Mercurial > docs > unix-phil
annotate unix-phil.ms @ 33:0bd43c4ad9f8
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| author | meillo@marmaro.de |
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| date | Thu, 25 Mar 2010 18:41:01 +0100 |
| parents | d632de027d77 |
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3 .\".nr VS 13 |
| 0 | 4 .de XX |
| 5 .pl 1v | |
| 6 .. | |
| 7 .em XX | |
| 1 | 8 .\".nr PI 0 |
| 9 .\".if t .nr PD .5v | |
| 10 .\".if n .nr PD 1v | |
| 0 | 11 .nr lu 0 |
| 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 |
| 17 | 17 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2 |
| 0 | 18 .if n .if \\n(.$=1 \&\\$1 |
| 19 .if n .if \\n(.$>1 \&\\$1\c | |
| 20 .if n .if \\n(.$>1 \&\\$2 | |
| 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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38 |
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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 | |
| 19 | 811 \s-1MH\s0's mail storage is (only little more than) a directory tree |
| 23 | 812 where mail folders are directories and mail messages are text files. |
| 19 | 813 Working with \s-1MH\s0's toolchest is much like working |
| 814 with Unix' toolchest: | |
| 815 \f(CWscan\fP is like \f(CWls\fP, | |
| 816 \f(CWshow\fP is like \f(CWcat\fP, | |
| 30 | 817 \f(CWfolder\fP is like \f(CWcd\fP/\f(CWpwd\fP, |
| 19 | 818 \f(CWrefile\fP is like \f(CWmv\fP, |
| 819 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 820 .PP | |
| 23 | 821 The context of tools in Unix is mainly the current working directory, |
| 19 | 822 the user identification, and the environment variables. |
| 823 \s-1MH\s0 extends this context by two more items: | |
| 23 | 824 .IP \(bu |
| 825 The current mail folder, which is similar to the current working directory. | |
| 826 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 827 of \f(CWpwd\fP and \f(CWcd\fP for directories. | |
| 828 .IP \(bu | |
| 829 The current message, relative to the current mail folder, | |
| 20 | 830 which enables commands like \f(CWnext\fP and \f(CWprev\fP. |
| 23 | 831 .LP |
| 19 | 832 In contrast to Unix' context, which is chained to the shell session, |
| 833 \s-1MH\s0's context is meant to be chained to a mail account. | |
| 20 | 834 But actually, the current message is a property of the mail folder, |
| 23 | 835 which appears to be a legacy. |
| 20 | 836 This will cause problems when multiple users work |
| 837 in one mail folder simultaneously. | |
| 30 | 838 .PP |
| 839 .I "Data storage. | |
| 840 How \s-1MH\s0 stores data was already mentioned. | |
| 841 Mail folders are directories (which contain a file | |
| 842 \&\f(CW.mh_sequences\fP) under the user's \s-1MH\s0 directory | |
| 843 (usually \f(CW$HOME/Mail\fP). | |
| 844 Mail messages are text files located in mail folders. | |
| 845 The files contain the messages as they were received. | |
| 846 The messages are numbered in ascending order in each folder. | |
| 847 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. | |
| 848 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 849 In the mbox format all messages are stored within one file. | |
| 850 This was a good solution in the early days, when messages | |
| 851 were only a few lines of text and were deleted soon. | |
| 852 Today, when single messages often include several megabytes | |
| 853 of attachments, it is a bad solution. | |
| 854 Another disadvantage of the mbox format is that it is | |
| 855 more difficult to write tools that work on mail messages, | |
| 856 because it is always necessary to first find and extract | |
| 857 the relevant message in the mbox file. | |
| 858 With the \s-1MH\s0 mailbox format, | |
| 859 each message is a self-standing item, by definition. | |
| 860 Also, the problem of concurrent access to one mailbox is | |
| 861 reduced to the problem of concurrent access to one message. | |
| 862 However, the issue of the shared parts of the context, | |
| 863 as mentioned above, remains. | |
| 864 Maildir is generally similar to \s-1MH\s0's format, | |
| 865 but modified towards guaranteed reliability. | |
| 866 This involves some complexity, unfortunately. | |
| 0 | 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 | |
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911 .B "Store data in flat text files" . |
| 30 | 912 FIXME |
| 20 | 913 |
| 914 .PP | |
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915 .B "Avoid captive user interfaces" . |
| 19 | 916 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 917 It offers all functions directly and without captive user interfaces. | |
| 30 | 918 If, nonetheless, users want a graphical user interface, |
| 20 | 919 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
| 19 | 920 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 921 This means, all email-related work is still done by \s-1MH\s0 tools, | |
| 20 | 922 but the frontend issues the appropriate calls when the user |
| 30 | 923 clicks on buttons. |
| 20 | 924 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 925 approach, because it does not limit the power of the backend itself. |
| 20 | 926 The frontend will anyway only be able to make a subset of the |
| 23 | 927 backend's power and flexibility available to the user. |
| 20 | 928 But if it is a separate program, |
| 929 then the missing parts can still be accessed at the backend directly. | |
| 19 | 930 If it is integrated, then this will hardly be possible. |
| 30 | 931 Further more, it is possible to have different frontends to the same |
| 932 backend. | |
| 19 | 933 |
| 934 .PP | |
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935 .B "Choose portability over efficiency |
| 20 | 936 and |
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937 .B "use shell scripts to increase leverage and portability" . |
| 20 | 938 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 939 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 940 .[ |
| 941 %T The KornShell: command and programming language | |
| 942 %A Morris I. Bolsky | |
| 943 %A David G. Korn | |
| 944 %I Prentice Hall | |
| 945 %D 1989 | |
| 30 | 946 %P 254\(en290 |
| 20 | 947 %O \s-1ISBN\s0: 0-13-516972-0 |
| 948 .] | |
| 30 | 949 They demonstrated, in chapter 18 of the book, a basic implementation |
| 20 | 950 of a subset of \s-1MH\s0 in ksh scripts. |
| 951 Of course, this was just a demonstration, but a brilliant one. | |
| 952 It shows how quickly one can implement such a prototype with shell scripts, | |
| 953 and how readable they are. | |
| 954 The implementation in the scripting language may not be very fast, | |
| 955 but it can be fast enough though, and this is all that matters. | |
| 956 By having the code in an interpreted language, like the shell, | |
| 957 portability becomes a minor issue, if we assume the interpreter | |
| 958 to be widespread. | |
| 959 This demonstration also shows how easy it is to create single programs | |
| 960 of a toolchest software. | |
| 30 | 961 There are eight tools (two of them have multiple names) and 16 functions |
| 962 with supporting code. | |
| 963 Each tool comprises between 12 and 38 lines of ksh, | |
| 964 in total about 200 lines. | |
| 965 The functions comprise between 3 and 78 lines of ksh, | |
| 966 in total about 450 lines. | |
| 20 | 967 Such small software is easy to write, easy to understand, |
| 968 and thus easy to maintain. | |
| 23 | 969 A toolchest improves the possibility to only write some parts |
| 20 | 970 and though create a working result. |
| 971 Expanding the toolchest without global changes will likely be | |
| 972 possible, too. | |
| 973 | |
| 974 .PP | |
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975 .B "Use software leverage to your advantage |
| 20 | 976 and the lesser tenet |
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977 .B "allow the user to tailor the environment |
| 20 | 978 are ideally followed in the design of \s-1MH\s0. |
| 21 | 979 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 980 directly define default options to programs. |
| 981 It is even possible to define different default options | |
| 21 | 982 depending on the name under which the program was called. |
| 983 Software leverage is heavily encouraged by the ease it is to | |
| 984 create shell scripts that run a specific command line, | |
| 30 | 985 built of several \s-1MH\s0 programs. |
| 21 | 986 There is few software that so much wants users to tailor their |
| 987 environment and to leverage the use of the software, like \s-1MH\s0. | |
| 988 Just to make one example: | |
| 23 | 989 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 990 program. |
| 30 | 991 It is possible to take one of the distributed format files |
| 21 | 992 or to write one yourself. |
| 993 To use the format as default for \f(CWscan\fP, a single line, | |
| 994 reading | |
| 995 .DS | |
| 996 .CW | |
| 997 scan: -form FORMATFILE | |
| 998 .DE | |
| 999 must be added to \f(CW.mh_profile\fP. | |
| 1000 If one wants this different format as an additional command, | |
| 23 | 1001 instead of changing the default, he needs to create a link to |
| 1002 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1003 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
| 30 | 1004 as the option should only be in effect when scan is called as |
| 21 | 1005 \f(CWscan2\fP. |
| 20 | 1006 |
| 1007 .PP | |
|
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1008 .B "Make every program a filter |
| 21 | 1009 is hard to find in \s-1MH\s0. |
| 1010 The reason therefore is that most of \s-1MH\s0's tools provide | |
| 1011 basic file system operations for the mailboxes. | |
| 30 | 1012 The reason is the same because of which |
| 21 | 1013 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP |
| 1014 aren't filters neither. | |
| 23 | 1015 However, they build a basis on which filters can operate. |
| 1016 \s-1MH\s0 does not provide many filters itself, but it is a basis | |
| 1017 to write filters for. | |
| 30 | 1018 An example would be a mail message text highlighter, |
| 1019 that means a program that makes use of a color terminal to display | |
| 1020 header lines, quotations, and signatures in distinct colors. | |
| 1021 The author's version of this program, for instance, | |
| 1022 is a 25 line awk script. | |
| 21 | 1023 |
| 1024 .PP | |
|
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1025 .B "Build a prototype as soon as possible |
| 21 | 1026 was again well followed by \s-1MH\s0. |
| 1027 This tenet, of course, focuses on early development, which is | |
| 1028 long time ago for \s-1MH\s0. | |
| 1029 But without following this guideline at the very beginning, | |
| 23 | 1030 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1031 to ever create \s-1MH\s0. | |
| 1032 In Bruce' own words: | |
| 21 | 1033 .QP |
| 30 | 1034 [...] but they [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1035 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1036 I proposed a very short project to prove the basic concepts, |
| 1037 and my management agreed. | |
| 1038 Looking back, I realize that I had been very lucky with my first design. | |
| 1039 Without nearly enough design work, | |
| 1040 I built a working environment and some header files | |
| 1041 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1042 inc, show/next/prev, and comp. | |
| 1043 [...] | |
| 1044 With these three, I was able to convince people that the structure was viable. | |
| 1045 This took about three weeks. | |
| 1046 .[ | |
| 1047 %O FIXME | |
| 1048 .] | |
| 0 | 1049 |
| 1050 .NH 2 | |
| 1051 Problems | |
| 1052 .LP | |
| 22 | 1053 \s-1MH\s0, for sure is not without problems. |
| 30 | 1054 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1055 .PP |
| 1056 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1057 when \s-1MH\s0 was designed. | |
| 1058 \s-1MH\s0 adopted to the changes pretty well, but it is limited. | |
| 1059 For example in development resources. | |
| 1060 \s-1MIME\s0 support and support for different character encodings | |
| 1061 is available, but only on a moderate level. | |
| 1062 More active developers could quickly improve there. | |
| 1063 It is also limited by design, which is the larger problem. | |
| 1064 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. | |
| 1065 These design conflicts are not easily solvable. | |
| 1066 Possibly, they require a redesign. | |
| 30 | 1067 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers, |
| 1068 hence \s-1MH\s0 may never work well with \s-1IMAP\s0. | |
| 22 | 1069 .PP |
| 1070 The other kind of problem is human habits. | |
| 1071 When in this world almost all \s-1MUA\s0s are monolithic, | |
| 1072 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 | |
| 1073 like \s-1MH\s0. | |
| 1074 The habits are so strong, that even people who understood the concept | |
| 30 | 1075 and advantages of \s-1MH\s0 do not like to switch, |
| 1076 simply because \s-1MH\s0 is different. | |
| 1077 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
| 1078 are quite outdated and thus not very appealing compared to the modern interfaces | |
| 1079 which monolithic \s-1MUA\s0s offer. | |
| 20 | 1080 |
| 1081 .NH 2 | |
| 1082 Summary \s-1MH\s0 | |
| 1083 .LP | |
| 31 | 1084 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design |
| 1085 and implementation. | |
| 1086 It consists of a toolchest of small tools, each of them does one job well. | |
| 1087 The tools are orthogonal to each other, to a large extend. | |
| 1088 However, for historical reasons, there also exist distinct tools | |
| 1089 that cover the same task. | |
| 1090 .PP | |
| 1091 The toolchest approach offers great flexibility to the user. | |
| 1092 He can use the complete power of the Unix shell with \s-1MH\s0. | |
| 1093 This makes \s-1MH\s0 a very powerful mail system. | |
| 1094 Extending and customizing \s-1MH\s0 is easy and encouraged, too. | |
| 1095 .PP | |
| 1096 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1097 Its overall design follows clear rules. | |
| 1098 The single tools do only one job, thus they are easy to understand, | |
| 1099 easy to write, and good to maintain. | |
| 1100 They are all independent and do not interfere with the others. | |
| 1101 Automated testing of their function is a straight forward task. | |
| 1102 .PP | |
| 1103 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1104 as its differentness is also its largest advantage. | |
| 1105 Unfortunately, for most people their habits are stronger | |
| 1106 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1107 |
| 8 | 1108 |
| 1109 | |
| 0 | 1110 .NH 1 |
| 1111 Case study: uzbl | |
| 32 | 1112 .LP |
| 1113 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
| 1114 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy. | |
| 1115 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''. | |
| 1116 It is pronounced the identical. | |
| 0 | 1117 |
| 1118 .NH 2 | |
| 32 | 1119 Historical background |
| 0 | 1120 .LP |
| 32 | 1121 Uzbl was started by Dieter Plaetinck in April 2009. |
| 1122 The idea was born in a thread in the Arch Linux forum. | |
| 1123 .[ | |
| 1124 %O http://bbs.archlinux.org/viewtopic.php?id=67463 | |
| 1125 .] | |
| 1126 After some discussion about failures of well known web browsers, | |
| 1127 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1128 of how a better web browser could look like. | |
| 1129 To the question of another member, if Plaetinck would write that program, | |
| 1130 because it would sound fantastic, Plaetinck replied: | |
| 1131 ``Maybe, if I find the time ;-)''. | |
| 1132 .PP | |
| 1133 Fortunately, he found the time. | |
| 1134 One day later, the first prototype was out. | |
| 1135 One week later, uzbl had an own website. | |
| 1136 One month after the first code showed up, | |
| 1137 a mailing list was installed to coordinate and discuss further development. | |
| 1138 A wiki was set up to store documentation and scripts that showed up on the | |
| 1139 mailing list and elsewhere. | |
| 1140 .PP | |
| 1141 In the, now, one year of uzbl's existance, it was heavily developed in various branches. | |
| 1142 Plaetinck's task became more and more to only merge the best code from the | |
| 1143 different branches into his main branch, and to apply patches. | |
| 1144 About once a month, Plaetinck released a new version. | |
| 1145 In September 2009, he presented several forks of uzbl. | |
| 1146 Uzbl, acutally, opened the field for a whole family of web browsers with similar shape. | |
| 1147 .PP | |
| 1148 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
| 1149 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
| 0 | 1150 |
| 1151 .NH 2 | |
| 32 | 1152 Contrasts to other web browsers |
| 0 | 1153 .LP |
| 32 | 1154 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1155 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1156 .PP | |
| 1157 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1158 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1159 It handles commands and events to interface other programs, | |
| 1160 and also displays webpages by using webkit as render engine. | |
| 1161 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, | |
| 1162 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1163 to form a ``complete'' web browser. | |
| 1164 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1165 so uzbl-core is included. | |
| 1166 .PP | |
| 1167 Unlike most other web browsers, uzbl is mainly the mediator between the | |
| 1168 various tools that cover single jobs of web browsing. | |
| 1169 Uzbl listens for commands on a named pipe (fifo), a Unix socket, and on stdin. | |
| 1170 It writes events to a Unix socket and to stdout. | |
| 1171 Loading a webpage in a running uzbl instance requires not more than: | |
| 1172 .DS | |
| 1173 .CW | |
| 1174 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1175 .DE | |
| 1176 The graphical rendering of the webpage is done by webkit, | |
| 1177 which is a library that cares about the whole rendering task. | |
| 1178 .PP | |
| 1179 Downloads, browsing history, bookmarks, and thelike are not provided | |
| 1180 by uzbl-core itself, as they are in other web browsers. | |
| 1181 Uzbl-browser only provides, so called, handler scripts that wrap | |
| 1182 external applications which provide such function. | |
| 1183 For instance, \fIwget\fP is used to download files and uzbl-browser | |
| 1184 includes a script that calls wget with appropriate options in | |
| 1185 a prepared environment. | |
| 1186 .PP | |
| 1187 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1188 This is their effort to achieve similar goals. | |
| 1189 But instead of using existing, external programs, the functions are | |
| 1190 integrated into the web browser, just not compiled into it. | |
| 0 | 1191 |
| 1192 .NH 2 | |
| 32 | 1193 Discussion of the design |
| 0 | 1194 .LP |
| 32 | 1195 This section discusses uzbl in regard of the Unix Philosophy, |
| 1196 as identified by Gancarz. | |
| 1197 | |
| 1198 .PP | |
|
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1199 .B "Small is beautiful |
| 32 | 1200 and |
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1201 .B "make each program do one thing well" . |
| 32 | 1202 |
| 1203 .PP | |
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1204 .B "Build a prototype as soon as possible" . |
| 32 | 1205 |
| 1206 .PP | |
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1207 .B "Use software leverage to your advantage |
| 32 | 1208 and |
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1209 .B "Use shell scripts to increase leverage and portability" . |
| 32 | 1210 |
| 1211 .PP | |
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1212 .B "Avoid captive user interfaces" . |
| 32 | 1213 |
| 1214 .PP | |
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1215 .B "Make every program a filter" . |
| 32 | 1216 |
| 0 | 1217 |
| 1218 .NH 2 | |
| 1219 Problems | |
| 1220 .LP | |
| 1221 broken web | |
| 1222 | |
| 8 | 1223 |
| 32 | 1224 .NH 2 |
| 1225 Summary uzbl | |
| 1226 .LP | |
| 1227 | |
| 1228 | |
| 8 | 1229 |
| 0 | 1230 .NH 1 |
| 1231 Final thoughts | |
| 1232 | |
| 1233 .NH 2 | |
| 1234 Quick summary | |
| 1235 .LP | |
| 1236 good design | |
| 1237 .LP | |
| 1238 unix phil | |
| 1239 .LP | |
| 1240 case studies | |
| 1241 | |
| 1242 .NH 2 | |
| 1243 Why people should choose | |
| 1244 .LP | |
| 1245 Make the right choice! | |
| 1246 | |
| 1247 .nr PI .5i | |
| 1248 .rm ]< | |
| 1249 .de ]< | |
| 1250 .LP | |
| 1251 .de FP | |
| 1252 .IP \\\\$1. | |
| 1253 \\.. | |
| 1254 .rm FS FE | |
| 1255 .. | |
| 1256 .SH | |
| 1257 References | |
| 1258 .[ | |
| 1259 $LIST$ | |
| 1260 .] | |
| 1261 .wh -1p |