Design

Table of Contents

4. Modularity

Encapsulation and Optimal Module Size

Compactness and Orthogonality

Compactness

Orthogonality

The SPOT Rule

Compactness and the Strong Single Center

The Value of Detachment

Software Is a Many-Layered Thing

Top-Down versus Bottom-Up

Glue Layers

Case Study: C Considered as Thin Glue

Libraries

Case Study: GIMP Plugins

Unix and Object-Oriented Languages

Coding for Modularity

5. Textuality

The Importance of Being Textual

Case Study: Unix Password File Format

Case Study: .newsrc Format

Case Study: The PNG Graphics File Format

Data File Metaformats

DSV Style

RFC 822 Format

Cookie-Jar Format

Record-Jar Format

XML

Windows INI Format

Unix Textual File Format Conventions

The Pros and Cons of File Compression

Application Protocol Design

Case Study: SMTP, a Simple Socket Protocol

Case Study: POP3, the Post Office Protocol

Case Study: IMAP, the Internet Message Access Protocol

Application Protocol Metaformats

The Classical Internet Application Metaprotocol

HTTP as a Universal Application Protocol

BEEP: Blocks Extensible Exchange Protocol

XML-RPC, SOAP, and Jabber

6. Transparency

Studying Cases

Case Study: audacity

Case Study: fetchmail's -v option

Case Study: GCC

Case Study: kmail

Case Study: SNG

Case Study: The Terminfo Database

Case Study: Freeciv Data Files

Designing for Transparency and Discoverability

The Zen of Transparency

Coding for Transparency and Discoverability

Transparency and Avoiding Overprotectiveness

Transparency and Editable Representations

Transparency, Fault Diagnosis, and Fault Recovery

Designing for Maintainability

7. Multiprogramming

Separating Complexity Control from Performance Tuning

Taxonomy of Unix IPC Methods

Handing off Tasks to Specialist Programs

Pipes, Redirection, and Filters

Wrappers

Security Wrappers and Bernstein Chaining

Slave Processes

Peer-to-Peer Inter-Process Communication

Problems and Methods to Avoid

Obsolescent Unix IPC Methods

Remote Procedure Calls

Threads — Threat or Menace?

Process Partitioning at the Design Level

8. Minilanguages

Understanding the Taxonomy of Languages

Applying Minilanguages

Case Study: sng

Case Study: Regular Expressions

Case Study: Glade

Case Study: m4

Case Study: XSLT

Case Study: The Documenter's Workbench Tools

Case Study: fetchmail Run-Control Syntax

Case Study: awk

Case Study: PostScript

Case Study: bc and dc

Case Study: Emacs Lisp

Case Study: JavaScript

Designing Minilanguages

Choosing the Right Complexity Level

Extending and Embedding Languages

Writing a Custom Grammar

Macros — Beware!

Language or Application Protocol?

9. Generation

Data-Driven Programming

Case Study: ascii

Case Study: Statistical Spam Filtering

Case Study: Metaclass Hacking in fetchmailconf

Ad-hoc Code Generation

Case Study: Generating Code for the ascii Displays

Case Study: Generating HTML Code for a Tabular List

10. Configuration

What Should Be Configurable?

Where Configurations Live

Run-Control Files

Case Study: The .netrc File

Portability to Other Operating Systems

Environment Variables

System Environment Variables

User Environment Variables

When to Use Environment Variables

Portability to Other Operating Systems

Command-Line Options

The -a to -z of Command-Line Options

Portability to Other Operating Systems

How to Choose among the Methods

Case Study: fetchmail

Case Study: The XFree86 Server

On Breaking These Rules

11. Interfaces

Applying the Rule of Least Surprise

History of Interface Design on Unix

Evaluating Interface Designs

Tradeoffs between CLI and Visual Interfaces

Case Study: Two Ways to Write a Calculator Program

Transparency, Expressiveness, and Configurability

Unix Interface Design Patterns

The Filter Pattern

The Cantrip Pattern

The Source Pattern

The Sink Pattern

The Compiler Pattern

The ed pattern

The Roguelike Pattern

The ‘Separated Engine and Interface’ Pattern

The CLI Server Pattern

Language-Based Interface Patterns

Applying Unix Interface-Design Patterns

The Polyvalent-Program Pattern

The Web Browser as a Universal Front End

Silence Is Golden

12. Optimization

Don't Just Do Something, Stand There!

Measure before Optimizing

Nonlocality Considered Harmful

Throughput vs. Latency

Batching Operations

Overlapping Operations

Caching Operation Results

13. Complexity

Speaking of Complexity

The Three Sources of Complexity

Tradeoffs between Interface and Implementation Complexity

Essential, Optional, and Accidental Complexity

Mapping Complexity

When Simplicity Is Not Enough

A Tale of Five Editors

ed

vi

Sam

Emacs

Wily

The Right Size for an Editor

Identifying the Complexity Problems

Compromise Doesn't Work

Is Emacs an Argument against the Unix Tradition?

The Right Size of Software