These GNU utilities form the foundation of effective file management, text processing, system monitoring, and networking on Linux Ubuntu systems:

• ls: Displays directory contents for navigation and review.
• cp: Copies files and directories, supporting recursive and force options.
• mv: Moves or renames files and directories without duplicating data.
• rm: Removes files or directories, including options for recursive deletion.
• mkdir: Creates new directories, including parent directory creation with options.
• rmdir: Removes empty directories from the filesystem.
• find: Searches for files in a directory tree based on name, type, time, and more.
• ln: Creates hard and symbolic links between files.
• chmod: Modifies permissions for files and directories to control access.
• chown: Changes file owner and group association for security and management.

Text Processing Utilities:

• cat: Concatenates and displays file content in the terminal.
• tac: Displays file content in reverse line order.
• head / tail: Shows the first or last lines of files for quick previews.
• less / more: Views file content page by page interactively.
• grep: Searches for pattern matches within file content.
• awk: Scans and processes structured text for automation and reporting.
• sed: Edits streams of text using powerful expressions.
• sort: Arranges lines in text files by specified criteria.
• uniq: Reports or filters out duplicate lines from sorted files.
• cut: Removes or selects specific columns or bytes from text.
• paste: Merges lines of files side-by-side.
• wc: Displays line, word, or byte counts for files.
• diff: Compares files line by line, showing differences.
• patch: Applies changes from patch files generated by diff.

File Compression and Archiving:

• tar: Archives multiple files into one for storage or distribution.
• gzip: Compresses or decompresses files using the gzip algorithm.
• gunzip: Decompresses files compressed with gzip.
• zip: Combines and compresses files using the zip format.
• unzip: Extracts files from zip archives.
• bzip2: Compresses files with the bzip2 algorithm.
• xz: Compresses files using the xz compression method.

System Monitoring:

• top: Displays real-time running processes and resource usage.
• ps: Shows a snapshot of active processes.
• df: Reports on disk space usage on mounted filesystems.
• du: Provides information about disk usage by files and directories.
• free: Presents a summary of system memory usage.
• vmstat: Displays virtual memory statistics and system performance.
• uptime: Shows how long the system has been running.
• lsof: Lists open files and which processes are using them.

Networking Utilities:

• ping: Tests network connectivity with remote hosts.
• ip: Views and configures network interfaces, routing, and tunneling (modern alternative to ifconfig).
• netstat: Displays network connections, routing tables, and interface statistics.
• ss: Reveals detailed socket statistics.
• traceroute: Traces the network path to a host.
• nslookup: Performs queries to Internet domain name servers for DNS diagnostics.
• dig: Conducts DNS lookups with extended output.
• curl: Transfers data from or to remote servers using supported protocols.
• wget: Retrieves files from the web using HTTP, HTTPS, or FTP.

The shell in Linux Ubuntu is a powerful command-line interface used to interact with the system. Below are important aspects to understand for effective shell usage and scripting.

Shell Types:

• Bash (Bourne Again Shell): The default and most widely used shell on Ubuntu, offering rich scripting capabilities.
• Dash: A lightweight, POSIX-compliant shell often used as the default system shell for scripts.
• sh: The original Bourne shell; often links to dash or bash for compatibility.
• zsh: An advanced interactive shell with powerful features and customization options.

Scripting Basics:

• Shell scripts typically start with a shebang line specifying the interpreter, for example, #!/bin/bash.
• Make scripts executable using chmod +x script.sh before running.

Variables:

NAME="Ubuntu"
echo "Hello, $NAME"

Variables hold values such as strings or numbers and are referenced with a leading $.

Conditional Statements:

if [ -f /etc/passwd ]; then
    echo "File exists"
else
    echo "File does not exist"
fi

Use conditionals to execute code based on tests (e.g., file existence).

Loops:

for FILE in *.txt
do
    echo "Processing $FILE"
done

Loops allow repetitive execution over items like files or lines.

Functions:

my_func() {
    echo "Parameter is $1"
}
my_func "example"

Functions encapsulate reusable code blocks and can accept parameters.

Scripting for Automation:

• Use the shebang #!/bin/bash to define the script interpreter.
• Set safety flags like set -euo pipefail to catch errors and undefined variables.
• Automate tasks with cron jobs using crontab -e for scheduling.
• Combine shell commands and utilities with pipelines to build powerful automation workflows.

Automating tasks on Linux Ubuntu using shell scripting improves efficiency and consistency, especially for network infrastructure deployment, maintenance, and provisioning. Below are essential practices and concepts for writing effective automation scripts.

Shebang and Interpreter Definition:

#!/bin/bash

The shebang at the top of scripts defines the shell interpreter to run the script. Bash is the most common choice on Ubuntu systems.

Strict Error Handling:

set -euo pipefail

Including this line enforces:

• Exiting immediately on command failure (-e).
• Treating unset variables as errors (-u).
• Ensuring pipeline errors are detected (-o pipefail).

Scheduling Automation with Cron:

Use crontab -e to create and edit scheduled jobs running scripts at specified intervals.

# Example: Run backup.sh every day at 2 AM
0 2 * * * /home/user/scripts/backup.sh

Cron syntax allows precise control over timing for repetitive automation tasks.

Pipelines and Command Chaining:

Combine multiple commands using pipes (|) and chaining operators to process data streams and automate workflows.

grep "error" /var/log/syslog | sort | uniq -c | tee errors_report.txt

This example extracts error lines, sorts, counts unique entries, and saves the report for review.

Using Variables and Parameters in Automation Scripts:

#!/bin/bash
LOGFILE="/var/log/syslog"
KEYWORD="$1"

grep "$KEYWORD" "$LOGFILE" > filtered_logs.txt

Parameters enhance script flexibility by allowing input at runtime.

Logging and Debugging:

• Redirect outputs and errors to log files to monitor script activities.
• Use set -x temporarily in scripts for debugging to trace command execution.

Best Practices:

• Write modular scripts by defining functions to reuse code efficiently.
• Validate inputs and check for errors before proceeding with commands.
• Document scripts with comments for maintainability.
• Test scripts in a safe environment before deploying in production.