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rework of MH's data storage section
author meillo@marmaro.de
date Thu, 25 Mar 2010 22:18:55 +0100
parents 0bd43c4ad9f8
children f11406a85319
rev   line source
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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@2 31 This paper discusses the importance of the Unix Philosophy in software design.
meillo@0 32 Today, few software designers are aware of these concepts,
meillo@3 33 and thus most modern software is limited and does not make use of software leverage.
meillo@0 34 Knowing and following the tenets of the Unix Philosophy makes software more valuable.
meillo@0 35 .AE
meillo@0 36
meillo@10 37 .\".if t .2C
meillo@2 38
meillo@2 39 .FS
meillo@2 40 .ps -1
meillo@2 41 This paper was prepared for the seminar ``Software Analysis'' at University Ulm.
meillo@2 42 Mentor was professor Schweiggert. 2010-02-05
meillo@2 43 .br
meillo@2 44 You may get this document from my website
meillo@2 45 .CW \s-1http://marmaro.de/docs
meillo@2 46 .FE
meillo@2 47
meillo@0 48 .NH 1
meillo@0 49 Introduction
meillo@0 50 .LP
meillo@0 51 Building a software is a process from an idea of the purpose of the software
meillo@3 52 to its release.
meillo@0 53 No matter \fIhow\fP the process is run, two things are common:
meillo@0 54 the initial idea and the release.
meillo@9 55 The process in between can be of any shape.
meillo@9 56 The the maintenance work after the release is ignored for the moment.
meillo@1 57 .PP
meillo@0 58 The process of building splits mainly in two parts:
meillo@0 59 the planning of what and how to build, and implementing the plan by writing code.
meillo@3 60 This paper focuses on the planning part \(en the designing of the software.
meillo@3 61 .PP
meillo@3 62 Software design is the plan of how the internals and externals of the software should look like,
meillo@3 63 based on the requirements.
meillo@9 64 This paper discusses the recommendations of the Unix Philosophy about software design.
meillo@3 65 .PP
meillo@3 66 The here discussed ideas can get applied by any development process.
meillo@9 67 The Unix Philosophy does recommend how the software development process should look like,
meillo@3 68 but this shall not be of matter here.
meillo@0 69 Similar, the question of how to write the code is out of focus.
meillo@1 70 .PP
meillo@3 71 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet.
meillo@1 72 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed.
meillo@3 73 It is no limited set of rules, but what people see to be common to typical Unix software.
meillo@1 74 Several people stated their view on the Unix Philosophy.
meillo@1 75 Best known are:
meillo@1 76 .IP \(bu
meillo@1 77 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
meillo@1 78 .[
meillo@1 79 %A M. D. McIlroy
meillo@1 80 %A E. N. Pinson
meillo@1 81 %A B. A. Taque
meillo@1 82 %T UNIX Time-Sharing System Forward
meillo@1 83 %J The Bell System Technical Journal
meillo@1 84 %D 1978
meillo@1 85 %V 57
meillo@1 86 %N 6
meillo@1 87 %P 1902
meillo@1 88 .]
meillo@1 89 .IP \(bu
meillo@1 90 Mike Gancarz' book ``The UNIX Philosophy''.
meillo@1 91 .[
meillo@1 92 %A Mike Gancarz
meillo@1 93 %T The UNIX Philosophy
meillo@1 94 %D 1995
meillo@1 95 %I Digital Press
meillo@1 96 .]
meillo@1 97 .IP \(bu
meillo@1 98 Eric S. Raymond's book ``The Art of UNIX Programming''.
meillo@1 99 .[
meillo@1 100 %A Eric S. Raymond
meillo@1 101 %T The Art of UNIX Programming
meillo@1 102 %D 2003
meillo@1 103 %I Addison-Wesley
meillo@2 104 %O .CW \s-1http://www.faqs.org/docs/artu/
meillo@1 105 .]
meillo@0 106 .LP
meillo@1 107 These different views on the Unix Philosophy have much in common.
meillo@3 108 Especially, the main concepts are similar for all of them.
meillo@1 109 But there are also points on which they differ.
meillo@1 110 This only underlines what the Unix Philosophy is:
meillo@1 111 A retrospective view on the main concepts of Unix software;
meillo@9 112 especially those that were successful and unique to Unix.
meillo@6 113 .\" really?
meillo@1 114 .PP
meillo@1 115 Before we will have a look at concrete concepts,
meillo@1 116 we discuss why software design is important
meillo@1 117 and what problems bad design introduces.
meillo@0 118
meillo@0 119
meillo@0 120 .NH 1
meillo@6 121 Importance of software design in general
meillo@0 122 .LP
meillo@2 123 Why should we design software at all?
meillo@6 124 It is general knowledge, that even a bad plan is better than no plan.
meillo@6 125 Ignoring software design is programming without a plan.
meillo@6 126 This will lead pretty sure to horrible results.
meillo@2 127 .PP
meillo@6 128 The design of a software is its internal and external shape.
meillo@6 129 The design talked about here has nothing to do with visual appearance.
meillo@6 130 If we see a program as a car, then its color is of no matter.
meillo@6 131 Its design would be the car's size, its shape, the number and position of doors,
meillo@6 132 the ratio of passenger and cargo transport, and so forth.
meillo@2 133 .PP
meillo@6 134 A software's design is about quality properties.
meillo@6 135 Each of the cars may be able to drive from A to B,
meillo@6 136 but it depends on its properties whether it is a good car for passenger transport or not.
meillo@6 137 It also depends on its properties if it is a good choice for a rough mountain area.
meillo@2 138 .PP
meillo@6 139 Requirements to a software are twofold: functional and non-functional.
meillo@6 140 Functional requirements are easier to define and to verify.
meillo@6 141 They are directly the software's functions.
meillo@6 142 Functional requirements are the reason why software gets written.
meillo@6 143 Someone has a problem and needs a tool to solve it.
meillo@6 144 Being able to solve the problem is the main functional requirement.
meillo@6 145 It is the driving force behind all programming effort.
meillo@2 146 .PP
meillo@6 147 On the other hand, there are also non-functional requirements.
meillo@6 148 They are called \fIquality\fP requirements, too.
meillo@6 149 The quality of a software is about properties that are not directly related to
meillo@6 150 the software's basic functions.
meillo@6 151 Quality aspects are about the properties that are overlooked at first sight.
meillo@2 152 .PP
meillo@6 153 Quality is of few matter when the software gets initially built,
meillo@9 154 but it will be of matter in usage and maintenance of the software.
meillo@6 155 A short-sighted might see in developing a software mainly building something up.
meillo@6 156 Reality shows, that building the software the first time is only a small amount
meillo@6 157 of the overall work.
meillo@9 158 Bug fixing, extending, rebuilding of parts \(en short: maintenance work \(en
meillo@6 159 does soon take over the major part of the time spent on a software.
meillo@6 160 Not to forget the usage of the software.
meillo@6 161 These processes are highly influenced by the software's quality.
meillo@6 162 Thus, quality should never be neglected.
meillo@6 163 The problem is that you hardly ``stumble over'' bad quality during the first build,
meillo@6 164 but this is the time when you should care about good quality most.
meillo@6 165 .PP
meillo@6 166 Software design is not about the basic function of a software;
meillo@6 167 this requirement will get satisfied anyway, as it is the main driving force behind the development.
meillo@6 168 Software design is about quality aspects of the software.
meillo@6 169 Good design will lead to good quality, bad design to bad quality.
meillo@6 170 The primary functions of the software will be affected modestly by bad quality,
meillo@6 171 but good quality can provide a lot of additional gain from the software,
meillo@6 172 even at places where one never expected it.
meillo@6 173 .PP
meillo@6 174 The ISO/IEC 9126-1 standard, part 1,
meillo@6 175 .[
meillo@9 176 %I International Organization for Standardization
meillo@6 177 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1
meillo@6 178 %C Geneve
meillo@6 179 %D 2001
meillo@6 180 .]
meillo@6 181 defines the quality model as consisting out of:
meillo@6 182 .IP \(bu
meillo@6 183 .I Functionality
meillo@6 184 (suitability, accuracy, inter\%operability, security)
meillo@6 185 .IP \(bu
meillo@6 186 .I Reliability
meillo@6 187 (maturity, fault tolerance, recoverability)
meillo@6 188 .IP \(bu
meillo@6 189 .I Usability
meillo@6 190 (understandability, learnability, operability, attractiveness)
meillo@6 191 .IP \(bu
meillo@6 192 .I Efficiency
meillo@9 193 (time behavior, resource utilization)
meillo@6 194 .IP \(bu
meillo@6 195 .I Maintainability
meillo@23 196 (analyzability, changeability, stability, testability)
meillo@6 197 .IP \(bu
meillo@6 198 .I Portability
meillo@6 199 (adaptability, installability, co-existence, replaceability)
meillo@6 200 .LP
meillo@6 201 These goals are parts of a software's design.
meillo@6 202 Good design can give these properties to a software,
meillo@6 203 bad designed software will miss them.
meillo@7 204 .PP
meillo@7 205 One further goal of software design is consistency.
meillo@7 206 Consistency eases understanding, working on, and using things.
meillo@7 207 Consistent internals and consistent interfaces to the outside can be provided by good design.
meillo@7 208 .PP
meillo@7 209 We should design software because good design avoids many problems during a software's lifetime.
meillo@7 210 And we should design software because good design can offer much gain,
meillo@7 211 that can be unrelated to the software main intend.
meillo@7 212 Indeed, we should spend much effort into good design to make the software more valuable.
meillo@7 213 The Unix Philosophy shows how to design software well.
meillo@7 214 It offers guidelines to achieve good quality and high gain for the effort spent.
meillo@0 215
meillo@0 216
meillo@0 217 .NH 1
meillo@0 218 The Unix Philosophy
meillo@4 219 .LP
meillo@4 220 The origins of the Unix Philosophy were already introduced.
meillo@8 221 This chapter explains the philosophy, oriented on Gancarz,
meillo@8 222 and shows concrete examples of its application.
meillo@5 223
meillo@16 224 .NH 2
meillo@14 225 Pipes
meillo@4 226 .LP
meillo@4 227 Following are some examples to demonstrate how applied Unix Philosophy feels like.
meillo@4 228 Knowledge of using the Unix shell is assumed.
meillo@4 229 .PP
meillo@4 230 Counting the number of files in the current directory:
meillo@9 231 .DS I 2n
meillo@4 232 .CW
meillo@9 233 .ps -1
meillo@4 234 ls | wc -l
meillo@4 235 .DE
meillo@4 236 The
meillo@4 237 .CW ls
meillo@4 238 command lists all files in the current directory, one per line,
meillo@4 239 and
meillo@4 240 .CW "wc -l
meillo@8 241 counts the number of lines.
meillo@4 242 .PP
meillo@8 243 Counting the number of files that do not contain ``foo'' in their name:
meillo@9 244 .DS I 2n
meillo@4 245 .CW
meillo@9 246 .ps -1
meillo@4 247 ls | grep -v foo | wc -l
meillo@4 248 .DE
meillo@4 249 Here, the list of files is filtered by
meillo@4 250 .CW grep
meillo@4 251 to remove all that contain ``foo''.
meillo@4 252 The rest is the same as in the previous example.
meillo@4 253 .PP
meillo@4 254 Finding the five largest entries in the current directory.
meillo@9 255 .DS I 2n
meillo@4 256 .CW
meillo@9 257 .ps -1
meillo@4 258 du -s * | sort -nr | sed 5q
meillo@4 259 .DE
meillo@4 260 .CW "du -s *
meillo@4 261 returns the recursively summed sizes of all files
meillo@8 262 \(en no matter if they are regular files or directories.
meillo@4 263 .CW "sort -nr
meillo@4 264 sorts the list numerically in reverse order.
meillo@4 265 Finally,
meillo@4 266 .CW "sed 5q
meillo@4 267 quits after it has printed the fifth line.
meillo@4 268 .PP
meillo@4 269 The presented command lines are examples of what Unix people would use
meillo@4 270 to get the desired output.
meillo@4 271 There are also other ways to get the same output.
meillo@4 272 It's a user's decision which way to go.
meillo@14 273 .PP
meillo@8 274 The examples show that many tasks on a Unix system
meillo@4 275 are accomplished by combining several small programs.
meillo@4 276 The connection between the single programs is denoted by the pipe operator `|'.
meillo@4 277 .PP
meillo@4 278 Pipes, and their extensive and easy use, are one of the great
meillo@4 279 achievements of the Unix system.
meillo@4 280 Pipes between programs have been possible in earlier operating systems,
meillo@4 281 but it has never been a so central part of the concept.
meillo@4 282 When, in the early seventies, Doug McIlroy introduced pipes for the
meillo@4 283 Unix system,
meillo@4 284 ``it was this concept and notation for linking several programs together
meillo@4 285 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
meillo@4 286 .[
meillo@4 287 %T Unix: An Oral History
meillo@5 288 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
meillo@4 289 .]
meillo@4 290 .PP
meillo@4 291 Being able to specify pipelines in an easy way is,
meillo@4 292 however, not enough by itself.
meillo@5 293 It is only one half.
meillo@4 294 The other is the design of the programs that are used in the pipeline.
meillo@8 295 They have to interfaces that allows them to be used in such a way.
meillo@5 296
meillo@16 297 .NH 2
meillo@14 298 Interface design
meillo@5 299 .LP
meillo@11 300 Unix is, first of all, simple \(en Everything is a file.
meillo@5 301 Files are sequences of bytes, without any special structure.
meillo@5 302 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
meillo@5 303 and write a stream of bytes to ``standard output'' (stdout).
meillo@5 304 .PP
meillo@8 305 If the files \fIare\fP sequences of bytes,
meillo@8 306 and the programs \fIare\fP filters on byte streams,
meillo@11 307 then there is exactly one standardized data interface.
meillo@5 308 Thus it is possible to combine them in any desired way.
meillo@5 309 .PP
meillo@5 310 Even a handful of small programs will yield a large set of combinations,
meillo@5 311 and thus a large set of different functions.
meillo@5 312 This is leverage!
meillo@5 313 If the programs are orthogonal to each other \(en the best case \(en
meillo@5 314 then the set of different functions is greatest.
meillo@5 315 .PP
meillo@11 316 Programs might also have a separate control interface,
meillo@11 317 besides their data interface.
meillo@11 318 The control interface is often called ``user interface'',
meillo@11 319 because it is usually designed to be used by humans.
meillo@11 320 The Unix Philosophy discourages to assume the user to be human.
meillo@11 321 Interactive use of software is slow use of software,
meillo@11 322 because the program waits for user input most of the time.
meillo@11 323 Interactive software requires the user to be in front of the computer
meillo@11 324 all the time.
meillo@11 325 Interactive software occupy the user's attention while they are running.
meillo@11 326 .PP
meillo@11 327 Now we come back to the idea of using several small programs, combined,
meillo@11 328 to have a more specific function.
meillo@11 329 If these single tools would all be interactive,
meillo@11 330 how would the user control them?
meillo@11 331 It is not only a problem to control several programs at once if they run at the same time,
meillo@11 332 it also very inefficient to have to control each of the single programs
meillo@11 333 that are intended to work as one large program.
meillo@11 334 Hence, the Unix Philosophy discourages programs to demand interactive use.
meillo@11 335 The behavior of programs should be defined at invocation.
meillo@11 336 This is done by specifying arguments (``command line switches'') to the program call.
meillo@11 337 Gancarz discusses this topic as ``avoid captive user interfaces''.
meillo@11 338 .[
meillo@11 339 %A Mike Gancarz
meillo@11 340 %T The UNIX Philosophy
meillo@11 341 %I Digital Press
meillo@11 342 %D 1995
meillo@11 343 %P 88 ff.
meillo@11 344 .]
meillo@11 345 .PP
meillo@11 346 Non-interactive use is, during development, also an advantage for testing.
meillo@11 347 Testing of interactive programs is much more complicated,
meillo@11 348 than testing of non-interactive programs.
meillo@5 349
meillo@16 350 .NH 2
meillo@8 351 The toolchest approach
meillo@5 352 .LP
meillo@5 353 A toolchest is a set of tools.
meillo@5 354 Instead of having one big tool for all tasks, one has many small tools,
meillo@5 355 each for one task.
meillo@5 356 Difficult tasks are solved by combining several of the small, simple tools.
meillo@5 357 .PP
meillo@11 358 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
meillo@11 359 that are filters on byte streams.
meillo@11 360 They are, to a large extend, unrelated in their function.
meillo@11 361 Hence, the Unix toolchest provides a large set of functions
meillo@11 362 that can be accessed by combining the programs in the desired way.
meillo@11 363 .PP
meillo@11 364 There are also advantages for developing small toolchest programs.
meillo@5 365 It is easier and less error-prone to write small programs.
meillo@5 366 It is also easier and less error-prone to write a large set of small programs,
meillo@5 367 than to write one large program with all the functionality included.
meillo@5 368 If the small programs are combinable, then they offer even a larger set
meillo@5 369 of functions than the single large program.
meillo@5 370 Hence, one gets two advantages out of writing small, combinable programs.
meillo@5 371 .PP
meillo@5 372 There are two drawbacks of the toolchest approach.
meillo@8 373 First, one simple, standardized, unidirectional interface has to be sufficient.
meillo@5 374 If one feels the need for more ``logic'' than a stream of bytes,
meillo@8 375 then a different approach might be of need.
meillo@13 376 But it is also possible, that he just can not imagine a design where
meillo@8 377 a stream of bytes is sufficient.
meillo@8 378 By becoming more familiar with the ``Unix style of thinking'',
meillo@8 379 developers will more often and easier find simple designs where
meillo@8 380 a stream of bytes is a sufficient interface.
meillo@8 381 .PP
meillo@8 382 The second drawback of a toolchest affects the users.
meillo@5 383 A toolchest is often more difficult to use for novices.
meillo@9 384 It is necessary to become familiar with each of the tools,
meillo@5 385 to be able to use the right one in a given situation.
meillo@9 386 Additionally, one needs to combine the tools in a senseful way on its own.
meillo@9 387 This is like a sharp knife \(en it is a powerful tool in the hand of a master,
meillo@5 388 but of no good value in the hand of an unskilled.
meillo@5 389 .PP
meillo@8 390 However, learning single, small tool of the toolchest is easier than
meillo@8 391 learning a complex tool.
meillo@8 392 The user will have a basic understanding of a yet unknown tool,
meillo@8 393 if the several tools of the toolchest have a common style.
meillo@8 394 He will be able to transfer knowledge over one tool to another.
meillo@8 395 .PP
meillo@8 396 Moreover, the second drawback can be removed easily by adding wrappers
meillo@8 397 around the single tools.
meillo@5 398 Novice users do not need to learn several tools if a professional wraps
meillo@8 399 the single commands into a more high-level script.
meillo@5 400 Note that the wrapper script still calls the small tools;
meillo@5 401 the wrapper script is just like a skin around.
meillo@8 402 No complexity is added this way,
meillo@8 403 but new programs can get created out of existing one with very low effort.
meillo@5 404 .PP
meillo@5 405 A wrapper script for finding the five largest entries in the current directory
meillo@5 406 could look like this:
meillo@9 407 .DS I 2n
meillo@5 408 .CW
meillo@9 409 .ps -1
meillo@5 410 #!/bin/sh
meillo@5 411 du -s * | sort -nr | sed 5q
meillo@5 412 .DE
meillo@5 413 The script itself is just a text file that calls the command line
meillo@5 414 a professional user would type in directly.
meillo@8 415 Making the program flexible on the number of entries it prints,
meillo@8 416 is easily possible:
meillo@9 417 .DS I 2n
meillo@8 418 .CW
meillo@9 419 .ps -1
meillo@8 420 #!/bin/sh
meillo@8 421 num=5
meillo@8 422 [ $# -eq 1 ] && num="$1"
meillo@8 423 du -sh * | sort -nr | sed "${num}q"
meillo@8 424 .DE
meillo@8 425 This script acts like the one before, when called without an argument.
meillo@8 426 But one can also specify a numerical argument to define the number of lines to print.
meillo@5 427
meillo@16 428 .NH 2
meillo@8 429 A powerful shell
meillo@8 430 .LP
meillo@10 431 It was already said, that the Unix shell provides the possibility to
meillo@10 432 combine small programs into large ones easily.
meillo@10 433 A powerful shell is a great feature in other ways, too.
meillo@8 434 .PP
meillo@10 435 For instance by including a scripting language.
meillo@10 436 The control statements are build into the shell.
meillo@8 437 The functions, however, are the normal programs, everyone can use on the system.
meillo@10 438 Thus, the programs are known, so learning to program in the shell is easy.
meillo@8 439 Using normal programs as functions in the shell programming language
meillo@10 440 is only possible because they are small and combinable tools in a toolchest style.
meillo@8 441 .PP
meillo@8 442 The Unix shell encourages to write small scripts out of other programs,
meillo@8 443 because it is so easy to do.
meillo@8 444 This is a great step towards automation.
meillo@8 445 It is wonderful if the effort to automate a task equals the effort
meillo@8 446 it takes to do it the second time by hand.
meillo@8 447 If it is so, then the user will be happy to automate everything he does more than once.
meillo@8 448 .PP
meillo@8 449 Small programs that do one job well, standardized interfaces between them,
meillo@8 450 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
meillo@8 451 this will inevitably produce software leverage.
meillo@8 452 Getting multiple times the benefit of an investment is a great offer.
meillo@10 453 .PP
meillo@10 454 The shell also encourages rapid prototyping.
meillo@10 455 Many well known programs started as quickly hacked shell scripts,
meillo@10 456 and turned into ``real'' programs, written in C, later.
meillo@10 457 Building a prototype first is a way to avoid the biggest problems
meillo@10 458 in application development.
meillo@10 459 Fred Brooks writes in ``No Silver Bullet'':
meillo@10 460 .[
meillo@10 461 %A Frederick P. Brooks, Jr.
meillo@10 462 %T No Silver Bullet: Essence and Accidents of Software Engineering
meillo@10 463 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference
meillo@10 464 %E H.-J. Kugler
meillo@10 465 %D 1986
meillo@10 466 %P 1069\(en1076
meillo@10 467 %I Elsevier Science B.V.
meillo@10 468 %C Amsterdam, The Netherlands
meillo@10 469 .]
meillo@10 470 .QP
meillo@10 471 The hardest single part of building a software system is deciding precisely what to build.
meillo@10 472 No other part of the conceptual work is so difficult as establishing the detailed
meillo@10 473 technical requirements, [...].
meillo@10 474 No other part of the work so cripples the resulting system if done wrong.
meillo@10 475 No other part is more difficult to rectify later.
meillo@10 476 .PP
meillo@10 477 Writing a prototype is a great method to become familiar with the requirements
meillo@10 478 and to actually run into real problems.
meillo@10 479 Today, prototyping is often seen as a first step in building a software.
meillo@10 480 This is, of course, good.
meillo@10 481 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
meillo@10 482 After having built the prototype, one might notice, that the prototype is already
meillo@10 483 \fIgood enough\fP.
meillo@10 484 Hence, no reimplementation, in a more sophisticated programming language, might be of need,
meillo@10 485 for the moment.
meillo@23 486 Maybe later, it might be necessary to rewrite the software, but not now.
meillo@10 487 .PP
meillo@10 488 By delaying further work, one keeps the flexibility to react easily on
meillo@10 489 changing requirements.
meillo@10 490 Software parts that are not written will not miss the requirements.
meillo@10 491
meillo@16 492 .NH 2
meillo@10 493 Worse is better
meillo@10 494 .LP
meillo@10 495 The Unix Philosophy aims for the 80% solution;
meillo@10 496 others call it the ``Worse is better'' approach.
meillo@10 497 .PP
meillo@10 498 First, practical experience shows, that it is almost never possible to define the
meillo@10 499 requirements completely and correctly the first time.
meillo@10 500 Hence one should not try to; it will fail anyway.
meillo@10 501 Second, practical experience shows, that requirements change during time.
meillo@10 502 Hence it is best to delay requirement-based design decisions as long as possible.
meillo@10 503 Also, the software should be small and flexible as long as possible
meillo@10 504 to react on changing requirements.
meillo@10 505 Shell scripts, for example, are more easily adjusted as C programs.
meillo@10 506 Third, practical experience shows, that maintenance is hard work.
meillo@10 507 Hence, one should keep the amount of software as small as possible;
meillo@10 508 it should just fulfill the \fIcurrent\fP requirements.
meillo@10 509 Software parts that will be written later, do not need maintenance now.
meillo@10 510 .PP
meillo@10 511 Starting with a prototype in a scripting language has several advantages:
meillo@10 512 .IP \(bu
meillo@10 513 As the initial effort is low, one will likely start right away.
meillo@10 514 .IP \(bu
meillo@10 515 As working parts are available soon, the real requirements can get identified soon.
meillo@10 516 .IP \(bu
meillo@10 517 When a software is usable, it gets used, and thus tested.
meillo@10 518 Hence problems will be found at early stages of the development.
meillo@10 519 .IP \(bu
meillo@10 520 The prototype might be enough for the moment,
meillo@10 521 thus further work on the software can be delayed to a time
meillo@10 522 when one knows better about the requirements and problems,
meillo@10 523 than now.
meillo@10 524 .IP \(bu
meillo@10 525 Implementing now only the parts that are actually needed now,
meillo@10 526 requires fewer maintenance work.
meillo@10 527 .IP \(bu
meillo@10 528 If the global situation changes so that the software is not needed anymore,
meillo@10 529 then less effort was spent into the project, than it would have be
meillo@10 530 when a different approach had been used.
meillo@10 531
meillo@16 532 .NH 2
meillo@11 533 Upgrowth and survival of software
meillo@11 534 .LP
meillo@12 535 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
meillo@13 536 Although these are just verbs, they do imply a specific view on the work process
meillo@13 537 they describe.
meillo@12 538 The better verb, however, is to \fIgrow\fP.
meillo@12 539 .PP
meillo@12 540 Creating software in the sense of the Unix Philosophy is an incremental process.
meillo@12 541 It starts with a first prototype, which evolves as requirements change.
meillo@12 542 A quickly hacked shell script might become a large, sophisticated,
meillo@13 543 compiled program this way.
meillo@13 544 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
meillo@13 545 While being alive it will get extended, rearranged, rebuilt (from scratch).
meillo@12 546 Growing software matches the view that ``software is never finished. It is only released.''
meillo@12 547 .[
meillo@13 548 %O FIXME
meillo@13 549 %A Mike Gancarz
meillo@13 550 %T The UNIX Philosophy
meillo@13 551 %P 26
meillo@12 552 .]
meillo@12 553 .PP
meillo@13 554 Software can be seen as being controlled by evolutionary processes.
meillo@13 555 Successful software is software that is used by many for a long time.
meillo@12 556 This implies that the software is needed, useful, and better than alternatives.
meillo@12 557 Darwin talks about: ``The survival of the fittest.''
meillo@12 558 .[
meillo@13 559 %O FIXME
meillo@13 560 %A Charles Darwin
meillo@12 561 .]
meillo@12 562 Transferred to software: The most successful software, is the fittest,
meillo@12 563 is the one that survives.
meillo@13 564 (This may be at the level of one creature, or at the level of one species.)
meillo@13 565 The fitness of software is affected mainly by four properties:
meillo@15 566 portability of code, portability of data, range of usability, and reusability of parts.
meillo@15 567 .\" .IP \(bu
meillo@15 568 .\" portability of code
meillo@15 569 .\" .IP \(bu
meillo@15 570 .\" portability of data
meillo@15 571 .\" .IP \(bu
meillo@15 572 .\" range of usability
meillo@15 573 .\" .IP \(bu
meillo@15 574 .\" reuseability of parts
meillo@13 575 .PP
meillo@15 576 (1)
meillo@15 577 .I "Portability of code
meillo@15 578 means, using high-level programming languages,
meillo@13 579 sticking to the standard,
meillo@13 580 and avoiding optimizations that introduce dependencies on specific hardware.
meillo@13 581 Hardware has a much lower lifetime than software.
meillo@13 582 By chaining software to a specific hardware,
meillo@13 583 the software's lifetime gets shortened to that of this hardware.
meillo@13 584 In contrast, software should be easy to port \(en
meillo@23 585 adaptation is the key to success.
meillo@13 586 .\" cf. practice of prog: ch08
meillo@13 587 .PP
meillo@15 588 (2)
meillo@15 589 .I "Portability of data
meillo@15 590 is best achieved by avoiding binary representations
meillo@13 591 to store data, because binary representations differ from machine to machine.
meillo@23 592 Textual representation is favored.
meillo@13 593 Historically, ASCII was the charset of choice.
meillo@13 594 In the future, UTF-8 might be the better choice, however.
meillo@13 595 Important is that it is a plain text representation in a
meillo@13 596 very common charset encoding.
meillo@13 597 Apart from being able to transfer data between machines,
meillo@13 598 readable data has the great advantage, that humans are able
meillo@13 599 to directly edit it with text editors and other tools from the Unix toolchest.
meillo@13 600 .\" gancarz tenet 5
meillo@13 601 .PP
meillo@15 602 (3)
meillo@15 603 A large
meillo@15 604 .I "range of usability
meillo@23 605 ensures good adaptation, and thus good survival.
meillo@13 606 It is a special distinction if a software becomes used in fields of action,
meillo@13 607 the original authors did never imagine.
meillo@13 608 Software that solves problems in a general way will likely be used
meillo@13 609 for all kinds of similar problems.
meillo@13 610 Being too specific limits the range of uses.
meillo@13 611 Requirements change through time, thus use cases change or even vanish.
meillo@13 612 A good example in this point is Allman's sendmail.
meillo@13 613 Allman identifies flexibility to be one major reason for sendmail's success:
meillo@13 614 .[
meillo@13 615 %O FIXME
meillo@13 616 %A Allman
meillo@13 617 %T sendmail
meillo@13 618 .]
meillo@13 619 .QP
meillo@13 620 Second, I limited myself to the routing function [...].
meillo@13 621 This was a departure from the dominant thought of the time, [...].
meillo@13 622 .QP
meillo@13 623 Third, the sendmail configuration file was flexible enough to adopt
meillo@13 624 to a rapidly changing world [...].
meillo@12 625 .LP
meillo@13 626 Successful software adopts itself to the changing world.
meillo@13 627 .PP
meillo@15 628 (4)
meillo@15 629 .I "Reuse of parts
meillo@15 630 is even one step further.
meillo@13 631 A software may completely lose its field of action,
meillo@13 632 but parts of which the software is build may be general and independent enough
meillo@13 633 to survive this death.
meillo@13 634 If software is build by combining small independent programs,
meillo@13 635 then there are parts readily available for reuse.
meillo@13 636 Who cares if the large program is a failure,
meillo@13 637 but parts of it become successful instead?
meillo@10 638
meillo@16 639 .NH 2
meillo@14 640 Summary
meillo@0 641 .LP
meillo@14 642 This chapter explained the central ideas of the Unix Philosophy.
meillo@14 643 For each of the ideas, it was exposed what advantages they introduce.
meillo@14 644 The Unix Philosophy are guidelines that help to write valuable software.
meillo@14 645 From the view point of a software developer or software designer,
meillo@14 646 the Unix Philosophy provides answers to many software design problem.
meillo@14 647 .PP
meillo@14 648 The various ideas of the Unix Philosophy are very interweaved
meillo@14 649 and can hardly be applied independently.
meillo@14 650 However, the probably most important messages are:
meillo@14 651 .I "``Do one thing well!''" ,
meillo@14 652 .I "``Keep it simple!''" ,
meillo@14 653 and
meillo@14 654 .I "``Use software leverage!''
meillo@0 655
meillo@8 656
meillo@8 657
meillo@0 658 .NH 1
meillo@19 659 Case study: \s-1MH\s0
meillo@18 660 .LP
meillo@30 661 The previous chapter introduced and explained the Unix Philosophy
meillo@18 662 from a general point of view.
meillo@30 663 The driving force were the guidelines; references to
meillo@18 664 existing software were given only sparsely.
meillo@18 665 In this and the next chapter, concrete software will be
meillo@18 666 the driving force in the discussion.
meillo@18 667 .PP
meillo@23 668 This first case study is about the mail user agents (\s-1MUA\s0)
meillo@23 669 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
meillo@23 670 (``new mail handler'').
meillo@23 671 \s-1MUA\s0s provide functions to read, compose, and organize mail,
meillo@23 672 but (ideally) not to transfer.
meillo@19 673 In this document, the name \s-1MH\s0 will be used for both of them.
meillo@19 674 A distinction will only be made if differences between
meillo@19 675 them are described.
meillo@18 676
meillo@0 677
meillo@0 678 .NH 2
meillo@19 679 Historical background
meillo@0 680 .LP
meillo@19 681 Electronic mail was available in Unix very early.
meillo@30 682 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
meillo@30 683 which was already present in the First Edition.
meillo@30 684 .[
meillo@30 685 %A Peter H. Salus
meillo@30 686 %T A Quarter Century of UNIX
meillo@30 687 %D 1994
meillo@30 688 %I Addison-Wesley
meillo@30 689 %P 41 f.
meillo@30 690 .]
meillo@30 691 It was a small program that either prints the user's mailbox file
meillo@19 692 or appends text to someone elses mailbox file,
meillo@19 693 depending on the command line arguments.
meillo@19 694 .[
meillo@19 695 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf
meillo@19 696 .]
meillo@19 697 It was a program that did one job well.
meillo@23 698 This job was emailing, which was very simple then.
meillo@19 699 .PP
meillo@23 700 Later, emailing became more powerful, and thus more complex.
meillo@19 701 The simple \f(CWmail\fP, which knew nothing of subjects,
meillo@19 702 independent handling of single messages,
meillo@19 703 and long-time storage of them, was not powerful enough anymore.
meillo@19 704 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
meillo@19 705 in 1978 to provide additional functions for emailing.
meillo@19 706 Mail was still one program, but now it was large and did
meillo@19 707 several jobs.
meillo@23 708 Its user interface is modeled after the one of \fIed\fP.
meillo@19 709 It is designed for humans, but is still scriptable.
meillo@23 710 \fImailx\fP is the adaptation of Berkeley Mail into System V.
meillo@19 711 .[
meillo@19 712 %A Gunnar Ritter
meillo@19 713 %O http://heirloom.sourceforge.net/mailx_history.html
meillo@19 714 .]
meillo@30 715 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
meillo@19 716 followed Mail's direction.
meillo@19 717 They are large, monolithic programs which include all emailing functions.
meillo@19 718 .PP
meillo@23 719 A different way was taken by the people of \s-1RAND\s0 Corporation.
meillo@19 720 In the beginning, they also had used a monolitic mail system,
meillo@30 721 called \s-1MS\s0 (for ``mail system'').
meillo@19 722 But in 1977, Stockton Gaines and Norman Shapiro
meillo@19 723 came up with a proposal of a new email system concept \(en
meillo@19 724 one that honors the Unix Philosophy.
meillo@19 725 The concept was implemented by Bruce Borden in 1978 and 1979.
meillo@19 726 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
meillo@18 727 .PP
meillo@18 728 Since then, \s-1RAND\s0, the University of California at Irvine and
meillo@19 729 at Berkeley, and several others have contributed to the software.
meillo@18 730 However, it's core concepts remained the same.
meillo@23 731 In the late 90s, when development of \s-1MH\s0 slowed down,
meillo@19 732 Richard Coleman started with \fInmh\fP, the new mail handler.
meillo@19 733 His goal was to improve \s-1MH\s0, especially in regard of
meillo@23 734 the requirements of modern emailing.
meillo@19 735 Today, nmh is developed by various people on the Internet.
meillo@18 736 .[
meillo@18 737 %T RAND and the Information Evolution: A History in Essays and Vignettes
meillo@18 738 %A Willis H. Ware
meillo@18 739 %D 2008
meillo@18 740 %I The RAND Corporation
meillo@18 741 %P 128\(en137
meillo@18 742 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/
meillo@18 743 .]
meillo@18 744 .[
meillo@18 745 %T MH & xmh: Email for Users & Programmers
meillo@18 746 %A Jerry Peek
meillo@18 747 %D 1991, 1992, 1995
meillo@18 748 %I O'Reilly & Associates, Inc.
meillo@18 749 %P Appendix B
meillo@18 750 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP
meillo@18 751 .]
meillo@0 752
meillo@0 753 .NH 2
meillo@20 754 Contrasts to monolithic mail systems
meillo@0 755 .LP
meillo@19 756 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
meillo@30 757 Although there might acutally exist further, very little known,
meillo@30 758 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
meillo@19 759 .PP
meillo@30 760 Monolithic \s-1MUA\s0s gather all their functions in one program.
meillo@30 761 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
meillo@23 762 Following is a list of important programs of \s-1MH\s0's toolchest
meillo@30 763 and their function.
meillo@30 764 It gives a feeling of how the toolchest looks like.
meillo@19 765 .IP \(bu
meillo@19 766 .CW inc :
meillo@30 767 incorporate new mail (this is how mail enters the system)
meillo@19 768 .IP \(bu
meillo@19 769 .CW scan :
meillo@19 770 list messages in folder
meillo@19 771 .IP \(bu
meillo@19 772 .CW show :
meillo@19 773 show message
meillo@19 774 .IP \(bu
meillo@19 775 .CW next\fR/\fPprev :
meillo@19 776 show next/previous message
meillo@19 777 .IP \(bu
meillo@19 778 .CW folder :
meillo@19 779 change current folder
meillo@19 780 .IP \(bu
meillo@19 781 .CW refile :
meillo@19 782 refile message into folder
meillo@19 783 .IP \(bu
meillo@19 784 .CW rmm :
meillo@19 785 remove message
meillo@19 786 .IP \(bu
meillo@19 787 .CW comp :
meillo@19 788 compose a new message
meillo@19 789 .IP \(bu
meillo@19 790 .CW repl :
meillo@19 791 reply to a message
meillo@19 792 .IP \(bu
meillo@19 793 .CW forw :
meillo@19 794 forward a message
meillo@19 795 .IP \(bu
meillo@19 796 .CW send :
meillo@30 797 send a prepared message (this is how mail leaves the system)
meillo@0 798 .LP
meillo@19 799 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
meillo@19 800 The user does not leave the shell to run \s-1MH\s0,
meillo@30 801 but he uses the various \s-1MH\s0 programs within the shell.
meillo@23 802 Using a monolithic program with a captive user interface
meillo@23 803 means ``entering'' the program, using it, and ``exiting'' the program.
meillo@23 804 Using toolchests like \s-1MH\s0 means running programs,
meillo@23 805 alone or in combinition with others, even from other toolchests,
meillo@23 806 without leaving the shell.
meillo@30 807
meillo@30 808 .NH 2
meillo@30 809 Data storage
meillo@30 810 .LP
meillo@34 811 \s-1MH\s0's mail storage is a directory tree under the user's
meillo@34 812 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
meillo@34 813 where mail folders are directories and mail messages are text files
meillo@34 814 within them.
meillo@34 815 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
meillo@34 816 the public message sequences of that folder, for instance new messages.
meillo@34 817 Mail messages are text files located in a mail folder.
meillo@34 818 The files contain the messages as they were received.
meillo@34 819 They are numbered in ascending order in each folder.
meillo@19 820 .PP
meillo@30 821 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
meillo@30 822 Alternatives are \fImbox\fP and \fImaildir\fP.
meillo@30 823 In the mbox format all messages are stored within one file.
meillo@30 824 This was a good solution in the early days, when messages
meillo@30 825 were only a few lines of text and were deleted soon.
meillo@30 826 Today, when single messages often include several megabytes
meillo@30 827 of attachments, it is a bad solution.
meillo@30 828 Another disadvantage of the mbox format is that it is
meillo@30 829 more difficult to write tools that work on mail messages,
meillo@30 830 because it is always necessary to first find and extract
meillo@30 831 the relevant message in the mbox file.
meillo@30 832 With the \s-1MH\s0 mailbox format,
meillo@30 833 each message is a self-standing item, by definition.
meillo@30 834 Also, the problem of concurrent access to one mailbox is
meillo@30 835 reduced to the problem of concurrent access to one message.
meillo@30 836 Maildir is generally similar to \s-1MH\s0's format,
meillo@30 837 but modified towards guaranteed reliability.
meillo@30 838 This involves some complexity, unfortunately.
meillo@34 839 .PP
meillo@34 840 Working with \s-1MH\s0's toolchest on mailboxes is much like
meillo@34 841 working with Unix' toolchest on directory trees:
meillo@34 842 \f(CWscan\fP is like \f(CWls\fP,
meillo@34 843 \f(CWshow\fP is like \f(CWcat\fP,
meillo@34 844 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
meillo@34 845 \f(CWrefile\fP is like \f(CWmv\fP,
meillo@34 846 and \f(CWrmm\fP is like \f(CWrm\fP.
meillo@34 847 .PP
meillo@34 848 The context of tools in Unix consists mainly the current working directory,
meillo@34 849 the user identification, and the environment variables.
meillo@34 850 \s-1MH\s0 extends this context by two more items:
meillo@34 851 .IP \(bu
meillo@34 852 The current mail folder, which is similar to the current working directory.
meillo@34 853 For mail folders, \f(CWfolder\fP provides the corresponding functionality
meillo@34 854 of \f(CWcd\fP and \f(CWpwd\fP for directories.
meillo@34 855 .IP \(bu
meillo@34 856 Sequences, which are named sets of messages in a mail folder.
meillo@34 857 The current message, relative to a mail folder, is a special sequence.
meillo@34 858 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
meillo@34 859 .LP
meillo@34 860 In contrast to Unix' context, which is chained to the shell session,
meillo@34 861 \s-1MH\s0's context is independent.
meillo@34 862 Usually there is one context for each user, but a user can have many
meillo@34 863 contexts.
meillo@34 864 Public sequences are an exception, as they belong to the mail folder.
meillo@34 865 .[
meillo@34 866 %O mh-profile(5) and mh-sequence(5)
meillo@34 867 .]
meillo@20 868
meillo@0 869 .NH 2
meillo@20 870 Discussion of the design
meillo@0 871 .LP
meillo@20 872 The following paragraphs discuss \s-1MH\s0 in regard to the tenets
meillo@23 873 of the Unix Philosophy which Gancarz identified.
meillo@20 874
meillo@20 875 .PP
meillo@33 876 .B "Small is beautiful
meillo@20 877 and
meillo@33 878 .B "do one thing well
meillo@20 879 are two design goals that are directly visible in \s-1MH\s0.
meillo@20 880 Gancarz actually presents \s-1MH\s0 as example under the headline
meillo@20 881 ``Making UNIX Do One Thing Well'':
meillo@20 882 .QP
meillo@20 883 [\s-1MH\s0] consists of a series of programs which
meillo@20 884 when combined give the user an enormous ability
meillo@20 885 to manipulate electronic mail messages.
meillo@20 886 A complex application, it shows that not only is it
meillo@20 887 possible to build large applications from smaller
meillo@20 888 components, but also that such designs are actually preferable.
meillo@20 889 .[
meillo@20 890 %A Mike Gancarz
meillo@20 891 %T unix-phil
meillo@20 892 %P 125
meillo@20 893 .]
meillo@20 894 .LP
meillo@20 895 The various small programs of \s-1MH\s0 were relatively easy
meillo@23 896 to write, because each of them is small, limited to one function,
meillo@23 897 and has clear boundaries.
meillo@20 898 For the same reasons, they are also good to maintain.
meillo@20 899 Further more, the system can easily get extended.
meillo@20 900 One only needs to put a new program into the toolchest.
meillo@23 901 This was done, for instance, when \s-1MIME\s0 support was added
meillo@20 902 (e.g. \f(CWmhbuild\fP).
meillo@20 903 Also, different programs can exist to do the basically same job
meillo@20 904 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
meillo@20 905 If someone needs a mail system with some additionally
meillo@23 906 functions that are available nowhere yet, he best takes a
meillo@20 907 toolchest system like \s-1MH\s0 where he can add the
meillo@20 908 functionality with little work.
meillo@20 909
meillo@20 910 .PP
meillo@34 911 .B "Store data in flat text files
meillo@34 912 is followed by \s-1MH\s0.
meillo@34 913 This is not surprising, because email messages are already plain text.
meillo@34 914 \s-1MH\s0 stores the messages as it receives them,
meillo@34 915 thus any other tool that works on RFC 2822 mail messages can operate
meillo@34 916 on the messages in an \s-1MH\s0 mailbox.
meillo@34 917 All other files \s-1MH\s0 uses are plain text too.
meillo@34 918 It is therefore possible and encouraged to use the text processing
meillo@34 919 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
meillo@20 920
meillo@20 921 .PP
meillo@33 922 .B "Avoid captive user interfaces" .
meillo@19 923 \s-1MH\s0 is perfectly suited for non-interactive use.
meillo@19 924 It offers all functions directly and without captive user interfaces.
meillo@30 925 If, nonetheless, users want a graphical user interface,
meillo@20 926 they can have it with \fIxmh\fP or \fIexmh\fP, too.
meillo@19 927 These are graphical frontends for the \s-1MH\s0 toolchest.
meillo@19 928 This means, all email-related work is still done by \s-1MH\s0 tools,
meillo@20 929 but the frontend issues the appropriate calls when the user
meillo@30 930 clicks on buttons.
meillo@20 931 Providing easy-to-use user interfaces in form of frontends is a good
meillo@19 932 approach, because it does not limit the power of the backend itself.
meillo@20 933 The frontend will anyway only be able to make a subset of the
meillo@23 934 backend's power and flexibility available to the user.
meillo@20 935 But if it is a separate program,
meillo@20 936 then the missing parts can still be accessed at the backend directly.
meillo@19 937 If it is integrated, then this will hardly be possible.
meillo@30 938 Further more, it is possible to have different frontends to the same
meillo@30 939 backend.
meillo@19 940
meillo@19 941 .PP
meillo@33 942 .B "Choose portability over efficiency
meillo@20 943 and
meillo@33 944 .B "use shell scripts to increase leverage and portability" .
meillo@20 945 These two tenets are indirectly, but nicely, demonstrated by
meillo@30 946 Bolsky and Korn in their book about the Korn Shell.
meillo@20 947 .[
meillo@20 948 %T The KornShell: command and programming language
meillo@20 949 %A Morris I. Bolsky
meillo@20 950 %A David G. Korn
meillo@20 951 %I Prentice Hall
meillo@20 952 %D 1989
meillo@30 953 %P 254\(en290
meillo@20 954 %O \s-1ISBN\s0: 0-13-516972-0
meillo@20 955 .]
meillo@30 956 They demonstrated, in chapter 18 of the book, a basic implementation
meillo@20 957 of a subset of \s-1MH\s0 in ksh scripts.
meillo@20 958 Of course, this was just a demonstration, but a brilliant one.
meillo@20 959 It shows how quickly one can implement such a prototype with shell scripts,
meillo@20 960 and how readable they are.
meillo@20 961 The implementation in the scripting language may not be very fast,
meillo@20 962 but it can be fast enough though, and this is all that matters.
meillo@20 963 By having the code in an interpreted language, like the shell,
meillo@20 964 portability becomes a minor issue, if we assume the interpreter
meillo@20 965 to be widespread.
meillo@20 966 This demonstration also shows how easy it is to create single programs
meillo@20 967 of a toolchest software.
meillo@30 968 There are eight tools (two of them have multiple names) and 16 functions
meillo@30 969 with supporting code.
meillo@30 970 Each tool comprises between 12 and 38 lines of ksh,
meillo@30 971 in total about 200 lines.
meillo@30 972 The functions comprise between 3 and 78 lines of ksh,
meillo@30 973 in total about 450 lines.
meillo@20 974 Such small software is easy to write, easy to understand,
meillo@20 975 and thus easy to maintain.
meillo@23 976 A toolchest improves the possibility to only write some parts
meillo@20 977 and though create a working result.
meillo@20 978 Expanding the toolchest without global changes will likely be
meillo@20 979 possible, too.
meillo@20 980
meillo@20 981 .PP
meillo@33 982 .B "Use software leverage to your advantage
meillo@20 983 and the lesser tenet
meillo@33 984 .B "allow the user to tailor the environment
meillo@20 985 are ideally followed in the design of \s-1MH\s0.
meillo@21 986 Tailoring the environment is heavily encouraged by the ability to
meillo@30 987 directly define default options to programs.
meillo@30 988 It is even possible to define different default options
meillo@21 989 depending on the name under which the program was called.
meillo@21 990 Software leverage is heavily encouraged by the ease it is to
meillo@21 991 create shell scripts that run a specific command line,
meillo@30 992 built of several \s-1MH\s0 programs.
meillo@21 993 There is few software that so much wants users to tailor their
meillo@21 994 environment and to leverage the use of the software, like \s-1MH\s0.
meillo@21 995 Just to make one example:
meillo@23 996 One might prefer a different listing format for the \f(CWscan\fP
meillo@21 997 program.
meillo@30 998 It is possible to take one of the distributed format files
meillo@21 999 or to write one yourself.
meillo@21 1000 To use the format as default for \f(CWscan\fP, a single line,
meillo@21 1001 reading
meillo@21 1002 .DS
meillo@21 1003 .CW
meillo@21 1004 scan: -form FORMATFILE
meillo@21 1005 .DE
meillo@21 1006 must be added to \f(CW.mh_profile\fP.
meillo@21 1007 If one wants this different format as an additional command,
meillo@23 1008 instead of changing the default, he needs to create a link to
meillo@23 1009 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
meillo@21 1010 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
meillo@30 1011 as the option should only be in effect when scan is called as
meillo@21 1012 \f(CWscan2\fP.
meillo@20 1013
meillo@20 1014 .PP
meillo@33 1015 .B "Make every program a filter
meillo@21 1016 is hard to find in \s-1MH\s0.
meillo@21 1017 The reason therefore is that most of \s-1MH\s0's tools provide
meillo@21 1018 basic file system operations for the mailboxes.
meillo@30 1019 The reason is the same because of which
meillo@21 1020 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP
meillo@21 1021 aren't filters neither.
meillo@23 1022 However, they build a basis on which filters can operate.
meillo@23 1023 \s-1MH\s0 does not provide many filters itself, but it is a basis
meillo@23 1024 to write filters for.
meillo@30 1025 An example would be a mail message text highlighter,
meillo@30 1026 that means a program that makes use of a color terminal to display
meillo@30 1027 header lines, quotations, and signatures in distinct colors.
meillo@30 1028 The author's version of this program, for instance,
meillo@30 1029 is a 25 line awk script.
meillo@21 1030
meillo@21 1031 .PP
meillo@33 1032 .B "Build a prototype as soon as possible
meillo@21 1033 was again well followed by \s-1MH\s0.
meillo@21 1034 This tenet, of course, focuses on early development, which is
meillo@21 1035 long time ago for \s-1MH\s0.
meillo@21 1036 But without following this guideline at the very beginning,
meillo@23 1037 Bruce Borden may have not convinced the management of \s-1RAND\s0
meillo@23 1038 to ever create \s-1MH\s0.
meillo@23 1039 In Bruce' own words:
meillo@21 1040 .QP
meillo@30 1041 [...] but they [Stockton Gaines and Norm Shapiro] were not able
meillo@23 1042 to convince anyone that such a system would be fast enough to be usable.
meillo@21 1043 I proposed a very short project to prove the basic concepts,
meillo@21 1044 and my management agreed.
meillo@21 1045 Looking back, I realize that I had been very lucky with my first design.
meillo@21 1046 Without nearly enough design work,
meillo@21 1047 I built a working environment and some header files
meillo@21 1048 with key structures and wrote the first few \s-1MH\s0 commands:
meillo@21 1049 inc, show/next/prev, and comp.
meillo@21 1050 [...]
meillo@21 1051 With these three, I was able to convince people that the structure was viable.
meillo@21 1052 This took about three weeks.
meillo@21 1053 .[
meillo@21 1054 %O FIXME
meillo@21 1055 .]
meillo@0 1056
meillo@0 1057 .NH 2
meillo@0 1058 Problems
meillo@0 1059 .LP
meillo@22 1060 \s-1MH\s0, for sure is not without problems.
meillo@30 1061 There are two main problems: one is technical, the other is about human behavior.
meillo@22 1062 .PP
meillo@22 1063 \s-1MH\s0 is old and email today is very different to email in the time
meillo@22 1064 when \s-1MH\s0 was designed.
meillo@22 1065 \s-1MH\s0 adopted to the changes pretty well, but it is limited.
meillo@22 1066 For example in development resources.
meillo@22 1067 \s-1MIME\s0 support and support for different character encodings
meillo@22 1068 is available, but only on a moderate level.
meillo@22 1069 More active developers could quickly improve there.
meillo@22 1070 It is also limited by design, which is the larger problem.
meillo@22 1071 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
meillo@22 1072 These design conflicts are not easily solvable.
meillo@22 1073 Possibly, they require a redesign.
meillo@30 1074 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers,
meillo@30 1075 hence \s-1MH\s0 may never work well with \s-1IMAP\s0.
meillo@22 1076 .PP
meillo@22 1077 The other kind of problem is human habits.
meillo@22 1078 When in this world almost all \s-1MUA\s0s are monolithic,
meillo@22 1079 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
meillo@22 1080 like \s-1MH\s0.
meillo@22 1081 The habits are so strong, that even people who understood the concept
meillo@30 1082 and advantages of \s-1MH\s0 do not like to switch,
meillo@30 1083 simply because \s-1MH\s0 is different.
meillo@30 1084 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
meillo@30 1085 are quite outdated and thus not very appealing compared to the modern interfaces
meillo@30 1086 which monolithic \s-1MUA\s0s offer.
meillo@20 1087
meillo@20 1088 .NH 2
meillo@20 1089 Summary \s-1MH\s0
meillo@20 1090 .LP
meillo@31 1091 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design
meillo@31 1092 and implementation.
meillo@31 1093 It consists of a toolchest of small tools, each of them does one job well.
meillo@31 1094 The tools are orthogonal to each other, to a large extend.
meillo@31 1095 However, for historical reasons, there also exist distinct tools
meillo@31 1096 that cover the same task.
meillo@31 1097 .PP
meillo@31 1098 The toolchest approach offers great flexibility to the user.
meillo@31 1099 He can use the complete power of the Unix shell with \s-1MH\s0.
meillo@31 1100 This makes \s-1MH\s0 a very powerful mail system.
meillo@31 1101 Extending and customizing \s-1MH\s0 is easy and encouraged, too.
meillo@31 1102 .PP
meillo@31 1103 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
meillo@31 1104 Its overall design follows clear rules.
meillo@31 1105 The single tools do only one job, thus they are easy to understand,
meillo@31 1106 easy to write, and good to maintain.
meillo@31 1107 They are all independent and do not interfere with the others.
meillo@31 1108 Automated testing of their function is a straight forward task.
meillo@31 1109 .PP
meillo@31 1110 It is sad, that \s-1MH\s0's differentness is its largest problem,
meillo@31 1111 as its differentness is also its largest advantage.
meillo@31 1112 Unfortunately, for most people their habits are stronger
meillo@31 1113 than the attraction of the clear design and the power, \s-1MH\s0 offers.
meillo@0 1114
meillo@8 1115
meillo@8 1116
meillo@0 1117 .NH 1
meillo@0 1118 Case study: uzbl
meillo@32 1119 .LP
meillo@32 1120 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
meillo@32 1121 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy.
meillo@32 1122 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''.
meillo@32 1123 It is pronounced the identical.
meillo@0 1124
meillo@0 1125 .NH 2
meillo@32 1126 Historical background
meillo@0 1127 .LP
meillo@32 1128 Uzbl was started by Dieter Plaetinck in April 2009.
meillo@32 1129 The idea was born in a thread in the Arch Linux forum.
meillo@32 1130 .[
meillo@32 1131 %O http://bbs.archlinux.org/viewtopic.php?id=67463
meillo@32 1132 .]
meillo@32 1133 After some discussion about failures of well known web browsers,
meillo@32 1134 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
meillo@32 1135 of how a better web browser could look like.
meillo@32 1136 To the question of another member, if Plaetinck would write that program,
meillo@32 1137 because it would sound fantastic, Plaetinck replied:
meillo@32 1138 ``Maybe, if I find the time ;-)''.
meillo@32 1139 .PP
meillo@32 1140 Fortunately, he found the time.
meillo@32 1141 One day later, the first prototype was out.
meillo@32 1142 One week later, uzbl had an own website.
meillo@32 1143 One month after the first code showed up,
meillo@32 1144 a mailing list was installed to coordinate and discuss further development.
meillo@32 1145 A wiki was set up to store documentation and scripts that showed up on the
meillo@32 1146 mailing list and elsewhere.
meillo@32 1147 .PP
meillo@32 1148 In the, now, one year of uzbl's existance, it was heavily developed in various branches.
meillo@32 1149 Plaetinck's task became more and more to only merge the best code from the
meillo@32 1150 different branches into his main branch, and to apply patches.
meillo@32 1151 About once a month, Plaetinck released a new version.
meillo@32 1152 In September 2009, he presented several forks of uzbl.
meillo@32 1153 Uzbl, acutally, opened the field for a whole family of web browsers with similar shape.
meillo@32 1154 .PP
meillo@32 1155 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
meillo@32 1156 In September 2009, the uzbl web browser was on \fISlashdot\fP.
meillo@0 1157
meillo@0 1158 .NH 2
meillo@32 1159 Contrasts to other web browsers
meillo@0 1160 .LP
meillo@32 1161 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
meillo@32 1162 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
meillo@32 1163 .PP
meillo@32 1164 Today, uzbl is divided into uzbl-core and uzbl-browser.
meillo@32 1165 Uzbl-core is, how its name already indicates, the core of uzbl.
meillo@32 1166 It handles commands and events to interface other programs,
meillo@32 1167 and also displays webpages by using webkit as render engine.
meillo@32 1168 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
meillo@32 1169 an event manager, yanking, pasting, page searching, zooming, and more stuff,
meillo@32 1170 to form a ``complete'' web browser.
meillo@32 1171 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
meillo@32 1172 so uzbl-core is included.
meillo@32 1173 .PP
meillo@32 1174 Unlike most other web browsers, uzbl is mainly the mediator between the
meillo@32 1175 various tools that cover single jobs of web browsing.
meillo@32 1176 Uzbl listens for commands on a named pipe (fifo), a Unix socket, and on stdin.
meillo@32 1177 It writes events to a Unix socket and to stdout.
meillo@32 1178 Loading a webpage in a running uzbl instance requires not more than:
meillo@32 1179 .DS
meillo@32 1180 .CW
meillo@32 1181 echo 'uri http://example.org' >/path/to/uzbl-fifo
meillo@32 1182 .DE
meillo@32 1183 The graphical rendering of the webpage is done by webkit,
meillo@32 1184 which is a library that cares about the whole rendering task.
meillo@32 1185 .PP
meillo@32 1186 Downloads, browsing history, bookmarks, and thelike are not provided
meillo@32 1187 by uzbl-core itself, as they are in other web browsers.
meillo@32 1188 Uzbl-browser only provides, so called, handler scripts that wrap
meillo@32 1189 external applications which provide such function.
meillo@32 1190 For instance, \fIwget\fP is used to download files and uzbl-browser
meillo@32 1191 includes a script that calls wget with appropriate options in
meillo@32 1192 a prepared environment.
meillo@32 1193 .PP
meillo@32 1194 Modern web browsers are proud to have addons, plugins, and modules, instead.
meillo@32 1195 This is their effort to achieve similar goals.
meillo@32 1196 But instead of using existing, external programs, the functions are
meillo@32 1197 integrated into the web browser, just not compiled into it.
meillo@0 1198
meillo@0 1199 .NH 2
meillo@32 1200 Discussion of the design
meillo@0 1201 .LP
meillo@32 1202 This section discusses uzbl in regard of the Unix Philosophy,
meillo@32 1203 as identified by Gancarz.
meillo@32 1204
meillo@32 1205 .PP
meillo@33 1206 .B "Small is beautiful
meillo@32 1207 and
meillo@33 1208 .B "make each program do one thing well" .
meillo@32 1209
meillo@32 1210 .PP
meillo@33 1211 .B "Build a prototype as soon as possible" .
meillo@32 1212
meillo@32 1213 .PP
meillo@33 1214 .B "Use software leverage to your advantage
meillo@32 1215 and
meillo@33 1216 .B "Use shell scripts to increase leverage and portability" .
meillo@32 1217
meillo@32 1218 .PP
meillo@33 1219 .B "Avoid captive user interfaces" .
meillo@32 1220
meillo@32 1221 .PP
meillo@33 1222 .B "Make every program a filter" .
meillo@32 1223
meillo@0 1224
meillo@0 1225 .NH 2
meillo@0 1226 Problems
meillo@0 1227 .LP
meillo@0 1228 broken web
meillo@0 1229
meillo@8 1230
meillo@32 1231 .NH 2
meillo@32 1232 Summary uzbl
meillo@32 1233 .LP
meillo@32 1234
meillo@32 1235
meillo@8 1236
meillo@0 1237 .NH 1
meillo@0 1238 Final thoughts
meillo@0 1239
meillo@0 1240 .NH 2
meillo@0 1241 Quick summary
meillo@0 1242 .LP
meillo@0 1243 good design
meillo@0 1244 .LP
meillo@0 1245 unix phil
meillo@0 1246 .LP
meillo@0 1247 case studies
meillo@0 1248
meillo@0 1249 .NH 2
meillo@0 1250 Why people should choose
meillo@0 1251 .LP
meillo@0 1252 Make the right choice!
meillo@0 1253
meillo@0 1254 .nr PI .5i
meillo@0 1255 .rm ]<
meillo@0 1256 .de ]<
meillo@0 1257 .LP
meillo@0 1258 .de FP
meillo@0 1259 .IP \\\\$1.
meillo@0 1260 \\..
meillo@0 1261 .rm FS FE
meillo@0 1262 ..
meillo@0 1263 .SH
meillo@0 1264 References
meillo@0 1265 .[
meillo@0 1266 $LIST$
meillo@0 1267 .]
meillo@0 1268 .wh -1p