Mercurial > docs > unix-phil
annotate unix-phil.ms @ 47:b6ae4a8ab1d3
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| author | meillo@marmaro.de |
|---|---|
| date | Mon, 12 Apr 2010 14:11:39 +0200 |
| parents | 98a1446744c7 |
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| 0 | 5 .de CW |
| 6 .nr PQ \\n(.f | |
| 7 .if t .ft CW | |
| 17 | 8 .ie ^\\$1^^ .if n .ul 999 |
| 0 | 9 .el .if n .ul 1 |
| 17 | 10 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2 |
| 0 | 11 .if n .if \\n(.$=1 \&\\$1 |
| 12 .if n .if \\n(.$>1 \&\\$1\c | |
| 13 .if n .if \\n(.$>1 \&\\$2 | |
| 14 .. | |
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| 0 | 16 .ds [. \ [ |
| 17 .ds .] ] | |
| 42 | 18 |
| 19 .rn NH _N | |
| 20 .de NH | |
| 21 .if '\\$1'1' .sp 2v | |
| 22 .if '\\$1'1' .nr PS +2 | |
| 23 ._N \\$1 | |
| 24 .if '\\$1'1' .nr PS -2 | |
| 25 .. | |
| 26 | |
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27 .am QP |
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31 .am DS |
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32 .CW |
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35 |
| 1 | 36 .\"---------------------------------------- |
| 42 | 37 |
| 0 | 38 .TL |
| 42 | 39 .ps +4 |
| 6 | 40 Why the Unix Philosophy still matters |
| 0 | 41 .AU |
| 42 markus schnalke <meillo@marmaro.de> | |
| 43 .AB | |
| 1 | 44 .ti \n(.iu |
| 39 | 45 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 46 Today, few software designers are aware of these concepts, |
| 39 | 47 and thus a lot of modern software is more limited than necessary |
| 48 and makes less use of software leverage than possible. | |
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49 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 50 .AE |
| 51 | |
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52 .FS |
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53 .ps -1 |
| 39 | 54 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
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55 Mentor was professor Franz Schweiggert. |
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56 Handed in on 2010-04-12. |
| 39 | 57 You may retrieve this document from |
| 58 .CW \s-1http://marmaro.de/docs \ . | |
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59 .FE |
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60 |
| 0 | 61 .NH 1 |
| 62 Introduction | |
| 42 | 63 .XS |
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64 .sp .5v |
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65 .B |
| 42 | 66 \*(SN Introduction |
| 67 .XE | |
| 0 | 68 .LP |
| 40 | 69 The Unix Philosophy is the essence of how the Unix operating system, |
| 70 especially its toolchest, was designed. | |
| 71 It is no limited set of fixed rules, | |
| 72 but a loose set of guidelines which tell how to write software that | |
| 73 suites well into Unix. | |
| 74 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 75 The Wikipedia has an accurate definition: | |
| 76 .[ | |
| 44 | 77 wikipedia |
| 78 unix philosophy | |
| 40 | 79 .] |
| 80 .QP | |
| 81 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 82 approaches to developing software based on the experience of leading | |
| 83 developers of the Unix operating system. | |
| 3 | 84 .PP |
| 40 | 85 As there is no single definition of the Unix Philosophy, |
| 86 several people have stated their view on what it comprises. | |
| 1 | 87 Best known are: |
| 88 .IP \(bu | |
| 89 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 90 .[ | |
| 44 | 91 mahoney |
| 92 oral history | |
| 1 | 93 .] |
| 94 .IP \(bu | |
| 95 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 96 .[ | |
| 44 | 97 gancarz |
| 98 unix philosophy | |
| 1 | 99 .] |
| 100 .IP \(bu | |
| 101 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 102 .[ | |
| 44 | 103 raymond |
| 104 art of unix programming | |
| 1 | 105 .] |
| 0 | 106 .LP |
| 1 | 107 These different views on the Unix Philosophy have much in common. |
| 40 | 108 Especially, the main concepts are similar in all of them. |
| 109 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 110 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 111 | |
| 112 .PP | |
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113 The Unix Philosophy explains how to design good software for Unix. |
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114 Many concepts described here, base on facilities of Unix. |
| 40 | 115 Other operating systems may not offer such facilities, |
| 41 | 116 hence it may not be possible to design software in the way of the |
| 117 Unix Philosophy for them. | |
| 118 .PP | |
| 119 The Unix Philosophy has an idea of how the process of software development | |
| 120 should look like, but large parts of the philosophy are quite independent | |
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121 from a concrete development process. |
| 41 | 122 However, one will soon recognize that some development processes work well |
| 123 with the ideas of the Unix Philosophy and support them, while others are | |
| 124 at cross-purposes. | |
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125 Kent Beck's books about Extreme Programming are valuable supplemental |
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126 resources on this topic. |
| 40 | 127 .PP |
| 41 | 128 The question of how to actually write code and how the code should looks |
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129 like in detail, are out of focus here. |
| 41 | 130 ``The Practice of Programming'' by Kernighan and Pike, |
| 131 .[ | |
| 44 | 132 kernighan pike |
| 133 practice of programming | |
| 41 | 134 .] |
| 135 is a good book that covers this topic. | |
| 136 Its point of view matches to the one of this paper. | |
| 0 | 137 |
| 138 .NH 1 | |
| 6 | 139 Importance of software design in general |
| 42 | 140 .XS |
| 141 .sp .5v | |
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142 .B |
| 42 | 143 \*(SN Importance of software design in general |
| 144 .XE | |
| 0 | 145 .LP |
| 40 | 146 Software design is the planning of how the internal structure |
| 147 and external interfaces of a software should look like. | |
| 39 | 148 It has nothing to do with visual appearance. |
| 149 If we take a program as a car, then its color is of no matter. | |
| 150 Its design would be the car's size, its shape, the locations of doors, | |
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151 the passenger/space ratio, the available controls and instruments, |
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152 and so forth. |
| 39 | 153 .PP |
| 154 Why should software get designed at all? | |
| 6 | 155 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 156 Not designing software means programming without plan. |
| 157 This will pretty sure lead to horrible results. | |
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158 Software that is horrible to use and horrible to maintain. |
| 39 | 159 These two aspects are the visible ones. |
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160 Often invisible though, are the wasted possible gains. |
| 39 | 161 Good software design can make these gains available. |
| 6 | 162 .PP |
| 39 | 163 A software's design deals with quality properties. |
| 164 Good design leads to good quality, and quality is important. | |
| 165 Any car may be able to drive from A to B, | |
| 166 but it depends on the car's properties whether it is a good choice | |
| 167 for passenger transport or not. | |
| 168 It depends on its properties if it is a good choice | |
| 169 for a rough mountain area. | |
| 170 And it depends on its properties if the ride will be fun. | |
| 171 | |
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172 .PP |
| 39 | 173 Requirements for a software are twofold: |
| 174 functional and non-functional. | |
| 175 .IP \(bu | |
| 176 Functional requirements define directly the software's functions. | |
| 177 They are the reason why software gets written. | |
| 178 Someone has a problem and needs a tool to solve it. | |
| 179 Being able to solve the problem is the main functional goal. | |
| 180 It is the driving force behind all programming effort. | |
| 6 | 181 Functional requirements are easier to define and to verify. |
| 39 | 182 .IP \(bu |
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183 Non-functional requirements are called \fIquality\fP requirements, too. |
| 39 | 184 The quality of a software are the properties that are not directly related to |
| 185 the software's basic functions. | |
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186 Tools of bad quality often do solve the problems they were written for, |
| 39 | 187 but introduce problems and difficulties for usage and development, later on. |
| 188 Quality aspects are often overlooked at first sight, | |
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189 and are often difficult to define clearly and to verify. |
| 6 | 190 .PP |
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191 Quality is hardly interesting when the software gets built initially, |
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192 but it has a high impact on usability and maintenance of the software, later. |
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193 A short-sighted might see in developing a software, mainly building something up. |
| 39 | 194 But experience shows, that building the software the first time is |
| 195 only a small amount of the overall work. | |
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196 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en |
| 6 | 197 does soon take over the major part of the time spent on a software. |
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198 And of course, the time spent actually using the software. |
| 6 | 199 These processes are highly influenced by the software's quality. |
| 39 | 200 Thus, quality must not be neglected. |
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201 However, the problem with quality is that you hardly ``stumble over'' |
| 39 | 202 bad quality during the first build, |
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203 although this is the time when you should care about good quality most. |
| 6 | 204 .PP |
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205 Software design has little to do with the basic function of a software \(en |
| 39 | 206 this requirement will get satisfied anyway. |
| 207 Software design is more about quality aspects of the software. | |
| 208 Good design leads to good quality, bad design to bad quality. | |
| 6 | 209 The primary functions of the software will be affected modestly by bad quality, |
| 39 | 210 but good quality can provide a lot of additional gain, |
| 6 | 211 even at places where one never expected it. |
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212 .PP |
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213 The ISO/IEC\|9126-1 standard, part\|1, |
| 6 | 214 .[ |
| 44 | 215 iso product quality |
| 6 | 216 .] |
| 217 defines the quality model as consisting out of: | |
| 218 .IP \(bu | |
| 219 .I Functionality | |
| 220 (suitability, accuracy, inter\%operability, security) | |
| 221 .IP \(bu | |
| 222 .I Reliability | |
| 223 (maturity, fault tolerance, recoverability) | |
| 224 .IP \(bu | |
| 225 .I Usability | |
| 226 (understandability, learnability, operability, attractiveness) | |
| 227 .IP \(bu | |
| 228 .I Efficiency | |
| 9 | 229 (time behavior, resource utilization) |
| 6 | 230 .IP \(bu |
| 231 .I Maintainability | |
| 23 | 232 (analyzability, changeability, stability, testability) |
| 6 | 233 .IP \(bu |
| 234 .I Portability | |
| 235 (adaptability, installability, co-existence, replaceability) | |
| 236 .LP | |
| 39 | 237 Good design can improve these properties of a software, |
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238 bad designed software likely suffers in these points. |
| 7 | 239 .PP |
| 240 One further goal of software design is consistency. | |
| 241 Consistency eases understanding, working on, and using things. | |
| 39 | 242 Consistent internal structure and consistent interfaces to the outside |
| 243 can be provided by good design. | |
| 7 | 244 .PP |
| 39 | 245 Software should be well designed because good design avoids many |
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246 problems during a software's lifetime. |
| 39 | 247 And software should be well designed because good design can offer |
| 248 much additional gain. | |
| 249 Indeed, much effort should be spent into good design to make software more valuable. | |
| 250 The Unix Philosophy shows a way of how to design software well. | |
| 7 | 251 It offers guidelines to achieve good quality and high gain for the effort spent. |
| 0 | 252 |
| 253 | |
| 254 .NH 1 | |
| 255 The Unix Philosophy | |
| 42 | 256 .XS |
| 257 .sp .5v | |
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258 .B |
| 42 | 259 \*(SN The Unix Philosophy |
| 260 .XE | |
| 4 | 261 .LP |
| 262 The origins of the Unix Philosophy were already introduced. | |
| 8 | 263 This chapter explains the philosophy, oriented on Gancarz, |
| 264 and shows concrete examples of its application. | |
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265 |
| 16 | 266 .NH 2 |
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267 Pipes |
| 42 | 268 .XS |
| 269 \*(SN Pipes | |
| 270 .XE | |
| 0 | 271 .LP |
| 4 | 272 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 273 Knowledge of using the Unix shell is assumed. | |
| 274 .PP | |
| 275 Counting the number of files in the current directory: | |
| 41 | 276 .DS |
| 4 | 277 ls | wc -l |
| 278 .DE | |
| 279 The | |
| 280 .CW ls | |
| 281 command lists all files in the current directory, one per line, | |
| 282 and | |
| 283 .CW "wc -l | |
| 8 | 284 counts the number of lines. |
| 4 | 285 .PP |
| 8 | 286 Counting the number of files that do not contain ``foo'' in their name: |
| 41 | 287 .DS |
| 4 | 288 ls | grep -v foo | wc -l |
| 289 .DE | |
| 290 Here, the list of files is filtered by | |
| 291 .CW grep | |
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292 to remove all lines that contain ``foo''. |
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293 The rest equals the previous example. |
| 4 | 294 .PP |
| 295 Finding the five largest entries in the current directory. | |
| 41 | 296 .DS |
| 4 | 297 du -s * | sort -nr | sed 5q |
| 298 .DE | |
| 299 .CW "du -s * | |
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300 returns the recursively summed sizes of all files in the current directory |
| 8 | 301 \(en no matter if they are regular files or directories. |
| 4 | 302 .CW "sort -nr |
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303 sorts the list numerically in reverse order (descending). |
| 4 | 304 Finally, |
| 305 .CW "sed 5q | |
| 306 quits after it has printed the fifth line. | |
| 307 .PP | |
| 308 The presented command lines are examples of what Unix people would use | |
| 309 to get the desired output. | |
| 310 There are also other ways to get the same output. | |
| 311 It's a user's decision which way to go. | |
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312 .PP |
| 8 | 313 The examples show that many tasks on a Unix system |
| 4 | 314 are accomplished by combining several small programs. |
| 315 The connection between the single programs is denoted by the pipe operator `|'. | |
| 316 .PP | |
| 317 Pipes, and their extensive and easy use, are one of the great | |
| 318 achievements of the Unix system. | |
| 319 Pipes between programs have been possible in earlier operating systems, | |
| 320 but it has never been a so central part of the concept. | |
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321 When, in the early seventies, Doug McIlroy introduced pipes into the |
| 4 | 322 Unix system, |
| 323 ``it was this concept and notation for linking several programs together | |
| 324 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 325 .[ | |
| 44 | 326 aughenbaugh |
| 327 unix oral history | |
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328 .] |
| 4 | 329 .PP |
| 330 Being able to specify pipelines in an easy way is, | |
| 331 however, not enough by itself. | |
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332 It is only one half. |
| 4 | 333 The other is the design of the programs that are used in the pipeline. |
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334 They need interfaces that allow them to be used in such a way. |
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335 |
| 16 | 336 .NH 2 |
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337 Interface design |
| 42 | 338 .XS |
| 339 \*(SN Interface design | |
| 340 .XE | |
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341 .LP |
| 11 | 342 Unix is, first of all, simple \(en Everything is a file. |
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343 Files are sequences of bytes, without any special structure. |
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344 Programs should be filters, which read a stream of bytes from standard input (stdin) |
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345 and write a stream of bytes to standard output (stdout). |
| 8 | 346 If the files \fIare\fP sequences of bytes, |
| 347 and the programs \fIare\fP filters on byte streams, | |
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348 then there is exactly one data interface. |
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349 Hence it is possible to combine programs in any desired way. |
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350 .PP |
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351 Even a handful of small programs yields a large set of combinations, |
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352 and thus a large set of different functions. |
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353 This is leverage! |
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354 If the programs are orthogonal to each other \(en the best case \(en |
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355 then the set of different functions is greatest. |
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356 .PP |
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357 Programs can also have a separate control interface, |
| 11 | 358 besides their data interface. |
| 359 The control interface is often called ``user interface'', | |
| 360 because it is usually designed to be used by humans. | |
| 361 The Unix Philosophy discourages to assume the user to be human. | |
| 362 Interactive use of software is slow use of software, | |
| 363 because the program waits for user input most of the time. | |
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364 Interactive software requires the user to be in front of the computer. |
| 11 | 365 Interactive software occupy the user's attention while they are running. |
| 366 .PP | |
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367 Now to come back to the idea of combining several small programs, |
| 11 | 368 to have a more specific function. |
| 369 If these single tools would all be interactive, | |
| 370 how would the user control them? | |
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371 It is not only a problem to control several programs at once, |
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372 if they run at the same time, |
| 11 | 373 it also very inefficient to have to control each of the single programs |
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374 that are intended to act as one large program. |
| 11 | 375 Hence, the Unix Philosophy discourages programs to demand interactive use. |
| 376 The behavior of programs should be defined at invocation. | |
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377 This is done by specifying arguments to the program call |
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378 (command line switches). |
| 11 | 379 Gancarz discusses this topic as ``avoid captive user interfaces''. |
| 46 | 380 .[ [ |
| 44 | 381 gancarz unix philosophy |
| 46 | 382 .], page 88 ff.] |
| 11 | 383 .PP |
| 384 Non-interactive use is, during development, also an advantage for testing. | |
| 385 Testing of interactive programs is much more complicated, | |
| 386 than testing of non-interactive programs. | |
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387 |
| 16 | 388 .NH 2 |
| 8 | 389 The toolchest approach |
| 42 | 390 .XS |
| 391 \*(SN The toolchest approach | |
| 392 .XE | |
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393 .LP |
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394 A toolchest is a set of tools. |
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395 Instead of having one big tool for all tasks, one has many small tools, |
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396 each for one task. |
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397 Difficult tasks are solved by combining several of the small, simple tools. |
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398 .PP |
| 11 | 399 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 400 that are filters on byte streams. | |
| 401 They are, to a large extend, unrelated in their function. | |
| 402 Hence, the Unix toolchest provides a large set of functions | |
| 403 that can be accessed by combining the programs in the desired way. | |
| 404 .PP | |
| 405 There are also advantages for developing small toolchest programs. | |
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406 It is easier and less error-prone to write small programs. |
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407 It is also easier and less error-prone to write a large set of small programs, |
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408 than to write one large program with all the functionality included. |
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409 If the small programs are combinable, then they offer even a larger set |
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410 of functions than the single large program. |
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411 Hence, one gets two advantages out of writing small, combinable programs: |
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412 They are easier to write and they offer a greater set of functions through |
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413 combination. |
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414 .PP |
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415 But there are also two main drawbacks of the toolchest approach. |
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416 First, one simple, standardized interface has to be sufficient. |
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417 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 418 then a different approach might be of need. |
| 13 | 419 But it is also possible, that he just can not imagine a design where |
| 8 | 420 a stream of bytes is sufficient. |
| 421 By becoming more familiar with the ``Unix style of thinking'', | |
| 422 developers will more often and easier find simple designs where | |
| 423 a stream of bytes is a sufficient interface. | |
| 424 .PP | |
| 425 The second drawback of a toolchest affects the users. | |
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426 A toolchest is often more difficult to use. |
| 9 | 427 It is necessary to become familiar with each of the tools, |
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428 to be able to use the right one in a given situation. |
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429 Additionally, one needs to combine the tools in a senseful way himself. |
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430 This is like a sharp knife \(en it is a powerful tool in the hand of a |
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431 master, but of no good value in the hand of an unskilled. |
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432 However, learning single, small tools of a toolchest is easier than |
| 8 | 433 learning a complex tool. |
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434 And the user will already have a basic understanding of a yet unknown tool, |
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435 if the tools of a toolchest have a common, consistent style. |
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436 He will be able to transfer knowledge over from one tool to another. |
| 8 | 437 .PP |
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438 Moreover, the second drawback can be removed to a large extend |
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439 by adding wrappers around the basic tools. |
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440 Novice users do not need to learn several tools, if a professional wraps |
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441 complete command lines into a higher-level script. |
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442 Note that the wrapper script still calls the small tools; |
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443 it is just like a skin around them. |
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444 No complexity is added this way. |
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445 But new programs can get created out of existing one with very low effort. |
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446 .PP |
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447 A wrapper script for finding the five largest entries in the current directory |
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448 could look like this: |
| 41 | 449 .DS |
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450 #!/bin/sh |
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451 du -s * | sort -nr | sed 5q |
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452 .DE |
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453 The script itself is just a text file that calls the command line, |
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454 which a professional user would type in directly. |
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455 It is probably worth to make the program flexible on the number of |
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456 entries it prints: |
| 41 | 457 .DS |
| 8 | 458 #!/bin/sh |
| 459 num=5 | |
| 460 [ $# -eq 1 ] && num="$1" | |
| 461 du -sh * | sort -nr | sed "${num}q" | |
| 462 .DE | |
| 463 This script acts like the one before, when called without an argument. | |
| 464 But one can also specify a numerical argument to define the number of lines to print. | |
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465 One can surely imagine even more flexible versions, however, |
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466 they will still relay on the external programs, |
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467 which do the actual work. |
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468 |
| 16 | 469 .NH 2 |
| 8 | 470 A powerful shell |
| 42 | 471 .XS |
| 472 \*(SN A powerful shell | |
| 473 .XE | |
| 8 | 474 .LP |
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475 The Unix shell provides the possibility to combine small programs into large ones. |
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476 But a powerful shell is a great feature in other ways, too. |
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477 For instance by being scriptable. |
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478 Control statements are build into the shell. |
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479 The functions, however, are the normal programs of the system. |
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480 Thus, as the programs are already known, |
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481 learning to program in the shell becomes easy. |
| 8 | 482 Using normal programs as functions in the shell programming language |
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483 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 484 .PP |
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485 The Unix shell encourages to write small scripts, |
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486 by combining existing programs, because it is so easy to do. |
| 8 | 487 This is a great step towards automation. |
| 488 It is wonderful if the effort to automate a task equals the effort | |
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489 to do the task a second time by hand. |
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490 If this holds, |
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491 then the user will be happy to automate everything he does more than once. |
| 8 | 492 .PP |
| 493 Small programs that do one job well, standardized interfaces between them, | |
| 494 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 495 this will inevitably produce software leverage. | |
| 496 Getting multiple times the benefit of an investment is a great offer. | |
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497 .PP |
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498 The shell also encourages rapid prototyping. |
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499 Many well known programs started as quickly hacked shell scripts, |
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500 and turned into ``real'' programs, written in C, later. |
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501 Building a prototype first, is a way to avoid the biggest problems |
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502 in application development. |
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503 Fred Brooks explains in ``No Silver Bullet'': |
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504 .[ |
| 44 | 505 brooks |
| 506 no silver bullet | |
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507 .] |
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508 .QP |
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509 The hardest single part of building a software system is deciding precisely what to build. |
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510 No other part of the conceptual work is so difficult as establishing the detailed |
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511 technical requirements, [...]. |
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512 No other part of the work so cripples the resulting system if done wrong. |
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513 No other part is more difficult to rectify later. |
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514 .PP |
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515 Writing a prototype is a great method for becoming familiar with the requirements |
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516 and to run into real problems early. |
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517 .[ [ |
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518 gancarz |
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519 unix philosophy |
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520 .], page 28 f.] |
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521 .PP |
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522 Prototyping is often seen as a first step in building a software. |
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523 This is, of course, good. |
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524 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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525 After having built the prototype, one might notice, that the prototype is already |
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526 \fIgood enough\fP. |
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527 Hence, no reimplementation, in a more sophisticated programming language, |
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528 might be of need, at least for the moment. |
| 23 | 529 Maybe later, it might be necessary to rewrite the software, but not now. |
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530 By delaying further work, one keeps the flexibility to react on |
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531 changing requirements. |
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532 Software parts that are not written will not miss the requirements. |
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533 |
| 16 | 534 .NH 2 |
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535 Worse is better |
| 42 | 536 .XS |
| 537 \*(SN Worse is better | |
| 538 .XE | |
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539 .LP |
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540 The Unix Philosophy aims for the 90% solution; |
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541 others call it the ``Worse is better'' approach. |
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542 Experience from real life projects shows: |
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543 .PP |
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544 (1) It is almost never possible to define the |
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545 requirements completely and correctly the first time. |
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546 Hence one should not try to; one will fail anyway. |
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547 .PP |
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548 (2) Requirements change during time. |
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549 Hence it is best to delay requirement-based design decisions as long as possible. |
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550 The software should be small and flexible as long as possible |
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551 to react on changing requirements. |
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552 Shell scripts, for example, are more easily adjusted as C programs. |
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553 .PP |
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554 (3) Maintenance work is hard work. |
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555 Hence, one should keep the amount of code as small as possible; |
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556 it should just fulfill the \fIcurrent\fP requirements. |
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557 Software parts that will be written in future, |
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558 do not need maintenance till then. |
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559 .PP |
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560 See Brooks' ``The Mythical Man-Month'' for reference. |
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561 .[ [ |
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562 brooks |
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563 mythical man-month |
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564 .], page 115 ff.] |
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565 .PP |
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566 Starting with a prototype in a scripting language has several advantages: |
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567 .IP \(bu |
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568 As the initial effort is low, one will likely start right away. |
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569 .IP \(bu |
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570 As working parts are available soon, the real requirements can get identified soon. |
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571 .IP \(bu |
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572 When a software is usable and valuable, it gets used, and thus tested. |
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573 Hence problems will be found at early stages of the development. |
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574 .IP \(bu |
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575 The prototype might be enough for the moment, |
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576 thus further work on the software can get delayed to a time |
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577 when one knows better about the requirements and problems, |
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578 than now. |
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579 .IP \(bu |
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580 Implementing now only the parts that are actually needed at the moment, |
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581 introduces fewer programming and maintenance work. |
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582 .IP \(bu |
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583 If the global situation changes so that the software is not needed anymore, |
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584 then less effort was spent into the project, than it would have be |
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585 when a different approach had been used. |
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586 |
| 16 | 587 .NH 2 |
| 11 | 588 Upgrowth and survival of software |
| 42 | 589 .XS |
| 590 \*(SN Upgrowth and survival of software | |
| 591 .XE | |
| 11 | 592 .LP |
| 12 | 593 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 594 Although these are just verbs, they do imply a specific view on the work process |
| 595 they describe. | |
| 12 | 596 The better verb, however, is to \fIgrow\fP. |
| 597 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 598 It starts with a first prototype, which evolves as requirements change. | |
| 599 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 600 compiled program this way. |
| 601 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
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602 While being alive it will get extended, rearranged, rebuilt. |
| 12 | 603 Growing software matches the view that ``software is never finished. It is only released.'' |
| 46 | 604 .[ [ |
| 44 | 605 gancarz |
| 606 unix philosophy | |
| 46 | 607 .], page 26] |
| 12 | 608 .PP |
| 13 | 609 Software can be seen as being controlled by evolutionary processes. |
| 610 Successful software is software that is used by many for a long time. | |
| 12 | 611 This implies that the software is needed, useful, and better than alternatives. |
| 612 Darwin talks about: ``The survival of the fittest.'' | |
| 613 .[ | |
| 44 | 614 darwin |
| 615 origin of species | |
| 12 | 616 .] |
| 617 Transferred to software: The most successful software, is the fittest, | |
| 618 is the one that survives. | |
| 13 | 619 (This may be at the level of one creature, or at the level of one species.) |
| 620 The fitness of software is affected mainly by four properties: | |
| 15 | 621 portability of code, portability of data, range of usability, and reusability of parts. |
| 13 | 622 .PP |
| 15 | 623 (1) |
| 624 .I "Portability of code | |
| 625 means, using high-level programming languages, | |
| 13 | 626 sticking to the standard, |
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627 .[ [ |
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628 kernighan pike |
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629 practice of programming |
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630 .], chapter\|8] |
| 13 | 631 and avoiding optimizations that introduce dependencies on specific hardware. |
| 632 Hardware has a much lower lifetime than software. | |
| 633 By chaining software to a specific hardware, | |
| 634 the software's lifetime gets shortened to that of this hardware. | |
| 635 In contrast, software should be easy to port \(en | |
| 23 | 636 adaptation is the key to success. |
| 13 | 637 .PP |
| 15 | 638 (2) |
| 639 .I "Portability of data | |
| 640 is best achieved by avoiding binary representations | |
| 13 | 641 to store data, because binary representations differ from machine to machine. |
| 23 | 642 Textual representation is favored. |
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643 Historically, \s-1ASCII\s0 was the charset of choice. |
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644 For the future, \s-1UTF\s0-8 might be the better choice. |
| 13 | 645 Important is that it is a plain text representation in a |
| 646 very common charset encoding. | |
| 647 Apart from being able to transfer data between machines, | |
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648 readable data has the great advantage, that humans are able to directly |
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649 read and edit it with text editors and other tools from the Unix toolchest. |
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650 .[ [ |
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651 gancarz |
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652 unix philosophy |
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653 .], page 56 ff.] |
| 12 | 654 .PP |
| 15 | 655 (3) |
| 656 A large | |
| 657 .I "range of usability | |
| 23 | 658 ensures good adaptation, and thus good survival. |
| 13 | 659 It is a special distinction if a software becomes used in fields of action, |
| 660 the original authors did never imagine. | |
| 661 Software that solves problems in a general way will likely be used | |
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662 for many kinds of similar problems. |
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663 Being too specific limits the range of usability. |
| 13 | 664 Requirements change through time, thus use cases change or even vanish. |
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665 As a good example in this point, |
| 13 | 666 Allman identifies flexibility to be one major reason for sendmail's success: |
| 667 .[ | |
| 44 | 668 allman |
| 669 sendmail | |
| 13 | 670 .] |
| 671 .QP | |
| 672 Second, I limited myself to the routing function [...]. | |
| 673 This was a departure from the dominant thought of the time, [...]. | |
| 674 .QP | |
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675 Third, the sendmail configuration file was flexible enough to adapt |
| 13 | 676 to a rapidly changing world [...]. |
| 677 .LP | |
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678 Successful software adapts itself to the changing world. |
| 12 | 679 .PP |
| 15 | 680 (4) |
| 681 .I "Reuse of parts | |
| 682 is even one step further. | |
| 13 | 683 A software may completely lose its field of action, |
| 684 but parts of which the software is build may be general and independent enough | |
| 685 to survive this death. | |
| 686 If software is build by combining small independent programs, | |
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687 then these parts are readily available for reuse. |
| 13 | 688 Who cares if the large program is a failure, |
| 689 but parts of it become successful instead? | |
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690 |
| 16 | 691 .NH 2 |
|
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692 Summary |
| 42 | 693 .XS |
| 694 \*(SN Summary | |
| 695 .XE | |
| 0 | 696 .LP |
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697 This chapter explained central ideas of the Unix Philosophy. |
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698 For each of the ideas, the advantages they introduce were explained. |
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699 The Unix Philosophy are guidelines that help to write more valuable software. |
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700 From the view point of a software developer or software designer, |
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701 the Unix Philosophy provides answers to many software design problem. |
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702 .PP |
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703 The various ideas of the Unix Philosophy are very interweaved |
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704 and can hardly be applied independently. |
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705 However, the probably most important messages are: |
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706 .I "``Keep it simple!''" , |
|
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707 .I "``Do one thing well!''" , |
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708 and |
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709 .I "``Use software leverage!'' |
| 0 | 710 |
| 8 | 711 |
| 712 | |
| 0 | 713 .NH 1 |
| 19 | 714 Case study: \s-1MH\s0 |
| 42 | 715 .XS |
| 716 .sp .5v | |
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717 .B |
| 42 | 718 \*(SN Case study: \s-1MH\s0 |
| 719 .XE | |
| 18 | 720 .LP |
| 30 | 721 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 722 from a general point of view. |
| 30 | 723 The driving force were the guidelines; references to |
| 18 | 724 existing software were given only sparsely. |
| 725 In this and the next chapter, concrete software will be | |
| 726 the driving force in the discussion. | |
| 727 .PP | |
| 23 | 728 This first case study is about the mail user agents (\s-1MUA\s0) |
| 729 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 730 (``new mail handler''). | |
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731 .[ |
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732 nmh website |
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733 .] |
| 23 | 734 \s-1MUA\s0s provide functions to read, compose, and organize mail, |
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735 but (ideally) not to transfer it. |
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736 In this document, the name \s-1MH\s0 will be used to include nmh. |
| 19 | 737 A distinction will only be made if differences between |
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738 \s-1MH\s0 and nmh are described. |
| 18 | 739 |
| 0 | 740 |
| 741 .NH 2 | |
| 19 | 742 Historical background |
| 42 | 743 .XS |
| 744 \*(SN Historical background | |
| 745 .XE | |
| 0 | 746 .LP |
| 19 | 747 Electronic mail was available in Unix very early. |
| 30 | 748 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 749 which was already present in the First Edition. | |
| 46 | 750 .[ [ |
| 44 | 751 salus |
| 752 quarter century of unix | |
| 46 | 753 .], page 41 f.] |
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754 It was a small program that either printed the user's mailbox file |
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755 or appended text to someone elses mailbox file, |
| 19 | 756 depending on the command line arguments. |
| 757 .[ | |
| 44 | 758 manual mail(1) |
| 19 | 759 .] |
| 760 It was a program that did one job well. | |
| 23 | 761 This job was emailing, which was very simple then. |
| 19 | 762 .PP |
| 23 | 763 Later, emailing became more powerful, and thus more complex. |
| 19 | 764 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 765 independent handling of single messages, | |
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766 and long-time email storage, was not powerful enough anymore. |
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767 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') |
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768 to provide additional functions for emailing. |
| 19 | 769 Mail was still one program, but now it was large and did |
| 770 several jobs. | |
| 23 | 771 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 772 It is designed for humans, but is still scriptable. |
| 23 | 773 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 774 .[ |
| 44 | 775 ritter |
| 776 mailx history | |
| 19 | 777 .] |
| 30 | 778 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 779 followed Mail's direction. |
| 780 They are large, monolithic programs which include all emailing functions. | |
| 781 .PP | |
| 23 | 782 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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783 In the beginning, they also had used a monolithic mail system, |
| 30 | 784 called \s-1MS\s0 (for ``mail system''). |
| 19 | 785 But in 1977, Stockton Gaines and Norman Shapiro |
| 786 came up with a proposal of a new email system concept \(en | |
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787 one that honored the Unix Philosophy. |
| 19 | 788 The concept was implemented by Bruce Borden in 1978 and 1979. |
| 789 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 790 .PP |
| 791 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 792 at Berkeley, and several others have contributed to the software. |
| 18 | 793 However, it's core concepts remained the same. |
| 23 | 794 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 795 Richard Coleman started with \fInmh\fP, the new mail handler. |
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796 His goal was to improve \s-1MH\s0 especially in regard of |
| 23 | 797 the requirements of modern emailing. |
| 19 | 798 Today, nmh is developed by various people on the Internet. |
| 18 | 799 .[ |
| 44 | 800 ware |
| 801 rand history | |
| 18 | 802 .] |
| 803 .[ | |
| 44 | 804 peek |
| 805 mh | |
| 18 | 806 .] |
| 0 | 807 |
| 808 .NH 2 | |
| 20 | 809 Contrasts to monolithic mail systems |
| 42 | 810 .XS |
| 811 \*(SN Contrasts to monolithic mail systems | |
| 812 .XE | |
| 0 | 813 .LP |
| 19 | 814 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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815 Although there might actually exist further, very little known, |
| 30 | 816 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 817 .PP |
| 30 | 818 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 819 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 820 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 821 and their function. |
| 822 It gives a feeling of how the toolchest looks like. | |
| 19 | 823 .IP \(bu |
| 824 .CW inc : | |
| 30 | 825 incorporate new mail (this is how mail enters the system) |
| 19 | 826 .IP \(bu |
| 827 .CW scan : | |
| 828 list messages in folder | |
| 829 .IP \(bu | |
| 830 .CW show : | |
| 831 show message | |
| 832 .IP \(bu | |
| 833 .CW next\fR/\fPprev : | |
| 834 show next/previous message | |
| 835 .IP \(bu | |
| 836 .CW folder : | |
| 837 change current folder | |
| 838 .IP \(bu | |
| 839 .CW refile : | |
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840 refile message into different folder |
| 19 | 841 .IP \(bu |
| 842 .CW rmm : | |
| 843 remove message | |
| 844 .IP \(bu | |
| 845 .CW comp : | |
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846 compose new message |
| 19 | 847 .IP \(bu |
| 848 .CW repl : | |
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849 reply to message |
| 19 | 850 .IP \(bu |
| 851 .CW forw : | |
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852 forward message |
| 19 | 853 .IP \(bu |
| 854 .CW send : | |
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855 send prepared message (this is how mail leaves the system) |
| 0 | 856 .LP |
| 19 | 857 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 858 The user does not leave the shell to run \s-1MH\s0, | |
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859 instead he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 860 Using a monolithic program with a captive user interface |
| 861 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 862 Using toolchests like \s-1MH\s0 means running programs, | |
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863 alone or in combination with others, also from other toolchests, |
| 23 | 864 without leaving the shell. |
| 30 | 865 |
| 866 .NH 2 | |
| 867 Data storage | |
| 42 | 868 .XS |
| 869 \*(SN Data storage | |
| 870 .XE | |
| 30 | 871 .LP |
| 34 | 872 \s-1MH\s0's mail storage is a directory tree under the user's |
| 873 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 874 where mail folders are directories and mail messages are text files | |
| 875 within them. | |
| 876 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
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877 the public message sequences of that folder, |
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878 for instance the \fIunseen\fP sequence for new messages. |
| 34 | 879 Mail messages are text files located in a mail folder. |
| 880 The files contain the messages as they were received. | |
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881 They are named by ascending numbers in each folder. |
| 19 | 882 .PP |
| 30 | 883 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 884 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 885 In the mbox format all messages are stored within one file. | |
| 886 This was a good solution in the early days, when messages | |
| 887 were only a few lines of text and were deleted soon. | |
| 888 Today, when single messages often include several megabytes | |
| 889 of attachments, it is a bad solution. | |
| 890 Another disadvantage of the mbox format is that it is | |
| 891 more difficult to write tools that work on mail messages, | |
| 892 because it is always necessary to first find and extract | |
| 893 the relevant message in the mbox file. | |
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894 With the \s-1MH\s0 mailbox format, each message is a separate file. |
| 30 | 895 Also, the problem of concurrent access to one mailbox is |
| 896 reduced to the problem of concurrent access to one message. | |
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897 The maildir format is generally similar to the \s-1MH\s0 format, |
| 30 | 898 but modified towards guaranteed reliability. |
| 899 This involves some complexity, unfortunately. | |
| 34 | 900 .PP |
| 901 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 902 working with Unix' toolchest on directory trees: | |
| 903 \f(CWscan\fP is like \f(CWls\fP, | |
| 904 \f(CWshow\fP is like \f(CWcat\fP, | |
| 905 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 906 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 907 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 908 .PP | |
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909 \s-1MH\s0 extends the context of processes in Unix by two more items, |
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910 for its tools: |
| 34 | 911 .IP \(bu |
| 912 The current mail folder, which is similar to the current working directory. | |
| 913 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 914 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 915 .IP \(bu | |
| 916 Sequences, which are named sets of messages in a mail folder. | |
| 917 The current message, relative to a mail folder, is a special sequence. | |
| 918 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 919 .LP | |
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920 In contrast to Unix' context, which is maintained by the kernel, |
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921 \s-1MH\s0's context must be maintained by the tools themselves. |
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922 Usually there is one context per user, which resides in his |
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923 \f(CWcontext\fP file in the \s-1MH\s0 directory, |
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924 but a user can have several contexts, too. |
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925 Public sequences are an exception, as they belong to a mail folder, |
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926 and reside in the \f(CW.mh_sequences\fP file there. |
| 34 | 927 .[ |
| 44 | 928 man page mh-profile mh-sequence |
| 34 | 929 .] |
| 20 | 930 |
| 0 | 931 .NH 2 |
| 20 | 932 Discussion of the design |
| 42 | 933 .XS |
| 934 \*(SN Discussion of the design | |
| 935 .XE | |
| 20 | 936 .LP |
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937 This section discusses \s-1MH\s0 in regard to the tenets |
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938 of the Unix Philosophy that Gancarz identified. |
| 20 | 939 |
| 940 .PP | |
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941 .B "Small is beautiful |
| 20 | 942 and |
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943 .B "do one thing well |
| 20 | 944 are two design goals that are directly visible in \s-1MH\s0. |
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945 Gancarz actually presents \s-1MH\s0 in his book as example under the |
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946 headline ``Making \s-1UNIX\s0 Do One Thing Well'': |
| 46 | 947 .[ [ |
| 44 | 948 gancarz |
| 949 unix philosophy | |
| 46 | 950 .], page 125 ff.] |
| 20 | 951 .QP |
| 952 [\s-1MH\s0] consists of a series of programs which | |
| 953 when combined give the user an enormous ability | |
| 954 to manipulate electronic mail messages. | |
| 955 A complex application, it shows that not only is it | |
| 956 possible to build large applications from smaller | |
| 957 components, but also that such designs are actually preferable. | |
| 0 | 958 .LP |
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959 The various programs of \s-1MH\s0 were relatively easy to write, |
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960 because each of them is small, limited to one function, |
| 23 | 961 and has clear boundaries. |
| 20 | 962 For the same reasons, they are also good to maintain. |
| 963 Further more, the system can easily get extended. | |
| 964 One only needs to put a new program into the toolchest. | |
| 23 | 965 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 966 (e.g. \f(CWmhbuild\fP). |
| 967 Also, different programs can exist to do the basically same job | |
| 968 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
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969 .PP |
| 20 | 970 If someone needs a mail system with some additionally |
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971 functions that are not available anywhere yet, he best expands a |
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972 toolchest system like \s-1MH\s0. |
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973 There he can add new functionality by simply adding additional |
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974 programs to the toolchest. |
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975 There he does not risk to break existing functionality by doing so. |
| 20 | 976 |
| 977 .PP | |
| 34 | 978 .B "Store data in flat text files |
| 979 is followed by \s-1MH\s0. | |
| 980 This is not surprising, because email messages are already plain text. | |
| 981 \s-1MH\s0 stores the messages as it receives them, | |
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982 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate |
| 34 | 983 on the messages in an \s-1MH\s0 mailbox. |
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984 All other files \s-1MH\s0 uses are plain text, too. |
| 34 | 985 It is therefore possible and encouraged to use the text processing |
| 986 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 987 |
| 988 .PP | |
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989 .B "Avoid captive user interfaces" . |
| 19 | 990 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 991 It offers all functions directly and without captive user interfaces. | |
| 30 | 992 If, nonetheless, users want a graphical user interface, |
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993 they can have it with \fIxmh\fP or \fIexmh\fP. |
| 19 | 994 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 995 This means, all email-related work is still done by \s-1MH\s0 tools, | |
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996 but the frontend calls the appropriate commands when the user |
| 30 | 997 clicks on buttons. |
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998 .PP |
| 20 | 999 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 1000 approach, because it does not limit the power of the backend itself. |
| 20 | 1001 The frontend will anyway only be able to make a subset of the |
| 23 | 1002 backend's power and flexibility available to the user. |
| 20 | 1003 But if it is a separate program, |
| 1004 then the missing parts can still be accessed at the backend directly. | |
| 19 | 1005 If it is integrated, then this will hardly be possible. |
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1006 An additional advantage is the possibility to have different frontends |
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1007 to the same backend. |
| 19 | 1008 |
| 1009 .PP | |
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1010 .B "Choose portability over efficiency |
| 20 | 1011 and |
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1012 .B "use shell scripts to increase leverage and portability" . |
| 20 | 1013 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 1014 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 1015 .[ |
| 44 | 1016 bolsky korn |
| 1017 korn shell | |
| 20 | 1018 .] |
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1019 Chapter\|18 of the book shows a basic implementation |
| 20 | 1020 of a subset of \s-1MH\s0 in ksh scripts. |
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1021 Of course, this is just a demonstration, but a brilliant one. |
| 20 | 1022 It shows how quickly one can implement such a prototype with shell scripts, |
| 1023 and how readable they are. | |
| 1024 The implementation in the scripting language may not be very fast, | |
| 1025 but it can be fast enough though, and this is all that matters. | |
| 1026 By having the code in an interpreted language, like the shell, | |
| 1027 portability becomes a minor issue, if we assume the interpreter | |
| 1028 to be widespread. | |
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1029 .PP |
| 20 | 1030 This demonstration also shows how easy it is to create single programs |
| 1031 of a toolchest software. | |
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1032 Eight tools (two of them have multiple names) and 16 functions |
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1033 with supporting code are presented to the reader. |
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1034 The tools comprise less than 40 lines of ksh each, |
| 30 | 1035 in total about 200 lines. |
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1036 The functions comprise less than 80 lines of ksh each, |
| 30 | 1037 in total about 450 lines. |
| 20 | 1038 Such small software is easy to write, easy to understand, |
| 1039 and thus easy to maintain. | |
| 23 | 1040 A toolchest improves the possibility to only write some parts |
| 20 | 1041 and though create a working result. |
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1042 Expanding the toolchest, even without global changes, |
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1043 will likely be possible. |
| 20 | 1044 |
| 1045 .PP | |
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1046 .B "Use software leverage to your advantage |
| 20 | 1047 and the lesser tenet |
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1048 .B "allow the user to tailor the environment |
| 20 | 1049 are ideally followed in the design of \s-1MH\s0. |
| 21 | 1050 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 1051 directly define default options to programs. |
| 1052 It is even possible to define different default options | |
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1053 depending on the name under which a program is called. |
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1054 Software leverage is heavily encouraged by the ease of |
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1055 creating shell scripts that run a specific command line, |
| 30 | 1056 built of several \s-1MH\s0 programs. |
| 21 | 1057 There is few software that so much wants users to tailor their |
| 1058 environment and to leverage the use of the software, like \s-1MH\s0. | |
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1059 .PP |
| 21 | 1060 Just to make one example: |
| 23 | 1061 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 1062 program. |
| 30 | 1063 It is possible to take one of the distributed format files |
| 21 | 1064 or to write one yourself. |
| 1065 To use the format as default for \f(CWscan\fP, a single line, | |
| 1066 reading | |
| 1067 .DS | |
| 1068 scan: -form FORMATFILE | |
| 1069 .DE | |
| 1070 must be added to \f(CW.mh_profile\fP. | |
| 1071 If one wants this different format as an additional command, | |
| 23 | 1072 instead of changing the default, he needs to create a link to |
| 1073 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1074 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
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1075 as the option should only be in effect for a program that is called as |
| 21 | 1076 \f(CWscan2\fP. |
| 20 | 1077 |
| 1078 .PP | |
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1079 .B "Make every program a filter |
| 21 | 1080 is hard to find in \s-1MH\s0. |
| 1081 The reason therefore is that most of \s-1MH\s0's tools provide | |
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1082 basic file system operations for mailboxes. |
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1083 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, |
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1084 and \f(CWrm\fP aren't filters neither. |
| 23 | 1085 \s-1MH\s0 does not provide many filters itself, but it is a basis |
| 1086 to write filters for. | |
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1087 An example would be a mail text highlighter, |
| 30 | 1088 that means a program that makes use of a color terminal to display |
| 1089 header lines, quotations, and signatures in distinct colors. | |
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1090 The author's version of such a program is an awk script with 25 lines. |
| 21 | 1091 |
| 1092 .PP | |
|
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1093 .B "Build a prototype as soon as possible |
| 21 | 1094 was again well followed by \s-1MH\s0. |
| 1095 This tenet, of course, focuses on early development, which is | |
| 1096 long time ago for \s-1MH\s0. | |
| 1097 But without following this guideline at the very beginning, | |
| 23 | 1098 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1099 to ever create \s-1MH\s0. | |
| 1100 In Bruce' own words: | |
| 46 | 1101 .[ [ |
| 44 | 1102 ware rand history |
| 46 | 1103 .], page 132] |
| 21 | 1104 .QP |
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1105 [...] but [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1106 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1107 I proposed a very short project to prove the basic concepts, |
| 1108 and my management agreed. | |
| 1109 Looking back, I realize that I had been very lucky with my first design. | |
| 1110 Without nearly enough design work, | |
| 1111 I built a working environment and some header files | |
| 1112 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1113 inc, show/next/prev, and comp. | |
| 1114 [...] | |
| 1115 With these three, I was able to convince people that the structure was viable. | |
| 1116 This took about three weeks. | |
| 0 | 1117 |
| 1118 .NH 2 | |
| 1119 Problems | |
| 42 | 1120 .XS |
| 1121 \*(SN Problems | |
| 1122 .XE | |
| 0 | 1123 .LP |
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1124 \s-1MH\s0 is not without problems. |
| 30 | 1125 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1126 .PP |
| 1127 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1128 when \s-1MH\s0 was designed. | |
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1129 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though. |
| 22 | 1130 \s-1MIME\s0 support and support for different character encodings |
| 1131 is available, but only on a moderate level. | |
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1132 This comes from limited development resources. |
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1133 More active developers could quickly change this. |
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1134 But \s-1MH\s0 is also limited by design, which is the larger problem. |
| 22 | 1135 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. |
| 1136 These design conflicts are not easily solvable. | |
| 1137 Possibly, they require a redesign. | |
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1138 \s-1IMAP\s0 may be too different to the classic mail model, |
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1139 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well. |
| 22 | 1140 .PP |
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1141 The other kind of problem are human habits. |
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1142 In this world, where almost all \s-1MUA\s0s are monolithic, |
| 22 | 1143 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 |
| 1144 like \s-1MH\s0. | |
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1145 The habits are so strong, that even people who understand the concept |
| 30 | 1146 and advantages of \s-1MH\s0 do not like to switch, |
| 1147 simply because \s-1MH\s0 is different. | |
| 1148 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
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1149 are quite outdated and thus not very appealing, compared to the modern interfaces |
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1150 of many monolithic \s-1MUA\s0s. |
| 20 | 1151 |
| 1152 .NH 2 | |
| 1153 Summary \s-1MH\s0 | |
| 42 | 1154 .XS |
| 1155 \*(SN Summary \s-1MH\s0 | |
| 1156 .XE | |
| 20 | 1157 .LP |
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1158 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design. |
| 31 | 1159 It consists of a toolchest of small tools, each of them does one job well. |
| 1160 The toolchest approach offers great flexibility to the user. | |
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1161 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0. |
| 31 | 1162 This makes \s-1MH\s0 a very powerful mail system. |
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1163 Extending and customizing \s-1MH\s0 is easy and encouraged. |
| 31 | 1164 .PP |
| 1165 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1166 Its overall design follows clear rules. | |
| 1167 The single tools do only one job, thus they are easy to understand, | |
| 1168 easy to write, and good to maintain. | |
| 1169 They are all independent and do not interfere with the others. | |
| 1170 Automated testing of their function is a straight forward task. | |
| 1171 .PP | |
| 1172 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1173 as its differentness is also its largest advantage. | |
| 1174 Unfortunately, for most people their habits are stronger | |
| 1175 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1176 |
| 8 | 1177 |
| 1178 | |
| 0 | 1179 .NH 1 |
| 1180 Case study: uzbl | |
| 42 | 1181 .XS |
| 1182 .sp .5v | |
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1183 .B |
| 42 | 1184 \*(SN Case study: uzbl |
| 1185 .XE | |
| 32 | 1186 .LP |
| 1187 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
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1188 which is an old and established software. |
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1189 This chapter covers uzbl, a fresh new project. |
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1190 Uzbl is a web browser that adheres to the Unix Philosophy. |
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1191 Its name comes from the \fILolspeak\fP word for ``usable''; |
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1192 it is pronounced identical. |
| 0 | 1193 |
| 1194 .NH 2 | |
| 32 | 1195 Historical background |
| 42 | 1196 .XS |
| 1197 \*(SN Historical background | |
| 1198 .XE | |
| 0 | 1199 .LP |
| 32 | 1200 Uzbl was started by Dieter Plaetinck in April 2009. |
| 44 | 1201 The idea was born in a thread in the Arch Linux Forums. |
| 32 | 1202 .[ |
| 44 | 1203 arch linux forums |
| 1204 browser | |
| 32 | 1205 .] |
| 1206 After some discussion about failures of well known web browsers, | |
| 1207 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1208 of how a better web browser could look like. | |
| 1209 To the question of another member, if Plaetinck would write that program, | |
| 1210 because it would sound fantastic, Plaetinck replied: | |
| 1211 ``Maybe, if I find the time ;-)''. | |
| 1212 .PP | |
| 1213 Fortunately, he found the time. | |
| 1214 One day later, the first prototype was out. | |
| 1215 One week later, uzbl had an own website. | |
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1216 .[ |
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1217 uzbl website |
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1218 .] |
| 32 | 1219 One month after the first code showed up, |
|
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1220 a mailing list was installed to coordinate and discuss further development, |
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1221 and a wiki was added to store documentation and scripts that showed up on the |
| 32 | 1222 mailing list and elsewhere. |
| 1223 .PP | |
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1224 In the, now, one year of uzbl's existence, it was heavily developed on various branches. |
| 32 | 1225 Plaetinck's task became more and more to only merge the best code from the |
| 1226 different branches into his main branch, and to apply patches. | |
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1227 .[ |
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1228 lwn uzbl |
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1229 .] |
| 32 | 1230 About once a month, Plaetinck released a new version. |
| 1231 In September 2009, he presented several forks of uzbl. | |
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1232 .[ [ |
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1233 uzbl website |
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1234 .], news archive] |
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1235 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1236 .PP |
| 1237 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
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1238 .[ |
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1239 lwn uzbl |
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1240 .] |
| 32 | 1241 In September 2009, the uzbl web browser was on \fISlashdot\fP. |
|
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1242 .[ |
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1243 slashdot uzbl |
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1244 .] |
| 0 | 1245 |
| 1246 .NH 2 | |
| 32 | 1247 Contrasts to other web browsers |
| 42 | 1248 .XS |
| 1249 \*(SN Contrasts to other web browsers | |
| 1250 .XE | |
| 0 | 1251 .LP |
| 32 | 1252 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1253 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1254 .PP | |
| 1255 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1256 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1257 It handles commands and events to interface other programs, | |
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1258 and also displays webpages by using \fIwebkit\fP as render engine. |
| 32 | 1259 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, |
| 1260 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1261 to form a ``complete'' web browser. | |
| 1262 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1263 so uzbl-core is included. | |
| 1264 .PP | |
| 1265 Unlike most other web browsers, uzbl is mainly the mediator between the | |
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1266 various tools that cover single jobs. |
| 35 | 1267 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1268 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1269 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1270 .DS |
| 1271 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1272 .DE | |
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1273 The graphical rendering of the webpage is done by webkit, |
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1274 a web content engine. |
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1275 Uzbl-core is built around libwebkit. |
| 32 | 1276 .PP |
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1277 Downloads, browsing history, bookmarks, and the like are not provided |
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1278 by the core itself, like they are in other web browsers. |
| 35 | 1279 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1280 external applications which provide the actual functionality. | |
| 32 | 1281 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1282 includes a script that calls wget with appropriate options in | |
| 1283 a prepared environment. | |
| 1284 .PP | |
| 1285 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1286 This is their effort to achieve similar goals. | |
| 35 | 1287 But instead of using existing, external programs, modern web browsers |
|
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1288 include these functions. |
| 0 | 1289 |
| 1290 .NH 2 | |
| 32 | 1291 Discussion of the design |
| 42 | 1292 .XS |
| 1293 \*(SN Discussion of the design | |
| 1294 .XE | |
| 0 | 1295 .LP |
| 32 | 1296 This section discusses uzbl in regard of the Unix Philosophy, |
| 1297 as identified by Gancarz. | |
| 1298 | |
| 1299 .PP | |
| 35 | 1300 .B "Make each program do one thing well" . |
| 1301 Uzbl tries to be a web browser and nothing else. | |
|
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1302 The common definition of a web browser is, of course, highly influenced by |
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1303 existing implementations of web browsers, although they are degenerated. |
| 35 | 1304 Web browsers should be programs to browse the web, and nothing more. |
|
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1305 This is the one thing they should do. |
|
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1306 .PP |
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1307 Web browsers should not, for instance, manage downloads. |
| 35 | 1308 This is the job download managers exist for. |
| 1309 Download managers do primary care about being good in downloading files. | |
| 1310 Modern web browsers provide download management only as a secondary feature. | |
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1311 How could they do this job better, than programs that exist only for |
| 35 | 1312 this very job? |
| 1313 And how could anyone want less than the best download manager available? | |
| 32 | 1314 .PP |
| 35 | 1315 A web browser's job is to let the user browse the web. |
| 1316 This means, navigating through websites by following links. | |
|
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1317 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1318 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1319 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1320 are also not the job of a web browser. |
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1321 They should be handled by external applications \(en |
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1322 ones which's job is to handle such data. |
| 35 | 1323 Uzbl strives to do it this way. |
|
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1324 .PP |
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1325 Remember Doug McIlroy: |
| 35 | 1326 .I |
| 1327 ``Write programs that do one thing and do it well. | |
| 1328 Write programs to work together.'' | |
| 1329 .R | |
| 1330 .PP | |
| 1331 The lesser tenet | |
| 1332 .B "allow the user to tailor the environment | |
| 1333 matches good here. | |
| 1334 There was the question, how anyone could want anything less than the | |
| 1335 best program for the job. | |
|
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1336 But as personal preferences matter, it is probably more important to ask: |
| 35 | 1337 How could anyone want something else than his preferred program for the job? |
|
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1338 .PP |
|
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1339 Usually users want one program for a specific job. |
| 35 | 1340 Hence, whenever the task is, for instance, downloading, |
|
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1341 the same download manager should be used. |
| 35 | 1342 More advanced users might want to have this download manager in this |
| 1343 situation and that one in that situation. | |
| 1344 They should be able to configure it this way. | |
| 1345 With uzbl, one can use any download manager the user wants. | |
|
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1346 To switch to a different one, only one line in a small handler script |
| 35 | 1347 needs to be changed. |
|
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1348 Alternatively it would be possible to query the program to use by |
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1349 reading a global file or an environment variable, in the handler script. |
|
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1350 .PP |
|
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1351 Uzbl does neither have its own download manager nor depends on a |
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1352 specific one, hence uzbl's browsing abilities will not be lowered by having |
| 35 | 1353 a bad download manager. |
|
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1354 Uzbl's download capabilities will be just as good as the ones of the best |
|
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1355 download manager available on the system. |
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1356 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1357 |
| 1358 .PP | |
|
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1359 .B "Use software leverage to your advantage" . |
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1360 Uzbl is designed to be extended by external tools. |
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1361 These external tools are usually wrapped by small handler shell scripts. |
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1362 Shell scripts are the glue in this approach. |
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1363 They make the various parts fit together. |
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1364 .PP |
|
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1365 The history mechanism of uzbl shall be presented as an example. |
|
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1366 Uzbl is configured to spawn a script to append an entry to the history |
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1367 whenever the event of a fully loaded page occurs. |
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1368 The script to append the entry to the history is not much more than: |
|
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1369 .DS |
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1370 #!/bin/sh |
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1371 file=/path/to/uzbl-history |
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1372 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1373 .DE |
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1374 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1375 .PP |
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1376 For loading an entry, a key is bound to spawn a load-from-history script. |
|
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1377 The script reverses the history to have newer entries first, |
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1378 then displays \fIdmenu\fP to let the user select an item, |
|
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1379 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
|
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1380 With error checking and corner case handling removed, |
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1381 the script looks like this: |
|
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1382 .DS |
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1383 #!/bin/sh |
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1384 file=/path/to/uzbl-history |
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1385 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1386 echo "uri $goto" > $4 |
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1387 .DE |
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1388 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1389 uzbl instance. |
| 32 | 1390 |
| 1391 .PP | |
|
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1392 .B "Avoid captive user interfaces" . |
|
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1393 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1394 a captive user interface. |
| 37 | 1395 But the difference to most other web browsers is, that uzbl is only |
|
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1396 the captive user interface frontend (and the core of the backend). |
|
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1397 Many parts of the backend are independent of uzbl. |
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1398 Some are distributed with uzbl, for some external programs, |
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1399 handler scripts are distributed, |
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1400 but arbitrary additional functionality can be added if desired. |
| 37 | 1401 .PP |
| 1402 The frontend is captive \(en that is true. | |
| 1403 This is okay for the task of browsing the web, as this task is only relevant | |
| 1404 for humans. | |
| 1405 Automated programs would \fIcrawl\fP the web. | |
| 1406 That means, they read the source directly. | |
| 1407 The source includes all the semantics. | |
| 1408 The graphical representation is just for humans to transfer the semantics | |
| 1409 more intuitively. | |
| 32 | 1410 |
| 1411 .PP | |
|
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1412 .B "Make every program a filter" . |
| 37 | 1413 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1414 Thus it is difficult to see what graphical web browsers should filter. | |
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1415 Graphical web browsers exist almost only to be interactively used by humans. |
| 37 | 1416 The only case when one might want to automate the rendering function is |
| 1417 to generate images of rendered webpages. | |
| 1418 | |
| 1419 .PP | |
| 1420 .B "Small is beautiful" | |
|
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1421 is not easy to apply to a web browser, because modern web technology |
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1422 is very complex, hence the rendering task is very complex. |
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1423 Modern web browsers have to consist of many thousand lines of code, |
| 37 | 1424 unfortunately. |
| 1425 Using the toolchest approach and wrappers can split the browser into | |
| 1426 several small parts, tough. | |
| 1427 .PP | |
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1428 As of March 2010, uzbl-core consists of about 3\,500 lines of C code. |
| 37 | 1429 The distribution includes another 3\,500 lines of Shell and Python code, |
| 1430 which are the handler scripts and plugins like a modal interface. | |
|
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1431 Further more, uzbl uses functionality of external tools like |
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1432 \fIwget\fP and \fInetcat\fP. |
| 37 | 1433 Up to this point, uzbl looks pretty neat and small. |
|
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1434 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1435 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1436 Unfortunately, small web render engines are not possible anymore |
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1437 because of the modern web. |
| 35 | 1438 |
| 1439 .PP | |
| 1440 .B "Build a prototype as soon as possible" . | |
| 1441 Plaetinck made his code public, right from the beginning. | |
|
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1442 Discussion and development was, and still is, open to everyone interested. |
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1443 Development versions of uzbl can be obtained very simply from the code |
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1444 repository. |
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1445 Within the first year of uzbl's existence, a new version was released |
| 35 | 1446 more often than once a month. |
|
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1447 Different forks and branches arose. |
|
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1448 They introduced new features, which were tested for suitability |
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1449 for the main branch. |
| 35 | 1450 The experiences of using prototypes influenced further development. |
| 1451 Actually, all development was community driven. | |
|
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1452 Plaetinck says, three months after uzbl's birth: |
| 35 | 1453 ``Right now I hardly code anything myself for Uzbl. |
| 1454 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1455 .[ | |
| 44 | 1456 lwn |
| 1457 uzbl | |
| 35 | 1458 .] |
| 32 | 1459 |
| 0 | 1460 |
| 1461 .NH 2 | |
| 1462 Problems | |
| 42 | 1463 .XS |
| 1464 \*(SN Problems | |
| 1465 .XE | |
| 0 | 1466 .LP |
|
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1467 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1468 It is sad, but people use what they know. |
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1469 Fortunately, uzbl's user interface can look and feel very much the |
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1470 same as the one of the well known web browsers, |
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1471 hiding the internal differences. |
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1472 But uzbl has to provide this similar look and feel to be accepted |
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1473 as a ``normal'' browser by ``normal'' users. |
| 37 | 1474 .PP |
|
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1475 Though, the more important problem is the modern web. |
|
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1476 The modern web is simply broken. |
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1477 It has state in a state-less protocol, |
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1478 it misuses technologies, |
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1479 and it is helplessly overloaded. |
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1480 The result are web content render engines that must consist |
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1481 of hundreds of thousands lines of code. |
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1482 They also must combine and integrate many different technologies, |
|
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1483 only to make our modern web accessible. |
|
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1484 Website to image converter are hardly possible to run without |
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1485 human interaction because of state in sessions, impossible |
|
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1486 deep-linking, and unautomatable technologies. |
| 37 | 1487 .PP |
|
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1488 The web was misused to provide all kinds of imaginable wishes. |
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1489 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1490 |
| 8 | 1491 |
| 32 | 1492 .NH 2 |
| 1493 Summary uzbl | |
| 42 | 1494 .XS |
| 1495 \*(SN Summary uzbl | |
| 1496 .XE | |
| 32 | 1497 .LP |
|
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1498 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1499 that is how uzbl is seen by its authors. |
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1500 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1501 It consists of independent parts that work together, |
|
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1502 while its core is mainly a mediator which glues the parts together. |
|
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1503 .PP |
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1504 Software leverage can excellently be seen in uzbl. |
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1505 External tools are used, independent tasks are separated |
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1506 in independent parts and glued together with small handler scripts. |
|
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1507 .PP |
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1508 As uzbl, more or less, consists of a set of tools and a bit |
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1509 of glue, anyone can put the parts together and expand it |
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1510 in any desired way. |
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1511 Uzbl is very flexible and customizable. |
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1512 These properties make it valuable for advanced users, |
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1513 but may keep novice users from using it. |
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1514 .PP |
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1515 But uzbl's main problem is the modern web, that makes it hard |
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1516 to design a sane web browser. |
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1517 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1518 |
| 8 | 1519 |
| 0 | 1520 .NH 1 |
| 1521 Final thoughts | |
| 42 | 1522 .XS |
| 1523 .sp .5v | |
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1524 .B |
| 42 | 1525 \*(SN Final thoughts |
| 1526 .XE | |
| 0 | 1527 |
| 1528 .NH 2 | |
| 1529 Quick summary | |
| 42 | 1530 .XS |
| 1531 \*(SN Quick summary | |
| 1532 .XE | |
| 0 | 1533 .LP |
| 1534 good design | |
| 1535 .LP | |
| 1536 unix phil | |
| 1537 .LP | |
| 1538 case studies | |
| 1539 | |
| 1540 .NH 2 | |
| 1541 Why people should choose | |
| 42 | 1542 .XS |
| 1543 \*(SN Why people should choose | |
| 1544 .XE | |
| 0 | 1545 .LP |
| 1546 Make the right choice! | |
| 1547 | |
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1548 |
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1549 .bp |
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1550 .TL |
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1551 References |
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1552 .LP |
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1553 .XS |
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1554 .sp .5v |
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1555 .B |
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1556 References |
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1557 .XE |
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1558 .ev r |
| 0 | 1559 .rm ]< |
| 1560 .de ]< | |
| 1561 .LP | |
| 1562 .de FP | |
| 1563 .IP \\\\$1. | |
| 1564 \\.. | |
| 1565 .rm FS FE | |
| 1566 .. | |
| 42 | 1567 .nr PS -1 |
| 1568 .nr VS -1 | |
| 0 | 1569 .[ |
| 1570 $LIST$ | |
| 1571 .] | |
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1572 .nr PS +1 |
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1573 .nr VS +1 |
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1574 .ev |
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1575 |
| 42 | 1576 .bp |
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1577 .TL |
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1578 Table of Contents |
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1579 .LP |
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1580 .PX no |