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a huge bunch of improvements of my wordings by Andrew Antle
author meillo@marmaro.de
date Sun, 18 Apr 2010 20:44:15 +0200
parents 840cbc667009
children
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meillo@49 1 .so style
meillo@42 2
meillo@0 3 .TL
meillo@42 4 .ps +4
meillo@6 5 Why the Unix Philosophy still matters
meillo@0 6 .AU
meillo@0 7 markus schnalke <meillo@marmaro.de>
meillo@0 8 .AB
meillo@1 9 .ti \n(.iu
meillo@39 10 This paper explains the importance of the Unix Philosophy for software design.
meillo@0 11 Today, few software designers are aware of these concepts,
meillo@39 12 and thus a lot of modern software is more limited than necessary
meillo@39 13 and makes less use of software leverage than possible.
meillo@38 14 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
meillo@0 15 .AE
meillo@0 16
meillo@2 17 .FS
meillo@2 18 .ps -1
meillo@39 19 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
meillo@47 20 Mentor was professor Franz Schweiggert.
meillo@55 21 Handed in on 2010-04-16.
meillo@39 22 You may retrieve this document from
meillo@39 23 .CW \s-1http://marmaro.de/docs \ .
meillo@2 24 .FE
meillo@2 25
meillo@48 26 .H 1 Introduction
meillo@0 27 .LP
meillo@40 28 The Unix Philosophy is the essence of how the Unix operating system,
meillo@40 29 especially its toolchest, was designed.
meillo@57 30 It is not a limited set of fixed rules,
meillo@40 31 but a loose set of guidelines which tell how to write software that
meillo@57 32 suites Unix well.
meillo@57 33 Actually, the Unix Philosophy describes what is common in typical Unix software.
meillo@40 34 The Wikipedia has an accurate definition:
meillo@40 35 .[
meillo@44 36 wikipedia
meillo@44 37 unix philosophy
meillo@40 38 .]
meillo@40 39 .QP
meillo@40 40 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
meillo@40 41 approaches to developing software based on the experience of leading
meillo@40 42 developers of the Unix operating system.
meillo@1 43 .PP
meillo@40 44 As there is no single definition of the Unix Philosophy,
meillo@40 45 several people have stated their view on what it comprises.
meillo@1 46 Best known are:
meillo@1 47 .IP \(bu
meillo@1 48 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
meillo@1 49 .[
meillo@44 50 mahoney
meillo@44 51 oral history
meillo@1 52 .]
meillo@1 53 .IP \(bu
meillo@1 54 Mike Gancarz' book ``The UNIX Philosophy''.
meillo@1 55 .[
meillo@44 56 gancarz
meillo@44 57 unix philosophy
meillo@1 58 .]
meillo@1 59 .IP \(bu
meillo@1 60 Eric S. Raymond's book ``The Art of UNIX Programming''.
meillo@1 61 .[
meillo@44 62 raymond
meillo@44 63 art of unix programming
meillo@1 64 .]
meillo@0 65 .LP
meillo@1 66 These different views on the Unix Philosophy have much in common.
meillo@40 67 Especially, the main concepts are similar in all of them.
meillo@40 68 McIlroy's definition can surely be called the core of the Unix Philosophy,
meillo@57 69 but the fundamental idea behind it all is ``small is beautiful''.
meillo@40 70
meillo@40 71 .PP
meillo@45 72 The Unix Philosophy explains how to design good software for Unix.
meillo@57 73 Many concepts described here are based on Unix facilities.
meillo@40 74 Other operating systems may not offer such facilities,
meillo@57 75 hence it may not be possible to design software for such systems
meillo@57 76 according to the Unix Philosophy.
meillo@40 77 .PP
meillo@57 78 The Unix Philosophy has an idea of what the process of software development
meillo@41 79 should look like, but large parts of the philosophy are quite independent
meillo@45 80 from a concrete development process.
meillo@41 81 However, one will soon recognize that some development processes work well
meillo@41 82 with the ideas of the Unix Philosophy and support them, while others are
meillo@41 83 at cross-purposes.
meillo@45 84 Kent Beck's books about Extreme Programming are valuable supplemental
meillo@45 85 resources on this topic.
meillo@1 86 .PP
meillo@57 87 The question of how to actually write code and how the code should look
meillo@57 88 in detail, are beyond the scope of this paper.
meillo@57 89 Kernighan and Pike's book ``The Practice of Programming''
meillo@41 90 .[
meillo@44 91 kernighan pike
meillo@44 92 practice of programming
meillo@41 93 .]
meillo@57 94 covers this topic.
meillo@57 95 Its point of view corresponds to the one espoused in this paper.
meillo@0 96
meillo@48 97 .H 1 "Importance of software design in general
meillo@0 98 .LP
meillo@57 99 Software design consists of planning how the internal structure
meillo@57 100 and external interfaces of software should look.
meillo@39 101 It has nothing to do with visual appearance.
meillo@57 102 If we were to compare a program to a car, then its color would not matter.
meillo@39 103 Its design would be the car's size, its shape, the locations of doors,
meillo@45 104 the passenger/space ratio, the available controls and instruments,
meillo@45 105 and so forth.
meillo@39 106 .PP
meillo@57 107 Why should software be designed at all?
meillo@57 108 It is accepted as general knowledge,
meillo@57 109 that even a bad plan is better than no plan.
meillo@57 110 Not designing software means programming without a plan.
meillo@57 111 This will surely lead to horrible results,
meillo@57 112 being horrible to use and horrible to maintain.
meillo@39 113 These two aspects are the visible ones.
meillo@45 114 Often invisible though, are the wasted possible gains.
meillo@39 115 Good software design can make these gains available.
meillo@2 116 .PP
meillo@57 117 A software's design deals with qualitative properties.
meillo@39 118 Good design leads to good quality, and quality is important.
meillo@57 119 Any car may be able to drive from point A to point B,
meillo@57 120 but it depends on the qualitative decisions made in the design of the vehicle,
meillo@57 121 whether it is a good choice for passenger transport or not,
meillo@57 122 whether it is a good choice for a rough mountain area,
meillo@57 123 and whether the ride will be fun.
meillo@39 124
meillo@2 125 .PP
meillo@57 126 Requirements for a piece of software are twofold:
meillo@39 127 functional and non-functional.
meillo@39 128 .IP \(bu
meillo@57 129 Functional requirements directly define the software's functions.
meillo@39 130 They are the reason why software gets written.
meillo@39 131 Someone has a problem and needs a tool to solve it.
meillo@39 132 Being able to solve the problem is the main functional goal.
meillo@57 133 This is the driving force behind all programming effort.
meillo@39 134 Functional requirements are easier to define and to verify.
meillo@39 135 .IP \(bu
meillo@45 136 Non-functional requirements are called \fIquality\fP requirements, too.
meillo@57 137 The quality of software shows through the properties that are not directly
meillo@57 138 related to the software's basic functions.
meillo@45 139 Tools of bad quality often do solve the problems they were written for,
meillo@57 140 but introduce problems and difficulties for usage and development later on.
meillo@57 141 Qualitative aspects are often overlooked at first sight,
meillo@45 142 and are often difficult to define clearly and to verify.
meillo@2 143 .PP
meillo@54 144 Quality is hardly interesting when software gets built initially,
meillo@57 145 but it has a high impact on usability and maintenance of the software later.
meillo@57 146 A short-sighted person might see the process of developing software as
meillo@57 147 one mainly concerned with building something up.
meillo@57 148 But, experience shows that building software the first time is
meillo@57 149 only a small portion of the overall work involved.
meillo@45 150 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en
meillo@57 151 soon take a large part of the time spent on a software project.
meillo@45 152 And of course, the time spent actually using the software.
meillo@6 153 These processes are highly influenced by the software's quality.
meillo@39 154 Thus, quality must not be neglected.
meillo@45 155 However, the problem with quality is that you hardly ``stumble over''
meillo@39 156 bad quality during the first build,
meillo@45 157 although this is the time when you should care about good quality most.
meillo@6 158 .PP
meillo@54 159 Software design has little to do with the basic function of software \(en
meillo@39 160 this requirement will get satisfied anyway.
meillo@57 161 Software design is more about quality aspects.
meillo@39 162 Good design leads to good quality, bad design to bad quality.
meillo@54 163 The primary functions of software will be affected modestly by bad quality,
meillo@57 164 but good quality can provide a lot of additional benefits,
meillo@57 165 even at places one never expected it.
meillo@6 166 .PP
meillo@45 167 The ISO/IEC\|9126-1 standard, part\|1,
meillo@6 168 .[
meillo@44 169 iso product quality
meillo@6 170 .]
meillo@57 171 defines the quality model as consisting of:
meillo@6 172 .IP \(bu
meillo@6 173 .I Functionality
meillo@6 174 (suitability, accuracy, inter\%operability, security)
meillo@6 175 .IP \(bu
meillo@6 176 .I Reliability
meillo@6 177 (maturity, fault tolerance, recoverability)
meillo@6 178 .IP \(bu
meillo@6 179 .I Usability
meillo@6 180 (understandability, learnability, operability, attractiveness)
meillo@6 181 .IP \(bu
meillo@6 182 .I Efficiency
meillo@9 183 (time behavior, resource utilization)
meillo@6 184 .IP \(bu
meillo@6 185 .I Maintainability
meillo@23 186 (analyzability, changeability, stability, testability)
meillo@6 187 .IP \(bu
meillo@6 188 .I Portability
meillo@6 189 (adaptability, installability, co-existence, replaceability)
meillo@6 190 .LP
meillo@57 191 Good design can improve these properties in software;
meillo@57 192 poorly designed software likely suffers in these areas.
meillo@7 193 .PP
meillo@7 194 One further goal of software design is consistency.
meillo@57 195 Consistency eases understanding, using, and working on things.
meillo@57 196 Consistent internal structure and consistent external interfaces
meillo@39 197 can be provided by good design.
meillo@7 198 .PP
meillo@39 199 Software should be well designed because good design avoids many
meillo@57 200 problems during its lifetime.
meillo@57 201 Also, because good design can offer much additional gain.
meillo@57 202 Indeed, much effort should be spent on good design to make software more valuable.
meillo@57 203 The Unix Philosophy provides a way to design software well.
meillo@7 204 It offers guidelines to achieve good quality and high gain for the effort spent.
meillo@0 205
meillo@0 206
meillo@48 207 .H 1 "The Unix Philosophy
meillo@4 208 .LP
meillo@61 209 The origins of the Unix Philosophy have already been introduced.
meillo@8 210 This chapter explains the philosophy, oriented on Gancarz,
meillo@55 211 .[
meillo@55 212 gancarz
meillo@55 213 unix philosophy
meillo@55 214 .]
meillo@8 215 and shows concrete examples of its application.
meillo@5 216
meillo@48 217 .H 2 Pipes
meillo@4 218 .LP
meillo@61 219 The following examples demonstrate how the Unix Philosophy is applied.
meillo@4 220 Knowledge of using the Unix shell is assumed.
meillo@4 221 .PP
meillo@4 222 Counting the number of files in the current directory:
meillo@41 223 .DS
meillo@4 224 ls | wc -l
meillo@4 225 .DE
meillo@4 226 The
meillo@4 227 .CW ls
meillo@4 228 command lists all files in the current directory, one per line,
meillo@4 229 and
meillo@4 230 .CW "wc -l
meillo@8 231 counts the number of lines.
meillo@4 232 .PP
meillo@8 233 Counting the number of files that do not contain ``foo'' in their name:
meillo@41 234 .DS
meillo@4 235 ls | grep -v foo | wc -l
meillo@4 236 .DE
meillo@4 237 Here, the list of files is filtered by
meillo@4 238 .CW grep
meillo@45 239 to remove all lines that contain ``foo''.
meillo@45 240 The rest equals the previous example.
meillo@4 241 .PP
meillo@61 242 Finding the five largest entries in the current directory:
meillo@41 243 .DS
meillo@4 244 du -s * | sort -nr | sed 5q
meillo@4 245 .DE
meillo@4 246 .CW "du -s *
meillo@45 247 returns the recursively summed sizes of all files in the current directory
meillo@8 248 \(en no matter if they are regular files or directories.
meillo@4 249 .CW "sort -nr
meillo@45 250 sorts the list numerically in reverse order (descending).
meillo@4 251 Finally,
meillo@4 252 .CW "sed 5q
meillo@4 253 quits after it has printed the fifth line.
meillo@4 254 .PP
meillo@4 255 The presented command lines are examples of what Unix people would use
meillo@4 256 to get the desired output.
meillo@61 257 There are other ways to get the same output;
meillo@61 258 it is the user's decision which way to go.
meillo@14 259 .PP
meillo@8 260 The examples show that many tasks on a Unix system
meillo@4 261 are accomplished by combining several small programs.
meillo@61 262 The connection between the programs is denoted by the pipe operator `|'.
meillo@4 263 .PP
meillo@4 264 Pipes, and their extensive and easy use, are one of the great
meillo@4 265 achievements of the Unix system.
meillo@61 266 Pipes were possible in earlier operating systems,
meillo@61 267 but never before have they been such a central part of the concept.
meillo@61 268 In the early seventies when Doug McIlroy introduced pipes into the
meillo@4 269 Unix system,
meillo@4 270 ``it was this concept and notation for linking several programs together
meillo@4 271 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
meillo@4 272 .[
meillo@44 273 aughenbaugh
meillo@44 274 unix oral history
meillo@45 275 .]
meillo@4 276 .PP
meillo@4 277 Being able to specify pipelines in an easy way is,
meillo@61 278 however, not enough by itself;
meillo@61 279 it is only one half.
meillo@4 280 The other is the design of the programs that are used in the pipeline.
meillo@61 281 They need interfaces that allow them to be used in this way.
meillo@5 282
meillo@48 283 .H 2 "Interface design
meillo@5 284 .LP
meillo@61 285 Unix is, first of all, simple \(en everything is a file.
meillo@5 286 Files are sequences of bytes, without any special structure.
meillo@45 287 Programs should be filters, which read a stream of bytes from standard input (stdin)
meillo@45 288 and write a stream of bytes to standard output (stdout).
meillo@8 289 If the files \fIare\fP sequences of bytes,
meillo@8 290 and the programs \fIare\fP filters on byte streams,
meillo@45 291 then there is exactly one data interface.
meillo@45 292 Hence it is possible to combine programs in any desired way.
meillo@5 293 .PP
meillo@45 294 Even a handful of small programs yields a large set of combinations,
meillo@5 295 and thus a large set of different functions.
meillo@5 296 This is leverage!
meillo@5 297 If the programs are orthogonal to each other \(en the best case \(en
meillo@5 298 then the set of different functions is greatest.
meillo@5 299 .PP
meillo@61 300 Programs can also have a separate control interface
meillo@61 301 in addition to their data interface.
meillo@61 302 The control interface is often called the ``user interface'',
meillo@11 303 because it is usually designed to be used by humans.
meillo@61 304 The Unix Philosophy discourages the assumption that the user will be human.
meillo@11 305 Interactive use of software is slow use of software,
meillo@11 306 because the program waits for user input most of the time.
meillo@61 307 Interactive software also requires the user to be in front of the computer,
meillo@61 308 occupying his attention during usage.
meillo@11 309 .PP
meillo@61 310 Now, back to the idea of combining several small programs
meillo@61 311 to perform a more specific function:
meillo@61 312 If these single tools were all interactive,
meillo@11 313 how would the user control them?
meillo@61 314 It is not only a problem to control several programs at once
meillo@61 315 if they run at the same time;
meillo@61 316 it is also very inefficient to have to control each program
meillo@61 317 when they are intended to act in concert.
meillo@61 318 Hence, the Unix Philosophy discourages designing programs which demand
meillo@61 319 interactive use.
meillo@11 320 The behavior of programs should be defined at invocation.
meillo@45 321 This is done by specifying arguments to the program call
meillo@45 322 (command line switches).
meillo@61 323 Gancarz discusses this topic as ``avoid[ing] captive user interfaces''.
meillo@46 324 .[ [
meillo@44 325 gancarz unix philosophy
meillo@46 326 .], page 88 ff.]
meillo@11 327 .PP
meillo@61 328 Non-interactive use is also an advantage for testing during development.
meillo@61 329 Testing interactive programs is much more complicated
meillo@61 330 than testing non-interactive counterparts.
meillo@5 331
meillo@48 332 .H 2 "The toolchest approach
meillo@5 333 .LP
meillo@5 334 A toolchest is a set of tools.
meillo@61 335 Instead of one big tool for all tasks, there are many small tools,
meillo@5 336 each for one task.
meillo@61 337 Difficult tasks are solved by combining several small, simple tools.
meillo@5 338 .PP
meillo@11 339 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
meillo@11 340 that are filters on byte streams.
meillo@54 341 They are, to a large extent, unrelated in their function.
meillo@11 342 Hence, the Unix toolchest provides a large set of functions
meillo@11 343 that can be accessed by combining the programs in the desired way.
meillo@11 344 .PP
meillo@61 345 The act of software development benefits from small toolchest programs, too.
meillo@61 346 Writing small programs is generally easier and less error-prone
meillo@61 347 than writing large programs.
meillo@61 348 Hence, writing a large set of small programs is still easier and
meillo@61 349 less error-prone than writing one large program with all the
meillo@61 350 functionality included.
meillo@61 351 If the small programs are combinable, then they offer even an even larger set
meillo@61 352 of functions than the single monolithic program.
meillo@45 353 Hence, one gets two advantages out of writing small, combinable programs:
meillo@45 354 They are easier to write and they offer a greater set of functions through
meillo@45 355 combination.
meillo@5 356 .PP
meillo@61 357 There are also two main drawbacks of the toolchest approach.
meillo@45 358 First, one simple, standardized interface has to be sufficient.
meillo@5 359 If one feels the need for more ``logic'' than a stream of bytes,
meillo@61 360 then a different approach might be required.
meillo@61 361 Also, a design where a stream of bytes is sufficient,
meillo@61 362 might not be conceivable.
meillo@8 363 By becoming more familiar with the ``Unix style of thinking'',
meillo@8 364 developers will more often and easier find simple designs where
meillo@8 365 a stream of bytes is a sufficient interface.
meillo@8 366 .PP
meillo@61 367 The second drawback of the toolchest approach concerns the users.
meillo@61 368 A toolchest is often more difficult to use because
meillo@61 369 it is necessary to become familiar with each tool and
meillo@61 370 be able to choose and use the right one in any given situation.
meillo@61 371 Additionally, one needs to know how to combine the tools in a sensible way.
meillo@61 372 The issue is similar to having a sharp knife \(en
meillo@61 373 it is a powerful tool in the hand of a master,
meillo@61 374 but of no value in the hand of an unskilled person.
meillo@61 375 However, learning single, small tools of a toolchest is often easier than
meillo@45 376 learning a complex tool.
meillo@61 377 The user will already have a basic understanding of an as yet unknown tool
meillo@45 378 if the tools of a toolchest have a common, consistent style.
meillo@61 379 He will be able to transfer knowledge of one tool to another.
meillo@5 380 .PP
meillo@61 381 This second drawback can be removed to a large extent
meillo@45 382 by adding wrappers around the basic tools.
meillo@61 383 Novice users do not need to learn several tools if a professional wraps
meillo@45 384 complete command lines into a higher-level script.
meillo@5 385 Note that the wrapper script still calls the small tools;
meillo@45 386 it is just like a skin around them.
meillo@61 387 No complexity is added this way,
meillo@61 388 but new programs can be created out of existing one with very little effort.
meillo@5 389 .PP
meillo@5 390 A wrapper script for finding the five largest entries in the current directory
meillo@61 391 might look like this:
meillo@41 392 .DS
meillo@5 393 #!/bin/sh
meillo@5 394 du -s * | sort -nr | sed 5q
meillo@5 395 .DE
meillo@61 396 The script itself is just a text file that calls the commands
meillo@61 397 that a professional user would type in directly.
meillo@61 398 It is probably beneficial to make the program flexible in regard to
meillo@61 399 the number of entries it prints:
meillo@41 400 .DS
meillo@8 401 #!/bin/sh
meillo@8 402 num=5
meillo@8 403 [ $# -eq 1 ] && num="$1"
meillo@8 404 du -sh * | sort -nr | sed "${num}q"
meillo@8 405 .DE
meillo@61 406 This script acts like the one before when called without an argument,
meillo@61 407 but the user can also specify a numerical argument to define the number
meillo@61 408 of lines to print.
meillo@61 409 One can surely imagine even more flexible versions;
meillo@61 410 however, they will still rely on the external programs
meillo@61 411 which actually do the work.
meillo@5 412
meillo@48 413 .H 2 "A powerful shell
meillo@8 414 .LP
meillo@61 415 The Unix shell provides the ability to combine small programs into large ones.
meillo@61 416 But a powerful shell is a great feature in other ways, too;
meillo@61 417 for instance, by being scriptable.
meillo@61 418 Control statements are built into the shell
meillo@61 419 and the functions are the normal programs of the system.
meillo@61 420 As the programs are already known,
meillo@45 421 learning to program in the shell becomes easy.
meillo@8 422 Using normal programs as functions in the shell programming language
meillo@10 423 is only possible because they are small and combinable tools in a toolchest style.
meillo@8 424 .PP
meillo@61 425 The Unix shell encourages writing small scripts,
meillo@61 426 by combining existing programs because it is so easy to do.
meillo@8 427 This is a great step towards automation.
meillo@8 428 It is wonderful if the effort to automate a task equals the effort
meillo@45 429 to do the task a second time by hand.
meillo@45 430 If this holds,
meillo@45 431 then the user will be happy to automate everything he does more than once.
meillo@8 432 .PP
meillo@8 433 Small programs that do one job well, standardized interfaces between them,
meillo@61 434 a mechanism to combine parts to larger parts, and an easy way to automate tasks
meillo@61 435 will inevitably produce software leverage,
meillo@61 436 achieving multiple times the benefit of the initial investment.
meillo@10 437 .PP
meillo@10 438 The shell also encourages rapid prototyping.
meillo@10 439 Many well known programs started as quickly hacked shell scripts,
meillo@61 440 and turned into ``real'' programs later written in C.
meillo@61 441 Building a prototype first is a way to avoid the biggest problems
meillo@10 442 in application development.
meillo@45 443 Fred Brooks explains in ``No Silver Bullet'':
meillo@10 444 .[
meillo@44 445 brooks
meillo@44 446 no silver bullet
meillo@10 447 .]
meillo@10 448 .QP
meillo@10 449 The hardest single part of building a software system is deciding precisely what to build.
meillo@10 450 No other part of the conceptual work is so difficult as establishing the detailed
meillo@10 451 technical requirements, [...].
meillo@10 452 No other part of the work so cripples the resulting system if done wrong.
meillo@10 453 No other part is more difficult to rectify later.
meillo@10 454 .PP
meillo@45 455 Writing a prototype is a great method for becoming familiar with the requirements
meillo@45 456 and to run into real problems early.
meillo@47 457 .[ [
meillo@47 458 gancarz
meillo@47 459 unix philosophy
meillo@47 460 .], page 28 f.]
meillo@45 461 .PP
meillo@54 462 Prototyping is often seen as a first step in building software.
meillo@10 463 This is, of course, good.
meillo@10 464 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
meillo@61 465 After having built the prototype, one might notice that the prototype is already
meillo@10 466 \fIgood enough\fP.
meillo@61 467 Hence, no reimplementation in a more sophisticated programming language
meillo@45 468 might be of need, at least for the moment.
meillo@23 469 Maybe later, it might be necessary to rewrite the software, but not now.
meillo@45 470 By delaying further work, one keeps the flexibility to react on
meillo@10 471 changing requirements.
meillo@10 472 Software parts that are not written will not miss the requirements.
meillo@61 473 Well known is Gordon Bell's classic saying:
meillo@61 474 ``The cheapest, fastest, and most reliable components are those
meillo@61 475 that aren't there.''
meillo@61 476 .\" FIXME: ref?
meillo@10 477
meillo@48 478 .H 2 "Worse is better
meillo@10 479 .LP
meillo@45 480 The Unix Philosophy aims for the 90% solution;
meillo@10 481 others call it the ``Worse is better'' approach.
meillo@47 482 Experience from real life projects shows:
meillo@10 483 .PP
meillo@61 484 (1) It is almost impossible to define the
meillo@10 485 requirements completely and correctly the first time.
meillo@45 486 Hence one should not try to; one will fail anyway.
meillo@45 487 .PP
meillo@45 488 (2) Requirements change during time.
meillo@10 489 Hence it is best to delay requirement-based design decisions as long as possible.
meillo@61 490 Software should be small and flexible as long as possible in order
meillo@61 491 to react to changing requirements.
meillo@61 492 Shell scripts, for example, are more easily adjusted than C programs.
meillo@45 493 .PP
meillo@45 494 (3) Maintenance work is hard work.
meillo@45 495 Hence, one should keep the amount of code as small as possible;
meillo@61 496 it should only fulfill the \fIcurrent\fP requirements.
meillo@61 497 Software parts that will be written in the future
meillo@61 498 do not need maintenance until that time.
meillo@10 499 .PP
meillo@47 500 See Brooks' ``The Mythical Man-Month'' for reference.
meillo@47 501 .[ [
meillo@47 502 brooks
meillo@47 503 mythical man-month
meillo@47 504 .], page 115 ff.]
meillo@47 505 .PP
meillo@10 506 Starting with a prototype in a scripting language has several advantages:
meillo@10 507 .IP \(bu
meillo@10 508 As the initial effort is low, one will likely start right away.
meillo@10 509 .IP \(bu
meillo@61 510 Real requirements can be identified quickly since working parts are
meillo@61 511 available sooner.
meillo@10 512 .IP \(bu
meillo@54 513 When software is usable and valuable, it gets used, and thus tested.
meillo@61 514 This ensures that problems will be found in the early stages of development.
meillo@10 515 .IP \(bu
meillo@61 516 The prototype might be enough for the moment;
meillo@61 517 thus, further work can be delayed until a time
meillo@61 518 when one knows about the requirements and problems more thoroughly.
meillo@10 519 .IP \(bu
meillo@61 520 Implementing only the parts that are actually needed at the moment
meillo@61 521 introduces less programming and maintenance work.
meillo@10 522 .IP \(bu
meillo@61 523 If the situation changes such that the software is not needed anymore,
meillo@61 524 then less effort was spent on the project than it would have been
meillo@61 525 if a different approach had been taken.
meillo@10 526
meillo@48 527 .H 2 "Upgrowth and survival of software
meillo@11 528 .LP
meillo@61 529 So far, \fIwriting\fP or \fIbuilding\fP software has been discussed.
meillo@61 530 Although ``writing'' and ``building'' are just verbs,
meillo@61 531 they do imply a specific view on the work process they describe.
meillo@61 532 A better verb would be to \fI``grow''\fP.
meillo@12 533 Creating software in the sense of the Unix Philosophy is an incremental process.
meillo@61 534 It starts with an initial prototype, which evolves as requirements change.
meillo@12 535 A quickly hacked shell script might become a large, sophisticated,
meillo@13 536 compiled program this way.
meillo@13 537 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
meillo@61 538 While alive, it will be extended, rearranged, rebuilt.
meillo@12 539 Growing software matches the view that ``software is never finished. It is only released.''
meillo@46 540 .[ [
meillo@44 541 gancarz
meillo@44 542 unix philosophy
meillo@46 543 .], page 26]
meillo@12 544 .PP
meillo@13 545 Software can be seen as being controlled by evolutionary processes.
meillo@13 546 Successful software is software that is used by many for a long time.
meillo@61 547 This implies that the software is necessary, useful, and better than the alternatives.
meillo@61 548 Darwin describes ``the survival of the fittest.''
meillo@12 549 .[
meillo@44 550 darwin
meillo@44 551 origin of species
meillo@12 552 .]
meillo@61 553 In relation to software, the most successful software is the fittest;
meillo@61 554 the one that survives.
meillo@13 555 (This may be at the level of one creature, or at the level of one species.)
meillo@13 556 The fitness of software is affected mainly by four properties:
meillo@15 557 portability of code, portability of data, range of usability, and reusability of parts.
meillo@13 558 .PP
meillo@15 559 (1)
meillo@61 560 .I "``Portability of code''
meillo@61 561 means using high-level programming languages,
meillo@13 562 sticking to the standard,
meillo@47 563 .[ [
meillo@47 564 kernighan pike
meillo@47 565 practice of programming
meillo@47 566 .], chapter\|8]
meillo@13 567 and avoiding optimizations that introduce dependencies on specific hardware.
meillo@61 568 Hardware has a much shorter lifespan than software.
meillo@61 569 By chaining software to specific hardware,
meillo@61 570 its lifetime is limited to that of this hardware.
meillo@13 571 In contrast, software should be easy to port \(en
meillo@23 572 adaptation is the key to success.
meillo@13 573 .PP
meillo@15 574 (2)
meillo@61 575 .I "``Portability of data''
meillo@15 576 is best achieved by avoiding binary representations
meillo@61 577 to store data, since binary representations differ from machine to machine.
meillo@23 578 Textual representation is favored.
meillo@61 579 Historically, \s-1ASCII\s0 was the character set of choice;
meillo@61 580 for the future, \s-1UTF\s0-8 might be the better way forward.
meillo@13 581 Important is that it is a plain text representation in a
meillo@61 582 very common character set encoding.
meillo@13 583 Apart from being able to transfer data between machines,
meillo@61 584 readable data has the great advantage that humans are able to directly
meillo@45 585 read and edit it with text editors and other tools from the Unix toolchest.
meillo@47 586 .[ [
meillo@47 587 gancarz
meillo@47 588 unix philosophy
meillo@47 589 .], page 56 ff.]
meillo@13 590 .PP
meillo@15 591 (3)
meillo@15 592 A large
meillo@61 593 .I "``range of usability''
meillo@23 594 ensures good adaptation, and thus good survival.
meillo@61 595 It is a special distinction when software becomes used in fields of endeavor,
meillo@61 596 the original authors never imagined.
meillo@13 597 Software that solves problems in a general way will likely be used
meillo@45 598 for many kinds of similar problems.
meillo@45 599 Being too specific limits the range of usability.
meillo@13 600 Requirements change through time, thus use cases change or even vanish.
meillo@61 601 As a good example of this point,
meillo@13 602 Allman identifies flexibility to be one major reason for sendmail's success:
meillo@13 603 .[
meillo@44 604 allman
meillo@44 605 sendmail
meillo@13 606 .]
meillo@13 607 .QP
meillo@13 608 Second, I limited myself to the routing function [...].
meillo@13 609 This was a departure from the dominant thought of the time, [...].
meillo@13 610 .QP
meillo@45 611 Third, the sendmail configuration file was flexible enough to adapt
meillo@13 612 to a rapidly changing world [...].
meillo@12 613 .LP
meillo@45 614 Successful software adapts itself to the changing world.
meillo@13 615 .PP
meillo@15 616 (4)
meillo@61 617 .I "``Reusability of parts''
meillo@61 618 goes one step further.
meillo@61 619 Software may become obsolete and completely lose its field of action,
meillo@61 620 but the constituent parts of the software may be general and independent enough
meillo@13 621 to survive this death.
meillo@54 622 If software is built by combining small independent programs,
meillo@45 623 then these parts are readily available for reuse.
meillo@61 624 Who cares that the large program is a failure,
meillo@61 625 if parts of it become successful instead?
meillo@10 626
meillo@48 627 .H 2 "Summary
meillo@0 628 .LP
meillo@61 629 This chapter explained ideas central to the Unix Philosophy.
meillo@45 630 For each of the ideas, the advantages they introduce were explained.
meillo@61 631 The Unix Philosophy is a set of guidelines that help in the design of
meillo@61 632 more valuable software.
meillo@61 633 From the viewpoint of a software developer or software designer,
meillo@61 634 the Unix Philosophy provides answers to many software design problems.
meillo@14 635 .PP
meillo@61 636 The various ideas comprising the Unix Philosophy are very interweaved
meillo@14 637 and can hardly be applied independently.
meillo@61 638 The most important messages are:
meillo@45 639 .I "``Keep it simple!''" ,
meillo@14 640 .I "``Do one thing well!''" ,
meillo@14 641 and
meillo@14 642 .I "``Use software leverage!''
meillo@0 643
meillo@8 644
meillo@8 645
meillo@48 646 .H 1 "Case study: \s-1MH\s0
meillo@18 647 .LP
meillo@30 648 The previous chapter introduced and explained the Unix Philosophy
meillo@18 649 from a general point of view.
meillo@61 650 The driving force was that of the guidelines;
meillo@61 651 references to existing software were given only sparsely.
meillo@18 652 In this and the next chapter, concrete software will be
meillo@18 653 the driving force in the discussion.
meillo@18 654 .PP
meillo@23 655 This first case study is about the mail user agents (\s-1MUA\s0)
meillo@54 656 \s-1MH\s0 (``mail handler'') and its descendant \fInmh\fP
meillo@23 657 (``new mail handler'').
meillo@47 658 .[
meillo@47 659 nmh website
meillo@47 660 .]
meillo@23 661 \s-1MUA\s0s provide functions to read, compose, and organize mail,
meillo@45 662 but (ideally) not to transfer it.
meillo@45 663 In this document, the name \s-1MH\s0 will be used to include nmh.
meillo@19 664 A distinction will only be made if differences between
meillo@45 665 \s-1MH\s0 and nmh are described.
meillo@18 666
meillo@0 667
meillo@48 668 .H 2 "Historical background
meillo@0 669 .LP
meillo@61 670 Electronic mail was available in Unix from a very early stage.
meillo@30 671 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
meillo@30 672 which was already present in the First Edition.
meillo@46 673 .[ [
meillo@44 674 salus
meillo@44 675 quarter century of unix
meillo@46 676 .], page 41 f.]
meillo@45 677 It was a small program that either printed the user's mailbox file
meillo@54 678 or appended text to someone else's mailbox file,
meillo@19 679 depending on the command line arguments.
meillo@19 680 .[
meillo@44 681 manual mail(1)
meillo@19 682 .]
meillo@19 683 It was a program that did one job well.
meillo@23 684 This job was emailing, which was very simple then.
meillo@19 685 .PP
meillo@23 686 Later, emailing became more powerful, and thus more complex.
meillo@19 687 The simple \f(CWmail\fP, which knew nothing of subjects,
meillo@19 688 independent handling of single messages,
meillo@61 689 and long-term email storage, was not powerful enough anymore.
meillo@61 690 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with a capital `M')
meillo@45 691 to provide additional functions for emailing.
meillo@61 692 Mail was still one program, but was large and did several jobs.
meillo@61 693 Its user interface was modeled after \fIed\fP.
meillo@61 694 Ed is designed for humans, but is still scriptable.
meillo@61 695 \fImailx\fP is the adaptation of Berkeley Mail for System V.
meillo@19 696 .[
meillo@44 697 ritter
meillo@44 698 mailx history
meillo@19 699 .]
meillo@61 700 Elm, pine, mutt, and a slew of graphical \s-1MUA\s0s
meillo@61 701 followed Mail's direction:
meillo@61 702 large, monolithic programs which included all emailing functions.
meillo@19 703 .PP
meillo@23 704 A different way was taken by the people of \s-1RAND\s0 Corporation.
meillo@61 705 Initially, they also had used a monolithic mail system
meillo@30 706 called \s-1MS\s0 (for ``mail system'').
meillo@19 707 But in 1977, Stockton Gaines and Norman Shapiro
meillo@61 708 came up with a proposal for a new email system concept \(en
meillo@45 709 one that honored the Unix Philosophy.
meillo@19 710 The concept was implemented by Bruce Borden in 1978 and 1979.
meillo@19 711 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
meillo@18 712 .PP
meillo@18 713 Since then, \s-1RAND\s0, the University of California at Irvine and
meillo@19 714 at Berkeley, and several others have contributed to the software.
meillo@18 715 However, it's core concepts remained the same.
meillo@23 716 In the late 90s, when development of \s-1MH\s0 slowed down,
meillo@19 717 Richard Coleman started with \fInmh\fP, the new mail handler.
meillo@61 718 His goal was to improve \s-1MH\s0 especially in regard to
meillo@23 719 the requirements of modern emailing.
meillo@19 720 Today, nmh is developed by various people on the Internet.
meillo@18 721 .[
meillo@44 722 ware
meillo@44 723 rand history
meillo@18 724 .]
meillo@18 725 .[
meillo@44 726 peek
meillo@44 727 mh
meillo@18 728 .]
meillo@0 729
meillo@48 730 .H 2 "Contrasts to monolithic mail systems
meillo@0 731 .LP
meillo@19 732 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
meillo@61 733 Although some very little known toolchest \s-1MUA\s0s might also exist,
meillo@61 734 this statement reflects the situation pretty well.
meillo@19 735 .PP
meillo@30 736 Monolithic \s-1MUA\s0s gather all their functions in one program.
meillo@30 737 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
meillo@23 738 Following is a list of important programs of \s-1MH\s0's toolchest
meillo@30 739 and their function.
meillo@61 740 It gives an indication of what the toolchest looks like.
meillo@19 741 .IP \(bu
meillo@19 742 .CW inc :
meillo@30 743 incorporate new mail (this is how mail enters the system)
meillo@19 744 .IP \(bu
meillo@19 745 .CW scan :
meillo@19 746 list messages in folder
meillo@19 747 .IP \(bu
meillo@19 748 .CW show :
meillo@19 749 show message
meillo@19 750 .IP \(bu
meillo@19 751 .CW next\fR/\fPprev :
meillo@19 752 show next/previous message
meillo@19 753 .IP \(bu
meillo@19 754 .CW folder :
meillo@19 755 change current folder
meillo@19 756 .IP \(bu
meillo@19 757 .CW refile :
meillo@45 758 refile message into different folder
meillo@19 759 .IP \(bu
meillo@19 760 .CW rmm :
meillo@19 761 remove message
meillo@19 762 .IP \(bu
meillo@19 763 .CW comp :
meillo@45 764 compose new message
meillo@19 765 .IP \(bu
meillo@19 766 .CW repl :
meillo@45 767 reply to message
meillo@19 768 .IP \(bu
meillo@19 769 .CW forw :
meillo@45 770 forward message
meillo@19 771 .IP \(bu
meillo@19 772 .CW send :
meillo@45 773 send prepared message (this is how mail leaves the system)
meillo@0 774 .LP
meillo@19 775 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
meillo@61 776 The user does not leave the shell to run \s-1MH\s0;
meillo@45 777 instead he uses the various \s-1MH\s0 programs within the shell.
meillo@23 778 Using a monolithic program with a captive user interface
meillo@23 779 means ``entering'' the program, using it, and ``exiting'' the program.
meillo@23 780 Using toolchests like \s-1MH\s0 means running programs,
meillo@45 781 alone or in combination with others, also from other toolchests,
meillo@23 782 without leaving the shell.
meillo@30 783
meillo@48 784 .H 2 "Data storage
meillo@30 785 .LP
meillo@61 786 \s-1MH\s0's mail storage consists of a hierarchy under the user's
meillo@34 787 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
meillo@34 788 where mail folders are directories and mail messages are text files
meillo@34 789 within them.
meillo@34 790 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
meillo@45 791 the public message sequences of that folder,
meillo@61 792 for instance, the \fIunseen\fP sequence for new messages.
meillo@34 793 Mail messages are text files located in a mail folder.
meillo@61 794 The files contain the messages as they were received,
meillo@61 795 and they are named by ascending numbers in each folder.
meillo@19 796 .PP
meillo@30 797 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
meillo@30 798 Alternatives are \fImbox\fP and \fImaildir\fP.
meillo@61 799 In the mbox format, all messages are stored within one file.
meillo@30 800 This was a good solution in the early days, when messages
meillo@61 801 were only a few lines of text deleted within a short period of time.
meillo@61 802 Today, with single messages often including several megabytes
meillo@61 803 of attachments, this is a bad solution.
meillo@30 804 Another disadvantage of the mbox format is that it is
meillo@30 805 more difficult to write tools that work on mail messages,
meillo@30 806 because it is always necessary to first find and extract
meillo@30 807 the relevant message in the mbox file.
meillo@45 808 With the \s-1MH\s0 mailbox format, each message is a separate file.
meillo@30 809 Also, the problem of concurrent access to one mailbox is
meillo@30 810 reduced to the problem of concurrent access to one message.
meillo@45 811 The maildir format is generally similar to the \s-1MH\s0 format,
meillo@30 812 but modified towards guaranteed reliability.
meillo@30 813 This involves some complexity, unfortunately.
meillo@34 814 .PP
meillo@34 815 Working with \s-1MH\s0's toolchest on mailboxes is much like
meillo@34 816 working with Unix' toolchest on directory trees:
meillo@34 817 \f(CWscan\fP is like \f(CWls\fP,
meillo@34 818 \f(CWshow\fP is like \f(CWcat\fP,
meillo@34 819 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
meillo@34 820 \f(CWrefile\fP is like \f(CWmv\fP,
meillo@34 821 and \f(CWrmm\fP is like \f(CWrm\fP.
meillo@34 822 .PP
meillo@61 823 \s-1MH\s0 extends the context of processes in Unix by two more items
meillo@45 824 for its tools:
meillo@34 825 .IP \(bu
meillo@34 826 The current mail folder, which is similar to the current working directory.
meillo@34 827 For mail folders, \f(CWfolder\fP provides the corresponding functionality
meillo@34 828 of \f(CWcd\fP and \f(CWpwd\fP for directories.
meillo@34 829 .IP \(bu
meillo@34 830 Sequences, which are named sets of messages in a mail folder.
meillo@34 831 The current message, relative to a mail folder, is a special sequence.
meillo@34 832 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
meillo@34 833 .LP
meillo@61 834 In contrast to the general process context in Unix,
meillo@61 835 which is maintained by the kernel,
meillo@45 836 \s-1MH\s0's context must be maintained by the tools themselves.
meillo@45 837 Usually there is one context per user, which resides in his
meillo@45 838 \f(CWcontext\fP file in the \s-1MH\s0 directory,
meillo@45 839 but a user can have several contexts, too.
meillo@45 840 Public sequences are an exception, as they belong to a mail folder,
meillo@45 841 and reside in the \f(CW.mh_sequences\fP file there.
meillo@34 842 .[
meillo@44 843 man page mh-profile mh-sequence
meillo@34 844 .]
meillo@20 845
meillo@48 846 .H 2 "Discussion of the design
meillo@0 847 .LP
meillo@45 848 This section discusses \s-1MH\s0 in regard to the tenets
meillo@45 849 of the Unix Philosophy that Gancarz identified.
meillo@20 850
meillo@20 851 .PP
meillo@33 852 .B "Small is beautiful
meillo@20 853 and
meillo@33 854 .B "do one thing well
meillo@20 855 are two design goals that are directly visible in \s-1MH\s0.
meillo@61 856 Gancarz actually uses \s-1MH\s0 in his book as example under the
meillo@45 857 headline ``Making \s-1UNIX\s0 Do One Thing Well'':
meillo@46 858 .[ [
meillo@44 859 gancarz
meillo@44 860 unix philosophy
meillo@46 861 .], page 125 ff.]
meillo@20 862 .QP
meillo@20 863 [\s-1MH\s0] consists of a series of programs which
meillo@20 864 when combined give the user an enormous ability
meillo@20 865 to manipulate electronic mail messages.
meillo@20 866 A complex application, it shows that not only is it
meillo@20 867 possible to build large applications from smaller
meillo@20 868 components, but also that such designs are actually preferable.
meillo@20 869 .LP
meillo@45 870 The various programs of \s-1MH\s0 were relatively easy to write,
meillo@61 871 because each one was small, limited to one function,
meillo@61 872 and had clear boundaries.
meillo@61 873 For the same reasons, they are also easy to maintain.
meillo@61 874 Further more, the system can easily get extended:
meillo@61 875 One only needs to place a new program into the toolchest.
meillo@61 876 This was done when \s-1MIME\s0 support was added
meillo@20 877 (e.g. \f(CWmhbuild\fP).
meillo@61 878 Also, different programs can exist to do basically the same job
meillo@20 879 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
meillo@45 880 .PP
meillo@61 881 If someone needs a mail system with some additional
meillo@61 882 functionality that is not available anywhere yet,
meillo@61 883 it is beneficial to expand a toolchest system like \s-1MH\s0.
meillo@45 884 There he can add new functionality by simply adding additional
meillo@61 885 programs to the toolchest;
meillo@61 886 he does not risk to break existing functionality by doing so.
meillo@20 887
meillo@20 888 .PP
meillo@61 889 .B "Store data in flat text files" ;
meillo@61 890 this principle was followed by \s-1MH\s0.
meillo@34 891 This is not surprising, because email messages are already plain text.
meillo@34 892 \s-1MH\s0 stores the messages as it receives them,
meillo@61 893 thus any other tool that works on \s-1RFC\s0\|2822 compliant mail
meillo@61 894 messages can operate
meillo@34 895 on the messages in an \s-1MH\s0 mailbox.
meillo@61 896 All other files \s-1MH\s0 uses are plain text as well.
meillo@34 897 It is therefore possible and encouraged to use the text processing
meillo@34 898 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
meillo@20 899
meillo@20 900 .PP
meillo@33 901 .B "Avoid captive user interfaces" .
meillo@19 902 \s-1MH\s0 is perfectly suited for non-interactive use.
meillo@61 903 It offers all functions directly, without captive user interfaces.
meillo@61 904 If users want a graphical user interface,
meillo@53 905 they can have it with \fIxmh\fP, \fIexmh\fP,
meillo@53 906 or with the Emacs interface \fImh-e\fP.
meillo@53 907 These are frontends for the \s-1MH\s0 toolchest.
meillo@61 908 This means all email-related work is still done by \s-1MH\s0 tools,
meillo@45 909 but the frontend calls the appropriate commands when the user
meillo@53 910 clicks on buttons or pushes a key.
meillo@45 911 .PP
meillo@61 912 Providing additional user interfaces in form of frontends is a good
meillo@19 913 approach, because it does not limit the power of the backend itself.
meillo@61 914 The frontend will only be able to make a subset of the
meillo@61 915 backend's power and flexibility available to the user,
meillo@61 916 but if it is a separate program,
meillo@20 917 then the missing parts can still be accessed at the backend directly.
meillo@61 918 If it is integrated, then this will be much more difficult.
meillo@61 919 An additional advantage is the ability to have different frontends
meillo@45 920 to the same backend.
meillo@19 921
meillo@19 922 .PP
meillo@33 923 .B "Choose portability over efficiency
meillo@20 924 and
meillo@33 925 .B "use shell scripts to increase leverage and portability" .
meillo@20 926 These two tenets are indirectly, but nicely, demonstrated by
meillo@30 927 Bolsky and Korn in their book about the Korn Shell.
meillo@20 928 .[
meillo@44 929 bolsky korn
meillo@44 930 korn shell
meillo@20 931 .]
meillo@45 932 Chapter\|18 of the book shows a basic implementation
meillo@20 933 of a subset of \s-1MH\s0 in ksh scripts.
meillo@61 934 This is just a demonstration, but a brilliant one.
meillo@20 935 It shows how quickly one can implement such a prototype with shell scripts,
meillo@20 936 and how readable they are.
meillo@61 937 The implementation in scripting language may not be very fast,
meillo@61 938 but it can be fast enough, and this is all that matters.
meillo@20 939 By having the code in an interpreted language, like the shell,
meillo@61 940 portability becomes a minor issue if we assume the interpreter
meillo@20 941 to be widespread.
meillo@45 942 .PP
meillo@20 943 This demonstration also shows how easy it is to create single programs
meillo@61 944 of toolchest software.
meillo@61 945 Eight tools (two of them having multiple names) and 16 functions
meillo@45 946 with supporting code are presented to the reader.
meillo@45 947 The tools comprise less than 40 lines of ksh each,
meillo@30 948 in total about 200 lines.
meillo@45 949 The functions comprise less than 80 lines of ksh each,
meillo@30 950 in total about 450 lines.
meillo@20 951 Such small software is easy to write, easy to understand,
meillo@20 952 and thus easy to maintain.
meillo@61 953 A toolchest improves one's ability to only write some parts of a
meillo@61 954 program while still creating a working result.
meillo@45 955 Expanding the toolchest, even without global changes,
meillo@45 956 will likely be possible.
meillo@20 957
meillo@20 958 .PP
meillo@33 959 .B "Use software leverage to your advantage
meillo@20 960 and the lesser tenet
meillo@33 961 .B "allow the user to tailor the environment
meillo@20 962 are ideally followed in the design of \s-1MH\s0.
meillo@21 963 Tailoring the environment is heavily encouraged by the ability to
meillo@30 964 directly define default options to programs.
meillo@30 965 It is even possible to define different default options
meillo@45 966 depending on the name under which a program is called.
meillo@45 967 Software leverage is heavily encouraged by the ease of
meillo@45 968 creating shell scripts that run a specific command line,
meillo@30 969 built of several \s-1MH\s0 programs.
meillo@61 970 There are few pieces of software that encourages users to tailor their
meillo@61 971 environment and to leverage the use of the software like \s-1MH\s0.
meillo@45 972 .PP
meillo@61 973 Just to cite one example:
meillo@23 974 One might prefer a different listing format for the \f(CWscan\fP
meillo@21 975 program.
meillo@30 976 It is possible to take one of the distributed format files
meillo@21 977 or to write one yourself.
meillo@21 978 To use the format as default for \f(CWscan\fP, a single line,
meillo@21 979 reading
meillo@21 980 .DS
meillo@21 981 scan: -form FORMATFILE
meillo@21 982 .DE
meillo@21 983 must be added to \f(CW.mh_profile\fP.
meillo@61 984 If one wants this alternative format available as an additional command,
meillo@61 985 instead of changing the default, he just needs to create a link to
meillo@23 986 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
meillo@21 987 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
meillo@61 988 as the option should only be in effect for a program that is invoked as
meillo@21 989 \f(CWscan2\fP.
meillo@20 990
meillo@20 991 .PP
meillo@33 992 .B "Make every program a filter
meillo@61 993 is hard to find implemented in \s-1MH\s0.
meillo@61 994 The reason is that most of \s-1MH\s0's tools provide
meillo@45 995 basic file system operations for mailboxes.
meillo@61 996 It is for the same reason because that \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP,
meillo@45 997 and \f(CWrm\fP aren't filters neither.
meillo@61 998 \s-1MH\s0 does not provide many filters itself,
meillo@61 999 but it provides a basis upon which to write filters.
meillo@45 1000 An example would be a mail text highlighter,
meillo@61 1001 a program that makes use of a color terminal to display header lines,
meillo@61 1002 quotations, and signatures in distinct colors.
meillo@45 1003 The author's version of such a program is an awk script with 25 lines.
meillo@21 1004
meillo@21 1005 .PP
meillo@33 1006 .B "Build a prototype as soon as possible
meillo@21 1007 was again well followed by \s-1MH\s0.
meillo@61 1008 This tenet, of course, focuses on early development, which is a
meillo@21 1009 long time ago for \s-1MH\s0.
meillo@21 1010 But without following this guideline at the very beginning,
meillo@23 1011 Bruce Borden may have not convinced the management of \s-1RAND\s0
meillo@23 1012 to ever create \s-1MH\s0.
meillo@23 1013 In Bruce' own words:
meillo@46 1014 .[ [
meillo@44 1015 ware rand history
meillo@46 1016 .], page 132]
meillo@21 1017 .QP
meillo@45 1018 [...] but [Stockton Gaines and Norm Shapiro] were not able
meillo@23 1019 to convince anyone that such a system would be fast enough to be usable.
meillo@21 1020 I proposed a very short project to prove the basic concepts,
meillo@21 1021 and my management agreed.
meillo@21 1022 Looking back, I realize that I had been very lucky with my first design.
meillo@21 1023 Without nearly enough design work,
meillo@21 1024 I built a working environment and some header files
meillo@21 1025 with key structures and wrote the first few \s-1MH\s0 commands:
meillo@21 1026 inc, show/next/prev, and comp.
meillo@21 1027 [...]
meillo@21 1028 With these three, I was able to convince people that the structure was viable.
meillo@21 1029 This took about three weeks.
meillo@0 1030
meillo@48 1031 .H 2 "Problems
meillo@0 1032 .LP
meillo@61 1033 \s-1MH\s0 is not without its problems.
meillo@61 1034 There are two main problems: one is technical, the other pertains to human behavior.
meillo@22 1035 .PP
meillo@61 1036 \s-1MH\s0 is old and email today is quite different than it was in the time
meillo@22 1037 when \s-1MH\s0 was designed.
meillo@61 1038 \s-1MH\s0 adapted to the changes fairly well, but it has its limitations.
meillo@22 1039 \s-1MIME\s0 support and support for different character encodings
meillo@22 1040 is available, but only on a moderate level.
meillo@45 1041 This comes from limited development resources.
meillo@61 1042 A larger and more active developer base could quickly remedy this.
meillo@45 1043 But \s-1MH\s0 is also limited by design, which is the larger problem.
meillo@54 1044 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extent.
meillo@61 1045 These design conflicts are not easily solvable
meillo@61 1046 and may require a redesign.
meillo@61 1047 \s-1IMAP\s0 may be too incompatible with the classic mail model,
meillo@61 1048 which \s-1MH\s0 covers, so \s-1MH\s0 may never support it well.
meillo@61 1049 (Using \s-1IMAP\s0 and a filesystem abstraction layer to only map
meillo@61 1050 a remote directory into the local filesystem, is a different topic.
meillo@61 1051 \s-1IMAP\s0 support is seen as being able to access the special
meillo@61 1052 mail features of the protocol.)
meillo@22 1053 .PP
meillo@61 1054 The other kind of problem relates to human habits.
meillo@45 1055 In this world, where almost all \s-1MUA\s0s are monolithic,
meillo@61 1056 it is very difficult to convince people to use a toolchest-style \s-1MUA\s0
meillo@22 1057 like \s-1MH\s0.
meillo@61 1058 These habits are so strong, that even people who understand the concept
meillo@61 1059 and advantages of \s-1MH\s0 are reluctant to switch,
meillo@30 1060 simply because \s-1MH\s0 is different.
meillo@61 1061 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar
meillo@61 1062 look and feel, are quite outdated and thus not very appealing in comparison
meillo@61 1063 to the modern interfaces of many monolithic \s-1MUA\s0s.
meillo@53 1064 One notable exception is \fImh-e\fP which provides an Emacs interface
meillo@53 1065 to \s-1MH\s0.
meillo@53 1066 \fIMh-e\fP looks much like \fImutt\fP or \fIpine\fP,
meillo@53 1067 but it has buttons, menus, and graphical display capabilities.
meillo@20 1068
meillo@53 1069 .H 2 "Summary
meillo@20 1070 .LP
meillo@45 1071 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design.
meillo@61 1072 It consists of a toolchest of small tools, each of which does one job well.
meillo@31 1073 The toolchest approach offers great flexibility to the user.
meillo@45 1074 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0.
meillo@61 1075 This makes \s-1MH\s0 a very powerful mail system,
meillo@61 1076 and extending and customizing \s-1MH\s0 is easy and encouraged.
meillo@31 1077 .PP
meillo@31 1078 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
meillo@31 1079 Its overall design follows clear rules.
meillo@61 1080 The single tools do only one job; thus they are easy to understand,
meillo@61 1081 write, and maintain.
meillo@31 1082 They are all independent and do not interfere with the others.
meillo@61 1083 Automated testing of their function is a straightforward task.
meillo@31 1084 .PP
meillo@61 1085 It is sad, that \s-1MH\s0's dissimilarity to other \s-1MUA\s0s is its
meillo@61 1086 largest problem, as this dissimilarity is also its largest advantage.
meillo@61 1087 Unfortunately, most people's habits are stronger
meillo@61 1088 than the attraction of the clear design and the power \s-1MH\s0 offers.
meillo@0 1089
meillo@8 1090
meillo@8 1091
meillo@48 1092 .H 1 "Case study: uzbl
meillo@32 1093 .LP
meillo@61 1094 The last chapter focused on the \s-1MUA\s0 \s-1MH\s0,
meillo@61 1095 which is an old and established piece of software.
meillo@45 1096 This chapter covers uzbl, a fresh new project.
meillo@45 1097 Uzbl is a web browser that adheres to the Unix Philosophy.
meillo@45 1098 Its name comes from the \fILolspeak\fP word for ``usable'';
meillo@61 1099 both are pronounced in the same way.
meillo@0 1100
meillo@48 1101 .H 2 "Historical background
meillo@0 1102 .LP
meillo@32 1103 Uzbl was started by Dieter Plaetinck in April 2009.
meillo@61 1104 The idea was born in a thread on the Arch Linux forums.
meillo@32 1105 .[
meillo@44 1106 arch linux forums
meillo@44 1107 browser
meillo@32 1108 .]
meillo@61 1109 After some discussion about the failures of well-known web browsers,
meillo@61 1110 Plaetinck (alias Dieter@be) came up with a rough proposal
meillo@61 1111 of how a better web browser could look.
meillo@61 1112 In response to another member who asked if Plaetinck would write this
meillo@61 1113 program because it sounded fantastic, Plaetinck replied:
meillo@32 1114 ``Maybe, if I find the time ;-)''.
meillo@32 1115 .PP
meillo@32 1116 Fortunately, he found the time.
meillo@32 1117 One day later, the first prototype was out.
meillo@61 1118 One week later, uzbl had its own website.
meillo@47 1119 .[
meillo@47 1120 uzbl website
meillo@47 1121 .]
meillo@61 1122 One month after the initial code was presented,
meillo@61 1123 a mailing list was set up to coordinate and discuss further development,
meillo@61 1124 and a wiki was added to store documentation and scripts that cropped up
meillo@61 1125 on the mailing list and elsewhere.
meillo@32 1126 .PP
meillo@61 1127 In the first year of uzbl's existence, it was heavily developed on various branches.
meillo@32 1128 Plaetinck's task became more and more to only merge the best code from the
meillo@32 1129 different branches into his main branch, and to apply patches.
meillo@47 1130 .[
meillo@47 1131 lwn uzbl
meillo@47 1132 .]
meillo@32 1133 About once a month, Plaetinck released a new version.
meillo@32 1134 In September 2009, he presented several forks of uzbl.
meillo@47 1135 .[ [
meillo@47 1136 uzbl website
meillo@47 1137 .], news archive]
meillo@61 1138 Uzbl actually opened the field for a whole family of web browsers with
meillo@61 1139 a similar design.
meillo@32 1140 .PP
meillo@61 1141 In July 2009, \fILinux Weekly News\fP published an interview with
meillo@61 1142 Plaetinck about uzbl.
meillo@47 1143 .[
meillo@47 1144 lwn uzbl
meillo@47 1145 .]
meillo@32 1146 In September 2009, the uzbl web browser was on \fISlashdot\fP.
meillo@47 1147 .[
meillo@47 1148 slashdot uzbl
meillo@47 1149 .]
meillo@0 1150
meillo@48 1151 .H 2 "Contrasts to other web browsers
meillo@0 1152 .LP
meillo@32 1153 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
meillo@32 1154 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
meillo@32 1155 .PP
meillo@32 1156 Today, uzbl is divided into uzbl-core and uzbl-browser.
meillo@61 1157 Uzbl-core is, as its name indicates, the core of uzbl.
meillo@61 1158 It handles commands and events to interface with other programs,
meillo@61 1159 and displays webpages by using \fIwebkit\fP as its rendering engine.
meillo@61 1160 Uzbl-browser combines uzbl-core with a selection of handler scripts,
meillo@61 1161 a status bar, an event manager, yanking, pasting, page searching,
meillo@61 1162 zooming, and much more functionality, to form a ``complete'' web browser.
meillo@61 1163 In the following text, the term ``uzbl'' usually refers to uzbl-browser,
meillo@32 1164 so uzbl-core is included.
meillo@32 1165 .PP
meillo@61 1166 Unlike most other web browsers, uzbl is mainly the mediator between
meillo@45 1167 various tools that cover single jobs.
meillo@61 1168 Uzbl listens for commands on a named pipe (fifo), a Unix socket,
meillo@35 1169 and on stdin, and it writes events to a Unix socket and to stdout.
meillo@35 1170 Loading a webpage in a running uzbl instance requires only:
meillo@32 1171 .DS
meillo@32 1172 echo 'uri http://example.org' >/path/to/uzbl-fifo
meillo@32 1173 .DE
meillo@61 1174 The rendering of the webpage is done by libwebkit,
meillo@61 1175 around which uzbl-core is built.
meillo@32 1176 .PP
meillo@45 1177 Downloads, browsing history, bookmarks, and the like are not provided
meillo@61 1178 by the core itself like they are in other web browsers.
meillo@61 1179 Uzbl-browser also only provides ``handler scripts'' which wrap
meillo@61 1180 external applications to provide the actual functionality.
meillo@32 1181 For instance, \fIwget\fP is used to download files and uzbl-browser
meillo@32 1182 includes a script that calls wget with appropriate options in
meillo@32 1183 a prepared environment.
meillo@32 1184 .PP
meillo@61 1185 Modern web browsers are proud to have addons, plugins, modules,
meillo@61 1186 and so forth.
meillo@32 1187 This is their effort to achieve similar goals.
meillo@61 1188 But instead of using existing external programs, modern web browsers
meillo@45 1189 include these functions.
meillo@0 1190
meillo@48 1191 .H 2 "Discussion of the design
meillo@0 1192 .LP
meillo@61 1193 This section discusses uzbl in regard to the Unix Philosophy,
meillo@32 1194 as identified by Gancarz.
meillo@32 1195
meillo@32 1196 .PP
meillo@35 1197 .B "Make each program do one thing well" .
meillo@35 1198 Uzbl tries to be a web browser and nothing else.
meillo@61 1199 The common definition of a web browser is highly influenced by
meillo@61 1200 existing implementations of web browsers.
meillo@61 1201 But a web browser should be a program to browse the web, and nothing more.
meillo@61 1202 This is the one thing it should do.
meillo@36 1203 .PP
meillo@61 1204 Web browsers should not, for instance, manage downloads;
meillo@61 1205 this is the job of download managers.
meillo@61 1206 A download manager is primary concerned with downloading files.
meillo@35 1207 Modern web browsers provide download management only as a secondary feature.
meillo@61 1208 How could they do this job better than programs that exist only for
meillo@35 1209 this very job?
meillo@61 1210 And why would anyone want less than the best download manager available?
meillo@32 1211 .PP
meillo@35 1212 A web browser's job is to let the user browse the web.
meillo@35 1213 This means, navigating through websites by following links.
meillo@36 1214 Rendering the \s-1HTML\s0 sources is a different job, too.
meillo@61 1215 In uzbl's case, this is covered by the webkit rendering engine.
meillo@61 1216 Handling audio and video content, PostScript, \s-1PDF\s0,
meillo@61 1217 and other such files are also not the job of a web browser.
meillo@61 1218 Such content should be handled by external programs
meillo@61 1219 that were written to handle such data.
meillo@35 1220 Uzbl strives to do it this way.
meillo@36 1221 .PP
meillo@61 1222 Remember Doug McIlroy's words:
meillo@35 1223 .I
meillo@35 1224 ``Write programs that do one thing and do it well.
meillo@35 1225 Write programs to work together.''
meillo@35 1226 .R
meillo@35 1227 .PP
meillo@35 1228 The lesser tenet
meillo@35 1229 .B "allow the user to tailor the environment
meillo@61 1230 applies here as well.
meillo@61 1231 Previously, the question, ``Why would anyone want anything less than the
meillo@61 1232 best program for the job?'' was put forward.
meillo@61 1233 But as personal preferences matter, it might be more important to ask:
meillo@61 1234 ``Why would anyone want something other than his preferred program for
meillo@61 1235 the job?''
meillo@36 1236 .PP
meillo@61 1237 Users typically want one program for a specific job.
meillo@61 1238 Hence, whenever one wishes to download something,
meillo@45 1239 the same download manager should be used.
meillo@61 1240 More advanced users might want to use one download manager in a certain
meillo@61 1241 situation and another in a different situation;
meillo@61 1242 they should be able to configure it this way.
meillo@61 1243 With uzbl, any download manager can be used.
meillo@61 1244 To switch to a different one, a single line in a small handler script
meillo@35 1245 needs to be changed.
meillo@61 1246 Alternatively, it would be possible to query which download manager to use by
meillo@61 1247 reading a global file or an environment variable in the handler script.
meillo@61 1248 Of course, uzbl can use a different handler script as well.
meillo@61 1249 This simply requires a one line change in uzbl's configuration file.
meillo@36 1250 .PP
meillo@61 1251 Uzbl neither has its own download manager nor depends on a specific one;
meillo@61 1252 hence, uzbl's browsing abilities will not be crippled by having
meillo@35 1253 a bad download manager.
meillo@61 1254 Uzbl's download capabilities will be as good as the best
meillo@36 1255 download manager available on the system.
meillo@38 1256 Of course, this applies to all of the other supplementary tools, too.
meillo@32 1257
meillo@32 1258 .PP
meillo@36 1259 .B "Use software leverage to your advantage" .
meillo@36 1260 Uzbl is designed to be extended by external tools.
meillo@36 1261 These external tools are usually wrapped by small handler shell scripts.
meillo@61 1262 Shell scripts form the basis for the glue which holds the various
meillo@61 1263 parts together.
meillo@36 1264 .PP
meillo@45 1265 The history mechanism of uzbl shall be presented as an example.
meillo@36 1266 Uzbl is configured to spawn a script to append an entry to the history
meillo@36 1267 whenever the event of a fully loaded page occurs.
meillo@45 1268 The script to append the entry to the history is not much more than:
meillo@36 1269 .DS
meillo@36 1270 #!/bin/sh
meillo@36 1271 file=/path/to/uzbl-history
meillo@36 1272 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
meillo@36 1273 .DE
meillo@61 1274 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title,
meillo@61 1275 respectively.
meillo@45 1276 .PP
meillo@45 1277 For loading an entry, a key is bound to spawn a load-from-history script.
meillo@36 1278 The script reverses the history to have newer entries first,
meillo@61 1279 displays \fIdmenu\fP to let the user select an item,
meillo@61 1280 and then writes the selected \s-1URL\s0 into uzbl's command input pipe.
meillo@45 1281 With error checking and corner case handling removed,
meillo@45 1282 the script looks like this:
meillo@36 1283 .DS
meillo@36 1284 #!/bin/sh
meillo@36 1285 file=/path/to/uzbl-history
meillo@36 1286 goto=`tac $file | dmenu | cut -d' ' -f 3`
meillo@36 1287 echo "uri $goto" > $4
meillo@36 1288 .DE
meillo@36 1289 \f(CW$4\fP expands to the path of the command input pipe of the current
meillo@36 1290 uzbl instance.
meillo@32 1291
meillo@32 1292 .PP
meillo@33 1293 .B "Avoid captive user interfaces" .
meillo@61 1294 One could say that uzbl, to a large extent, actually \fIis\fP
meillo@36 1295 a captive user interface.
meillo@61 1296 But the difference from other web browsers is that uzbl is only
meillo@45 1297 the captive user interface frontend (and the core of the backend).
meillo@38 1298 Many parts of the backend are independent of uzbl.
meillo@61 1299 For some external programs, handler scripts are distributed with uzbl;
meillo@61 1300 but arbitrary additional functionality can always be added if desired.
meillo@37 1301 .PP
meillo@37 1302 The frontend is captive \(en that is true.
meillo@37 1303 This is okay for the task of browsing the web, as this task is only relevant
meillo@61 1304 to humans.
meillo@61 1305 Automated programs would \fIcrawl\fP the web, that means,
meillo@61 1306 read the source directly, including all semantics.
meillo@61 1307 The graphical representation is just for humans to understand the semantics
meillo@37 1308 more intuitively.
meillo@32 1309
meillo@32 1310 .PP
meillo@33 1311 .B "Make every program a filter" .
meillo@37 1312 Graphical web browsers are almost dead ends in the chain of information flow.
meillo@37 1313 Thus it is difficult to see what graphical web browsers should filter.
meillo@61 1314 Graphical web browsers exist almost exclusively to be interactively used
meillo@61 1315 by humans.
meillo@61 1316 The only case in which one might want to automate the rendering function is
meillo@37 1317 to generate images of rendered webpages.
meillo@37 1318
meillo@37 1319 .PP
meillo@37 1320 .B "Small is beautiful"
meillo@61 1321 is not easy to apply to a web browser because modern web technology
meillo@61 1322 is very complex; hence, the rendering task is very complex.
meillo@61 1323 Unfortunately, modern web browsers ``have'' to consist of many thousand
meillo@61 1324 lines of code,
meillo@61 1325 Using the toolchest approach and wrappers can help to split the browser
meillo@61 1326 into several small parts, though.
meillo@37 1327 .PP
meillo@45 1328 As of March 2010, uzbl-core consists of about 3\,500 lines of C code.
meillo@37 1329 The distribution includes another 3\,500 lines of Shell and Python code,
meillo@61 1330 which are the handler scripts and plugins like one to provide a modal
meillo@61 1331 interface.
meillo@61 1332 Further more, uzbl makes use of external tools like
meillo@54 1333 \fIwget\fP and \fIsocat\fP.
meillo@37 1334 Up to this point, uzbl looks pretty neat and small.
meillo@61 1335 The ugly part of uzbl is the rendering engine, webkit.
meillo@37 1336 Webkit consists of roughly 400\,000 (!) lines of code.
meillo@61 1337 Unfortunately, small rendering engines are not feasible anymore
meillo@61 1338 due to the nature of the modern web.
meillo@35 1339
meillo@35 1340 .PP
meillo@35 1341 .B "Build a prototype as soon as possible" .
meillo@61 1342 Plaetinck made his code public right from the beginning.
meillo@61 1343 Discussion and development was, and still is, open to everyone interested,
meillo@61 1344 and development versions of uzbl can be obtained very easily from the
meillo@61 1345 code repository.
meillo@38 1346 Within the first year of uzbl's existence, a new version was released
meillo@35 1347 more often than once a month.
meillo@61 1348 Different forks and branches arose introducing new features which were
meillo@61 1349 then considered for merging into the main branch.
meillo@61 1350 The experiences with using prototypes influenced further development.
meillo@35 1351 Actually, all development was community driven.
meillo@38 1352 Plaetinck says, three months after uzbl's birth:
meillo@35 1353 ``Right now I hardly code anything myself for Uzbl.
meillo@35 1354 I just merge in other people's code, ponder a lot, and lead the discussions.''
meillo@35 1355 .[
meillo@44 1356 lwn
meillo@44 1357 uzbl
meillo@35 1358 .]
meillo@32 1359
meillo@0 1360
meillo@48 1361 .H 2 "Problems
meillo@0 1362 .LP
meillo@61 1363 Similar to \s-1MH\s0, uzbl suffers from being different.
meillo@38 1364 It is sad, but people use what they know.
meillo@61 1365 Fortunately, uzbl's user interface can be made to look and feel very similar
meillo@61 1366 to the one of the well known web browsers,
meillo@38 1367 hiding the internal differences.
meillo@38 1368 But uzbl has to provide this similar look and feel to be accepted
meillo@38 1369 as a ``normal'' browser by ``normal'' users.
meillo@37 1370 .PP
meillo@61 1371 The more important problem here is the modern web.
meillo@38 1372 The modern web is simply broken.
meillo@61 1373 It has state in a state-less protocol, misuses technologies,
meillo@61 1374 and is helplessly overloaded.
meillo@61 1375 This results in rendering engines that ``must'' consist
meillo@61 1376 of hundreds of thousands of lines of code.
meillo@61 1377 They also must combine and integrate many different technologies
meillo@61 1378 to make our modern web accessible.
meillo@61 1379 This results, however, in a failing attempt to provide good usability.
meillo@61 1380 Website-to-image converters are almost impossible to run without
meillo@38 1381 human interaction because of state in sessions, impossible
meillo@61 1382 deep-linking, and ``unautomatable'' technologies.
meillo@37 1383 .PP
meillo@61 1384 The web was misused in order to attempt to fulfill all kinds of wishes.
meillo@61 1385 Now web browsers, and ultimately users, suffer from it.
meillo@37 1386
meillo@8 1387
meillo@51 1388 .H 2 "Summary
meillo@32 1389 .LP
meillo@38 1390 ``Uzbl is a browser that adheres to the Unix Philosophy'',
meillo@61 1391 is how uzbl is seen by its authors.
meillo@38 1392 Indeed, uzbl follows the Unix Philosophy in many ways.
meillo@38 1393 It consists of independent parts that work together,
meillo@45 1394 while its core is mainly a mediator which glues the parts together.
meillo@38 1395 .PP
meillo@61 1396 Software leverage is put to excellent use.
meillo@61 1397 External tools are used, independent tasks are separated out
meillo@61 1398 to independent parts and glued together with small handler scripts.
meillo@38 1399 .PP
meillo@61 1400 Since uzbl roughly consists of a set of tools and a bit of glue,
meillo@61 1401 anyone can put the parts together and expand it in any desired way.
meillo@61 1402 Flexibility and customization are properties that make it valuable
meillo@61 1403 for advanced users, but may keep novice users from understanding
meillo@61 1404 and using it.
meillo@38 1405 .PP
meillo@61 1406 But uzbl's main problem is the modern web, which makes it very difficult
meillo@38 1407 to design a sane web browser.
meillo@38 1408 Despite this bad situation, uzbl does a fairly good job.
meillo@32 1409
meillo@8 1410
meillo@48 1411 .H 1 "Final thoughts
meillo@0 1412
meillo@0 1413 .LP
meillo@50 1414 This paper explained why good design is important.
meillo@61 1415 It introduced the Unix Philosophy as a set of guidelines that encourage
meillo@61 1416 good design in order to create good quality software.
meillo@61 1417 Then, real world software that was designed with the Unix Philosophy
meillo@61 1418 in mind was discussed.
meillo@50 1419 .PP
meillo@61 1420 Throughout this paper, the aim was do explain \fIwhy\fP something
meillo@50 1421 should be done the Unix way.
meillo@61 1422 Reasons were given to substantiate the claim that the Unix Philosophy
meillo@61 1423 is a preferable way of designing software.
meillo@50 1424 .PP
meillo@50 1425 The Unix Philosophy is close to the software developer's point of view.
meillo@61 1426 Its main goal is taming the beast known as ``software complexity''.
meillo@61 1427 Hence it strives first and foremost for simplicity of software.
meillo@61 1428 It might appear that usability for humans is a minor goal,
meillo@61 1429 but actually, the Unix Philosophy sees usability as a result of sound design.
meillo@61 1430 Sound design does not need to be ultimately intuitive,
meillo@50 1431 but it will provide a consistent way to access the enormous power
meillo@50 1432 of software leverage.
meillo@50 1433 .PP
meillo@61 1434 Being able to solve some specific concrete problem becomes less and less
meillo@61 1435 important as there is software available for nearly every possible task
meillo@61 1436 today.
meillo@50 1437 But the quality of software matters.
meillo@50 1438 It is important that we have \fIgood\fP software.
meillo@50 1439 .sp
meillo@0 1440 .LP
meillo@50 1441 .B "But why the Unix Philosophy?
meillo@50 1442 .PP
meillo@50 1443 The largest problem of software development is the complexity involved.
meillo@50 1444 It is the only part of the job that computers cannot take over.
meillo@61 1445 The Unix Philosophy fights complexity, as it is the main enemy.
meillo@50 1446 .PP
meillo@50 1447 On the other hand,
meillo@61 1448 the most unique advantage of software is its ability to leverage.
meillo@50 1449 Current software still fails to make the best possible use of this ability.
meillo@61 1450 The Unix Philosophy concentrates on exploiting this great opportunity.
meillo@0 1451
meillo@47 1452
meillo@47 1453 .bp
meillo@47 1454 .TL
meillo@47 1455 References
meillo@47 1456 .LP
meillo@47 1457 .XS
meillo@47 1458 .sp .5v
meillo@47 1459 .B
meillo@47 1460 References
meillo@47 1461 .XE
meillo@47 1462 .ev r
meillo@42 1463 .nr PS -1
meillo@42 1464 .nr VS -1
meillo@0 1465 .[
meillo@0 1466 $LIST$
meillo@0 1467 .]
meillo@47 1468 .nr PS +1
meillo@47 1469 .nr VS +1
meillo@47 1470 .ev
meillo@47 1471
meillo@42 1472 .bp
meillo@47 1473 .TL
meillo@47 1474 Table of Contents
meillo@47 1475 .LP
meillo@47 1476 .PX no