Mercurial > docs > unix-phil
annotate unix-phil.ms @ 37:9282c4cea18c
more about uzbl design
| author | meillo@marmaro.de |
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| date | Sat, 03 Apr 2010 10:33:33 +0200 |
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3 .nr VS 13 |
| 0 | 4 .de XX |
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| 6 .. | |
| 7 .em XX | |
| 1 | 8 .\".nr PI 0 |
| 9 .\".if t .nr PD .5v | |
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| 12 .de CW | |
| 13 .nr PQ \\n(.f | |
| 14 .if t .ft CW | |
| 17 | 15 .ie ^\\$1^^ .if n .ul 999 |
| 0 | 16 .el .if n .ul 1 |
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| 0 | 18 .if n .if \\n(.$=1 \&\\$1 |
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| 21 .. | |
| 22 .ds [. \ [ | |
| 23 .ds .] ] | |
| 1 | 24 .\"---------------------------------------- |
| 0 | 25 .TL |
| 6 | 26 Why the Unix Philosophy still matters |
| 0 | 27 .AU |
| 28 markus schnalke <meillo@marmaro.de> | |
| 29 .AB | |
| 1 | 30 .ti \n(.iu |
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31 This paper discusses the importance of the Unix Philosophy in software design. |
| 0 | 32 Today, few software designers are aware of these concepts, |
| 3 | 33 and thus most modern software is limited and does not make use of software leverage. |
| 0 | 34 Knowing and following the tenets of the Unix Philosophy makes software more valuable. |
| 35 .AE | |
| 36 | |
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37 .\".if t .2C |
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39 .FS |
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40 .ps -1 |
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41 This paper was prepared for the seminar ``Software Analysis'' at University Ulm. |
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42 Mentor was professor Schweiggert. 2010-02-05 |
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43 .br |
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44 You may get this document from my website |
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45 .CW \s-1http://marmaro.de/docs |
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46 .FE |
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47 |
| 0 | 48 .NH 1 |
| 49 Introduction | |
| 50 .LP | |
| 51 Building a software is a process from an idea of the purpose of the software | |
| 3 | 52 to its release. |
| 0 | 53 No matter \fIhow\fP the process is run, two things are common: |
| 54 the initial idea and the release. | |
| 9 | 55 The process in between can be of any shape. |
| 56 The the maintenance work after the release is ignored for the moment. | |
| 1 | 57 .PP |
| 0 | 58 The process of building splits mainly in two parts: |
| 59 the planning of what and how to build, and implementing the plan by writing code. | |
| 3 | 60 This paper focuses on the planning part \(en the designing of the software. |
| 61 .PP | |
| 62 Software design is the plan of how the internals and externals of the software should look like, | |
| 63 based on the requirements. | |
| 9 | 64 This paper discusses the recommendations of the Unix Philosophy about software design. |
| 3 | 65 .PP |
| 66 The here discussed ideas can get applied by any development process. | |
| 9 | 67 The Unix Philosophy does recommend how the software development process should look like, |
| 3 | 68 but this shall not be of matter here. |
| 0 | 69 Similar, the question of how to write the code is out of focus. |
| 1 | 70 .PP |
| 3 | 71 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet. |
| 1 | 72 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed. |
| 3 | 73 It is no limited set of rules, but what people see to be common to typical Unix software. |
| 1 | 74 Several people stated their view on the Unix Philosophy. |
| 75 Best known are: | |
| 76 .IP \(bu | |
| 77 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 78 .[ | |
| 79 %A M. D. McIlroy | |
| 80 %A E. N. Pinson | |
| 81 %A B. A. Taque | |
| 82 %T UNIX Time-Sharing System Forward | |
| 83 %J The Bell System Technical Journal | |
| 84 %D 1978 | |
| 85 %V 57 | |
| 86 %N 6 | |
| 87 %P 1902 | |
| 88 .] | |
| 89 .IP \(bu | |
| 90 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 91 .[ | |
| 92 %A Mike Gancarz | |
| 93 %T The UNIX Philosophy | |
| 94 %D 1995 | |
| 95 %I Digital Press | |
| 96 .] | |
| 97 .IP \(bu | |
| 98 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 99 .[ | |
| 100 %A Eric S. Raymond | |
| 101 %T The Art of UNIX Programming | |
| 102 %D 2003 | |
| 103 %I Addison-Wesley | |
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104 %O .CW \s-1http://www.faqs.org/docs/artu/ |
| 1 | 105 .] |
| 0 | 106 .LP |
| 1 | 107 These different views on the Unix Philosophy have much in common. |
| 3 | 108 Especially, the main concepts are similar for all of them. |
| 1 | 109 But there are also points on which they differ. |
| 110 This only underlines what the Unix Philosophy is: | |
| 111 A retrospective view on the main concepts of Unix software; | |
| 9 | 112 especially those that were successful and unique to Unix. |
| 6 | 113 .\" really? |
| 1 | 114 .PP |
| 115 Before we will have a look at concrete concepts, | |
| 116 we discuss why software design is important | |
| 117 and what problems bad design introduces. | |
| 0 | 118 |
| 119 | |
| 120 .NH 1 | |
| 6 | 121 Importance of software design in general |
| 0 | 122 .LP |
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123 Why should we design software at all? |
| 6 | 124 It is general knowledge, that even a bad plan is better than no plan. |
| 125 Ignoring software design is programming without a plan. | |
| 126 This will lead pretty sure to horrible results. | |
| 127 .PP | |
| 128 The design of a software is its internal and external shape. | |
| 129 The design talked about here has nothing to do with visual appearance. | |
| 130 If we see a program as a car, then its color is of no matter. | |
| 131 Its design would be the car's size, its shape, the number and position of doors, | |
| 132 the ratio of passenger and cargo transport, and so forth. | |
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133 .PP |
| 6 | 134 A software's design is about quality properties. |
| 135 Each of the cars may be able to drive from A to B, | |
| 136 but it depends on its properties whether it is a good car for passenger transport or not. | |
| 137 It also depends on its properties if it is a good choice for a rough mountain area. | |
| 138 .PP | |
| 139 Requirements to a software are twofold: functional and non-functional. | |
| 140 Functional requirements are easier to define and to verify. | |
| 141 They are directly the software's functions. | |
| 142 Functional requirements are the reason why software gets written. | |
| 143 Someone has a problem and needs a tool to solve it. | |
| 144 Being able to solve the problem is the main functional requirement. | |
| 145 It is the driving force behind all programming effort. | |
| 146 .PP | |
| 147 On the other hand, there are also non-functional requirements. | |
| 148 They are called \fIquality\fP requirements, too. | |
| 149 The quality of a software is about properties that are not directly related to | |
| 150 the software's basic functions. | |
| 151 Quality aspects are about the properties that are overlooked at first sight. | |
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152 .PP |
| 6 | 153 Quality is of few matter when the software gets initially built, |
| 9 | 154 but it will be of matter in usage and maintenance of the software. |
| 6 | 155 A short-sighted might see in developing a software mainly building something up. |
| 156 Reality shows, that building the software the first time is only a small amount | |
| 157 of the overall work. | |
| 9 | 158 Bug fixing, extending, rebuilding of parts \(en short: maintenance work \(en |
| 6 | 159 does soon take over the major part of the time spent on a software. |
| 160 Not to forget the usage of the software. | |
| 161 These processes are highly influenced by the software's quality. | |
| 162 Thus, quality should never be neglected. | |
| 163 The problem is that you hardly ``stumble over'' bad quality during the first build, | |
| 164 but this is the time when you should care about good quality most. | |
| 165 .PP | |
| 166 Software design is not about the basic function of a software; | |
| 167 this requirement will get satisfied anyway, as it is the main driving force behind the development. | |
| 168 Software design is about quality aspects of the software. | |
| 169 Good design will lead to good quality, bad design to bad quality. | |
| 170 The primary functions of the software will be affected modestly by bad quality, | |
| 171 but good quality can provide a lot of additional gain from the software, | |
| 172 even at places where one never expected it. | |
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173 .PP |
| 6 | 174 The ISO/IEC 9126-1 standard, part 1, |
| 175 .[ | |
| 9 | 176 %I International Organization for Standardization |
| 6 | 177 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1 |
| 178 %C Geneve | |
| 179 %D 2001 | |
| 180 .] | |
| 181 defines the quality model as consisting out of: | |
| 182 .IP \(bu | |
| 183 .I Functionality | |
| 184 (suitability, accuracy, inter\%operability, security) | |
| 185 .IP \(bu | |
| 186 .I Reliability | |
| 187 (maturity, fault tolerance, recoverability) | |
| 188 .IP \(bu | |
| 189 .I Usability | |
| 190 (understandability, learnability, operability, attractiveness) | |
| 191 .IP \(bu | |
| 192 .I Efficiency | |
| 9 | 193 (time behavior, resource utilization) |
| 6 | 194 .IP \(bu |
| 195 .I Maintainability | |
| 23 | 196 (analyzability, changeability, stability, testability) |
| 6 | 197 .IP \(bu |
| 198 .I Portability | |
| 199 (adaptability, installability, co-existence, replaceability) | |
| 200 .LP | |
| 201 These goals are parts of a software's design. | |
| 202 Good design can give these properties to a software, | |
| 203 bad designed software will miss them. | |
| 7 | 204 .PP |
| 205 One further goal of software design is consistency. | |
| 206 Consistency eases understanding, working on, and using things. | |
| 207 Consistent internals and consistent interfaces to the outside can be provided by good design. | |
| 208 .PP | |
| 209 We should design software because good design avoids many problems during a software's lifetime. | |
| 210 And we should design software because good design can offer much gain, | |
| 211 that can be unrelated to the software main intend. | |
| 212 Indeed, we should spend much effort into good design to make the software more valuable. | |
| 213 The Unix Philosophy shows how to design software well. | |
| 214 It offers guidelines to achieve good quality and high gain for the effort spent. | |
| 0 | 215 |
| 216 | |
| 217 .NH 1 | |
| 218 The Unix Philosophy | |
| 4 | 219 .LP |
| 220 The origins of the Unix Philosophy were already introduced. | |
| 8 | 221 This chapter explains the philosophy, oriented on Gancarz, |
| 222 and shows concrete examples of its application. | |
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223 |
| 16 | 224 .NH 2 |
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225 Pipes |
| 0 | 226 .LP |
| 4 | 227 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 228 Knowledge of using the Unix shell is assumed. | |
| 229 .PP | |
| 230 Counting the number of files in the current directory: | |
| 9 | 231 .DS I 2n |
| 4 | 232 .CW |
| 9 | 233 .ps -1 |
| 4 | 234 ls | wc -l |
| 235 .DE | |
| 236 The | |
| 237 .CW ls | |
| 238 command lists all files in the current directory, one per line, | |
| 239 and | |
| 240 .CW "wc -l | |
| 8 | 241 counts the number of lines. |
| 4 | 242 .PP |
| 8 | 243 Counting the number of files that do not contain ``foo'' in their name: |
| 9 | 244 .DS I 2n |
| 4 | 245 .CW |
| 9 | 246 .ps -1 |
| 4 | 247 ls | grep -v foo | wc -l |
| 248 .DE | |
| 249 Here, the list of files is filtered by | |
| 250 .CW grep | |
| 251 to remove all that contain ``foo''. | |
| 252 The rest is the same as in the previous example. | |
| 253 .PP | |
| 254 Finding the five largest entries in the current directory. | |
| 9 | 255 .DS I 2n |
| 4 | 256 .CW |
| 9 | 257 .ps -1 |
| 4 | 258 du -s * | sort -nr | sed 5q |
| 259 .DE | |
| 260 .CW "du -s * | |
| 261 returns the recursively summed sizes of all files | |
| 8 | 262 \(en no matter if they are regular files or directories. |
| 4 | 263 .CW "sort -nr |
| 264 sorts the list numerically in reverse order. | |
| 265 Finally, | |
| 266 .CW "sed 5q | |
| 267 quits after it has printed the fifth line. | |
| 268 .PP | |
| 269 The presented command lines are examples of what Unix people would use | |
| 270 to get the desired output. | |
| 271 There are also other ways to get the same output. | |
| 272 It's a user's decision which way to go. | |
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273 .PP |
| 8 | 274 The examples show that many tasks on a Unix system |
| 4 | 275 are accomplished by combining several small programs. |
| 276 The connection between the single programs is denoted by the pipe operator `|'. | |
| 277 .PP | |
| 278 Pipes, and their extensive and easy use, are one of the great | |
| 279 achievements of the Unix system. | |
| 280 Pipes between programs have been possible in earlier operating systems, | |
| 281 but it has never been a so central part of the concept. | |
| 282 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 283 Unix system, | |
| 284 ``it was this concept and notation for linking several programs together | |
| 285 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 286 .[ | |
| 287 %T Unix: An Oral History | |
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288 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
| 4 | 289 .] |
| 290 .PP | |
| 291 Being able to specify pipelines in an easy way is, | |
| 292 however, not enough by itself. | |
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293 It is only one half. |
| 4 | 294 The other is the design of the programs that are used in the pipeline. |
| 8 | 295 They have to interfaces that allows them to be used in such a way. |
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296 |
| 16 | 297 .NH 2 |
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298 Interface design |
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299 .LP |
| 11 | 300 Unix is, first of all, simple \(en Everything is a file. |
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301 Files are sequences of bytes, without any special structure. |
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302 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin) |
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303 and write a stream of bytes to ``standard output'' (stdout). |
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304 .PP |
| 8 | 305 If the files \fIare\fP sequences of bytes, |
| 306 and the programs \fIare\fP filters on byte streams, | |
| 11 | 307 then there is exactly one standardized data interface. |
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308 Thus it is possible to combine them in any desired way. |
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309 .PP |
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310 Even a handful of small programs will yield a large set of combinations, |
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311 and thus a large set of different functions. |
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312 This is leverage! |
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313 If the programs are orthogonal to each other \(en the best case \(en |
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314 then the set of different functions is greatest. |
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315 .PP |
| 11 | 316 Programs might also have a separate control interface, |
| 317 besides their data interface. | |
| 318 The control interface is often called ``user interface'', | |
| 319 because it is usually designed to be used by humans. | |
| 320 The Unix Philosophy discourages to assume the user to be human. | |
| 321 Interactive use of software is slow use of software, | |
| 322 because the program waits for user input most of the time. | |
| 323 Interactive software requires the user to be in front of the computer | |
| 324 all the time. | |
| 325 Interactive software occupy the user's attention while they are running. | |
| 326 .PP | |
| 327 Now we come back to the idea of using several small programs, combined, | |
| 328 to have a more specific function. | |
| 329 If these single tools would all be interactive, | |
| 330 how would the user control them? | |
| 331 It is not only a problem to control several programs at once if they run at the same time, | |
| 332 it also very inefficient to have to control each of the single programs | |
| 333 that are intended to work as one large program. | |
| 334 Hence, the Unix Philosophy discourages programs to demand interactive use. | |
| 335 The behavior of programs should be defined at invocation. | |
| 336 This is done by specifying arguments (``command line switches'') to the program call. | |
| 337 Gancarz discusses this topic as ``avoid captive user interfaces''. | |
| 338 .[ | |
| 339 %A Mike Gancarz | |
| 340 %T The UNIX Philosophy | |
| 341 %I Digital Press | |
| 342 %D 1995 | |
| 343 %P 88 ff. | |
| 344 .] | |
| 345 .PP | |
| 346 Non-interactive use is, during development, also an advantage for testing. | |
| 347 Testing of interactive programs is much more complicated, | |
| 348 than testing of non-interactive programs. | |
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349 |
| 16 | 350 .NH 2 |
| 8 | 351 The toolchest approach |
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352 .LP |
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353 A toolchest is a set of tools. |
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354 Instead of having one big tool for all tasks, one has many small tools, |
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355 each for one task. |
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356 Difficult tasks are solved by combining several of the small, simple tools. |
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357 .PP |
| 11 | 358 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 359 that are filters on byte streams. | |
| 360 They are, to a large extend, unrelated in their function. | |
| 361 Hence, the Unix toolchest provides a large set of functions | |
| 362 that can be accessed by combining the programs in the desired way. | |
| 363 .PP | |
| 364 There are also advantages for developing small toolchest programs. | |
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365 It is easier and less error-prone to write small programs. |
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366 It is also easier and less error-prone to write a large set of small programs, |
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367 than to write one large program with all the functionality included. |
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368 If the small programs are combinable, then they offer even a larger set |
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369 of functions than the single large program. |
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370 Hence, one gets two advantages out of writing small, combinable programs. |
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371 .PP |
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372 There are two drawbacks of the toolchest approach. |
| 8 | 373 First, one simple, standardized, unidirectional interface has to be sufficient. |
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374 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 375 then a different approach might be of need. |
| 13 | 376 But it is also possible, that he just can not imagine a design where |
| 8 | 377 a stream of bytes is sufficient. |
| 378 By becoming more familiar with the ``Unix style of thinking'', | |
| 379 developers will more often and easier find simple designs where | |
| 380 a stream of bytes is a sufficient interface. | |
| 381 .PP | |
| 382 The second drawback of a toolchest affects the users. | |
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383 A toolchest is often more difficult to use for novices. |
| 9 | 384 It is necessary to become familiar with each of the tools, |
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385 to be able to use the right one in a given situation. |
| 9 | 386 Additionally, one needs to combine the tools in a senseful way on its own. |
| 387 This is like a sharp knife \(en it is a powerful tool in the hand of a master, | |
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388 but of no good value in the hand of an unskilled. |
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389 .PP |
| 8 | 390 However, learning single, small tool of the toolchest is easier than |
| 391 learning a complex tool. | |
| 392 The user will have a basic understanding of a yet unknown tool, | |
| 393 if the several tools of the toolchest have a common style. | |
| 394 He will be able to transfer knowledge over one tool to another. | |
| 395 .PP | |
| 396 Moreover, the second drawback can be removed easily by adding wrappers | |
| 397 around the single tools. | |
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398 Novice users do not need to learn several tools if a professional wraps |
| 8 | 399 the single commands into a more high-level script. |
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400 Note that the wrapper script still calls the small tools; |
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401 the wrapper script is just like a skin around. |
| 8 | 402 No complexity is added this way, |
| 403 but new programs can get created out of existing one with very low effort. | |
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404 .PP |
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405 A wrapper script for finding the five largest entries in the current directory |
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406 could look like this: |
| 9 | 407 .DS I 2n |
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408 .CW |
| 9 | 409 .ps -1 |
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410 #!/bin/sh |
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411 du -s * | sort -nr | sed 5q |
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412 .DE |
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413 The script itself is just a text file that calls the command line |
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414 a professional user would type in directly. |
| 8 | 415 Making the program flexible on the number of entries it prints, |
| 416 is easily possible: | |
| 9 | 417 .DS I 2n |
| 8 | 418 .CW |
| 9 | 419 .ps -1 |
| 8 | 420 #!/bin/sh |
| 421 num=5 | |
| 422 [ $# -eq 1 ] && num="$1" | |
| 423 du -sh * | sort -nr | sed "${num}q" | |
| 424 .DE | |
| 425 This script acts like the one before, when called without an argument. | |
| 426 But one can also specify a numerical argument to define the number of lines to print. | |
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427 |
| 16 | 428 .NH 2 |
| 8 | 429 A powerful shell |
| 430 .LP | |
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431 It was already said, that the Unix shell provides the possibility to |
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432 combine small programs into large ones easily. |
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433 A powerful shell is a great feature in other ways, too. |
| 8 | 434 .PP |
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435 For instance by including a scripting language. |
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436 The control statements are build into the shell. |
| 8 | 437 The functions, however, are the normal programs, everyone can use on the system. |
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438 Thus, the programs are known, so learning to program in the shell is easy. |
| 8 | 439 Using normal programs as functions in the shell programming language |
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440 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 441 .PP |
| 442 The Unix shell encourages to write small scripts out of other programs, | |
| 443 because it is so easy to do. | |
| 444 This is a great step towards automation. | |
| 445 It is wonderful if the effort to automate a task equals the effort | |
| 446 it takes to do it the second time by hand. | |
| 447 If it is so, then the user will be happy to automate everything he does more than once. | |
| 448 .PP | |
| 449 Small programs that do one job well, standardized interfaces between them, | |
| 450 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 451 this will inevitably produce software leverage. | |
| 452 Getting multiple times the benefit of an investment is a great offer. | |
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453 .PP |
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454 The shell also encourages rapid prototyping. |
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455 Many well known programs started as quickly hacked shell scripts, |
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456 and turned into ``real'' programs, written in C, later. |
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457 Building a prototype first is a way to avoid the biggest problems |
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458 in application development. |
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459 Fred Brooks writes in ``No Silver Bullet'': |
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460 .[ |
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461 %A Frederick P. Brooks, Jr. |
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462 %T No Silver Bullet: Essence and Accidents of Software Engineering |
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463 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference |
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464 %E H.-J. Kugler |
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465 %D 1986 |
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466 %P 1069\(en1076 |
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467 %I Elsevier Science B.V. |
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468 %C Amsterdam, The Netherlands |
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469 .] |
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470 .QP |
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471 The hardest single part of building a software system is deciding precisely what to build. |
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472 No other part of the conceptual work is so difficult as establishing the detailed |
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473 technical requirements, [...]. |
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474 No other part of the work so cripples the resulting system if done wrong. |
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475 No other part is more difficult to rectify later. |
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476 .PP |
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477 Writing a prototype is a great method to become familiar with the requirements |
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478 and to actually run into real problems. |
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479 Today, prototyping is often seen as a first step in building a software. |
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480 This is, of course, good. |
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481 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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482 After having built the prototype, one might notice, that the prototype is already |
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483 \fIgood enough\fP. |
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484 Hence, no reimplementation, in a more sophisticated programming language, might be of need, |
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485 for the moment. |
| 23 | 486 Maybe later, it might be necessary to rewrite the software, but not now. |
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487 .PP |
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488 By delaying further work, one keeps the flexibility to react easily on |
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489 changing requirements. |
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490 Software parts that are not written will not miss the requirements. |
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491 |
| 16 | 492 .NH 2 |
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493 Worse is better |
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494 .LP |
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495 The Unix Philosophy aims for the 80% solution; |
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496 others call it the ``Worse is better'' approach. |
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497 .PP |
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498 First, practical experience shows, that it is almost never possible to define the |
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499 requirements completely and correctly the first time. |
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500 Hence one should not try to; it will fail anyway. |
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501 Second, practical experience shows, that requirements change during time. |
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502 Hence it is best to delay requirement-based design decisions as long as possible. |
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503 Also, the software should be small and flexible as long as possible |
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504 to react on changing requirements. |
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505 Shell scripts, for example, are more easily adjusted as C programs. |
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506 Third, practical experience shows, that maintenance is hard work. |
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507 Hence, one should keep the amount of software as small as possible; |
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508 it should just fulfill the \fIcurrent\fP requirements. |
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509 Software parts that will be written later, do not need maintenance now. |
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510 .PP |
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511 Starting with a prototype in a scripting language has several advantages: |
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512 .IP \(bu |
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513 As the initial effort is low, one will likely start right away. |
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514 .IP \(bu |
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515 As working parts are available soon, the real requirements can get identified soon. |
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516 .IP \(bu |
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517 When a software is usable, it gets used, and thus tested. |
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518 Hence problems will be found at early stages of the development. |
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519 .IP \(bu |
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520 The prototype might be enough for the moment, |
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521 thus further work on the software can be delayed to a time |
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522 when one knows better about the requirements and problems, |
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523 than now. |
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524 .IP \(bu |
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525 Implementing now only the parts that are actually needed now, |
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526 requires fewer maintenance work. |
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527 .IP \(bu |
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528 If the global situation changes so that the software is not needed anymore, |
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529 then less effort was spent into the project, than it would have be |
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530 when a different approach had been used. |
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531 |
| 16 | 532 .NH 2 |
| 11 | 533 Upgrowth and survival of software |
| 534 .LP | |
| 12 | 535 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 536 Although these are just verbs, they do imply a specific view on the work process |
| 537 they describe. | |
| 12 | 538 The better verb, however, is to \fIgrow\fP. |
| 539 .PP | |
| 540 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 541 It starts with a first prototype, which evolves as requirements change. | |
| 542 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 543 compiled program this way. |
| 544 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
| 545 While being alive it will get extended, rearranged, rebuilt (from scratch). | |
| 12 | 546 Growing software matches the view that ``software is never finished. It is only released.'' |
| 547 .[ | |
| 13 | 548 %O FIXME |
| 549 %A Mike Gancarz | |
| 550 %T The UNIX Philosophy | |
| 551 %P 26 | |
| 12 | 552 .] |
| 553 .PP | |
| 13 | 554 Software can be seen as being controlled by evolutionary processes. |
| 555 Successful software is software that is used by many for a long time. | |
| 12 | 556 This implies that the software is needed, useful, and better than alternatives. |
| 557 Darwin talks about: ``The survival of the fittest.'' | |
| 558 .[ | |
| 13 | 559 %O FIXME |
| 560 %A Charles Darwin | |
| 12 | 561 .] |
| 562 Transferred to software: The most successful software, is the fittest, | |
| 563 is the one that survives. | |
| 13 | 564 (This may be at the level of one creature, or at the level of one species.) |
| 565 The fitness of software is affected mainly by four properties: | |
| 15 | 566 portability of code, portability of data, range of usability, and reusability of parts. |
| 567 .\" .IP \(bu | |
| 568 .\" portability of code | |
| 569 .\" .IP \(bu | |
| 570 .\" portability of data | |
| 571 .\" .IP \(bu | |
| 572 .\" range of usability | |
| 573 .\" .IP \(bu | |
| 574 .\" reuseability of parts | |
| 13 | 575 .PP |
| 15 | 576 (1) |
| 577 .I "Portability of code | |
| 578 means, using high-level programming languages, | |
| 13 | 579 sticking to the standard, |
| 580 and avoiding optimizations that introduce dependencies on specific hardware. | |
| 581 Hardware has a much lower lifetime than software. | |
| 582 By chaining software to a specific hardware, | |
| 583 the software's lifetime gets shortened to that of this hardware. | |
| 584 In contrast, software should be easy to port \(en | |
| 23 | 585 adaptation is the key to success. |
| 13 | 586 .\" cf. practice of prog: ch08 |
| 587 .PP | |
| 15 | 588 (2) |
| 589 .I "Portability of data | |
| 590 is best achieved by avoiding binary representations | |
| 13 | 591 to store data, because binary representations differ from machine to machine. |
| 23 | 592 Textual representation is favored. |
| 13 | 593 Historically, ASCII was the charset of choice. |
| 594 In the future, UTF-8 might be the better choice, however. | |
| 595 Important is that it is a plain text representation in a | |
| 596 very common charset encoding. | |
| 597 Apart from being able to transfer data between machines, | |
| 598 readable data has the great advantage, that humans are able | |
| 599 to directly edit it with text editors and other tools from the Unix toolchest. | |
| 600 .\" gancarz tenet 5 | |
| 12 | 601 .PP |
| 15 | 602 (3) |
| 603 A large | |
| 604 .I "range of usability | |
| 23 | 605 ensures good adaptation, and thus good survival. |
| 13 | 606 It is a special distinction if a software becomes used in fields of action, |
| 607 the original authors did never imagine. | |
| 608 Software that solves problems in a general way will likely be used | |
| 609 for all kinds of similar problems. | |
| 610 Being too specific limits the range of uses. | |
| 611 Requirements change through time, thus use cases change or even vanish. | |
| 612 A good example in this point is Allman's sendmail. | |
| 613 Allman identifies flexibility to be one major reason for sendmail's success: | |
| 614 .[ | |
| 615 %O FIXME | |
| 616 %A Allman | |
| 617 %T sendmail | |
| 618 .] | |
| 619 .QP | |
| 620 Second, I limited myself to the routing function [...]. | |
| 621 This was a departure from the dominant thought of the time, [...]. | |
| 622 .QP | |
| 623 Third, the sendmail configuration file was flexible enough to adopt | |
| 624 to a rapidly changing world [...]. | |
| 625 .LP | |
| 626 Successful software adopts itself to the changing world. | |
| 12 | 627 .PP |
| 15 | 628 (4) |
| 629 .I "Reuse of parts | |
| 630 is even one step further. | |
| 13 | 631 A software may completely lose its field of action, |
| 632 but parts of which the software is build may be general and independent enough | |
| 633 to survive this death. | |
| 634 If software is build by combining small independent programs, | |
| 635 then there are parts readily available for reuse. | |
| 636 Who cares if the large program is a failure, | |
| 637 but parts of it become successful instead? | |
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638 |
| 16 | 639 .NH 2 |
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640 Summary |
| 0 | 641 .LP |
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642 This chapter explained the central ideas of the Unix Philosophy. |
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643 For each of the ideas, it was exposed what advantages they introduce. |
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644 The Unix Philosophy are guidelines that help to write valuable software. |
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645 From the view point of a software developer or software designer, |
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646 the Unix Philosophy provides answers to many software design problem. |
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647 .PP |
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648 The various ideas of the Unix Philosophy are very interweaved |
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649 and can hardly be applied independently. |
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650 However, the probably most important messages are: |
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651 .I "``Do one thing well!''" , |
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652 .I "``Keep it simple!''" , |
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653 and |
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654 .I "``Use software leverage!'' |
| 0 | 655 |
| 8 | 656 |
| 657 | |
| 0 | 658 .NH 1 |
| 19 | 659 Case study: \s-1MH\s0 |
| 18 | 660 .LP |
| 30 | 661 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 662 from a general point of view. |
| 30 | 663 The driving force were the guidelines; references to |
| 18 | 664 existing software were given only sparsely. |
| 665 In this and the next chapter, concrete software will be | |
| 666 the driving force in the discussion. | |
| 667 .PP | |
| 23 | 668 This first case study is about the mail user agents (\s-1MUA\s0) |
| 669 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 670 (``new mail handler''). | |
| 671 \s-1MUA\s0s provide functions to read, compose, and organize mail, | |
| 672 but (ideally) not to transfer. | |
| 19 | 673 In this document, the name \s-1MH\s0 will be used for both of them. |
| 674 A distinction will only be made if differences between | |
| 675 them are described. | |
| 18 | 676 |
| 0 | 677 |
| 678 .NH 2 | |
| 19 | 679 Historical background |
| 0 | 680 .LP |
| 19 | 681 Electronic mail was available in Unix very early. |
| 30 | 682 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 683 which was already present in the First Edition. | |
| 684 .[ | |
| 685 %A Peter H. Salus | |
| 686 %T A Quarter Century of UNIX | |
| 687 %D 1994 | |
| 688 %I Addison-Wesley | |
| 689 %P 41 f. | |
| 690 .] | |
| 691 It was a small program that either prints the user's mailbox file | |
| 19 | 692 or appends text to someone elses mailbox file, |
| 693 depending on the command line arguments. | |
| 694 .[ | |
| 695 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf | |
| 696 .] | |
| 697 It was a program that did one job well. | |
| 23 | 698 This job was emailing, which was very simple then. |
| 19 | 699 .PP |
| 23 | 700 Later, emailing became more powerful, and thus more complex. |
| 19 | 701 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 702 independent handling of single messages, | |
| 703 and long-time storage of them, was not powerful enough anymore. | |
| 704 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') | |
| 705 in 1978 to provide additional functions for emailing. | |
| 706 Mail was still one program, but now it was large and did | |
| 707 several jobs. | |
| 23 | 708 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 709 It is designed for humans, but is still scriptable. |
| 23 | 710 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 711 .[ |
| 712 %A Gunnar Ritter | |
| 713 %O http://heirloom.sourceforge.net/mailx_history.html | |
| 714 .] | |
| 30 | 715 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 716 followed Mail's direction. |
| 717 They are large, monolithic programs which include all emailing functions. | |
| 718 .PP | |
| 23 | 719 A different way was taken by the people of \s-1RAND\s0 Corporation. |
| 19 | 720 In the beginning, they also had used a monolitic mail system, |
| 30 | 721 called \s-1MS\s0 (for ``mail system''). |
| 19 | 722 But in 1977, Stockton Gaines and Norman Shapiro |
| 723 came up with a proposal of a new email system concept \(en | |
| 724 one that honors the Unix Philosophy. | |
| 725 The concept was implemented by Bruce Borden in 1978 and 1979. | |
| 726 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 727 .PP |
| 728 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 729 at Berkeley, and several others have contributed to the software. |
| 18 | 730 However, it's core concepts remained the same. |
| 23 | 731 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 732 Richard Coleman started with \fInmh\fP, the new mail handler. |
| 733 His goal was to improve \s-1MH\s0, especially in regard of | |
| 23 | 734 the requirements of modern emailing. |
| 19 | 735 Today, nmh is developed by various people on the Internet. |
| 18 | 736 .[ |
| 737 %T RAND and the Information Evolution: A History in Essays and Vignettes | |
| 738 %A Willis H. Ware | |
| 739 %D 2008 | |
| 740 %I The RAND Corporation | |
| 741 %P 128\(en137 | |
| 742 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/ | |
| 743 .] | |
| 744 .[ | |
| 745 %T MH & xmh: Email for Users & Programmers | |
| 746 %A Jerry Peek | |
| 747 %D 1991, 1992, 1995 | |
| 748 %I O'Reilly & Associates, Inc. | |
| 749 %P Appendix B | |
| 750 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP | |
| 751 .] | |
| 0 | 752 |
| 753 .NH 2 | |
| 20 | 754 Contrasts to monolithic mail systems |
| 0 | 755 .LP |
| 19 | 756 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
| 30 | 757 Although there might acutally exist further, very little known, |
| 758 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. | |
| 19 | 759 .PP |
| 30 | 760 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 761 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 762 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 763 and their function. |
| 764 It gives a feeling of how the toolchest looks like. | |
| 19 | 765 .IP \(bu |
| 766 .CW inc : | |
| 30 | 767 incorporate new mail (this is how mail enters the system) |
| 19 | 768 .IP \(bu |
| 769 .CW scan : | |
| 770 list messages in folder | |
| 771 .IP \(bu | |
| 772 .CW show : | |
| 773 show message | |
| 774 .IP \(bu | |
| 775 .CW next\fR/\fPprev : | |
| 776 show next/previous message | |
| 777 .IP \(bu | |
| 778 .CW folder : | |
| 779 change current folder | |
| 780 .IP \(bu | |
| 781 .CW refile : | |
| 782 refile message into folder | |
| 783 .IP \(bu | |
| 784 .CW rmm : | |
| 785 remove message | |
| 786 .IP \(bu | |
| 787 .CW comp : | |
| 788 compose a new message | |
| 789 .IP \(bu | |
| 790 .CW repl : | |
| 791 reply to a message | |
| 792 .IP \(bu | |
| 793 .CW forw : | |
| 794 forward a message | |
| 795 .IP \(bu | |
| 796 .CW send : | |
| 30 | 797 send a prepared message (this is how mail leaves the system) |
| 0 | 798 .LP |
| 19 | 799 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 800 The user does not leave the shell to run \s-1MH\s0, | |
| 30 | 801 but he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 802 Using a monolithic program with a captive user interface |
| 803 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 804 Using toolchests like \s-1MH\s0 means running programs, | |
| 805 alone or in combinition with others, even from other toolchests, | |
| 806 without leaving the shell. | |
| 30 | 807 |
| 808 .NH 2 | |
| 809 Data storage | |
| 810 .LP | |
| 34 | 811 \s-1MH\s0's mail storage is a directory tree under the user's |
| 812 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 813 where mail folders are directories and mail messages are text files | |
| 814 within them. | |
| 815 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
| 816 the public message sequences of that folder, for instance new messages. | |
| 817 Mail messages are text files located in a mail folder. | |
| 818 The files contain the messages as they were received. | |
| 819 They are numbered in ascending order in each folder. | |
| 19 | 820 .PP |
| 30 | 821 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 822 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 823 In the mbox format all messages are stored within one file. | |
| 824 This was a good solution in the early days, when messages | |
| 825 were only a few lines of text and were deleted soon. | |
| 826 Today, when single messages often include several megabytes | |
| 827 of attachments, it is a bad solution. | |
| 828 Another disadvantage of the mbox format is that it is | |
| 829 more difficult to write tools that work on mail messages, | |
| 830 because it is always necessary to first find and extract | |
| 831 the relevant message in the mbox file. | |
| 832 With the \s-1MH\s0 mailbox format, | |
| 833 each message is a self-standing item, by definition. | |
| 834 Also, the problem of concurrent access to one mailbox is | |
| 835 reduced to the problem of concurrent access to one message. | |
| 836 Maildir is generally similar to \s-1MH\s0's format, | |
| 837 but modified towards guaranteed reliability. | |
| 838 This involves some complexity, unfortunately. | |
| 34 | 839 .PP |
| 840 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 841 working with Unix' toolchest on directory trees: | |
| 842 \f(CWscan\fP is like \f(CWls\fP, | |
| 843 \f(CWshow\fP is like \f(CWcat\fP, | |
| 844 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 845 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 846 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 847 .PP | |
| 848 The context of tools in Unix consists mainly the current working directory, | |
| 849 the user identification, and the environment variables. | |
| 850 \s-1MH\s0 extends this context by two more items: | |
| 851 .IP \(bu | |
| 852 The current mail folder, which is similar to the current working directory. | |
| 853 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 854 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 855 .IP \(bu | |
| 856 Sequences, which are named sets of messages in a mail folder. | |
| 857 The current message, relative to a mail folder, is a special sequence. | |
| 858 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 859 .LP | |
| 860 In contrast to Unix' context, which is chained to the shell session, | |
| 861 \s-1MH\s0's context is independent. | |
| 862 Usually there is one context for each user, but a user can have many | |
| 863 contexts. | |
| 864 Public sequences are an exception, as they belong to the mail folder. | |
| 865 .[ | |
| 866 %O mh-profile(5) and mh-sequence(5) | |
| 867 .] | |
| 20 | 868 |
| 0 | 869 .NH 2 |
| 20 | 870 Discussion of the design |
| 871 .LP | |
| 872 The following paragraphs discuss \s-1MH\s0 in regard to the tenets | |
| 23 | 873 of the Unix Philosophy which Gancarz identified. |
| 20 | 874 |
| 875 .PP | |
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876 .B "Small is beautiful |
| 20 | 877 and |
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878 .B "do one thing well |
| 20 | 879 are two design goals that are directly visible in \s-1MH\s0. |
| 880 Gancarz actually presents \s-1MH\s0 as example under the headline | |
| 881 ``Making UNIX Do One Thing Well'': | |
| 882 .QP | |
| 883 [\s-1MH\s0] consists of a series of programs which | |
| 884 when combined give the user an enormous ability | |
| 885 to manipulate electronic mail messages. | |
| 886 A complex application, it shows that not only is it | |
| 887 possible to build large applications from smaller | |
| 888 components, but also that such designs are actually preferable. | |
| 889 .[ | |
| 890 %A Mike Gancarz | |
| 891 %T unix-phil | |
| 892 %P 125 | |
| 893 .] | |
| 0 | 894 .LP |
| 20 | 895 The various small programs of \s-1MH\s0 were relatively easy |
| 23 | 896 to write, because each of them is small, limited to one function, |
| 897 and has clear boundaries. | |
| 20 | 898 For the same reasons, they are also good to maintain. |
| 899 Further more, the system can easily get extended. | |
| 900 One only needs to put a new program into the toolchest. | |
| 23 | 901 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 902 (e.g. \f(CWmhbuild\fP). |
| 903 Also, different programs can exist to do the basically same job | |
| 904 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
| 905 If someone needs a mail system with some additionally | |
| 23 | 906 functions that are available nowhere yet, he best takes a |
| 20 | 907 toolchest system like \s-1MH\s0 where he can add the |
| 908 functionality with little work. | |
| 909 | |
| 910 .PP | |
| 34 | 911 .B "Store data in flat text files |
| 912 is followed by \s-1MH\s0. | |
| 913 This is not surprising, because email messages are already plain text. | |
| 914 \s-1MH\s0 stores the messages as it receives them, | |
| 915 thus any other tool that works on RFC 2822 mail messages can operate | |
| 916 on the messages in an \s-1MH\s0 mailbox. | |
| 917 All other files \s-1MH\s0 uses are plain text too. | |
| 918 It is therefore possible and encouraged to use the text processing | |
| 919 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 920 |
| 921 .PP | |
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922 .B "Avoid captive user interfaces" . |
| 19 | 923 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 924 It offers all functions directly and without captive user interfaces. | |
| 30 | 925 If, nonetheless, users want a graphical user interface, |
| 20 | 926 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
| 19 | 927 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 928 This means, all email-related work is still done by \s-1MH\s0 tools, | |
| 20 | 929 but the frontend issues the appropriate calls when the user |
| 30 | 930 clicks on buttons. |
| 20 | 931 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 932 approach, because it does not limit the power of the backend itself. |
| 20 | 933 The frontend will anyway only be able to make a subset of the |
| 23 | 934 backend's power and flexibility available to the user. |
| 20 | 935 But if it is a separate program, |
| 936 then the missing parts can still be accessed at the backend directly. | |
| 19 | 937 If it is integrated, then this will hardly be possible. |
| 30 | 938 Further more, it is possible to have different frontends to the same |
| 939 backend. | |
| 19 | 940 |
| 941 .PP | |
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942 .B "Choose portability over efficiency |
| 20 | 943 and |
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944 .B "use shell scripts to increase leverage and portability" . |
| 20 | 945 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 946 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 947 .[ |
| 948 %T The KornShell: command and programming language | |
| 949 %A Morris I. Bolsky | |
| 950 %A David G. Korn | |
| 951 %I Prentice Hall | |
| 952 %D 1989 | |
| 30 | 953 %P 254\(en290 |
| 20 | 954 %O \s-1ISBN\s0: 0-13-516972-0 |
| 955 .] | |
| 30 | 956 They demonstrated, in chapter 18 of the book, a basic implementation |
| 20 | 957 of a subset of \s-1MH\s0 in ksh scripts. |
| 958 Of course, this was just a demonstration, but a brilliant one. | |
| 959 It shows how quickly one can implement such a prototype with shell scripts, | |
| 960 and how readable they are. | |
| 961 The implementation in the scripting language may not be very fast, | |
| 962 but it can be fast enough though, and this is all that matters. | |
| 963 By having the code in an interpreted language, like the shell, | |
| 964 portability becomes a minor issue, if we assume the interpreter | |
| 965 to be widespread. | |
| 966 This demonstration also shows how easy it is to create single programs | |
| 967 of a toolchest software. | |
| 30 | 968 There are eight tools (two of them have multiple names) and 16 functions |
| 969 with supporting code. | |
| 970 Each tool comprises between 12 and 38 lines of ksh, | |
| 971 in total about 200 lines. | |
| 972 The functions comprise between 3 and 78 lines of ksh, | |
| 973 in total about 450 lines. | |
| 20 | 974 Such small software is easy to write, easy to understand, |
| 975 and thus easy to maintain. | |
| 23 | 976 A toolchest improves the possibility to only write some parts |
| 20 | 977 and though create a working result. |
| 978 Expanding the toolchest without global changes will likely be | |
| 979 possible, too. | |
| 980 | |
| 981 .PP | |
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982 .B "Use software leverage to your advantage |
| 20 | 983 and the lesser tenet |
|
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984 .B "allow the user to tailor the environment |
| 20 | 985 are ideally followed in the design of \s-1MH\s0. |
| 21 | 986 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 987 directly define default options to programs. |
| 988 It is even possible to define different default options | |
| 21 | 989 depending on the name under which the program was called. |
| 990 Software leverage is heavily encouraged by the ease it is to | |
| 991 create shell scripts that run a specific command line, | |
| 30 | 992 built of several \s-1MH\s0 programs. |
| 21 | 993 There is few software that so much wants users to tailor their |
| 994 environment and to leverage the use of the software, like \s-1MH\s0. | |
| 995 Just to make one example: | |
| 23 | 996 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 997 program. |
| 30 | 998 It is possible to take one of the distributed format files |
| 21 | 999 or to write one yourself. |
| 1000 To use the format as default for \f(CWscan\fP, a single line, | |
| 1001 reading | |
| 1002 .DS | |
| 1003 .CW | |
| 1004 scan: -form FORMATFILE | |
| 1005 .DE | |
| 1006 must be added to \f(CW.mh_profile\fP. | |
| 1007 If one wants this different format as an additional command, | |
| 23 | 1008 instead of changing the default, he needs to create a link to |
| 1009 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1010 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
| 30 | 1011 as the option should only be in effect when scan is called as |
| 21 | 1012 \f(CWscan2\fP. |
| 20 | 1013 |
| 1014 .PP | |
|
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1015 .B "Make every program a filter |
| 21 | 1016 is hard to find in \s-1MH\s0. |
| 1017 The reason therefore is that most of \s-1MH\s0's tools provide | |
| 1018 basic file system operations for the mailboxes. | |
| 30 | 1019 The reason is the same because of which |
| 21 | 1020 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP |
| 1021 aren't filters neither. | |
| 23 | 1022 However, they build a basis on which filters can operate. |
| 1023 \s-1MH\s0 does not provide many filters itself, but it is a basis | |
| 1024 to write filters for. | |
| 30 | 1025 An example would be a mail message text highlighter, |
| 1026 that means a program that makes use of a color terminal to display | |
| 1027 header lines, quotations, and signatures in distinct colors. | |
| 1028 The author's version of this program, for instance, | |
| 1029 is a 25 line awk script. | |
| 21 | 1030 |
| 1031 .PP | |
|
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1032 .B "Build a prototype as soon as possible |
| 21 | 1033 was again well followed by \s-1MH\s0. |
| 1034 This tenet, of course, focuses on early development, which is | |
| 1035 long time ago for \s-1MH\s0. | |
| 1036 But without following this guideline at the very beginning, | |
| 23 | 1037 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1038 to ever create \s-1MH\s0. | |
| 1039 In Bruce' own words: | |
| 21 | 1040 .QP |
| 30 | 1041 [...] but they [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1042 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1043 I proposed a very short project to prove the basic concepts, |
| 1044 and my management agreed. | |
| 1045 Looking back, I realize that I had been very lucky with my first design. | |
| 1046 Without nearly enough design work, | |
| 1047 I built a working environment and some header files | |
| 1048 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1049 inc, show/next/prev, and comp. | |
| 1050 [...] | |
| 1051 With these three, I was able to convince people that the structure was viable. | |
| 1052 This took about three weeks. | |
| 1053 .[ | |
| 1054 %O FIXME | |
| 1055 .] | |
| 0 | 1056 |
| 1057 .NH 2 | |
| 1058 Problems | |
| 1059 .LP | |
| 22 | 1060 \s-1MH\s0, for sure is not without problems. |
| 30 | 1061 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1062 .PP |
| 1063 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1064 when \s-1MH\s0 was designed. | |
| 1065 \s-1MH\s0 adopted to the changes pretty well, but it is limited. | |
| 1066 For example in development resources. | |
| 1067 \s-1MIME\s0 support and support for different character encodings | |
| 1068 is available, but only on a moderate level. | |
| 1069 More active developers could quickly improve there. | |
| 1070 It is also limited by design, which is the larger problem. | |
| 1071 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. | |
| 1072 These design conflicts are not easily solvable. | |
| 1073 Possibly, they require a redesign. | |
| 30 | 1074 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers, |
| 1075 hence \s-1MH\s0 may never work well with \s-1IMAP\s0. | |
| 22 | 1076 .PP |
| 1077 The other kind of problem is human habits. | |
| 1078 When in this world almost all \s-1MUA\s0s are monolithic, | |
| 1079 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 | |
| 1080 like \s-1MH\s0. | |
| 1081 The habits are so strong, that even people who understood the concept | |
| 30 | 1082 and advantages of \s-1MH\s0 do not like to switch, |
| 1083 simply because \s-1MH\s0 is different. | |
| 1084 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
| 1085 are quite outdated and thus not very appealing compared to the modern interfaces | |
| 1086 which monolithic \s-1MUA\s0s offer. | |
| 20 | 1087 |
| 1088 .NH 2 | |
| 1089 Summary \s-1MH\s0 | |
| 1090 .LP | |
| 31 | 1091 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design |
| 1092 and implementation. | |
| 1093 It consists of a toolchest of small tools, each of them does one job well. | |
| 1094 The tools are orthogonal to each other, to a large extend. | |
| 1095 However, for historical reasons, there also exist distinct tools | |
| 1096 that cover the same task. | |
| 1097 .PP | |
| 1098 The toolchest approach offers great flexibility to the user. | |
| 1099 He can use the complete power of the Unix shell with \s-1MH\s0. | |
| 1100 This makes \s-1MH\s0 a very powerful mail system. | |
| 1101 Extending and customizing \s-1MH\s0 is easy and encouraged, too. | |
| 1102 .PP | |
| 1103 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1104 Its overall design follows clear rules. | |
| 1105 The single tools do only one job, thus they are easy to understand, | |
| 1106 easy to write, and good to maintain. | |
| 1107 They are all independent and do not interfere with the others. | |
| 1108 Automated testing of their function is a straight forward task. | |
| 1109 .PP | |
| 1110 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1111 as its differentness is also its largest advantage. | |
| 1112 Unfortunately, for most people their habits are stronger | |
| 1113 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1114 |
| 8 | 1115 |
| 1116 | |
| 0 | 1117 .NH 1 |
| 1118 Case study: uzbl | |
| 32 | 1119 .LP |
| 1120 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
| 1121 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy. | |
| 1122 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''. | |
| 1123 It is pronounced the identical. | |
| 0 | 1124 |
| 1125 .NH 2 | |
| 32 | 1126 Historical background |
| 0 | 1127 .LP |
| 32 | 1128 Uzbl was started by Dieter Plaetinck in April 2009. |
| 1129 The idea was born in a thread in the Arch Linux forum. | |
| 1130 .[ | |
| 1131 %O http://bbs.archlinux.org/viewtopic.php?id=67463 | |
| 1132 .] | |
| 1133 After some discussion about failures of well known web browsers, | |
| 1134 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1135 of how a better web browser could look like. | |
| 1136 To the question of another member, if Plaetinck would write that program, | |
| 1137 because it would sound fantastic, Plaetinck replied: | |
| 1138 ``Maybe, if I find the time ;-)''. | |
| 1139 .PP | |
| 1140 Fortunately, he found the time. | |
| 1141 One day later, the first prototype was out. | |
| 1142 One week later, uzbl had an own website. | |
| 1143 One month after the first code showed up, | |
| 1144 a mailing list was installed to coordinate and discuss further development. | |
| 1145 A wiki was set up to store documentation and scripts that showed up on the | |
| 1146 mailing list and elsewhere. | |
| 1147 .PP | |
| 1148 In the, now, one year of uzbl's existance, it was heavily developed in various branches. | |
| 1149 Plaetinck's task became more and more to only merge the best code from the | |
| 1150 different branches into his main branch, and to apply patches. | |
| 1151 About once a month, Plaetinck released a new version. | |
| 1152 In September 2009, he presented several forks of uzbl. | |
| 1153 Uzbl, acutally, opened the field for a whole family of web browsers with similar shape. | |
| 1154 .PP | |
| 1155 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
| 1156 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
| 0 | 1157 |
| 1158 .NH 2 | |
| 32 | 1159 Contrasts to other web browsers |
| 0 | 1160 .LP |
| 32 | 1161 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1162 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1163 .PP | |
| 1164 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1165 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1166 It handles commands and events to interface other programs, | |
| 1167 and also displays webpages by using webkit as render engine. | |
| 1168 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, | |
| 1169 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1170 to form a ``complete'' web browser. | |
| 1171 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1172 so uzbl-core is included. | |
| 1173 .PP | |
| 1174 Unlike most other web browsers, uzbl is mainly the mediator between the | |
| 1175 various tools that cover single jobs of web browsing. | |
| 35 | 1176 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1177 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1178 The graphical rendering of the webpage is done by webkit, a web content engine. | |
| 1179 Uzbl-core is build around this library. | |
| 1180 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1181 .DS |
| 1182 .CW | |
| 1183 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1184 .DE | |
| 1185 .PP | |
| 1186 Downloads, browsing history, bookmarks, and thelike are not provided | |
| 1187 by uzbl-core itself, as they are in other web browsers. | |
| 35 | 1188 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1189 external applications which provide the actual functionality. | |
| 32 | 1190 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1191 includes a script that calls wget with appropriate options in | |
| 1192 a prepared environment. | |
| 1193 .PP | |
| 1194 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1195 This is their effort to achieve similar goals. | |
| 35 | 1196 But instead of using existing, external programs, modern web browsers |
| 1197 include these functions, although they might be loaded at runtime. | |
| 0 | 1198 |
| 1199 .NH 2 | |
| 32 | 1200 Discussion of the design |
| 0 | 1201 .LP |
| 32 | 1202 This section discusses uzbl in regard of the Unix Philosophy, |
| 1203 as identified by Gancarz. | |
| 1204 | |
| 1205 .PP | |
| 35 | 1206 .B "Make each program do one thing well" . |
| 1207 Uzbl tries to be a web browser and nothing else. | |
|
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1208 The common definition of a web browser is, of course, highly influenced by |
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1209 existing implementations of web browsers, although they are degenerated. |
| 35 | 1210 Web browsers should be programs to browse the web, and nothing more. |
| 1211 This is the one thing they should do, as demanded by the Unix Philosophy. | |
|
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1212 .PP |
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1213 Web browsers should, for instance, not manage downloads. |
| 35 | 1214 This is the job download managers exist for. |
| 1215 Download managers do primary care about being good in downloading files. | |
| 1216 Modern web browsers provide download management only as a secondary feature. | |
| 1217 How could they perform this job better, than programs that exist only for | |
| 1218 this very job? | |
| 1219 And how could anyone want less than the best download manager available? | |
| 32 | 1220 .PP |
| 35 | 1221 A web browser's job is to let the user browse the web. |
| 1222 This means, navigating through websites by following links. | |
|
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1223 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1224 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1225 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1226 are also not the job of a web browser. |
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1227 They should be handled by external applications \(en |
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1228 ones which's job is to handle such data. |
| 35 | 1229 Uzbl strives to do it this way. |
|
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1230 .PP |
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1231 Remember Doug McIlroy: |
| 35 | 1232 .I |
| 1233 ``Write programs that do one thing and do it well. | |
| 1234 Write programs to work together.'' | |
| 1235 .R | |
| 1236 .PP | |
| 1237 The lesser tenet | |
| 1238 .B "allow the user to tailor the environment | |
| 1239 matches good here. | |
| 1240 There was the question, how anyone could want anything less than the | |
| 1241 best program for the job. | |
|
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1242 But as personal preferences matter much, |
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1243 it is probably more important to ask: |
| 35 | 1244 How could anyone want something else than his preferred program for the job? |
|
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1245 .PP |
| 35 | 1246 Usually users want one program for one job. |
| 1247 Hence, whenever the task is, for instance, downloading, | |
|
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1248 exactly one download manager should be used. |
| 35 | 1249 More advanced users might want to have this download manager in this |
| 1250 situation and that one in that situation. | |
| 1251 They should be able to configure it this way. | |
| 1252 With uzbl, one can use any download manager the user wants. | |
|
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1253 To switch to a different one, only one line in a small handler script |
| 35 | 1254 needs to be changed. |
|
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1255 Alternatively it would be possible to query an entry in a global file |
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1256 or an environment variable, which specifies the download manager to use, |
| 35 | 1257 in the handler script. |
|
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1258 .PP |
| 35 | 1259 As uzbl does neither have its own download manager nor depends on a |
| 1260 specific one, thus uzbl's browsing abilities will not be lowered by having | |
| 1261 a bad download manager. | |
|
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1262 Uzbl's download capabilities will just as good as the ones of the best |
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1263 download manager available on the system. |
| 35 | 1264 Of course, this applies to all of the other supplimentary tools, too. |
| 32 | 1265 |
| 1266 .PP | |
|
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1267 .B "Use software leverage to your advantage" . |
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1268 Shell scripts are a good choice to extend uzbl. |
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1269 Uzbl is designed to be extended by external tools. |
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1270 These external tools are usually wrapped by small handler shell scripts. |
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1271 Shell scripts are the glue in this approach. |
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1272 They make the various parts fit together. |
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1273 .PP |
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1274 As an example, the history mechanism of uzbl shall be presented. |
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1275 Uzbl is configured to spawn a script to append an entry to the history |
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1276 whenever the event of a fully loaded page occurs. |
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1277 The script to append the entry to the history not much more than: |
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1278 .DS |
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1279 .CW |
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1280 #!/bin/sh |
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1281 file=/path/to/uzbl-history |
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1282 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1283 .DE |
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1284 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1285 For loading an entry, a key is bound to spawn a load from history script. |
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1286 The script reverses the history to have newer entries first, |
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1287 then displays \fIdmenu\fP to select an item, |
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1288 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
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1289 With error checking and corner cases removed, the script looks like this: |
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1290 .DS |
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1291 .CW |
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1292 #!/bin/sh |
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1293 file=/path/to/uzbl-history |
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1294 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1295 echo "uri $goto" > $4 |
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1296 .DE |
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1297 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1298 uzbl instance. |
| 32 | 1299 |
| 1300 .PP | |
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1301 .B "Avoid captive user interfaces" . |
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1302 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1303 a captive user interface. |
| 37 | 1304 But the difference to most other web browsers is, that uzbl is only |
| 1305 the captive user interface frontend and the core of the backend. | |
| 1306 Many parts of the backend are independed of uzbl. | |
| 1307 Some are distributed with uzbl, for some external programs, handler scripts | |
| 1308 are distributed, arbitrary additional functionality can be added if desired. | |
| 1309 .PP | |
| 1310 The frontend is captive \(en that is true. | |
| 1311 This is okay for the task of browsing the web, as this task is only relevant | |
| 1312 for humans. | |
| 1313 Automated programs would \fIcrawl\fP the web. | |
| 1314 That means, they read the source directly. | |
| 1315 The source includes all the semantics. | |
| 1316 The graphical representation is just for humans to transfer the semantics | |
| 1317 more intuitively. | |
| 32 | 1318 |
| 1319 .PP | |
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1320 .B "Make every program a filter" . |
| 37 | 1321 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1322 Thus it is difficult to see what graphical web browsers should filter. | |
| 1323 Graphical web browsers exist almost only for interactive use by humans. | |
| 1324 The only case when one might want to automate the rendering function is | |
| 1325 to generate images of rendered webpages. | |
| 1326 | |
| 1327 .PP | |
| 1328 .B "Small is beautiful" | |
| 1329 is not easy to apply to a web browser, primary because the rendering task | |
| 1330 is very complex. | |
| 1331 Modern web browsers will always consist of many thousand lines of code, | |
| 1332 unfortunately. | |
| 1333 Using the toolchest approach and wrappers can split the browser into | |
| 1334 several small parts, tough. | |
| 1335 .PP | |
| 1336 Uzbl-core consists of about 3\,500 lines of C code. | |
| 1337 The distribution includes another 3\,500 lines of Shell and Python code, | |
| 1338 which are the handler scripts and plugins like a modal interface. | |
| 1339 Further more, uzbl uses external tools like \fIwget\fP, \fInetcat\fP. | |
| 1340 Up to this point, uzbl looks pretty neat and small. | |
| 1341 The ugly part of uzbl is the web content renderer webkit. | |
| 1342 Webkit consists of roughly 400\,000 (!) lines of code. | |
| 35 | 1343 |
| 1344 .PP | |
| 1345 .B "Build a prototype as soon as possible" . | |
| 1346 Plaetinck made his code public, right from the beginning. | |
| 1347 Discussion and development was open to everyone interessted. | |
| 1348 Within this first year of uzbl's existance, a new version was released, | |
| 1349 more often than once a month. | |
| 1350 Development version can be optained very simply from the code repository. | |
| 1351 Different forks and branches arose, new features were tested for suitability. | |
| 1352 The experiences of using prototypes influenced further development. | |
| 1353 Actually, all development was community driven. | |
| 1354 Plaetinck says: | |
| 1355 ``Right now I hardly code anything myself for Uzbl. | |
| 1356 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1357 .[ | |
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1358 %A FIXME |
| 35 | 1359 %O http://lwn.net/Articles/341245/ |
| 1360 .] | |
| 32 | 1361 |
| 0 | 1362 |
| 1363 .NH 2 | |
| 1364 Problems | |
| 1365 .LP | |
| 1366 broken web | |
| 1367 | |
| 37 | 1368 .PP |
| 1369 But all functionality should be accessable at the backend too. | |
| 1370 Uzbl fails here, mainly because of webkit. | |
| 1371 Uzbl is not clearly separated into frontend and backend, | |
| 1372 especially the render engine is not an separate building part, | |
| 1373 like, for instance, the download manager is. | |
| 1374 This comes from the design of webkit. | |
| 1375 Webkit is not a self-standing program but a library to include. | |
| 1376 This might be of need for a graphical application to avoid complexity, | |
| 1377 but webkit has a lot of features included that do not belong to the | |
| 1378 webpage rendering job; a browsing history is just one example. | |
| 1379 .PP | |
| 1380 Ideally, webkit would just render the source of a webpage into a | |
| 1381 nice formated representation. | |
| 1382 .PP | |
| 1383 be a black box | |
| 1384 | |
| 1385 | |
| 8 | 1386 |
| 32 | 1387 .NH 2 |
| 1388 Summary uzbl | |
| 1389 .LP | |
| 1390 | |
| 1391 | |
| 8 | 1392 |
| 0 | 1393 .NH 1 |
| 1394 Final thoughts | |
| 1395 | |
| 1396 .NH 2 | |
| 1397 Quick summary | |
| 1398 .LP | |
| 1399 good design | |
| 1400 .LP | |
| 1401 unix phil | |
| 1402 .LP | |
| 1403 case studies | |
| 1404 | |
| 1405 .NH 2 | |
| 1406 Why people should choose | |
| 1407 .LP | |
| 1408 Make the right choice! | |
| 1409 | |
| 1410 .nr PI .5i | |
| 1411 .rm ]< | |
| 1412 .de ]< | |
| 1413 .LP | |
| 1414 .de FP | |
| 1415 .IP \\\\$1. | |
| 1416 \\.. | |
| 1417 .rm FS FE | |
| 1418 .. | |
| 1419 .SH | |
| 1420 References | |
| 1421 .[ | |
| 1422 $LIST$ | |
| 1423 .] | |
| 1424 .wh -1p |