count": "numberOfUsers" }
]

Explanation:

$match: Filters users whose phone numbers start with +1 (940) using a regular expression.
$count: Counts the resulting users.

11. User Registered Most Recently

[
  { "$sort": { "registered": -1 } },
  { "$limit": 1 }
]

Explanation:

$sort: Sorts users by the registered field in descending order.
$limit: Outputs the most recently registered user.

12. Categorize Users by Favorite Fruit

[
  { "$group": { "_id": "$favoriteFruit", "users": { "$push": "$name" } } },
  { "$addFields": { "numberOfUsers": { "$size": "$users" } } },
  { "$sort": { "numberOfUsers": -1 } }
]

Explanation:

$group: Groups users by their favorite fruit and collects their names.
$addFields: Adds a field numberOfUsers containing the size of the users array for each fruit.
$sort: Sorts the fruits by the number of users in descending order.

13. Users with "ad" as Their Second Tag

[
  { "$match": { "tags.1": "ad" } },
  { "$count": "numberOfUsers" }
]

Explanation:

$match: Filters users whose second tag (tags[1]) is ad.
$count: Counts these users.

14. Users with Both "enim" and "id" Tags

[
  { "$match": { "tags": { "$all": ["enim", "id"] } } }
]

Explanation:

$match: Filters users whose tags array contains both enim and id.

15. Companies Located in the USA and Their Counts

[
  { "$match": { "company.location.country": "USA" } },
  { "$group": { "_id": "$company.title", "NumberOfCompanies": { "$sum": 1 } } }
]

Explanation:

$match: Filters companies located in the USA.
$group: Groups companies by their title and counts occurrences.

16. Authors Who Have Written Books in a Specific Genre

Scenario 1: One Author per Book

[
  { "$match": { "genre": "Dystopian" } },
  { "$lookup": { "from": "authors", "localField": "author_id", "foreignField": "_id", "as": "author" } },
  { "$addFields": { "author": { "$arrayElemAt": ["$author", 0] } } },
  { "$project": { "author.name": 1, "author.birth_year": 1, "_id": 0 } }
]

Explanation:

$match: Filters books with the genre Dystopian.
$lookup: Joins the authors collection based on author_id.
$addFields: Extracts the first author from the author array.
$project: Outputs only the author’s name and birth year.

Scenario 2: Multiple Authors per Book

[
  {
    "$match": {
      "genre": "Classic"
    }
  },
  {
    "$lookup": {
      "from": "authors",
      "localField": "author_id",
      "foreignField": "_id",
      "as": "authors",
      "pipeline": [
        {
          "$project": {
            "name": 1,
            "birth_year": 1,
            "_id": 0
          }
        }
      ]
    }
  },
  {
    "$project": {
      "title": 1,
      "authors": 1,
      "_id": 0
    }
  }
]

Explanation:

$match: Filters books with the genre Classic.
$lookup: Joins the authors collection, linking by author_id and adding a list of authors under the authors field.
pipeline: Limits fields returned from the joined authors documents to just name and birth_year.
$project: Outputs the book title and the list of authors.

17. Books Grouped by Genre with Total Count per Genre

[
  {
    "$group": {
      "_id": "$genre",
      "totalBooks": {
        "$sum": 1
      }
    }
  },
  {
    "$sort": {
      "totalBooks": -1
    }
  }
]

Explanation:

$group: Groups books by genre and calculates the total number of books per genre.
$sort: Sorts the genres in descending order of book count.

18. Books Written by Authors Born Before 1900

[
  {
    "$lookup": {
      "from": "authors",
      "localField": "author_id",
      "foreignField": "_id",
      "as": "author"
    }
  },
  {
    "$unwind": "$author"
  },
  {
    "$match": {
      "author.birth_year": {
        "$lt": 1900
      }
    }
  },
  {
    "$project": {
      "title": 1,
      "author.name": 1,
      "_id": 0
    }
  }
]

Explanation:

$lookup: Joins the authors collection.
$unwind: Deconstructs the author array, creating a document for each author-book pair.
$match: Filters authors born before 1900.
$project: Outputs the book title and the author’s name.

19. Total Books Written by Each Author

[
  {
    "$group": {
      "_id": "$author_id",
      "totalBooks": {
        "$sum": 1
      }
    }
  },
  {
    "$lookup": {
      "from": "authors",
      "localField": "_id",
      "foreignField": "_id",
      "as": "author"
    }
  },
  {
    "$unwind": "$author"
  },
  {
    "$project": {
      "author.name": 1,
      "totalBooks": 1,
      "_id": 0
    }
  }
]

Explanation:

$group: Groups books by author_id and calculates the total number of books per author.
$lookup: Joins the authors collection to add author details.
$unwind: Deconstructs the author array for each document.
$project: Outputs the author’s name and their total book count.

To get a better understanding of the mongodb aggregation I would suggest this short playlist by Hitesh Choudhary on youtube

TMUX: Terminal Multiplexer

Mohammad Ridowan Sikder — Fri, 04 Oct 2024 08:26:01 +0000

TMUX is a powerful tool that allows you to manage multiple terminal sessions within a single window. This guide covers the basics and some customization tips to enhance your terminal experience.

Getting Started

Installation

On Debian-based systems, you can install tmux using:

sudo apt install tmux

Basic Usage

Start a new session:

   tmux

The Prefix Key:
- TMUX uses a prefix key to distinguish its commands from regular terminal input.
- The default prefix is Ctrl+b. Press this before any TMUX command.
Detach from a session:
- Press the prefix, then d
List all sessions:

   tmux list-sessions

Or use the shortcut: prefix + s

Attach to a session:

   tmux attach -t [session-name]
   # Shorthand version:
   tmux a -t [session-name]

To attach to the most recent session:

tmux a

Rename a session:
- prefix + $

Managing Panes and Windows

Panes

Split vertically: prefix + %
Split horizontally: prefix + "
Navigate panes: prefix + arrow keys
Close a pane:
- Type exit or
- prefix + x

Windows

Create a new window: prefix + c
Navigate windows:
- Previous: prefix + p
- Next: prefix + n
Close a window: prefix + &
Rename a window: prefix + ,

Customization

While TMUX works great out of the box, customizing it can improve your workflow and aesthetics.

Create a config file:

   nano ~/.tmux.conf

Example customizations:

   # Use C-j and C-f as prefix keys
   set-option -g prefix C-j
   set-option -g prefix2 C-f

   # Easier window splitting
   bind-key v split-window -h
   bind-key h split-window -v

For a quick start with great customizations, check out this popular config: gpakosz/.tmux

Remember, the beauty of TMUX lies in its flexibility. Experiment with different settings to find what works best for you. Happy multiplexing!