I/O & Text Processing

9. I/O & Text Processing#

In this chapter, you’ll master the art of handling data streams—reading from standard input, writing to standard output, and redirecting I/O to files and processes. You’ll learn how bash works with file descriptors, how to combine commands through pipes, and how to manipulate text using powerful tools like sed, awk, and regular expressions. These skills form the foundation of data processing in bash, enabling you to transform, filter, extract, and analyze text data with precision. By the end, you’ll be able to build sophisticated text processing pipelines that automate complex data workflows.

What You'll Learn

By the end of this chapter, you will be able to:

✓ Understand standard streams: stdin, stdout, stderr ✓ Redirect input and output to/from files ✓ Use pipes to connect commands together ✓ Work with file descriptors and advanced I/O ✓ Read input from users and files ✓ Write formatted output and logging ✓ Process text using sed and awk ✓ Build complex data processing pipelines ✓ Handle multiple input sources simultaneously ✓ Debug I/O problems in scripts

Chapter Map

Section

Topic

Key Concepts

0902

Standard Streams & Redirection

stdin/stdout/stderr, >, >>, <, 2>, &>

0903

Pipes & Data Flow

|, command chaining, process substitution

0904

Reading Input

read, input methods, user interaction

0905

Writing Output

echo, printf, logging, formatting

0906

Text Processing

sed, awk, grep, regular expressions

0907

Lab: Data Processing Pipelines

Hands-on exercises with real data

Why This Matters

Input/Output and text processing are the heart of Unix philosophy:

  • Data processing: Transform gigabytes of data without loading into memory

  • Automation: Read logs, configuration files, and user input

  • Integration: Pipe data between tools to build powerful workflows

  • Analysis: Extract, filter, and analyze text-based data

  • System administration: Process logs, monitor output, generate reports

Real-world impact: A sysadmin can process a 10GB log file in seconds using pipelines. The same task in a programming language might take minutes and require code to be written.

Prerequisites

You should already understand:

  • Variables and variable expansion (Chapter 5)

  • Operators and conditionals (Chapters 6-7)

  • Basic file operations and navigation (Chapters 1-3)

  • Basic text tools like grep and pipes

If you’re unfamiliar with pipes or redirection, review Chapter 4 first.

What You'll Learn

By the end of this chapter, you will be able to:

✓ Understand standard streams: stdin, stdout, stderr ✓ Redirect input and output to/from files ✓ Use pipes to connect commands together ✓ Work with file descriptors and advanced I/O ✓ Read input from users and files ✓ Write formatted output and logging ✓ Process text using sed and awk ✓ Build complex data processing pipelines ✓ Handle multiple input sources simultaneously ✓ Debug I/O problems in scripts

Chapter Map

Section

Topic

Key Concepts

0902

Standard Streams & Redirection

stdin/stdout/stderr, >, >>, <, 2>, &>

0903

Pipes & Data Flow

|, command chaining, process substitution

0904

Reading Input

read, input methods, user interaction

0905

Writing Output

echo, printf, logging, formatting

0906

Text Processing

sed, awk, grep, regular expressions

0907

Lab: Data Processing Pipelines

Hands-on exercises with real data

Why This Matters

Input/Output and text processing are the heart of Unix philosophy:

  • Data processing: Transform gigabytes of data without loading into memory

  • Automation: Read logs, configuration files, and user input

  • Integration: Pipe data between tools to build powerful workflows

  • Analysis: Extract, filter, and analyze text-based data

  • System administration: Process logs, monitor output, generate reports

Real-world impact: A sysadmin can process a 10GB log file in seconds using pipelines. The same task in a programming language might take minutes and require code to be written.

Prerequisites

You should already understand:

  • Variables and variable expansion (Chapter 5)

  • Operators and conditionals (Chapters 6-7)

  • Basic file operations and navigation (Chapters 1-3)

  • Basic text tools like grep and pipes

If you’re unfamiliar with pipes or redirection, review Chapter 4 first.