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author meillo@marmaro.de
date Thu, 08 Apr 2010 16:47:11 +0200
parents 3628e9649046
children 422679bdf384
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meillo@0 21 ..
meillo@0 22 .ds [. \ [
meillo@0 23 .ds .] ]
meillo@1 24 .\"----------------------------------------
meillo@0 25 .TL
meillo@6 26 Why the Unix Philosophy still matters
meillo@0 27 .AU
meillo@0 28 markus schnalke <meillo@marmaro.de>
meillo@0 29 .AB
meillo@1 30 .ti \n(.iu
meillo@39 31 This paper explains the importance of the Unix Philosophy for software design.
meillo@0 32 Today, few software designers are aware of these concepts,
meillo@39 33 and thus a lot of modern software is more limited than necessary
meillo@39 34 and makes less use of software leverage than possible.
meillo@38 35 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
meillo@0 36 .AE
meillo@0 37
meillo@10 38 .\".if t .2C
meillo@2 39
meillo@2 40 .FS
meillo@2 41 .ps -1
meillo@39 42 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
meillo@39 43 Mentor was professor Schweiggert. 2010-04-05
meillo@2 44 .br
meillo@39 45 You may retrieve this document from
meillo@39 46 .CW \s-1http://marmaro.de/docs \ .
meillo@2 47 .FE
meillo@2 48
meillo@0 49 .NH 1
meillo@0 50 Introduction
meillo@0 51 .LP
meillo@0 52 Building a software is a process from an idea of the purpose of the software
meillo@3 53 to its release.
meillo@0 54 No matter \fIhow\fP the process is run, two things are common:
meillo@0 55 the initial idea and the release.
meillo@9 56 The process in between can be of any shape.
meillo@9 57 The the maintenance work after the release is ignored for the moment.
meillo@1 58 .PP
meillo@0 59 The process of building splits mainly in two parts:
meillo@0 60 the planning of what and how to build, and implementing the plan by writing code.
meillo@3 61 This paper focuses on the planning part \(en the designing of the software.
meillo@3 62 .PP
meillo@3 63 Software design is the plan of how the internals and externals of the software should look like,
meillo@3 64 based on the requirements.
meillo@9 65 This paper discusses the recommendations of the Unix Philosophy about software design.
meillo@3 66 .PP
meillo@3 67 The here discussed ideas can get applied by any development process.
meillo@9 68 The Unix Philosophy does recommend how the software development process should look like,
meillo@3 69 but this shall not be of matter here.
meillo@0 70 Similar, the question of how to write the code is out of focus.
meillo@1 71 .PP
meillo@3 72 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet.
meillo@1 73 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed.
meillo@3 74 It is no limited set of rules, but what people see to be common to typical Unix software.
meillo@1 75 Several people stated their view on the Unix Philosophy.
meillo@1 76 Best known are:
meillo@1 77 .IP \(bu
meillo@1 78 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
meillo@1 79 .[
meillo@1 80 %A M. D. McIlroy
meillo@1 81 %A E. N. Pinson
meillo@1 82 %A B. A. Taque
meillo@1 83 %T UNIX Time-Sharing System Forward
meillo@1 84 %J The Bell System Technical Journal
meillo@1 85 %D 1978
meillo@1 86 %V 57
meillo@1 87 %N 6
meillo@1 88 %P 1902
meillo@1 89 .]
meillo@1 90 .IP \(bu
meillo@1 91 Mike Gancarz' book ``The UNIX Philosophy''.
meillo@1 92 .[
meillo@1 93 %A Mike Gancarz
meillo@1 94 %T The UNIX Philosophy
meillo@1 95 %D 1995
meillo@1 96 %I Digital Press
meillo@1 97 .]
meillo@1 98 .IP \(bu
meillo@1 99 Eric S. Raymond's book ``The Art of UNIX Programming''.
meillo@1 100 .[
meillo@1 101 %A Eric S. Raymond
meillo@1 102 %T The Art of UNIX Programming
meillo@1 103 %D 2003
meillo@1 104 %I Addison-Wesley
meillo@2 105 %O .CW \s-1http://www.faqs.org/docs/artu/
meillo@1 106 .]
meillo@0 107 .LP
meillo@1 108 These different views on the Unix Philosophy have much in common.
meillo@3 109 Especially, the main concepts are similar for all of them.
meillo@1 110 But there are also points on which they differ.
meillo@1 111 This only underlines what the Unix Philosophy is:
meillo@1 112 A retrospective view on the main concepts of Unix software;
meillo@9 113 especially those that were successful and unique to Unix.
meillo@6 114 .\" really?
meillo@1 115 .PP
meillo@1 116 Before we will have a look at concrete concepts,
meillo@1 117 we discuss why software design is important
meillo@1 118 and what problems bad design introduces.
meillo@0 119
meillo@0 120
meillo@0 121 .NH 1
meillo@6 122 Importance of software design in general
meillo@0 123 .LP
meillo@39 124 The design of a software describes its internal and external shape,
meillo@39 125 meaning structure and interfaces.
meillo@39 126 It has nothing to do with visual appearance.
meillo@39 127 If we take a program as a car, then its color is of no matter.
meillo@39 128 Its design would be the car's size, its shape, the locations of doors,
meillo@39 129 the passenger/space ratio, the luggage capacity, and so forth.
meillo@39 130 .PP
meillo@39 131 Why should software get designed at all?
meillo@6 132 It is general knowledge, that even a bad plan is better than no plan.
meillo@39 133 Not designing software means programming without plan.
meillo@39 134 This will pretty sure lead to horrible results.
meillo@39 135 Horrible to use and horrible to maintain.
meillo@39 136 These two aspects are the visible ones.
meillo@39 137 Often invisible are the wasted possible gains.
meillo@39 138 Good software design can make these gains available.
meillo@2 139 .PP
meillo@39 140 A software's design deals with quality properties.
meillo@39 141 Good design leads to good quality, and quality is important.
meillo@39 142 Any car may be able to drive from A to B,
meillo@39 143 but it depends on the car's properties whether it is a good choice
meillo@39 144 for passenger transport or not.
meillo@39 145 It depends on its properties if it is a good choice
meillo@39 146 for a rough mountain area.
meillo@39 147 And it depends on its properties if the ride will be fun.
meillo@39 148
meillo@2 149 .PP
meillo@39 150 Requirements for a software are twofold:
meillo@39 151 functional and non-functional.
meillo@39 152 .IP \(bu
meillo@39 153 Functional requirements define directly the software's functions.
meillo@39 154 They are the reason why software gets written.
meillo@39 155 Someone has a problem and needs a tool to solve it.
meillo@39 156 Being able to solve the problem is the main functional goal.
meillo@39 157 It is the driving force behind all programming effort.
meillo@39 158 Functional requirements are easier to define and to verify.
meillo@39 159 .IP \(bu
meillo@39 160 Non-functional requirements are also called \fIquality\fP requirements.
meillo@39 161 The quality of a software are the properties that are not directly related to
meillo@39 162 the software's basic functions.
meillo@39 163 Tools of bad quality often solve the problems they were written for,
meillo@39 164 but introduce problems and difficulties for usage and development, later on.
meillo@39 165 Quality aspects are often overlooked at first sight,
meillo@39 166 and they are often difficult to define clearly and to verify.
meillo@2 167 .PP
meillo@39 168 Quality is of few matter when the software gets built initially,
meillo@39 169 but it is of matter for usage and maintenance of the software.
meillo@6 170 A short-sighted might see in developing a software mainly building something up.
meillo@39 171 But experience shows, that building the software the first time is
meillo@39 172 only a small amount of the overall work.
meillo@39 173 Bug fixing, extending, rebuilding of parts
meillo@39 174 \(en maintenance work, for short \(en
meillo@6 175 does soon take over the major part of the time spent on a software.
meillo@6 176 Not to forget the usage of the software.
meillo@6 177 These processes are highly influenced by the software's quality.
meillo@39 178 Thus, quality must not be neglected.
meillo@39 179 The problem with quality is that you hardly ``stumble over''
meillo@39 180 bad quality during the first build,
meillo@6 181 but this is the time when you should care about good quality most.
meillo@6 182 .PP
meillo@39 183 Software design is less the basic function of a software \(en
meillo@39 184 this requirement will get satisfied anyway.
meillo@39 185 Software design is more about quality aspects of the software.
meillo@39 186 Good design leads to good quality, bad design to bad quality.
meillo@6 187 The primary functions of the software will be affected modestly by bad quality,
meillo@39 188 but good quality can provide a lot of additional gain,
meillo@6 189 even at places where one never expected it.
meillo@6 190 .PP
meillo@6 191 The ISO/IEC 9126-1 standard, part 1,
meillo@6 192 .[
meillo@9 193 %I International Organization for Standardization
meillo@6 194 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1
meillo@6 195 %C Geneve
meillo@6 196 %D 2001
meillo@6 197 .]
meillo@6 198 defines the quality model as consisting out of:
meillo@6 199 .IP \(bu
meillo@6 200 .I Functionality
meillo@6 201 (suitability, accuracy, inter\%operability, security)
meillo@6 202 .IP \(bu
meillo@6 203 .I Reliability
meillo@6 204 (maturity, fault tolerance, recoverability)
meillo@6 205 .IP \(bu
meillo@6 206 .I Usability
meillo@6 207 (understandability, learnability, operability, attractiveness)
meillo@6 208 .IP \(bu
meillo@6 209 .I Efficiency
meillo@9 210 (time behavior, resource utilization)
meillo@6 211 .IP \(bu
meillo@6 212 .I Maintainability
meillo@23 213 (analyzability, changeability, stability, testability)
meillo@6 214 .IP \(bu
meillo@6 215 .I Portability
meillo@6 216 (adaptability, installability, co-existence, replaceability)
meillo@6 217 .LP
meillo@39 218 Good design can improve these properties of a software,
meillo@39 219 bad designed software probably suffers from not having them.
meillo@7 220 .PP
meillo@7 221 One further goal of software design is consistency.
meillo@7 222 Consistency eases understanding, working on, and using things.
meillo@39 223 Consistent internal structure and consistent interfaces to the outside
meillo@39 224 can be provided by good design.
meillo@7 225 .PP
meillo@39 226 Software should be well designed because good design avoids many
meillo@39 227 problems during the software's lifetime.
meillo@39 228 And software should be well designed because good design can offer
meillo@39 229 much additional gain.
meillo@39 230 Indeed, much effort should be spent into good design to make software more valuable.
meillo@39 231 The Unix Philosophy shows a way of how to design software well.
meillo@7 232 It offers guidelines to achieve good quality and high gain for the effort spent.
meillo@0 233
meillo@0 234
meillo@0 235 .NH 1
meillo@0 236 The Unix Philosophy
meillo@4 237 .LP
meillo@4 238 The origins of the Unix Philosophy were already introduced.
meillo@8 239 This chapter explains the philosophy, oriented on Gancarz,
meillo@8 240 and shows concrete examples of its application.
meillo@5 241
meillo@16 242 .NH 2
meillo@14 243 Pipes
meillo@4 244 .LP
meillo@4 245 Following are some examples to demonstrate how applied Unix Philosophy feels like.
meillo@4 246 Knowledge of using the Unix shell is assumed.
meillo@4 247 .PP
meillo@4 248 Counting the number of files in the current directory:
meillo@9 249 .DS I 2n
meillo@4 250 .CW
meillo@9 251 .ps -1
meillo@4 252 ls | wc -l
meillo@4 253 .DE
meillo@4 254 The
meillo@4 255 .CW ls
meillo@4 256 command lists all files in the current directory, one per line,
meillo@4 257 and
meillo@4 258 .CW "wc -l
meillo@8 259 counts the number of lines.
meillo@4 260 .PP
meillo@8 261 Counting the number of files that do not contain ``foo'' in their name:
meillo@9 262 .DS I 2n
meillo@4 263 .CW
meillo@9 264 .ps -1
meillo@4 265 ls | grep -v foo | wc -l
meillo@4 266 .DE
meillo@4 267 Here, the list of files is filtered by
meillo@4 268 .CW grep
meillo@4 269 to remove all that contain ``foo''.
meillo@4 270 The rest is the same as in the previous example.
meillo@4 271 .PP
meillo@4 272 Finding the five largest entries in the current directory.
meillo@9 273 .DS I 2n
meillo@4 274 .CW
meillo@9 275 .ps -1
meillo@4 276 du -s * | sort -nr | sed 5q
meillo@4 277 .DE
meillo@4 278 .CW "du -s *
meillo@4 279 returns the recursively summed sizes of all files
meillo@8 280 \(en no matter if they are regular files or directories.
meillo@4 281 .CW "sort -nr
meillo@4 282 sorts the list numerically in reverse order.
meillo@4 283 Finally,
meillo@4 284 .CW "sed 5q
meillo@4 285 quits after it has printed the fifth line.
meillo@4 286 .PP
meillo@4 287 The presented command lines are examples of what Unix people would use
meillo@4 288 to get the desired output.
meillo@4 289 There are also other ways to get the same output.
meillo@4 290 It's a user's decision which way to go.
meillo@14 291 .PP
meillo@8 292 The examples show that many tasks on a Unix system
meillo@4 293 are accomplished by combining several small programs.
meillo@4 294 The connection between the single programs is denoted by the pipe operator `|'.
meillo@4 295 .PP
meillo@4 296 Pipes, and their extensive and easy use, are one of the great
meillo@4 297 achievements of the Unix system.
meillo@4 298 Pipes between programs have been possible in earlier operating systems,
meillo@4 299 but it has never been a so central part of the concept.
meillo@4 300 When, in the early seventies, Doug McIlroy introduced pipes for the
meillo@4 301 Unix system,
meillo@4 302 ``it was this concept and notation for linking several programs together
meillo@4 303 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
meillo@4 304 .[
meillo@4 305 %T Unix: An Oral History
meillo@5 306 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
meillo@4 307 .]
meillo@4 308 .PP
meillo@4 309 Being able to specify pipelines in an easy way is,
meillo@4 310 however, not enough by itself.
meillo@5 311 It is only one half.
meillo@4 312 The other is the design of the programs that are used in the pipeline.
meillo@8 313 They have to interfaces that allows them to be used in such a way.
meillo@5 314
meillo@16 315 .NH 2
meillo@14 316 Interface design
meillo@5 317 .LP
meillo@11 318 Unix is, first of all, simple \(en Everything is a file.
meillo@5 319 Files are sequences of bytes, without any special structure.
meillo@5 320 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
meillo@5 321 and write a stream of bytes to ``standard output'' (stdout).
meillo@5 322 .PP
meillo@8 323 If the files \fIare\fP sequences of bytes,
meillo@8 324 and the programs \fIare\fP filters on byte streams,
meillo@11 325 then there is exactly one standardized data interface.
meillo@5 326 Thus it is possible to combine them in any desired way.
meillo@5 327 .PP
meillo@5 328 Even a handful of small programs will yield a large set of combinations,
meillo@5 329 and thus a large set of different functions.
meillo@5 330 This is leverage!
meillo@5 331 If the programs are orthogonal to each other \(en the best case \(en
meillo@5 332 then the set of different functions is greatest.
meillo@5 333 .PP
meillo@11 334 Programs might also have a separate control interface,
meillo@11 335 besides their data interface.
meillo@11 336 The control interface is often called ``user interface'',
meillo@11 337 because it is usually designed to be used by humans.
meillo@11 338 The Unix Philosophy discourages to assume the user to be human.
meillo@11 339 Interactive use of software is slow use of software,
meillo@11 340 because the program waits for user input most of the time.
meillo@11 341 Interactive software requires the user to be in front of the computer
meillo@11 342 all the time.
meillo@11 343 Interactive software occupy the user's attention while they are running.
meillo@11 344 .PP
meillo@11 345 Now we come back to the idea of using several small programs, combined,
meillo@11 346 to have a more specific function.
meillo@11 347 If these single tools would all be interactive,
meillo@11 348 how would the user control them?
meillo@11 349 It is not only a problem to control several programs at once if they run at the same time,
meillo@11 350 it also very inefficient to have to control each of the single programs
meillo@11 351 that are intended to work as one large program.
meillo@11 352 Hence, the Unix Philosophy discourages programs to demand interactive use.
meillo@11 353 The behavior of programs should be defined at invocation.
meillo@11 354 This is done by specifying arguments (``command line switches'') to the program call.
meillo@11 355 Gancarz discusses this topic as ``avoid captive user interfaces''.
meillo@11 356 .[
meillo@11 357 %A Mike Gancarz
meillo@11 358 %T The UNIX Philosophy
meillo@11 359 %I Digital Press
meillo@11 360 %D 1995
meillo@11 361 %P 88 ff.
meillo@11 362 .]
meillo@11 363 .PP
meillo@11 364 Non-interactive use is, during development, also an advantage for testing.
meillo@11 365 Testing of interactive programs is much more complicated,
meillo@11 366 than testing of non-interactive programs.
meillo@5 367
meillo@16 368 .NH 2
meillo@8 369 The toolchest approach
meillo@5 370 .LP
meillo@5 371 A toolchest is a set of tools.
meillo@5 372 Instead of having one big tool for all tasks, one has many small tools,
meillo@5 373 each for one task.
meillo@5 374 Difficult tasks are solved by combining several of the small, simple tools.
meillo@5 375 .PP
meillo@11 376 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
meillo@11 377 that are filters on byte streams.
meillo@11 378 They are, to a large extend, unrelated in their function.
meillo@11 379 Hence, the Unix toolchest provides a large set of functions
meillo@11 380 that can be accessed by combining the programs in the desired way.
meillo@11 381 .PP
meillo@11 382 There are also advantages for developing small toolchest programs.
meillo@5 383 It is easier and less error-prone to write small programs.
meillo@5 384 It is also easier and less error-prone to write a large set of small programs,
meillo@5 385 than to write one large program with all the functionality included.
meillo@5 386 If the small programs are combinable, then they offer even a larger set
meillo@5 387 of functions than the single large program.
meillo@5 388 Hence, one gets two advantages out of writing small, combinable programs.
meillo@5 389 .PP
meillo@5 390 There are two drawbacks of the toolchest approach.
meillo@8 391 First, one simple, standardized, unidirectional interface has to be sufficient.
meillo@5 392 If one feels the need for more ``logic'' than a stream of bytes,
meillo@8 393 then a different approach might be of need.
meillo@13 394 But it is also possible, that he just can not imagine a design where
meillo@8 395 a stream of bytes is sufficient.
meillo@8 396 By becoming more familiar with the ``Unix style of thinking'',
meillo@8 397 developers will more often and easier find simple designs where
meillo@8 398 a stream of bytes is a sufficient interface.
meillo@8 399 .PP
meillo@8 400 The second drawback of a toolchest affects the users.
meillo@5 401 A toolchest is often more difficult to use for novices.
meillo@9 402 It is necessary to become familiar with each of the tools,
meillo@5 403 to be able to use the right one in a given situation.
meillo@9 404 Additionally, one needs to combine the tools in a senseful way on its own.
meillo@9 405 This is like a sharp knife \(en it is a powerful tool in the hand of a master,
meillo@5 406 but of no good value in the hand of an unskilled.
meillo@5 407 .PP
meillo@8 408 However, learning single, small tool of the toolchest is easier than
meillo@8 409 learning a complex tool.
meillo@8 410 The user will have a basic understanding of a yet unknown tool,
meillo@8 411 if the several tools of the toolchest have a common style.
meillo@8 412 He will be able to transfer knowledge over one tool to another.
meillo@8 413 .PP
meillo@8 414 Moreover, the second drawback can be removed easily by adding wrappers
meillo@8 415 around the single tools.
meillo@5 416 Novice users do not need to learn several tools if a professional wraps
meillo@8 417 the single commands into a more high-level script.
meillo@5 418 Note that the wrapper script still calls the small tools;
meillo@5 419 the wrapper script is just like a skin around.
meillo@8 420 No complexity is added this way,
meillo@8 421 but new programs can get created out of existing one with very low effort.
meillo@5 422 .PP
meillo@5 423 A wrapper script for finding the five largest entries in the current directory
meillo@5 424 could look like this:
meillo@9 425 .DS I 2n
meillo@5 426 .CW
meillo@9 427 .ps -1
meillo@5 428 #!/bin/sh
meillo@5 429 du -s * | sort -nr | sed 5q
meillo@5 430 .DE
meillo@5 431 The script itself is just a text file that calls the command line
meillo@5 432 a professional user would type in directly.
meillo@8 433 Making the program flexible on the number of entries it prints,
meillo@8 434 is easily possible:
meillo@9 435 .DS I 2n
meillo@8 436 .CW
meillo@9 437 .ps -1
meillo@8 438 #!/bin/sh
meillo@8 439 num=5
meillo@8 440 [ $# -eq 1 ] && num="$1"
meillo@8 441 du -sh * | sort -nr | sed "${num}q"
meillo@8 442 .DE
meillo@8 443 This script acts like the one before, when called without an argument.
meillo@8 444 But one can also specify a numerical argument to define the number of lines to print.
meillo@5 445
meillo@16 446 .NH 2
meillo@8 447 A powerful shell
meillo@8 448 .LP
meillo@10 449 It was already said, that the Unix shell provides the possibility to
meillo@10 450 combine small programs into large ones easily.
meillo@10 451 A powerful shell is a great feature in other ways, too.
meillo@8 452 .PP
meillo@10 453 For instance by including a scripting language.
meillo@10 454 The control statements are build into the shell.
meillo@8 455 The functions, however, are the normal programs, everyone can use on the system.
meillo@10 456 Thus, the programs are known, so learning to program in the shell is easy.
meillo@8 457 Using normal programs as functions in the shell programming language
meillo@10 458 is only possible because they are small and combinable tools in a toolchest style.
meillo@8 459 .PP
meillo@8 460 The Unix shell encourages to write small scripts out of other programs,
meillo@8 461 because it is so easy to do.
meillo@8 462 This is a great step towards automation.
meillo@8 463 It is wonderful if the effort to automate a task equals the effort
meillo@8 464 it takes to do it the second time by hand.
meillo@8 465 If it is so, then the user will be happy to automate everything he does more than once.
meillo@8 466 .PP
meillo@8 467 Small programs that do one job well, standardized interfaces between them,
meillo@8 468 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
meillo@8 469 this will inevitably produce software leverage.
meillo@8 470 Getting multiple times the benefit of an investment is a great offer.
meillo@10 471 .PP
meillo@10 472 The shell also encourages rapid prototyping.
meillo@10 473 Many well known programs started as quickly hacked shell scripts,
meillo@10 474 and turned into ``real'' programs, written in C, later.
meillo@10 475 Building a prototype first is a way to avoid the biggest problems
meillo@10 476 in application development.
meillo@10 477 Fred Brooks writes in ``No Silver Bullet'':
meillo@10 478 .[
meillo@10 479 %A Frederick P. Brooks, Jr.
meillo@10 480 %T No Silver Bullet: Essence and Accidents of Software Engineering
meillo@10 481 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference
meillo@10 482 %E H.-J. Kugler
meillo@10 483 %D 1986
meillo@10 484 %P 1069\(en1076
meillo@10 485 %I Elsevier Science B.V.
meillo@10 486 %C Amsterdam, The Netherlands
meillo@10 487 .]
meillo@10 488 .QP
meillo@10 489 The hardest single part of building a software system is deciding precisely what to build.
meillo@10 490 No other part of the conceptual work is so difficult as establishing the detailed
meillo@10 491 technical requirements, [...].
meillo@10 492 No other part of the work so cripples the resulting system if done wrong.
meillo@10 493 No other part is more difficult to rectify later.
meillo@10 494 .PP
meillo@10 495 Writing a prototype is a great method to become familiar with the requirements
meillo@10 496 and to actually run into real problems.
meillo@10 497 Today, prototyping is often seen as a first step in building a software.
meillo@10 498 This is, of course, good.
meillo@10 499 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
meillo@10 500 After having built the prototype, one might notice, that the prototype is already
meillo@10 501 \fIgood enough\fP.
meillo@10 502 Hence, no reimplementation, in a more sophisticated programming language, might be of need,
meillo@10 503 for the moment.
meillo@23 504 Maybe later, it might be necessary to rewrite the software, but not now.
meillo@10 505 .PP
meillo@10 506 By delaying further work, one keeps the flexibility to react easily on
meillo@10 507 changing requirements.
meillo@10 508 Software parts that are not written will not miss the requirements.
meillo@10 509
meillo@16 510 .NH 2
meillo@10 511 Worse is better
meillo@10 512 .LP
meillo@10 513 The Unix Philosophy aims for the 80% solution;
meillo@10 514 others call it the ``Worse is better'' approach.
meillo@10 515 .PP
meillo@10 516 First, practical experience shows, that it is almost never possible to define the
meillo@10 517 requirements completely and correctly the first time.
meillo@10 518 Hence one should not try to; it will fail anyway.
meillo@10 519 Second, practical experience shows, that requirements change during time.
meillo@10 520 Hence it is best to delay requirement-based design decisions as long as possible.
meillo@10 521 Also, the software should be small and flexible as long as possible
meillo@10 522 to react on changing requirements.
meillo@10 523 Shell scripts, for example, are more easily adjusted as C programs.
meillo@10 524 Third, practical experience shows, that maintenance is hard work.
meillo@10 525 Hence, one should keep the amount of software as small as possible;
meillo@10 526 it should just fulfill the \fIcurrent\fP requirements.
meillo@10 527 Software parts that will be written later, do not need maintenance now.
meillo@10 528 .PP
meillo@10 529 Starting with a prototype in a scripting language has several advantages:
meillo@10 530 .IP \(bu
meillo@10 531 As the initial effort is low, one will likely start right away.
meillo@10 532 .IP \(bu
meillo@10 533 As working parts are available soon, the real requirements can get identified soon.
meillo@10 534 .IP \(bu
meillo@10 535 When a software is usable, it gets used, and thus tested.
meillo@10 536 Hence problems will be found at early stages of the development.
meillo@10 537 .IP \(bu
meillo@10 538 The prototype might be enough for the moment,
meillo@10 539 thus further work on the software can be delayed to a time
meillo@10 540 when one knows better about the requirements and problems,
meillo@10 541 than now.
meillo@10 542 .IP \(bu
meillo@10 543 Implementing now only the parts that are actually needed now,
meillo@10 544 requires fewer maintenance work.
meillo@10 545 .IP \(bu
meillo@10 546 If the global situation changes so that the software is not needed anymore,
meillo@10 547 then less effort was spent into the project, than it would have be
meillo@10 548 when a different approach had been used.
meillo@10 549
meillo@16 550 .NH 2
meillo@11 551 Upgrowth and survival of software
meillo@11 552 .LP
meillo@12 553 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
meillo@13 554 Although these are just verbs, they do imply a specific view on the work process
meillo@13 555 they describe.
meillo@12 556 The better verb, however, is to \fIgrow\fP.
meillo@12 557 .PP
meillo@12 558 Creating software in the sense of the Unix Philosophy is an incremental process.
meillo@12 559 It starts with a first prototype, which evolves as requirements change.
meillo@12 560 A quickly hacked shell script might become a large, sophisticated,
meillo@13 561 compiled program this way.
meillo@13 562 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
meillo@13 563 While being alive it will get extended, rearranged, rebuilt (from scratch).
meillo@12 564 Growing software matches the view that ``software is never finished. It is only released.''
meillo@12 565 .[
meillo@13 566 %O FIXME
meillo@13 567 %A Mike Gancarz
meillo@13 568 %T The UNIX Philosophy
meillo@13 569 %P 26
meillo@12 570 .]
meillo@12 571 .PP
meillo@13 572 Software can be seen as being controlled by evolutionary processes.
meillo@13 573 Successful software is software that is used by many for a long time.
meillo@12 574 This implies that the software is needed, useful, and better than alternatives.
meillo@12 575 Darwin talks about: ``The survival of the fittest.''
meillo@12 576 .[
meillo@13 577 %O FIXME
meillo@13 578 %A Charles Darwin
meillo@12 579 .]
meillo@12 580 Transferred to software: The most successful software, is the fittest,
meillo@12 581 is the one that survives.
meillo@13 582 (This may be at the level of one creature, or at the level of one species.)
meillo@13 583 The fitness of software is affected mainly by four properties:
meillo@15 584 portability of code, portability of data, range of usability, and reusability of parts.
meillo@15 585 .\" .IP \(bu
meillo@15 586 .\" portability of code
meillo@15 587 .\" .IP \(bu
meillo@15 588 .\" portability of data
meillo@15 589 .\" .IP \(bu
meillo@15 590 .\" range of usability
meillo@15 591 .\" .IP \(bu
meillo@15 592 .\" reuseability of parts
meillo@13 593 .PP
meillo@15 594 (1)
meillo@15 595 .I "Portability of code
meillo@15 596 means, using high-level programming languages,
meillo@13 597 sticking to the standard,
meillo@13 598 and avoiding optimizations that introduce dependencies on specific hardware.
meillo@13 599 Hardware has a much lower lifetime than software.
meillo@13 600 By chaining software to a specific hardware,
meillo@13 601 the software's lifetime gets shortened to that of this hardware.
meillo@13 602 In contrast, software should be easy to port \(en
meillo@23 603 adaptation is the key to success.
meillo@13 604 .\" cf. practice of prog: ch08
meillo@13 605 .PP
meillo@15 606 (2)
meillo@15 607 .I "Portability of data
meillo@15 608 is best achieved by avoiding binary representations
meillo@13 609 to store data, because binary representations differ from machine to machine.
meillo@23 610 Textual representation is favored.
meillo@13 611 Historically, ASCII was the charset of choice.
meillo@13 612 In the future, UTF-8 might be the better choice, however.
meillo@13 613 Important is that it is a plain text representation in a
meillo@13 614 very common charset encoding.
meillo@13 615 Apart from being able to transfer data between machines,
meillo@13 616 readable data has the great advantage, that humans are able
meillo@13 617 to directly edit it with text editors and other tools from the Unix toolchest.
meillo@13 618 .\" gancarz tenet 5
meillo@13 619 .PP
meillo@15 620 (3)
meillo@15 621 A large
meillo@15 622 .I "range of usability
meillo@23 623 ensures good adaptation, and thus good survival.
meillo@13 624 It is a special distinction if a software becomes used in fields of action,
meillo@13 625 the original authors did never imagine.
meillo@13 626 Software that solves problems in a general way will likely be used
meillo@13 627 for all kinds of similar problems.
meillo@13 628 Being too specific limits the range of uses.
meillo@13 629 Requirements change through time, thus use cases change or even vanish.
meillo@13 630 A good example in this point is Allman's sendmail.
meillo@13 631 Allman identifies flexibility to be one major reason for sendmail's success:
meillo@13 632 .[
meillo@13 633 %O FIXME
meillo@13 634 %A Allman
meillo@13 635 %T sendmail
meillo@13 636 .]
meillo@13 637 .QP
meillo@13 638 Second, I limited myself to the routing function [...].
meillo@13 639 This was a departure from the dominant thought of the time, [...].
meillo@13 640 .QP
meillo@13 641 Third, the sendmail configuration file was flexible enough to adopt
meillo@13 642 to a rapidly changing world [...].
meillo@12 643 .LP
meillo@13 644 Successful software adopts itself to the changing world.
meillo@13 645 .PP
meillo@15 646 (4)
meillo@15 647 .I "Reuse of parts
meillo@15 648 is even one step further.
meillo@13 649 A software may completely lose its field of action,
meillo@13 650 but parts of which the software is build may be general and independent enough
meillo@13 651 to survive this death.
meillo@13 652 If software is build by combining small independent programs,
meillo@13 653 then there are parts readily available for reuse.
meillo@13 654 Who cares if the large program is a failure,
meillo@13 655 but parts of it become successful instead?
meillo@10 656
meillo@16 657 .NH 2
meillo@14 658 Summary
meillo@0 659 .LP
meillo@14 660 This chapter explained the central ideas of the Unix Philosophy.
meillo@14 661 For each of the ideas, it was exposed what advantages they introduce.
meillo@14 662 The Unix Philosophy are guidelines that help to write valuable software.
meillo@14 663 From the view point of a software developer or software designer,
meillo@14 664 the Unix Philosophy provides answers to many software design problem.
meillo@14 665 .PP
meillo@14 666 The various ideas of the Unix Philosophy are very interweaved
meillo@14 667 and can hardly be applied independently.
meillo@14 668 However, the probably most important messages are:
meillo@14 669 .I "``Do one thing well!''" ,
meillo@14 670 .I "``Keep it simple!''" ,
meillo@14 671 and
meillo@14 672 .I "``Use software leverage!''
meillo@0 673
meillo@8 674
meillo@8 675
meillo@0 676 .NH 1
meillo@19 677 Case study: \s-1MH\s0
meillo@18 678 .LP
meillo@30 679 The previous chapter introduced and explained the Unix Philosophy
meillo@18 680 from a general point of view.
meillo@30 681 The driving force were the guidelines; references to
meillo@18 682 existing software were given only sparsely.
meillo@18 683 In this and the next chapter, concrete software will be
meillo@18 684 the driving force in the discussion.
meillo@18 685 .PP
meillo@23 686 This first case study is about the mail user agents (\s-1MUA\s0)
meillo@23 687 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
meillo@23 688 (``new mail handler'').
meillo@23 689 \s-1MUA\s0s provide functions to read, compose, and organize mail,
meillo@23 690 but (ideally) not to transfer.
meillo@19 691 In this document, the name \s-1MH\s0 will be used for both of them.
meillo@19 692 A distinction will only be made if differences between
meillo@19 693 them are described.
meillo@18 694
meillo@0 695
meillo@0 696 .NH 2
meillo@19 697 Historical background
meillo@0 698 .LP
meillo@19 699 Electronic mail was available in Unix very early.
meillo@30 700 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
meillo@30 701 which was already present in the First Edition.
meillo@30 702 .[
meillo@30 703 %A Peter H. Salus
meillo@30 704 %T A Quarter Century of UNIX
meillo@30 705 %D 1994
meillo@30 706 %I Addison-Wesley
meillo@30 707 %P 41 f.
meillo@30 708 .]
meillo@30 709 It was a small program that either prints the user's mailbox file
meillo@19 710 or appends text to someone elses mailbox file,
meillo@19 711 depending on the command line arguments.
meillo@19 712 .[
meillo@19 713 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf
meillo@19 714 .]
meillo@19 715 It was a program that did one job well.
meillo@23 716 This job was emailing, which was very simple then.
meillo@19 717 .PP
meillo@23 718 Later, emailing became more powerful, and thus more complex.
meillo@19 719 The simple \f(CWmail\fP, which knew nothing of subjects,
meillo@19 720 independent handling of single messages,
meillo@19 721 and long-time storage of them, was not powerful enough anymore.
meillo@19 722 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
meillo@19 723 in 1978 to provide additional functions for emailing.
meillo@19 724 Mail was still one program, but now it was large and did
meillo@19 725 several jobs.
meillo@23 726 Its user interface is modeled after the one of \fIed\fP.
meillo@19 727 It is designed for humans, but is still scriptable.
meillo@23 728 \fImailx\fP is the adaptation of Berkeley Mail into System V.
meillo@19 729 .[
meillo@19 730 %A Gunnar Ritter
meillo@19 731 %O http://heirloom.sourceforge.net/mailx_history.html
meillo@19 732 .]
meillo@30 733 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
meillo@19 734 followed Mail's direction.
meillo@19 735 They are large, monolithic programs which include all emailing functions.
meillo@19 736 .PP
meillo@23 737 A different way was taken by the people of \s-1RAND\s0 Corporation.
meillo@38 738 In the beginning, they also had used a monolithic mail system,
meillo@30 739 called \s-1MS\s0 (for ``mail system'').
meillo@19 740 But in 1977, Stockton Gaines and Norman Shapiro
meillo@19 741 came up with a proposal of a new email system concept \(en
meillo@19 742 one that honors the Unix Philosophy.
meillo@19 743 The concept was implemented by Bruce Borden in 1978 and 1979.
meillo@19 744 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
meillo@18 745 .PP
meillo@18 746 Since then, \s-1RAND\s0, the University of California at Irvine and
meillo@19 747 at Berkeley, and several others have contributed to the software.
meillo@18 748 However, it's core concepts remained the same.
meillo@23 749 In the late 90s, when development of \s-1MH\s0 slowed down,
meillo@19 750 Richard Coleman started with \fInmh\fP, the new mail handler.
meillo@19 751 His goal was to improve \s-1MH\s0, especially in regard of
meillo@23 752 the requirements of modern emailing.
meillo@19 753 Today, nmh is developed by various people on the Internet.
meillo@18 754 .[
meillo@18 755 %T RAND and the Information Evolution: A History in Essays and Vignettes
meillo@18 756 %A Willis H. Ware
meillo@18 757 %D 2008
meillo@18 758 %I The RAND Corporation
meillo@18 759 %P 128\(en137
meillo@18 760 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/
meillo@18 761 .]
meillo@18 762 .[
meillo@18 763 %T MH & xmh: Email for Users & Programmers
meillo@18 764 %A Jerry Peek
meillo@18 765 %D 1991, 1992, 1995
meillo@18 766 %I O'Reilly & Associates, Inc.
meillo@18 767 %P Appendix B
meillo@18 768 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP
meillo@18 769 .]
meillo@0 770
meillo@0 771 .NH 2
meillo@20 772 Contrasts to monolithic mail systems
meillo@0 773 .LP
meillo@19 774 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
meillo@38 775 Although there might actually exist further, very little known,
meillo@30 776 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
meillo@19 777 .PP
meillo@30 778 Monolithic \s-1MUA\s0s gather all their functions in one program.
meillo@30 779 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
meillo@23 780 Following is a list of important programs of \s-1MH\s0's toolchest
meillo@30 781 and their function.
meillo@30 782 It gives a feeling of how the toolchest looks like.
meillo@19 783 .IP \(bu
meillo@19 784 .CW inc :
meillo@30 785 incorporate new mail (this is how mail enters the system)
meillo@19 786 .IP \(bu
meillo@19 787 .CW scan :
meillo@19 788 list messages in folder
meillo@19 789 .IP \(bu
meillo@19 790 .CW show :
meillo@19 791 show message
meillo@19 792 .IP \(bu
meillo@19 793 .CW next\fR/\fPprev :
meillo@19 794 show next/previous message
meillo@19 795 .IP \(bu
meillo@19 796 .CW folder :
meillo@19 797 change current folder
meillo@19 798 .IP \(bu
meillo@19 799 .CW refile :
meillo@19 800 refile message into folder
meillo@19 801 .IP \(bu
meillo@19 802 .CW rmm :
meillo@19 803 remove message
meillo@19 804 .IP \(bu
meillo@19 805 .CW comp :
meillo@19 806 compose a new message
meillo@19 807 .IP \(bu
meillo@19 808 .CW repl :
meillo@19 809 reply to a message
meillo@19 810 .IP \(bu
meillo@19 811 .CW forw :
meillo@19 812 forward a message
meillo@19 813 .IP \(bu
meillo@19 814 .CW send :
meillo@30 815 send a prepared message (this is how mail leaves the system)
meillo@0 816 .LP
meillo@19 817 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
meillo@19 818 The user does not leave the shell to run \s-1MH\s0,
meillo@30 819 but he uses the various \s-1MH\s0 programs within the shell.
meillo@23 820 Using a monolithic program with a captive user interface
meillo@23 821 means ``entering'' the program, using it, and ``exiting'' the program.
meillo@23 822 Using toolchests like \s-1MH\s0 means running programs,
meillo@38 823 alone or in combination with others, even from other toolchests,
meillo@23 824 without leaving the shell.
meillo@30 825
meillo@30 826 .NH 2
meillo@30 827 Data storage
meillo@30 828 .LP
meillo@34 829 \s-1MH\s0's mail storage is a directory tree under the user's
meillo@34 830 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
meillo@34 831 where mail folders are directories and mail messages are text files
meillo@34 832 within them.
meillo@34 833 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
meillo@34 834 the public message sequences of that folder, for instance new messages.
meillo@34 835 Mail messages are text files located in a mail folder.
meillo@34 836 The files contain the messages as they were received.
meillo@34 837 They are numbered in ascending order in each folder.
meillo@19 838 .PP
meillo@30 839 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
meillo@30 840 Alternatives are \fImbox\fP and \fImaildir\fP.
meillo@30 841 In the mbox format all messages are stored within one file.
meillo@30 842 This was a good solution in the early days, when messages
meillo@30 843 were only a few lines of text and were deleted soon.
meillo@30 844 Today, when single messages often include several megabytes
meillo@30 845 of attachments, it is a bad solution.
meillo@30 846 Another disadvantage of the mbox format is that it is
meillo@30 847 more difficult to write tools that work on mail messages,
meillo@30 848 because it is always necessary to first find and extract
meillo@30 849 the relevant message in the mbox file.
meillo@30 850 With the \s-1MH\s0 mailbox format,
meillo@30 851 each message is a self-standing item, by definition.
meillo@30 852 Also, the problem of concurrent access to one mailbox is
meillo@30 853 reduced to the problem of concurrent access to one message.
meillo@30 854 Maildir is generally similar to \s-1MH\s0's format,
meillo@30 855 but modified towards guaranteed reliability.
meillo@30 856 This involves some complexity, unfortunately.
meillo@34 857 .PP
meillo@34 858 Working with \s-1MH\s0's toolchest on mailboxes is much like
meillo@34 859 working with Unix' toolchest on directory trees:
meillo@34 860 \f(CWscan\fP is like \f(CWls\fP,
meillo@34 861 \f(CWshow\fP is like \f(CWcat\fP,
meillo@34 862 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
meillo@34 863 \f(CWrefile\fP is like \f(CWmv\fP,
meillo@34 864 and \f(CWrmm\fP is like \f(CWrm\fP.
meillo@34 865 .PP
meillo@34 866 The context of tools in Unix consists mainly the current working directory,
meillo@34 867 the user identification, and the environment variables.
meillo@34 868 \s-1MH\s0 extends this context by two more items:
meillo@34 869 .IP \(bu
meillo@34 870 The current mail folder, which is similar to the current working directory.
meillo@34 871 For mail folders, \f(CWfolder\fP provides the corresponding functionality
meillo@34 872 of \f(CWcd\fP and \f(CWpwd\fP for directories.
meillo@34 873 .IP \(bu
meillo@34 874 Sequences, which are named sets of messages in a mail folder.
meillo@34 875 The current message, relative to a mail folder, is a special sequence.
meillo@34 876 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
meillo@34 877 .LP
meillo@34 878 In contrast to Unix' context, which is chained to the shell session,
meillo@34 879 \s-1MH\s0's context is independent.
meillo@34 880 Usually there is one context for each user, but a user can have many
meillo@34 881 contexts.
meillo@34 882 Public sequences are an exception, as they belong to the mail folder.
meillo@34 883 .[
meillo@34 884 %O mh-profile(5) and mh-sequence(5)
meillo@34 885 .]
meillo@20 886
meillo@0 887 .NH 2
meillo@20 888 Discussion of the design
meillo@0 889 .LP
meillo@20 890 The following paragraphs discuss \s-1MH\s0 in regard to the tenets
meillo@23 891 of the Unix Philosophy which Gancarz identified.
meillo@20 892
meillo@20 893 .PP
meillo@33 894 .B "Small is beautiful
meillo@20 895 and
meillo@33 896 .B "do one thing well
meillo@20 897 are two design goals that are directly visible in \s-1MH\s0.
meillo@20 898 Gancarz actually presents \s-1MH\s0 as example under the headline
meillo@20 899 ``Making UNIX Do One Thing Well'':
meillo@20 900 .QP
meillo@20 901 [\s-1MH\s0] consists of a series of programs which
meillo@20 902 when combined give the user an enormous ability
meillo@20 903 to manipulate electronic mail messages.
meillo@20 904 A complex application, it shows that not only is it
meillo@20 905 possible to build large applications from smaller
meillo@20 906 components, but also that such designs are actually preferable.
meillo@20 907 .[
meillo@20 908 %A Mike Gancarz
meillo@20 909 %T unix-phil
meillo@20 910 %P 125
meillo@20 911 .]
meillo@20 912 .LP
meillo@20 913 The various small programs of \s-1MH\s0 were relatively easy
meillo@23 914 to write, because each of them is small, limited to one function,
meillo@23 915 and has clear boundaries.
meillo@20 916 For the same reasons, they are also good to maintain.
meillo@20 917 Further more, the system can easily get extended.
meillo@20 918 One only needs to put a new program into the toolchest.
meillo@23 919 This was done, for instance, when \s-1MIME\s0 support was added
meillo@20 920 (e.g. \f(CWmhbuild\fP).
meillo@20 921 Also, different programs can exist to do the basically same job
meillo@20 922 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
meillo@20 923 If someone needs a mail system with some additionally
meillo@23 924 functions that are available nowhere yet, he best takes a
meillo@20 925 toolchest system like \s-1MH\s0 where he can add the
meillo@20 926 functionality with little work.
meillo@20 927
meillo@20 928 .PP
meillo@34 929 .B "Store data in flat text files
meillo@34 930 is followed by \s-1MH\s0.
meillo@34 931 This is not surprising, because email messages are already plain text.
meillo@34 932 \s-1MH\s0 stores the messages as it receives them,
meillo@34 933 thus any other tool that works on RFC 2822 mail messages can operate
meillo@34 934 on the messages in an \s-1MH\s0 mailbox.
meillo@34 935 All other files \s-1MH\s0 uses are plain text too.
meillo@34 936 It is therefore possible and encouraged to use the text processing
meillo@34 937 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
meillo@20 938
meillo@20 939 .PP
meillo@33 940 .B "Avoid captive user interfaces" .
meillo@19 941 \s-1MH\s0 is perfectly suited for non-interactive use.
meillo@19 942 It offers all functions directly and without captive user interfaces.
meillo@30 943 If, nonetheless, users want a graphical user interface,
meillo@20 944 they can have it with \fIxmh\fP or \fIexmh\fP, too.
meillo@19 945 These are graphical frontends for the \s-1MH\s0 toolchest.
meillo@19 946 This means, all email-related work is still done by \s-1MH\s0 tools,
meillo@20 947 but the frontend issues the appropriate calls when the user
meillo@30 948 clicks on buttons.
meillo@20 949 Providing easy-to-use user interfaces in form of frontends is a good
meillo@19 950 approach, because it does not limit the power of the backend itself.
meillo@20 951 The frontend will anyway only be able to make a subset of the
meillo@23 952 backend's power and flexibility available to the user.
meillo@20 953 But if it is a separate program,
meillo@20 954 then the missing parts can still be accessed at the backend directly.
meillo@19 955 If it is integrated, then this will hardly be possible.
meillo@30 956 Further more, it is possible to have different frontends to the same
meillo@30 957 backend.
meillo@19 958
meillo@19 959 .PP
meillo@33 960 .B "Choose portability over efficiency
meillo@20 961 and
meillo@33 962 .B "use shell scripts to increase leverage and portability" .
meillo@20 963 These two tenets are indirectly, but nicely, demonstrated by
meillo@30 964 Bolsky and Korn in their book about the Korn Shell.
meillo@20 965 .[
meillo@20 966 %T The KornShell: command and programming language
meillo@20 967 %A Morris I. Bolsky
meillo@20 968 %A David G. Korn
meillo@20 969 %I Prentice Hall
meillo@20 970 %D 1989
meillo@30 971 %P 254\(en290
meillo@20 972 %O \s-1ISBN\s0: 0-13-516972-0
meillo@20 973 .]
meillo@30 974 They demonstrated, in chapter 18 of the book, a basic implementation
meillo@20 975 of a subset of \s-1MH\s0 in ksh scripts.
meillo@20 976 Of course, this was just a demonstration, but a brilliant one.
meillo@20 977 It shows how quickly one can implement such a prototype with shell scripts,
meillo@20 978 and how readable they are.
meillo@20 979 The implementation in the scripting language may not be very fast,
meillo@20 980 but it can be fast enough though, and this is all that matters.
meillo@20 981 By having the code in an interpreted language, like the shell,
meillo@20 982 portability becomes a minor issue, if we assume the interpreter
meillo@20 983 to be widespread.
meillo@20 984 This demonstration also shows how easy it is to create single programs
meillo@20 985 of a toolchest software.
meillo@30 986 There are eight tools (two of them have multiple names) and 16 functions
meillo@30 987 with supporting code.
meillo@30 988 Each tool comprises between 12 and 38 lines of ksh,
meillo@30 989 in total about 200 lines.
meillo@30 990 The functions comprise between 3 and 78 lines of ksh,
meillo@30 991 in total about 450 lines.
meillo@20 992 Such small software is easy to write, easy to understand,
meillo@20 993 and thus easy to maintain.
meillo@23 994 A toolchest improves the possibility to only write some parts
meillo@20 995 and though create a working result.
meillo@20 996 Expanding the toolchest without global changes will likely be
meillo@20 997 possible, too.
meillo@20 998
meillo@20 999 .PP
meillo@33 1000 .B "Use software leverage to your advantage
meillo@20 1001 and the lesser tenet
meillo@33 1002 .B "allow the user to tailor the environment
meillo@20 1003 are ideally followed in the design of \s-1MH\s0.
meillo@21 1004 Tailoring the environment is heavily encouraged by the ability to
meillo@30 1005 directly define default options to programs.
meillo@30 1006 It is even possible to define different default options
meillo@21 1007 depending on the name under which the program was called.
meillo@21 1008 Software leverage is heavily encouraged by the ease it is to
meillo@21 1009 create shell scripts that run a specific command line,
meillo@30 1010 built of several \s-1MH\s0 programs.
meillo@21 1011 There is few software that so much wants users to tailor their
meillo@21 1012 environment and to leverage the use of the software, like \s-1MH\s0.
meillo@21 1013 Just to make one example:
meillo@23 1014 One might prefer a different listing format for the \f(CWscan\fP
meillo@21 1015 program.
meillo@30 1016 It is possible to take one of the distributed format files
meillo@21 1017 or to write one yourself.
meillo@21 1018 To use the format as default for \f(CWscan\fP, a single line,
meillo@21 1019 reading
meillo@21 1020 .DS
meillo@21 1021 .CW
meillo@21 1022 scan: -form FORMATFILE
meillo@21 1023 .DE
meillo@21 1024 must be added to \f(CW.mh_profile\fP.
meillo@21 1025 If one wants this different format as an additional command,
meillo@23 1026 instead of changing the default, he needs to create a link to
meillo@23 1027 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
meillo@21 1028 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
meillo@30 1029 as the option should only be in effect when scan is called as
meillo@21 1030 \f(CWscan2\fP.
meillo@20 1031
meillo@20 1032 .PP
meillo@33 1033 .B "Make every program a filter
meillo@21 1034 is hard to find in \s-1MH\s0.
meillo@21 1035 The reason therefore is that most of \s-1MH\s0's tools provide
meillo@21 1036 basic file system operations for the mailboxes.
meillo@30 1037 The reason is the same because of which
meillo@21 1038 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP
meillo@21 1039 aren't filters neither.
meillo@23 1040 However, they build a basis on which filters can operate.
meillo@23 1041 \s-1MH\s0 does not provide many filters itself, but it is a basis
meillo@23 1042 to write filters for.
meillo@30 1043 An example would be a mail message text highlighter,
meillo@30 1044 that means a program that makes use of a color terminal to display
meillo@30 1045 header lines, quotations, and signatures in distinct colors.
meillo@30 1046 The author's version of this program, for instance,
meillo@30 1047 is a 25 line awk script.
meillo@21 1048
meillo@21 1049 .PP
meillo@33 1050 .B "Build a prototype as soon as possible
meillo@21 1051 was again well followed by \s-1MH\s0.
meillo@21 1052 This tenet, of course, focuses on early development, which is
meillo@21 1053 long time ago for \s-1MH\s0.
meillo@21 1054 But without following this guideline at the very beginning,
meillo@23 1055 Bruce Borden may have not convinced the management of \s-1RAND\s0
meillo@23 1056 to ever create \s-1MH\s0.
meillo@23 1057 In Bruce' own words:
meillo@21 1058 .QP
meillo@30 1059 [...] but they [Stockton Gaines and Norm Shapiro] were not able
meillo@23 1060 to convince anyone that such a system would be fast enough to be usable.
meillo@21 1061 I proposed a very short project to prove the basic concepts,
meillo@21 1062 and my management agreed.
meillo@21 1063 Looking back, I realize that I had been very lucky with my first design.
meillo@21 1064 Without nearly enough design work,
meillo@21 1065 I built a working environment and some header files
meillo@21 1066 with key structures and wrote the first few \s-1MH\s0 commands:
meillo@21 1067 inc, show/next/prev, and comp.
meillo@21 1068 [...]
meillo@21 1069 With these three, I was able to convince people that the structure was viable.
meillo@21 1070 This took about three weeks.
meillo@21 1071 .[
meillo@21 1072 %O FIXME
meillo@21 1073 .]
meillo@0 1074
meillo@0 1075 .NH 2
meillo@0 1076 Problems
meillo@0 1077 .LP
meillo@22 1078 \s-1MH\s0, for sure is not without problems.
meillo@30 1079 There are two main problems: one is technical, the other is about human behavior.
meillo@22 1080 .PP
meillo@22 1081 \s-1MH\s0 is old and email today is very different to email in the time
meillo@22 1082 when \s-1MH\s0 was designed.
meillo@22 1083 \s-1MH\s0 adopted to the changes pretty well, but it is limited.
meillo@22 1084 For example in development resources.
meillo@22 1085 \s-1MIME\s0 support and support for different character encodings
meillo@22 1086 is available, but only on a moderate level.
meillo@22 1087 More active developers could quickly improve there.
meillo@22 1088 It is also limited by design, which is the larger problem.
meillo@22 1089 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
meillo@22 1090 These design conflicts are not easily solvable.
meillo@22 1091 Possibly, they require a redesign.
meillo@30 1092 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers,
meillo@30 1093 hence \s-1MH\s0 may never work well with \s-1IMAP\s0.
meillo@22 1094 .PP
meillo@22 1095 The other kind of problem is human habits.
meillo@22 1096 When in this world almost all \s-1MUA\s0s are monolithic,
meillo@22 1097 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
meillo@22 1098 like \s-1MH\s0.
meillo@22 1099 The habits are so strong, that even people who understood the concept
meillo@30 1100 and advantages of \s-1MH\s0 do not like to switch,
meillo@30 1101 simply because \s-1MH\s0 is different.
meillo@30 1102 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
meillo@30 1103 are quite outdated and thus not very appealing compared to the modern interfaces
meillo@30 1104 which monolithic \s-1MUA\s0s offer.
meillo@20 1105
meillo@20 1106 .NH 2
meillo@20 1107 Summary \s-1MH\s0
meillo@20 1108 .LP
meillo@31 1109 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design
meillo@31 1110 and implementation.
meillo@31 1111 It consists of a toolchest of small tools, each of them does one job well.
meillo@31 1112 The tools are orthogonal to each other, to a large extend.
meillo@31 1113 However, for historical reasons, there also exist distinct tools
meillo@31 1114 that cover the same task.
meillo@31 1115 .PP
meillo@31 1116 The toolchest approach offers great flexibility to the user.
meillo@31 1117 He can use the complete power of the Unix shell with \s-1MH\s0.
meillo@31 1118 This makes \s-1MH\s0 a very powerful mail system.
meillo@31 1119 Extending and customizing \s-1MH\s0 is easy and encouraged, too.
meillo@31 1120 .PP
meillo@31 1121 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
meillo@31 1122 Its overall design follows clear rules.
meillo@31 1123 The single tools do only one job, thus they are easy to understand,
meillo@31 1124 easy to write, and good to maintain.
meillo@31 1125 They are all independent and do not interfere with the others.
meillo@31 1126 Automated testing of their function is a straight forward task.
meillo@31 1127 .PP
meillo@31 1128 It is sad, that \s-1MH\s0's differentness is its largest problem,
meillo@31 1129 as its differentness is also its largest advantage.
meillo@31 1130 Unfortunately, for most people their habits are stronger
meillo@31 1131 than the attraction of the clear design and the power, \s-1MH\s0 offers.
meillo@0 1132
meillo@8 1133
meillo@8 1134
meillo@0 1135 .NH 1
meillo@0 1136 Case study: uzbl
meillo@32 1137 .LP
meillo@32 1138 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
meillo@32 1139 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy.
meillo@32 1140 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''.
meillo@32 1141 It is pronounced the identical.
meillo@0 1142
meillo@0 1143 .NH 2
meillo@32 1144 Historical background
meillo@0 1145 .LP
meillo@32 1146 Uzbl was started by Dieter Plaetinck in April 2009.
meillo@32 1147 The idea was born in a thread in the Arch Linux forum.
meillo@32 1148 .[
meillo@32 1149 %O http://bbs.archlinux.org/viewtopic.php?id=67463
meillo@32 1150 .]
meillo@32 1151 After some discussion about failures of well known web browsers,
meillo@32 1152 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
meillo@32 1153 of how a better web browser could look like.
meillo@32 1154 To the question of another member, if Plaetinck would write that program,
meillo@32 1155 because it would sound fantastic, Plaetinck replied:
meillo@32 1156 ``Maybe, if I find the time ;-)''.
meillo@32 1157 .PP
meillo@32 1158 Fortunately, he found the time.
meillo@32 1159 One day later, the first prototype was out.
meillo@32 1160 One week later, uzbl had an own website.
meillo@32 1161 One month after the first code showed up,
meillo@32 1162 a mailing list was installed to coordinate and discuss further development.
meillo@32 1163 A wiki was set up to store documentation and scripts that showed up on the
meillo@32 1164 mailing list and elsewhere.
meillo@32 1165 .PP
meillo@38 1166 In the, now, one year of uzbl's existence, it was heavily developed in various branches.
meillo@32 1167 Plaetinck's task became more and more to only merge the best code from the
meillo@32 1168 different branches into his main branch, and to apply patches.
meillo@32 1169 About once a month, Plaetinck released a new version.
meillo@32 1170 In September 2009, he presented several forks of uzbl.
meillo@38 1171 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
meillo@32 1172 .PP
meillo@32 1173 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
meillo@32 1174 In September 2009, the uzbl web browser was on \fISlashdot\fP.
meillo@0 1175
meillo@0 1176 .NH 2
meillo@32 1177 Contrasts to other web browsers
meillo@0 1178 .LP
meillo@32 1179 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
meillo@32 1180 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
meillo@32 1181 .PP
meillo@32 1182 Today, uzbl is divided into uzbl-core and uzbl-browser.
meillo@32 1183 Uzbl-core is, how its name already indicates, the core of uzbl.
meillo@32 1184 It handles commands and events to interface other programs,
meillo@32 1185 and also displays webpages by using webkit as render engine.
meillo@32 1186 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
meillo@32 1187 an event manager, yanking, pasting, page searching, zooming, and more stuff,
meillo@32 1188 to form a ``complete'' web browser.
meillo@32 1189 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
meillo@32 1190 so uzbl-core is included.
meillo@32 1191 .PP
meillo@32 1192 Unlike most other web browsers, uzbl is mainly the mediator between the
meillo@32 1193 various tools that cover single jobs of web browsing.
meillo@35 1194 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
meillo@35 1195 and on stdin, and it writes events to a Unix socket and to stdout.
meillo@35 1196 The graphical rendering of the webpage is done by webkit, a web content engine.
meillo@35 1197 Uzbl-core is build around this library.
meillo@35 1198 Loading a webpage in a running uzbl instance requires only:
meillo@32 1199 .DS
meillo@32 1200 .CW
meillo@32 1201 echo 'uri http://example.org' >/path/to/uzbl-fifo
meillo@32 1202 .DE
meillo@32 1203 .PP
meillo@32 1204 Downloads, browsing history, bookmarks, and thelike are not provided
meillo@32 1205 by uzbl-core itself, as they are in other web browsers.
meillo@35 1206 Uzbl-browser also only provides, so called, handler scripts that wrap
meillo@35 1207 external applications which provide the actual functionality.
meillo@32 1208 For instance, \fIwget\fP is used to download files and uzbl-browser
meillo@32 1209 includes a script that calls wget with appropriate options in
meillo@32 1210 a prepared environment.
meillo@32 1211 .PP
meillo@32 1212 Modern web browsers are proud to have addons, plugins, and modules, instead.
meillo@32 1213 This is their effort to achieve similar goals.
meillo@35 1214 But instead of using existing, external programs, modern web browsers
meillo@35 1215 include these functions, although they might be loaded at runtime.
meillo@0 1216
meillo@0 1217 .NH 2
meillo@32 1218 Discussion of the design
meillo@0 1219 .LP
meillo@32 1220 This section discusses uzbl in regard of the Unix Philosophy,
meillo@32 1221 as identified by Gancarz.
meillo@32 1222
meillo@32 1223 .PP
meillo@35 1224 .B "Make each program do one thing well" .
meillo@35 1225 Uzbl tries to be a web browser and nothing else.
meillo@36 1226 The common definition of a web browser is, of course, highly influenced by
meillo@36 1227 existing implementations of web browsers, although they are degenerated.
meillo@35 1228 Web browsers should be programs to browse the web, and nothing more.
meillo@35 1229 This is the one thing they should do, as demanded by the Unix Philosophy.
meillo@36 1230 .PP
meillo@36 1231 Web browsers should, for instance, not manage downloads.
meillo@35 1232 This is the job download managers exist for.
meillo@35 1233 Download managers do primary care about being good in downloading files.
meillo@35 1234 Modern web browsers provide download management only as a secondary feature.
meillo@35 1235 How could they perform this job better, than programs that exist only for
meillo@35 1236 this very job?
meillo@35 1237 And how could anyone want less than the best download manager available?
meillo@32 1238 .PP
meillo@35 1239 A web browser's job is to let the user browse the web.
meillo@35 1240 This means, navigating through websites by following links.
meillo@36 1241 Rendering the \s-1HTML\s0 sources is a different job, too.
meillo@36 1242 It is covered by the webkit render engine, in uzbl's case.
meillo@35 1243 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
meillo@36 1244 are also not the job of a web browser.
meillo@36 1245 They should be handled by external applications \(en
meillo@36 1246 ones which's job is to handle such data.
meillo@35 1247 Uzbl strives to do it this way.
meillo@36 1248 .PP
meillo@36 1249 Remember Doug McIlroy:
meillo@35 1250 .I
meillo@35 1251 ``Write programs that do one thing and do it well.
meillo@35 1252 Write programs to work together.''
meillo@35 1253 .R
meillo@35 1254 .PP
meillo@35 1255 The lesser tenet
meillo@35 1256 .B "allow the user to tailor the environment
meillo@35 1257 matches good here.
meillo@35 1258 There was the question, how anyone could want anything less than the
meillo@35 1259 best program for the job.
meillo@36 1260 But as personal preferences matter much,
meillo@36 1261 it is probably more important to ask:
meillo@35 1262 How could anyone want something else than his preferred program for the job?
meillo@36 1263 .PP
meillo@35 1264 Usually users want one program for one job.
meillo@35 1265 Hence, whenever the task is, for instance, downloading,
meillo@36 1266 exactly one download manager should be used.
meillo@35 1267 More advanced users might want to have this download manager in this
meillo@35 1268 situation and that one in that situation.
meillo@35 1269 They should be able to configure it this way.
meillo@35 1270 With uzbl, one can use any download manager the user wants.
meillo@36 1271 To switch to a different one, only one line in a small handler script
meillo@35 1272 needs to be changed.
meillo@36 1273 Alternatively it would be possible to query an entry in a global file
meillo@36 1274 or an environment variable, which specifies the download manager to use,
meillo@35 1275 in the handler script.
meillo@36 1276 .PP
meillo@35 1277 As uzbl does neither have its own download manager nor depends on a
meillo@35 1278 specific one, thus uzbl's browsing abilities will not be lowered by having
meillo@35 1279 a bad download manager.
meillo@36 1280 Uzbl's download capabilities will just as good as the ones of the best
meillo@36 1281 download manager available on the system.
meillo@38 1282 Of course, this applies to all of the other supplementary tools, too.
meillo@32 1283
meillo@32 1284 .PP
meillo@36 1285 .B "Use software leverage to your advantage" .
meillo@36 1286 Shell scripts are a good choice to extend uzbl.
meillo@36 1287 Uzbl is designed to be extended by external tools.
meillo@36 1288 These external tools are usually wrapped by small handler shell scripts.
meillo@36 1289 Shell scripts are the glue in this approach.
meillo@36 1290 They make the various parts fit together.
meillo@36 1291 .PP
meillo@36 1292 As an example, the history mechanism of uzbl shall be presented.
meillo@36 1293 Uzbl is configured to spawn a script to append an entry to the history
meillo@36 1294 whenever the event of a fully loaded page occurs.
meillo@36 1295 The script to append the entry to the history not much more than:
meillo@36 1296 .DS
meillo@36 1297 .CW
meillo@36 1298 #!/bin/sh
meillo@36 1299 file=/path/to/uzbl-history
meillo@36 1300 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
meillo@36 1301 .DE
meillo@36 1302 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
meillo@36 1303 For loading an entry, a key is bound to spawn a load from history script.
meillo@36 1304 The script reverses the history to have newer entries first,
meillo@36 1305 then displays \fIdmenu\fP to select an item,
meillo@36 1306 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
meillo@36 1307 With error checking and corner cases removed, the script looks like this:
meillo@36 1308 .DS
meillo@36 1309 .CW
meillo@36 1310 #!/bin/sh
meillo@36 1311 file=/path/to/uzbl-history
meillo@36 1312 goto=`tac $file | dmenu | cut -d' ' -f 3`
meillo@36 1313 echo "uri $goto" > $4
meillo@36 1314 .DE
meillo@36 1315 \f(CW$4\fP expands to the path of the command input pipe of the current
meillo@36 1316 uzbl instance.
meillo@32 1317
meillo@32 1318 .PP
meillo@33 1319 .B "Avoid captive user interfaces" .
meillo@36 1320 One could say, that uzbl, to a large extend, actually \fIis\fP
meillo@36 1321 a captive user interface.
meillo@37 1322 But the difference to most other web browsers is, that uzbl is only
meillo@37 1323 the captive user interface frontend and the core of the backend.
meillo@38 1324 Many parts of the backend are independent of uzbl.
meillo@37 1325 Some are distributed with uzbl, for some external programs, handler scripts
meillo@37 1326 are distributed, arbitrary additional functionality can be added if desired.
meillo@37 1327 .PP
meillo@37 1328 The frontend is captive \(en that is true.
meillo@37 1329 This is okay for the task of browsing the web, as this task is only relevant
meillo@37 1330 for humans.
meillo@37 1331 Automated programs would \fIcrawl\fP the web.
meillo@37 1332 That means, they read the source directly.
meillo@37 1333 The source includes all the semantics.
meillo@37 1334 The graphical representation is just for humans to transfer the semantics
meillo@37 1335 more intuitively.
meillo@32 1336
meillo@32 1337 .PP
meillo@33 1338 .B "Make every program a filter" .
meillo@37 1339 Graphical web browsers are almost dead ends in the chain of information flow.
meillo@37 1340 Thus it is difficult to see what graphical web browsers should filter.
meillo@37 1341 Graphical web browsers exist almost only for interactive use by humans.
meillo@37 1342 The only case when one might want to automate the rendering function is
meillo@37 1343 to generate images of rendered webpages.
meillo@37 1344
meillo@37 1345 .PP
meillo@37 1346 .B "Small is beautiful"
meillo@38 1347 is not easy to apply to a web browser, primary because modern web technology
meillo@38 1348 is very complex; hence the rendering task is very complex.
meillo@37 1349 Modern web browsers will always consist of many thousand lines of code,
meillo@37 1350 unfortunately.
meillo@37 1351 Using the toolchest approach and wrappers can split the browser into
meillo@37 1352 several small parts, tough.
meillo@37 1353 .PP
meillo@37 1354 Uzbl-core consists of about 3\,500 lines of C code.
meillo@37 1355 The distribution includes another 3\,500 lines of Shell and Python code,
meillo@37 1356 which are the handler scripts and plugins like a modal interface.
meillo@38 1357 Further more, uzbl uses functionality of external tools like
meillo@38 1358 \fIwget\fP and \fInetcat\fP.
meillo@37 1359 Up to this point, uzbl looks pretty neat and small.
meillo@38 1360 The ugly part of uzbl is the web content renderer, webkit.
meillo@37 1361 Webkit consists of roughly 400\,000 (!) lines of code.
meillo@38 1362 Unfortunately, small web render engines are not possible anymore
meillo@38 1363 because of the modern web.
meillo@38 1364 The problems section will explain this in more detail.
meillo@35 1365
meillo@35 1366 .PP
meillo@35 1367 .B "Build a prototype as soon as possible" .
meillo@35 1368 Plaetinck made his code public, right from the beginning.
meillo@38 1369 Discussion and development was, and still is, open to everyone interested.
meillo@38 1370 Development versions of uzbl can be obtained very simply from the code
meillo@38 1371 repository.
meillo@38 1372 Within the first year of uzbl's existence, a new version was released
meillo@35 1373 more often than once a month.
meillo@38 1374 Different forks and branches arose.
meillo@38 1375 They introduced new features, which were tested for suitability.
meillo@35 1376 The experiences of using prototypes influenced further development.
meillo@35 1377 Actually, all development was community driven.
meillo@38 1378 Plaetinck says, three months after uzbl's birth:
meillo@35 1379 ``Right now I hardly code anything myself for Uzbl.
meillo@35 1380 I just merge in other people's code, ponder a lot, and lead the discussions.''
meillo@35 1381 .[
meillo@36 1382 %A FIXME
meillo@35 1383 %O http://lwn.net/Articles/341245/
meillo@35 1384 .]
meillo@32 1385
meillo@0 1386
meillo@0 1387 .NH 2
meillo@0 1388 Problems
meillo@0 1389 .LP
meillo@38 1390 Similar to \s-1MH\s0, uzbl, too suffers from being different.
meillo@38 1391 It is sad, but people use what they know.
meillo@38 1392 Fortunately, uzbl's user interface can look and feel very much the
meillo@38 1393 same as the one of the well known web browsers,
meillo@38 1394 hiding the internal differences.
meillo@38 1395 But uzbl has to provide this similar look and feel to be accepted
meillo@38 1396 as a ``normal'' browser by ``normal'' users.
meillo@37 1397 .PP
meillo@38 1398 The more important problem is the modern web.
meillo@38 1399 The modern web is simply broken.
meillo@38 1400 It has state in a state-less protocol,
meillo@38 1401 it misuses technologies,
meillo@38 1402 and it is helplessly overloaded.
meillo@38 1403 The result are web content render engines that must consist
meillo@38 1404 of hundreds of thousands lines of code.
meillo@38 1405 They also must combine and integrate many different technologies,
meillo@38 1406 only to make our modern web usable.
meillo@38 1407 Website to image converter are hardly possible to run without
meillo@38 1408 human interaction because of state in sessions, impossible
meillo@38 1409 deep-linking, and unautomatable technologies.
meillo@37 1410 .PP
meillo@38 1411 The web was misused to provide all kinds of imaginable wishes.
meillo@38 1412 Now web browsers, and eventually the users, suffer from it.
meillo@37 1413
meillo@8 1414
meillo@32 1415 .NH 2
meillo@32 1416 Summary uzbl
meillo@32 1417 .LP
meillo@38 1418 ``Uzbl is a browser that adheres to the Unix Philosophy'',
meillo@38 1419 that is how uzbl is seen by its authors.
meillo@38 1420 Indeed, uzbl follows the Unix Philosophy in many ways.
meillo@38 1421 It consists of independent parts that work together,
meillo@38 1422 its core is mainly a mediator which glues the parts together.
meillo@38 1423 .PP
meillo@38 1424 Software leverage can excellently be seen in uzbl.
meillo@38 1425 It makes use of external tools, separates independent tasks
meillo@38 1426 in independent parts, and glues them together with small
meillo@38 1427 handler scripts, around uzbl-core.
meillo@38 1428 .PP
meillo@38 1429 As uzbl, more or less, consists of a set of tools and a bit
meillo@38 1430 of glue, anyone can put the parts together and expand it
meillo@38 1431 in any desired way.
meillo@38 1432 Uzbl is very flexible and customizable.
meillo@38 1433 These properties make it valuable for advanced users,
meillo@38 1434 but may keep novice users from using it.
meillo@38 1435 .PP
meillo@38 1436 Uzbl's main problem is the modern web, that makes it hard
meillo@38 1437 to design a sane web browser.
meillo@38 1438 Despite this bad situation, uzbl does a fairly good job.
meillo@32 1439
meillo@8 1440
meillo@0 1441 .NH 1
meillo@0 1442 Final thoughts
meillo@0 1443
meillo@0 1444 .NH 2
meillo@0 1445 Quick summary
meillo@0 1446 .LP
meillo@0 1447 good design
meillo@0 1448 .LP
meillo@0 1449 unix phil
meillo@0 1450 .LP
meillo@0 1451 case studies
meillo@0 1452
meillo@0 1453 .NH 2
meillo@0 1454 Why people should choose
meillo@0 1455 .LP
meillo@0 1456 Make the right choice!
meillo@0 1457
meillo@0 1458 .nr PI .5i
meillo@0 1459 .rm ]<
meillo@0 1460 .de ]<
meillo@0 1461 .LP
meillo@0 1462 .de FP
meillo@0 1463 .IP \\\\$1.
meillo@0 1464 \\..
meillo@0 1465 .rm FS FE
meillo@0 1466 ..
meillo@0 1467 .SH
meillo@0 1468 References
meillo@0 1469 .[
meillo@0 1470 $LIST$
meillo@0 1471 .]
meillo@0 1472 .wh -1p