Mercurial > docs > unix-phil
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| author | meillo@marmaro.de |
|---|---|
| date | Thu, 15 Apr 2010 23:04:07 +0200 |
| parents | acd63ecc3606 |
| children | 840cbc667009 |
| rev | line source |
|---|---|
| 49 | 1 .so style |
| 42 | 2 |
| 0 | 3 .TL |
| 42 | 4 .ps +4 |
| 6 | 5 Why the Unix Philosophy still matters |
| 0 | 6 .AU |
| 7 markus schnalke <meillo@marmaro.de> | |
| 8 .AB | |
| 1 | 9 .ti \n(.iu |
| 39 | 10 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 11 Today, few software designers are aware of these concepts, |
| 39 | 12 and thus a lot of modern software is more limited than necessary |
| 13 and makes less use of software leverage than possible. | |
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14 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 15 .AE |
| 16 | |
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17 .FS |
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18 .ps -1 |
| 39 | 19 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
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20 Mentor was professor Franz Schweiggert. |
| 55 | 21 Handed in on 2010-04-16. |
| 39 | 22 You may retrieve this document from |
| 23 .CW \s-1http://marmaro.de/docs \ . | |
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26 .H 1 Introduction |
| 0 | 27 .LP |
| 40 | 28 The Unix Philosophy is the essence of how the Unix operating system, |
| 29 especially its toolchest, was designed. | |
| 30 It is no limited set of fixed rules, | |
| 31 but a loose set of guidelines which tell how to write software that | |
| 32 suites well into Unix. | |
| 33 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 34 The Wikipedia has an accurate definition: | |
| 35 .[ | |
| 44 | 36 wikipedia |
| 37 unix philosophy | |
| 40 | 38 .] |
| 39 .QP | |
| 40 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 41 approaches to developing software based on the experience of leading | |
| 42 developers of the Unix operating system. | |
| 3 | 43 .PP |
| 40 | 44 As there is no single definition of the Unix Philosophy, |
| 45 several people have stated their view on what it comprises. | |
| 1 | 46 Best known are: |
| 47 .IP \(bu | |
| 48 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 49 .[ | |
| 44 | 50 mahoney |
| 51 oral history | |
| 1 | 52 .] |
| 53 .IP \(bu | |
| 54 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 55 .[ | |
| 44 | 56 gancarz |
| 57 unix philosophy | |
| 1 | 58 .] |
| 59 .IP \(bu | |
| 60 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 61 .[ | |
| 44 | 62 raymond |
| 63 art of unix programming | |
| 1 | 64 .] |
| 0 | 65 .LP |
| 1 | 66 These different views on the Unix Philosophy have much in common. |
| 40 | 67 Especially, the main concepts are similar in all of them. |
| 68 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 69 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 70 | |
| 71 .PP | |
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72 The Unix Philosophy explains how to design good software for Unix. |
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73 Many concepts described here, base on facilities of Unix. |
| 40 | 74 Other operating systems may not offer such facilities, |
| 41 | 75 hence it may not be possible to design software in the way of the |
| 76 Unix Philosophy for them. | |
| 77 .PP | |
| 78 The Unix Philosophy has an idea of how the process of software development | |
| 79 should look like, but large parts of the philosophy are quite independent | |
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80 from a concrete development process. |
| 41 | 81 However, one will soon recognize that some development processes work well |
| 82 with the ideas of the Unix Philosophy and support them, while others are | |
| 83 at cross-purposes. | |
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84 Kent Beck's books about Extreme Programming are valuable supplemental |
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85 resources on this topic. |
| 40 | 86 .PP |
| 41 | 87 The question of how to actually write code and how the code should looks |
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88 like in detail, are out of focus here. |
| 41 | 89 ``The Practice of Programming'' by Kernighan and Pike, |
| 90 .[ | |
| 44 | 91 kernighan pike |
| 92 practice of programming | |
| 41 | 93 .] |
| 94 is a good book that covers this topic. | |
| 95 Its point of view matches to the one of this paper. | |
| 0 | 96 |
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97 .H 1 "Importance of software design in general |
| 0 | 98 .LP |
| 40 | 99 Software design is the planning of how the internal structure |
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100 and external interfaces of software should look like. |
| 39 | 101 It has nothing to do with visual appearance. |
| 102 If we take a program as a car, then its color is of no matter. | |
| 103 Its design would be the car's size, its shape, the locations of doors, | |
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104 the passenger/space ratio, the available controls and instruments, |
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105 and so forth. |
| 39 | 106 .PP |
| 107 Why should software get designed at all? | |
| 6 | 108 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 109 Not designing software means programming without plan. |
| 110 This will pretty sure lead to horrible results. | |
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111 Software that is horrible to use and horrible to maintain. |
| 39 | 112 These two aspects are the visible ones. |
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113 Often invisible though, are the wasted possible gains. |
| 39 | 114 Good software design can make these gains available. |
| 6 | 115 .PP |
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116 Software design deals with quality properties. |
| 39 | 117 Good design leads to good quality, and quality is important. |
| 118 Any car may be able to drive from A to B, | |
| 119 but it depends on the car's properties whether it is a good choice | |
| 120 for passenger transport or not. | |
| 121 It depends on its properties if it is a good choice | |
| 122 for a rough mountain area. | |
| 123 And it depends on its properties if the ride will be fun. | |
| 124 | |
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125 .PP |
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126 Requirements for software are twofold: |
| 39 | 127 functional and non-functional. |
| 128 .IP \(bu | |
| 129 Functional requirements define directly the software's functions. | |
| 130 They are the reason why software gets written. | |
| 131 Someone has a problem and needs a tool to solve it. | |
| 132 Being able to solve the problem is the main functional goal. | |
| 133 It is the driving force behind all programming effort. | |
| 6 | 134 Functional requirements are easier to define and to verify. |
| 39 | 135 .IP \(bu |
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136 Non-functional requirements are called \fIquality\fP requirements, too. |
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137 The quality of software are the properties that are not directly related to |
| 39 | 138 the software's basic functions. |
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139 Tools of bad quality often do solve the problems they were written for, |
| 39 | 140 but introduce problems and difficulties for usage and development, later on. |
| 141 Quality aspects are often overlooked at first sight, | |
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142 and are often difficult to define clearly and to verify. |
| 6 | 143 .PP |
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144 Quality is hardly interesting when software gets built initially, |
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145 but it has a high impact on usability and maintenance, later. |
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146 A short-sighted might see in developing software, mainly building something up. |
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147 But experience shows, that building software the first time is |
| 39 | 148 only a small amount of the overall work. |
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149 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en |
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150 does soon take over the major part of the time spent on a software project. |
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151 And of course, the time spent actually using the software. |
| 6 | 152 These processes are highly influenced by the software's quality. |
| 39 | 153 Thus, quality must not be neglected. |
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154 However, the problem with quality is that you hardly ``stumble over'' |
| 39 | 155 bad quality during the first build, |
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156 although this is the time when you should care about good quality most. |
| 6 | 157 .PP |
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158 Software design has little to do with the basic function of software \(en |
| 39 | 159 this requirement will get satisfied anyway. |
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160 Software design is more about quality aspects of software. |
| 39 | 161 Good design leads to good quality, bad design to bad quality. |
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162 The primary functions of software will be affected modestly by bad quality, |
| 39 | 163 but good quality can provide a lot of additional gain, |
| 6 | 164 even at places where one never expected it. |
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165 .PP |
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166 The ISO/IEC\|9126-1 standard, part\|1, |
| 6 | 167 .[ |
| 44 | 168 iso product quality |
| 6 | 169 .] |
| 170 defines the quality model as consisting out of: | |
| 171 .IP \(bu | |
| 172 .I Functionality | |
| 173 (suitability, accuracy, inter\%operability, security) | |
| 174 .IP \(bu | |
| 175 .I Reliability | |
| 176 (maturity, fault tolerance, recoverability) | |
| 177 .IP \(bu | |
| 178 .I Usability | |
| 179 (understandability, learnability, operability, attractiveness) | |
| 180 .IP \(bu | |
| 181 .I Efficiency | |
| 9 | 182 (time behavior, resource utilization) |
| 6 | 183 .IP \(bu |
| 184 .I Maintainability | |
| 23 | 185 (analyzability, changeability, stability, testability) |
| 6 | 186 .IP \(bu |
| 187 .I Portability | |
| 188 (adaptability, installability, co-existence, replaceability) | |
| 189 .LP | |
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190 Good design can improve these properties of software, |
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191 bad designed software likely suffers in these points. |
| 7 | 192 .PP |
| 193 One further goal of software design is consistency. | |
| 194 Consistency eases understanding, working on, and using things. | |
| 39 | 195 Consistent internal structure and consistent interfaces to the outside |
| 196 can be provided by good design. | |
| 7 | 197 .PP |
| 39 | 198 Software should be well designed because good design avoids many |
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199 problems during a software project's lifetime. |
| 39 | 200 And software should be well designed because good design can offer |
| 201 much additional gain. | |
| 202 Indeed, much effort should be spent into good design to make software more valuable. | |
| 203 The Unix Philosophy shows a way of how to design software well. | |
| 7 | 204 It offers guidelines to achieve good quality and high gain for the effort spent. |
| 0 | 205 |
| 206 | |
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207 .H 1 "The Unix Philosophy |
| 4 | 208 .LP |
| 209 The origins of the Unix Philosophy were already introduced. | |
| 8 | 210 This chapter explains the philosophy, oriented on Gancarz, |
| 55 | 211 .[ |
| 212 gancarz | |
| 213 unix philosophy | |
| 214 .] | |
| 8 | 215 and shows concrete examples of its application. |
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216 |
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217 .H 2 Pipes |
| 0 | 218 .LP |
| 4 | 219 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 220 Knowledge of using the Unix shell is assumed. | |
| 221 .PP | |
| 222 Counting the number of files in the current directory: | |
| 41 | 223 .DS |
| 4 | 224 ls | wc -l |
| 225 .DE | |
| 226 The | |
| 227 .CW ls | |
| 228 command lists all files in the current directory, one per line, | |
| 229 and | |
| 230 .CW "wc -l | |
| 8 | 231 counts the number of lines. |
| 4 | 232 .PP |
| 8 | 233 Counting the number of files that do not contain ``foo'' in their name: |
| 41 | 234 .DS |
| 4 | 235 ls | grep -v foo | wc -l |
| 236 .DE | |
| 237 Here, the list of files is filtered by | |
| 238 .CW grep | |
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239 to remove all lines that contain ``foo''. |
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240 The rest equals the previous example. |
| 4 | 241 .PP |
| 242 Finding the five largest entries in the current directory. | |
| 41 | 243 .DS |
| 4 | 244 du -s * | sort -nr | sed 5q |
| 245 .DE | |
| 246 .CW "du -s * | |
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247 returns the recursively summed sizes of all files in the current directory |
| 8 | 248 \(en no matter if they are regular files or directories. |
| 4 | 249 .CW "sort -nr |
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250 sorts the list numerically in reverse order (descending). |
| 4 | 251 Finally, |
| 252 .CW "sed 5q | |
| 253 quits after it has printed the fifth line. | |
| 254 .PP | |
| 255 The presented command lines are examples of what Unix people would use | |
| 256 to get the desired output. | |
| 257 There are also other ways to get the same output. | |
| 258 It's a user's decision which way to go. | |
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259 .PP |
| 8 | 260 The examples show that many tasks on a Unix system |
| 4 | 261 are accomplished by combining several small programs. |
| 262 The connection between the single programs is denoted by the pipe operator `|'. | |
| 263 .PP | |
| 264 Pipes, and their extensive and easy use, are one of the great | |
| 265 achievements of the Unix system. | |
| 266 Pipes between programs have been possible in earlier operating systems, | |
| 267 but it has never been a so central part of the concept. | |
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268 When, in the early seventies, Doug McIlroy introduced pipes into the |
| 4 | 269 Unix system, |
| 270 ``it was this concept and notation for linking several programs together | |
| 271 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 272 .[ | |
| 44 | 273 aughenbaugh |
| 274 unix oral history | |
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275 .] |
| 4 | 276 .PP |
| 277 Being able to specify pipelines in an easy way is, | |
| 278 however, not enough by itself. | |
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279 It is only one half. |
| 4 | 280 The other is the design of the programs that are used in the pipeline. |
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281 They need interfaces that allow them to be used in such a way. |
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282 |
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283 .H 2 "Interface design |
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284 .LP |
| 11 | 285 Unix is, first of all, simple \(en Everything is a file. |
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286 Files are sequences of bytes, without any special structure. |
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287 Programs should be filters, which read a stream of bytes from standard input (stdin) |
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288 and write a stream of bytes to standard output (stdout). |
| 8 | 289 If the files \fIare\fP sequences of bytes, |
| 290 and the programs \fIare\fP filters on byte streams, | |
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291 then there is exactly one data interface. |
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292 Hence it is possible to combine programs in any desired way. |
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293 .PP |
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294 Even a handful of small programs yields a large set of combinations, |
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295 and thus a large set of different functions. |
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296 This is leverage! |
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297 If the programs are orthogonal to each other \(en the best case \(en |
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298 then the set of different functions is greatest. |
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299 .PP |
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300 Programs can also have a separate control interface, |
| 11 | 301 besides their data interface. |
| 302 The control interface is often called ``user interface'', | |
| 303 because it is usually designed to be used by humans. | |
| 304 The Unix Philosophy discourages to assume the user to be human. | |
| 305 Interactive use of software is slow use of software, | |
| 306 because the program waits for user input most of the time. | |
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307 Interactive software requires the user to be in front of the computer. |
| 11 | 308 Interactive software occupy the user's attention while they are running. |
| 309 .PP | |
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310 Now to come back to the idea of combining several small programs, |
| 11 | 311 to have a more specific function. |
| 312 If these single tools would all be interactive, | |
| 313 how would the user control them? | |
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314 It is not only a problem to control several programs at once, |
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315 if they run at the same time, |
| 11 | 316 it also very inefficient to have to control each of the single programs |
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317 that are intended to act as one large program. |
| 11 | 318 Hence, the Unix Philosophy discourages programs to demand interactive use. |
| 319 The behavior of programs should be defined at invocation. | |
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320 This is done by specifying arguments to the program call |
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321 (command line switches). |
| 11 | 322 Gancarz discusses this topic as ``avoid captive user interfaces''. |
| 46 | 323 .[ [ |
| 44 | 324 gancarz unix philosophy |
| 46 | 325 .], page 88 ff.] |
| 11 | 326 .PP |
| 327 Non-interactive use is, during development, also an advantage for testing. | |
| 328 Testing of interactive programs is much more complicated, | |
| 329 than testing of non-interactive programs. | |
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330 |
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331 .H 2 "The toolchest approach |
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332 .LP |
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333 A toolchest is a set of tools. |
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334 Instead of having one big tool for all tasks, one has many small tools, |
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335 each for one task. |
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336 Difficult tasks are solved by combining several of the small, simple tools. |
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337 .PP |
| 11 | 338 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 339 that are filters on byte streams. | |
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340 They are, to a large extent, unrelated in their function. |
| 11 | 341 Hence, the Unix toolchest provides a large set of functions |
| 342 that can be accessed by combining the programs in the desired way. | |
| 343 .PP | |
| 344 There are also advantages for developing small toolchest programs. | |
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345 It is easier and less error-prone to write small programs. |
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346 It is also easier and less error-prone to write a large set of small programs, |
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347 than to write one large program with all the functionality included. |
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348 If the small programs are combinable, then they offer even a larger set |
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349 of functions than the single large program. |
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350 Hence, one gets two advantages out of writing small, combinable programs: |
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351 They are easier to write and they offer a greater set of functions through |
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352 combination. |
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353 .PP |
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354 But there are also two main drawbacks of the toolchest approach. |
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355 First, one simple, standardized interface has to be sufficient. |
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356 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 357 then a different approach might be of need. |
| 13 | 358 But it is also possible, that he just can not imagine a design where |
| 8 | 359 a stream of bytes is sufficient. |
| 360 By becoming more familiar with the ``Unix style of thinking'', | |
| 361 developers will more often and easier find simple designs where | |
| 362 a stream of bytes is a sufficient interface. | |
| 363 .PP | |
| 364 The second drawback of a toolchest affects the users. | |
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365 A toolchest is often more difficult to use. |
| 9 | 366 It is necessary to become familiar with each of the tools, |
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367 to be able to use the right one in a given situation. |
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368 Additionally, one needs to combine the tools in a sensible way himself. |
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369 This is like a sharp knife \(en it is a powerful tool in the hand of a |
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370 master, but of no good value in the hand of an unskilled. |
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371 However, learning single, small tools of a toolchest is easier than |
| 8 | 372 learning a complex tool. |
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373 And the user will already have a basic understanding of a yet unknown tool, |
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374 if the tools of a toolchest have a common, consistent style. |
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375 He will be able to transfer knowledge over from one tool to another. |
| 8 | 376 .PP |
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377 Moreover, the second drawback can be removed to a large extent |
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378 by adding wrappers around the basic tools. |
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379 Novice users do not need to learn several tools, if a professional wraps |
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380 complete command lines into a higher-level script. |
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381 Note that the wrapper script still calls the small tools; |
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382 it is just like a skin around them. |
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383 No complexity is added this way. |
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384 But new programs can get created out of existing one with very low effort. |
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385 .PP |
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386 A wrapper script for finding the five largest entries in the current directory |
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387 could look like this: |
| 41 | 388 .DS |
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389 #!/bin/sh |
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390 du -s * | sort -nr | sed 5q |
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391 .DE |
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392 The script itself is just a text file that calls the command line, |
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393 which a professional user would type in directly. |
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394 It is probably worth to make the program flexible on the number of |
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395 entries it prints: |
| 41 | 396 .DS |
| 8 | 397 #!/bin/sh |
| 398 num=5 | |
| 399 [ $# -eq 1 ] && num="$1" | |
| 400 du -sh * | sort -nr | sed "${num}q" | |
| 401 .DE | |
| 402 This script acts like the one before, when called without an argument. | |
| 403 But one can also specify a numerical argument to define the number of lines to print. | |
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404 One can surely imagine even more flexible versions, however, |
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405 they will still relay on the external programs, |
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406 which do the actual work. |
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407 |
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408 .H 2 "A powerful shell |
| 8 | 409 .LP |
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410 The Unix shell provides the possibility to combine small programs into large ones. |
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411 But a powerful shell is a great feature in other ways, too. |
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412 For instance by being scriptable. |
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413 Control statements are built into the shell. |
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414 The functions, however, are the normal programs of the system. |
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415 Thus, as the programs are already known, |
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416 learning to program in the shell becomes easy. |
| 8 | 417 Using normal programs as functions in the shell programming language |
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418 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 419 .PP |
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420 The Unix shell encourages to write small scripts, |
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421 by combining existing programs, because it is so easy to do. |
| 8 | 422 This is a great step towards automation. |
| 423 It is wonderful if the effort to automate a task equals the effort | |
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424 to do the task a second time by hand. |
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425 If this holds, |
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426 then the user will be happy to automate everything he does more than once. |
| 8 | 427 .PP |
| 428 Small programs that do one job well, standardized interfaces between them, | |
| 429 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 430 this will inevitably produce software leverage. | |
| 431 Getting multiple times the benefit of an investment is a great offer. | |
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432 .PP |
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433 The shell also encourages rapid prototyping. |
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434 Many well known programs started as quickly hacked shell scripts, |
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435 and turned into ``real'' programs, written in C, later. |
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436 Building a prototype first, is a way to avoid the biggest problems |
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437 in application development. |
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438 Fred Brooks explains in ``No Silver Bullet'': |
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439 .[ |
| 44 | 440 brooks |
| 441 no silver bullet | |
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442 .] |
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443 .QP |
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444 The hardest single part of building a software system is deciding precisely what to build. |
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445 No other part of the conceptual work is so difficult as establishing the detailed |
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446 technical requirements, [...]. |
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447 No other part of the work so cripples the resulting system if done wrong. |
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448 No other part is more difficult to rectify later. |
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449 .PP |
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450 Writing a prototype is a great method for becoming familiar with the requirements |
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451 and to run into real problems early. |
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452 .[ [ |
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453 gancarz |
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454 unix philosophy |
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455 .], page 28 f.] |
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456 .PP |
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457 Prototyping is often seen as a first step in building software. |
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458 This is, of course, good. |
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459 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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460 After having built the prototype, one might notice, that the prototype is already |
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461 \fIgood enough\fP. |
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462 Hence, no reimplementation, in a more sophisticated programming language, |
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463 might be of need, at least for the moment. |
| 23 | 464 Maybe later, it might be necessary to rewrite the software, but not now. |
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465 By delaying further work, one keeps the flexibility to react on |
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466 changing requirements. |
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467 Software parts that are not written will not miss the requirements. |
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468 |
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469 .H 2 "Worse is better |
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470 .LP |
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471 The Unix Philosophy aims for the 90% solution; |
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472 others call it the ``Worse is better'' approach. |
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473 Experience from real life projects shows: |
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474 .PP |
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475 (1) It is almost never possible to define the |
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476 requirements completely and correctly the first time. |
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477 Hence one should not try to; one will fail anyway. |
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478 .PP |
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479 (2) Requirements change during time. |
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480 Hence it is best to delay requirement-based design decisions as long as possible. |
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481 Software should be small and flexible as long as possible |
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482 to react on changing requirements. |
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483 Shell scripts, for example, are more easily adjusted as C programs. |
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484 .PP |
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485 (3) Maintenance work is hard work. |
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486 Hence, one should keep the amount of code as small as possible; |
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487 it should just fulfill the \fIcurrent\fP requirements. |
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488 Software parts that will be written in future, |
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489 do not need maintenance till then. |
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490 .PP |
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491 See Brooks' ``The Mythical Man-Month'' for reference. |
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492 .[ [ |
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493 brooks |
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494 mythical man-month |
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495 .], page 115 ff.] |
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496 .PP |
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497 Starting with a prototype in a scripting language has several advantages: |
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498 .IP \(bu |
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499 As the initial effort is low, one will likely start right away. |
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500 .IP \(bu |
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501 As working parts are available soon, the real requirements can get identified soon. |
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502 .IP \(bu |
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503 When software is usable and valuable, it gets used, and thus tested. |
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504 Hence problems will be found at early stages of the development. |
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505 .IP \(bu |
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506 The prototype might be enough for the moment, |
| 51 | 507 thus further work can get delayed to a time |
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508 when one knows better about the requirements and problems, |
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509 than now. |
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510 .IP \(bu |
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511 Implementing now only the parts that are actually needed at the moment, |
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512 introduces fewer programming and maintenance work. |
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513 .IP \(bu |
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514 If the global situation changes so that the software is not needed anymore, |
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515 then less effort was spent into the project, than it would have be |
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516 when a different approach had been used. |
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517 |
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518 .H 2 "Upgrowth and survival of software |
| 11 | 519 .LP |
| 12 | 520 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 521 Although these are just verbs, they do imply a specific view on the work process |
| 522 they describe. | |
| 12 | 523 The better verb, however, is to \fIgrow\fP. |
| 524 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 525 It starts with a first prototype, which evolves as requirements change. | |
| 526 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 527 compiled program this way. |
| 528 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
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529 While being alive it will get extended, rearranged, rebuilt. |
| 12 | 530 Growing software matches the view that ``software is never finished. It is only released.'' |
| 46 | 531 .[ [ |
| 44 | 532 gancarz |
| 533 unix philosophy | |
| 46 | 534 .], page 26] |
| 12 | 535 .PP |
| 13 | 536 Software can be seen as being controlled by evolutionary processes. |
| 537 Successful software is software that is used by many for a long time. | |
| 12 | 538 This implies that the software is needed, useful, and better than alternatives. |
| 539 Darwin talks about: ``The survival of the fittest.'' | |
| 540 .[ | |
| 44 | 541 darwin |
| 542 origin of species | |
| 12 | 543 .] |
| 544 Transferred to software: The most successful software, is the fittest, | |
| 545 is the one that survives. | |
| 13 | 546 (This may be at the level of one creature, or at the level of one species.) |
| 547 The fitness of software is affected mainly by four properties: | |
| 15 | 548 portability of code, portability of data, range of usability, and reusability of parts. |
| 13 | 549 .PP |
| 15 | 550 (1) |
| 551 .I "Portability of code | |
| 552 means, using high-level programming languages, | |
| 13 | 553 sticking to the standard, |
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554 .[ [ |
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555 kernighan pike |
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556 practice of programming |
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557 .], chapter\|8] |
| 13 | 558 and avoiding optimizations that introduce dependencies on specific hardware. |
| 559 Hardware has a much lower lifetime than software. | |
| 560 By chaining software to a specific hardware, | |
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561 its lifetime gets shortened to that of this hardware. |
| 13 | 562 In contrast, software should be easy to port \(en |
| 23 | 563 adaptation is the key to success. |
| 13 | 564 .PP |
| 15 | 565 (2) |
| 566 .I "Portability of data | |
| 567 is best achieved by avoiding binary representations | |
| 13 | 568 to store data, because binary representations differ from machine to machine. |
| 23 | 569 Textual representation is favored. |
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570 Historically, \s-1ASCII\s0 was the charset of choice. |
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571 For the future, \s-1UTF\s0-8 might be the better choice. |
| 13 | 572 Important is that it is a plain text representation in a |
| 573 very common charset encoding. | |
| 574 Apart from being able to transfer data between machines, | |
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575 readable data has the great advantage, that humans are able to directly |
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576 read and edit it with text editors and other tools from the Unix toolchest. |
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577 .[ [ |
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578 gancarz |
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579 unix philosophy |
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580 .], page 56 ff.] |
| 12 | 581 .PP |
| 15 | 582 (3) |
| 583 A large | |
| 584 .I "range of usability | |
| 23 | 585 ensures good adaptation, and thus good survival. |
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586 It is a special distinction if software becomes used in fields of action, |
| 13 | 587 the original authors did never imagine. |
| 588 Software that solves problems in a general way will likely be used | |
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589 for many kinds of similar problems. |
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590 Being too specific limits the range of usability. |
| 13 | 591 Requirements change through time, thus use cases change or even vanish. |
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592 As a good example in this point, |
| 13 | 593 Allman identifies flexibility to be one major reason for sendmail's success: |
| 594 .[ | |
| 44 | 595 allman |
| 596 sendmail | |
| 13 | 597 .] |
| 598 .QP | |
| 599 Second, I limited myself to the routing function [...]. | |
| 600 This was a departure from the dominant thought of the time, [...]. | |
| 601 .QP | |
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602 Third, the sendmail configuration file was flexible enough to adapt |
| 13 | 603 to a rapidly changing world [...]. |
| 604 .LP | |
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605 Successful software adapts itself to the changing world. |
| 12 | 606 .PP |
| 15 | 607 (4) |
| 608 .I "Reuse of parts | |
| 609 is even one step further. | |
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610 Software may completely lose its field of action, |
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611 but parts of which the software is built may be general and independent enough |
| 13 | 612 to survive this death. |
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613 If software is built by combining small independent programs, |
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614 then these parts are readily available for reuse. |
| 13 | 615 Who cares if the large program is a failure, |
| 616 but parts of it become successful instead? | |
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617 |
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618 .H 2 "Summary |
| 0 | 619 .LP |
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620 This chapter explained central ideas of the Unix Philosophy. |
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621 For each of the ideas, the advantages they introduce were explained. |
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622 The Unix Philosophy are guidelines that help to write more valuable software. |
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623 From the view point of a software developer or software designer, |
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624 the Unix Philosophy provides answers to many software design problem. |
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625 .PP |
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626 The various ideas of the Unix Philosophy are very interweaved |
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627 and can hardly be applied independently. |
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628 However, the probably most important messages are: |
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629 .I "``Keep it simple!''" , |
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630 .I "``Do one thing well!''" , |
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631 and |
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632 .I "``Use software leverage!'' |
| 0 | 633 |
| 8 | 634 |
| 635 | |
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636 .H 1 "Case study: \s-1MH\s0 |
| 18 | 637 .LP |
| 30 | 638 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 639 from a general point of view. |
| 30 | 640 The driving force were the guidelines; references to |
| 18 | 641 existing software were given only sparsely. |
| 642 In this and the next chapter, concrete software will be | |
| 643 the driving force in the discussion. | |
| 644 .PP | |
| 23 | 645 This first case study is about the mail user agents (\s-1MUA\s0) |
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646 \s-1MH\s0 (``mail handler'') and its descendant \fInmh\fP |
| 23 | 647 (``new mail handler''). |
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648 .[ |
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649 nmh website |
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650 .] |
| 23 | 651 \s-1MUA\s0s provide functions to read, compose, and organize mail, |
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652 but (ideally) not to transfer it. |
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653 In this document, the name \s-1MH\s0 will be used to include nmh. |
| 19 | 654 A distinction will only be made if differences between |
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655 \s-1MH\s0 and nmh are described. |
| 18 | 656 |
| 0 | 657 |
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658 .H 2 "Historical background |
| 0 | 659 .LP |
| 19 | 660 Electronic mail was available in Unix very early. |
| 30 | 661 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 662 which was already present in the First Edition. | |
| 46 | 663 .[ [ |
| 44 | 664 salus |
| 665 quarter century of unix | |
| 46 | 666 .], page 41 f.] |
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667 It was a small program that either printed the user's mailbox file |
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668 or appended text to someone else's mailbox file, |
| 19 | 669 depending on the command line arguments. |
| 670 .[ | |
| 44 | 671 manual mail(1) |
| 19 | 672 .] |
| 673 It was a program that did one job well. | |
| 23 | 674 This job was emailing, which was very simple then. |
| 19 | 675 .PP |
| 23 | 676 Later, emailing became more powerful, and thus more complex. |
| 19 | 677 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 678 independent handling of single messages, | |
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679 and long-time email storage, was not powerful enough anymore. |
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680 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') |
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681 to provide additional functions for emailing. |
| 19 | 682 Mail was still one program, but now it was large and did |
| 683 several jobs. | |
| 23 | 684 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 685 It is designed for humans, but is still scriptable. |
| 23 | 686 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 687 .[ |
| 44 | 688 ritter |
| 689 mailx history | |
| 19 | 690 .] |
| 30 | 691 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 692 followed Mail's direction. |
| 693 They are large, monolithic programs which include all emailing functions. | |
| 694 .PP | |
| 23 | 695 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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696 In the beginning, they also had used a monolithic mail system, |
| 30 | 697 called \s-1MS\s0 (for ``mail system''). |
| 19 | 698 But in 1977, Stockton Gaines and Norman Shapiro |
| 699 came up with a proposal of a new email system concept \(en | |
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700 one that honored the Unix Philosophy. |
| 19 | 701 The concept was implemented by Bruce Borden in 1978 and 1979. |
| 702 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 703 .PP |
| 704 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 705 at Berkeley, and several others have contributed to the software. |
| 18 | 706 However, it's core concepts remained the same. |
| 23 | 707 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 708 Richard Coleman started with \fInmh\fP, the new mail handler. |
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709 His goal was to improve \s-1MH\s0 especially in regard of |
| 23 | 710 the requirements of modern emailing. |
| 19 | 711 Today, nmh is developed by various people on the Internet. |
| 18 | 712 .[ |
| 44 | 713 ware |
| 714 rand history | |
| 18 | 715 .] |
| 716 .[ | |
| 44 | 717 peek |
| 718 mh | |
| 18 | 719 .] |
| 0 | 720 |
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721 .H 2 "Contrasts to monolithic mail systems |
| 0 | 722 .LP |
| 19 | 723 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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724 Although there might actually exist further, very little known, |
| 30 | 725 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 726 .PP |
| 30 | 727 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 728 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 729 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 730 and their function. |
| 731 It gives a feeling of how the toolchest looks like. | |
| 19 | 732 .IP \(bu |
| 733 .CW inc : | |
| 30 | 734 incorporate new mail (this is how mail enters the system) |
| 19 | 735 .IP \(bu |
| 736 .CW scan : | |
| 737 list messages in folder | |
| 738 .IP \(bu | |
| 739 .CW show : | |
| 740 show message | |
| 741 .IP \(bu | |
| 742 .CW next\fR/\fPprev : | |
| 743 show next/previous message | |
| 744 .IP \(bu | |
| 745 .CW folder : | |
| 746 change current folder | |
| 747 .IP \(bu | |
| 748 .CW refile : | |
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749 refile message into different folder |
| 19 | 750 .IP \(bu |
| 751 .CW rmm : | |
| 752 remove message | |
| 753 .IP \(bu | |
| 754 .CW comp : | |
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755 compose new message |
| 19 | 756 .IP \(bu |
| 757 .CW repl : | |
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758 reply to message |
| 19 | 759 .IP \(bu |
| 760 .CW forw : | |
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761 forward message |
| 19 | 762 .IP \(bu |
| 763 .CW send : | |
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764 send prepared message (this is how mail leaves the system) |
| 0 | 765 .LP |
| 19 | 766 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 767 The user does not leave the shell to run \s-1MH\s0, | |
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768 instead he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 769 Using a monolithic program with a captive user interface |
| 770 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 771 Using toolchests like \s-1MH\s0 means running programs, | |
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772 alone or in combination with others, also from other toolchests, |
| 23 | 773 without leaving the shell. |
| 30 | 774 |
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775 .H 2 "Data storage |
| 30 | 776 .LP |
| 34 | 777 \s-1MH\s0's mail storage is a directory tree under the user's |
| 778 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 779 where mail folders are directories and mail messages are text files | |
| 780 within them. | |
| 781 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
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782 the public message sequences of that folder, |
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783 for instance the \fIunseen\fP sequence for new messages. |
| 34 | 784 Mail messages are text files located in a mail folder. |
| 785 The files contain the messages as they were received. | |
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786 They are named by ascending numbers in each folder. |
| 19 | 787 .PP |
| 30 | 788 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 789 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 790 In the mbox format all messages are stored within one file. | |
| 791 This was a good solution in the early days, when messages | |
| 792 were only a few lines of text and were deleted soon. | |
| 793 Today, when single messages often include several megabytes | |
| 794 of attachments, it is a bad solution. | |
| 795 Another disadvantage of the mbox format is that it is | |
| 796 more difficult to write tools that work on mail messages, | |
| 797 because it is always necessary to first find and extract | |
| 798 the relevant message in the mbox file. | |
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799 With the \s-1MH\s0 mailbox format, each message is a separate file. |
| 30 | 800 Also, the problem of concurrent access to one mailbox is |
| 801 reduced to the problem of concurrent access to one message. | |
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802 The maildir format is generally similar to the \s-1MH\s0 format, |
| 30 | 803 but modified towards guaranteed reliability. |
| 804 This involves some complexity, unfortunately. | |
| 34 | 805 .PP |
| 806 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 807 working with Unix' toolchest on directory trees: | |
| 808 \f(CWscan\fP is like \f(CWls\fP, | |
| 809 \f(CWshow\fP is like \f(CWcat\fP, | |
| 810 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 811 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 812 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 813 .PP | |
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814 \s-1MH\s0 extends the context of processes in Unix by two more items, |
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815 for its tools: |
| 34 | 816 .IP \(bu |
| 817 The current mail folder, which is similar to the current working directory. | |
| 818 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 819 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 820 .IP \(bu | |
| 821 Sequences, which are named sets of messages in a mail folder. | |
| 822 The current message, relative to a mail folder, is a special sequence. | |
| 823 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 824 .LP | |
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825 In contrast to Unix' context, which is maintained by the kernel, |
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826 \s-1MH\s0's context must be maintained by the tools themselves. |
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827 Usually there is one context per user, which resides in his |
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828 \f(CWcontext\fP file in the \s-1MH\s0 directory, |
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829 but a user can have several contexts, too. |
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830 Public sequences are an exception, as they belong to a mail folder, |
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831 and reside in the \f(CW.mh_sequences\fP file there. |
| 34 | 832 .[ |
| 44 | 833 man page mh-profile mh-sequence |
| 34 | 834 .] |
| 20 | 835 |
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836 .H 2 "Discussion of the design |
| 20 | 837 .LP |
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838 This section discusses \s-1MH\s0 in regard to the tenets |
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839 of the Unix Philosophy that Gancarz identified. |
| 20 | 840 |
| 841 .PP | |
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842 .B "Small is beautiful |
| 20 | 843 and |
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844 .B "do one thing well |
| 20 | 845 are two design goals that are directly visible in \s-1MH\s0. |
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846 Gancarz actually presents \s-1MH\s0 in his book as example under the |
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847 headline ``Making \s-1UNIX\s0 Do One Thing Well'': |
| 46 | 848 .[ [ |
| 44 | 849 gancarz |
| 850 unix philosophy | |
| 46 | 851 .], page 125 ff.] |
| 20 | 852 .QP |
| 853 [\s-1MH\s0] consists of a series of programs which | |
| 854 when combined give the user an enormous ability | |
| 855 to manipulate electronic mail messages. | |
| 856 A complex application, it shows that not only is it | |
| 857 possible to build large applications from smaller | |
| 858 components, but also that such designs are actually preferable. | |
| 0 | 859 .LP |
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860 The various programs of \s-1MH\s0 were relatively easy to write, |
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861 because each of them is small, limited to one function, |
| 23 | 862 and has clear boundaries. |
| 20 | 863 For the same reasons, they are also good to maintain. |
| 864 Further more, the system can easily get extended. | |
| 865 One only needs to put a new program into the toolchest. | |
| 23 | 866 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 867 (e.g. \f(CWmhbuild\fP). |
| 868 Also, different programs can exist to do the basically same job | |
| 869 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
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870 .PP |
| 20 | 871 If someone needs a mail system with some additionally |
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872 functions that are not available anywhere yet, he best expands a |
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873 toolchest system like \s-1MH\s0. |
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874 There he can add new functionality by simply adding additional |
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875 programs to the toolchest. |
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876 There he does not risk to break existing functionality by doing so. |
| 20 | 877 |
| 878 .PP | |
| 34 | 879 .B "Store data in flat text files |
| 880 is followed by \s-1MH\s0. | |
| 881 This is not surprising, because email messages are already plain text. | |
| 882 \s-1MH\s0 stores the messages as it receives them, | |
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883 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate |
| 34 | 884 on the messages in an \s-1MH\s0 mailbox. |
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885 All other files \s-1MH\s0 uses are plain text, too. |
| 34 | 886 It is therefore possible and encouraged to use the text processing |
| 887 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 888 |
| 889 .PP | |
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890 .B "Avoid captive user interfaces" . |
| 19 | 891 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 892 It offers all functions directly and without captive user interfaces. | |
| 30 | 893 If, nonetheless, users want a graphical user interface, |
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894 they can have it with \fIxmh\fP, \fIexmh\fP, |
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895 or with the Emacs interface \fImh-e\fP. |
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896 These are frontends for the \s-1MH\s0 toolchest. |
| 19 | 897 This means, all email-related work is still done by \s-1MH\s0 tools, |
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898 but the frontend calls the appropriate commands when the user |
|
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899 clicks on buttons or pushes a key. |
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900 .PP |
| 20 | 901 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 902 approach, because it does not limit the power of the backend itself. |
| 20 | 903 The frontend will anyway only be able to make a subset of the |
| 23 | 904 backend's power and flexibility available to the user. |
| 20 | 905 But if it is a separate program, |
| 906 then the missing parts can still be accessed at the backend directly. | |
| 19 | 907 If it is integrated, then this will hardly be possible. |
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908 An additional advantage is the possibility to have different frontends |
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909 to the same backend. |
| 19 | 910 |
| 911 .PP | |
|
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912 .B "Choose portability over efficiency |
| 20 | 913 and |
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914 .B "use shell scripts to increase leverage and portability" . |
| 20 | 915 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 916 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 917 .[ |
| 44 | 918 bolsky korn |
| 919 korn shell | |
| 20 | 920 .] |
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921 Chapter\|18 of the book shows a basic implementation |
| 20 | 922 of a subset of \s-1MH\s0 in ksh scripts. |
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923 Of course, this is just a demonstration, but a brilliant one. |
| 20 | 924 It shows how quickly one can implement such a prototype with shell scripts, |
| 925 and how readable they are. | |
| 926 The implementation in the scripting language may not be very fast, | |
| 927 but it can be fast enough though, and this is all that matters. | |
| 928 By having the code in an interpreted language, like the shell, | |
| 929 portability becomes a minor issue, if we assume the interpreter | |
| 930 to be widespread. | |
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931 .PP |
| 20 | 932 This demonstration also shows how easy it is to create single programs |
| 933 of a toolchest software. | |
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934 Eight tools (two of them have multiple names) and 16 functions |
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935 with supporting code are presented to the reader. |
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936 The tools comprise less than 40 lines of ksh each, |
| 30 | 937 in total about 200 lines. |
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938 The functions comprise less than 80 lines of ksh each, |
| 30 | 939 in total about 450 lines. |
| 20 | 940 Such small software is easy to write, easy to understand, |
| 941 and thus easy to maintain. | |
| 23 | 942 A toolchest improves the possibility to only write some parts |
| 20 | 943 and though create a working result. |
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944 Expanding the toolchest, even without global changes, |
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945 will likely be possible. |
| 20 | 946 |
| 947 .PP | |
|
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948 .B "Use software leverage to your advantage |
| 20 | 949 and the lesser tenet |
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950 .B "allow the user to tailor the environment |
| 20 | 951 are ideally followed in the design of \s-1MH\s0. |
| 21 | 952 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 953 directly define default options to programs. |
| 954 It is even possible to define different default options | |
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955 depending on the name under which a program is called. |
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956 Software leverage is heavily encouraged by the ease of |
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957 creating shell scripts that run a specific command line, |
| 30 | 958 built of several \s-1MH\s0 programs. |
| 21 | 959 There is few software that so much wants users to tailor their |
| 960 environment and to leverage the use of the software, like \s-1MH\s0. | |
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961 .PP |
| 21 | 962 Just to make one example: |
| 23 | 963 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 964 program. |
| 30 | 965 It is possible to take one of the distributed format files |
| 21 | 966 or to write one yourself. |
| 967 To use the format as default for \f(CWscan\fP, a single line, | |
| 968 reading | |
| 969 .DS | |
| 970 scan: -form FORMATFILE | |
| 971 .DE | |
| 972 must be added to \f(CW.mh_profile\fP. | |
| 973 If one wants this different format as an additional command, | |
| 23 | 974 instead of changing the default, he needs to create a link to |
| 975 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 976 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
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977 as the option should only be in effect for a program that is called as |
| 21 | 978 \f(CWscan2\fP. |
| 20 | 979 |
| 980 .PP | |
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981 .B "Make every program a filter |
| 21 | 982 is hard to find in \s-1MH\s0. |
| 983 The reason therefore is that most of \s-1MH\s0's tools provide | |
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984 basic file system operations for mailboxes. |
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985 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, |
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986 and \f(CWrm\fP aren't filters neither. |
| 23 | 987 \s-1MH\s0 does not provide many filters itself, but it is a basis |
| 988 to write filters for. | |
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989 An example would be a mail text highlighter, |
| 30 | 990 that means a program that makes use of a color terminal to display |
| 991 header lines, quotations, and signatures in distinct colors. | |
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992 The author's version of such a program is an awk script with 25 lines. |
| 21 | 993 |
| 994 .PP | |
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995 .B "Build a prototype as soon as possible |
| 21 | 996 was again well followed by \s-1MH\s0. |
| 997 This tenet, of course, focuses on early development, which is | |
| 998 long time ago for \s-1MH\s0. | |
| 999 But without following this guideline at the very beginning, | |
| 23 | 1000 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1001 to ever create \s-1MH\s0. | |
| 1002 In Bruce' own words: | |
| 46 | 1003 .[ [ |
| 44 | 1004 ware rand history |
| 46 | 1005 .], page 132] |
| 21 | 1006 .QP |
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1007 [...] but [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1008 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1009 I proposed a very short project to prove the basic concepts, |
| 1010 and my management agreed. | |
| 1011 Looking back, I realize that I had been very lucky with my first design. | |
| 1012 Without nearly enough design work, | |
| 1013 I built a working environment and some header files | |
| 1014 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1015 inc, show/next/prev, and comp. | |
| 1016 [...] | |
| 1017 With these three, I was able to convince people that the structure was viable. | |
| 1018 This took about three weeks. | |
| 0 | 1019 |
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1020 .H 2 "Problems |
| 0 | 1021 .LP |
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1022 \s-1MH\s0 is not without problems. |
| 30 | 1023 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1024 .PP |
| 1025 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1026 when \s-1MH\s0 was designed. | |
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1027 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though. |
| 22 | 1028 \s-1MIME\s0 support and support for different character encodings |
| 1029 is available, but only on a moderate level. | |
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1030 This comes from limited development resources. |
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1031 More active developers could quickly change this. |
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1032 But \s-1MH\s0 is also limited by design, which is the larger problem. |
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1033 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extent. |
| 22 | 1034 These design conflicts are not easily solvable. |
| 1035 Possibly, they require a redesign. | |
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1036 \s-1IMAP\s0 may be too different to the classic mail model, |
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1037 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well. |
| 22 | 1038 .PP |
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1039 The other kind of problem are human habits. |
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1040 In this world, where almost all \s-1MUA\s0s are monolithic, |
| 22 | 1041 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 |
| 1042 like \s-1MH\s0. | |
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1043 The habits are so strong, that even people who understand the concept |
| 30 | 1044 and advantages of \s-1MH\s0 do not like to switch, |
| 1045 simply because \s-1MH\s0 is different. | |
| 1046 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
|
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1047 are quite outdated and thus not very appealing, compared to the modern interfaces |
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1048 of many monolithic \s-1MUA\s0s. |
|
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1049 One notable exception is \fImh-e\fP which provides an Emacs interface |
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1050 to \s-1MH\s0. |
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1051 \fIMh-e\fP looks much like \fImutt\fP or \fIpine\fP, |
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1052 but it has buttons, menus, and graphical display capabilities. |
| 20 | 1053 |
|
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1054 .H 2 "Summary |
| 20 | 1055 .LP |
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1056 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design. |
| 31 | 1057 It consists of a toolchest of small tools, each of them does one job well. |
| 1058 The toolchest approach offers great flexibility to the user. | |
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1059 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0. |
| 31 | 1060 This makes \s-1MH\s0 a very powerful mail system. |
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1061 Extending and customizing \s-1MH\s0 is easy and encouraged. |
| 31 | 1062 .PP |
| 1063 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1064 Its overall design follows clear rules. | |
| 1065 The single tools do only one job, thus they are easy to understand, | |
| 1066 easy to write, and good to maintain. | |
| 1067 They are all independent and do not interfere with the others. | |
| 1068 Automated testing of their function is a straight forward task. | |
| 1069 .PP | |
| 1070 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1071 as its differentness is also its largest advantage. | |
| 1072 Unfortunately, for most people their habits are stronger | |
| 1073 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1074 |
| 8 | 1075 |
| 1076 | |
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1077 .H 1 "Case study: uzbl |
| 32 | 1078 .LP |
| 1079 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
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1080 which is an old and established software. |
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1081 This chapter covers uzbl, a fresh new project. |
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1082 Uzbl is a web browser that adheres to the Unix Philosophy. |
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1083 Its name comes from the \fILolspeak\fP word for ``usable''; |
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1084 it is pronounced identical. |
| 0 | 1085 |
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1086 .H 2 "Historical background |
| 0 | 1087 .LP |
| 32 | 1088 Uzbl was started by Dieter Plaetinck in April 2009. |
| 44 | 1089 The idea was born in a thread in the Arch Linux Forums. |
| 32 | 1090 .[ |
| 44 | 1091 arch linux forums |
| 1092 browser | |
| 32 | 1093 .] |
| 1094 After some discussion about failures of well known web browsers, | |
| 1095 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1096 of how a better web browser could look like. | |
| 1097 To the question of another member, if Plaetinck would write that program, | |
| 1098 because it would sound fantastic, Plaetinck replied: | |
| 1099 ``Maybe, if I find the time ;-)''. | |
| 1100 .PP | |
| 1101 Fortunately, he found the time. | |
| 1102 One day later, the first prototype was out. | |
| 1103 One week later, uzbl had an own website. | |
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1104 .[ |
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1105 uzbl website |
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1106 .] |
| 32 | 1107 One month after the first code showed up, |
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1108 a mailing list was installed to coordinate and discuss further development, |
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1109 and a wiki was added to store documentation and scripts that showed up on the |
| 32 | 1110 mailing list and elsewhere. |
| 1111 .PP | |
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1112 In the, now, one year of uzbl's existence, it was heavily developed on various branches. |
| 32 | 1113 Plaetinck's task became more and more to only merge the best code from the |
| 1114 different branches into his main branch, and to apply patches. | |
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1115 .[ |
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1116 lwn uzbl |
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1117 .] |
| 32 | 1118 About once a month, Plaetinck released a new version. |
| 1119 In September 2009, he presented several forks of uzbl. | |
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1120 .[ [ |
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1121 uzbl website |
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1122 .], news archive] |
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1123 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1124 .PP |
| 1125 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
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1126 .[ |
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1127 lwn uzbl |
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1128 .] |
| 32 | 1129 In September 2009, the uzbl web browser was on \fISlashdot\fP. |
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1130 .[ |
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1131 slashdot uzbl |
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1132 .] |
| 0 | 1133 |
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1134 .H 2 "Contrasts to other web browsers |
| 0 | 1135 .LP |
| 32 | 1136 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1137 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1138 .PP | |
| 1139 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1140 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1141 It handles commands and events to interface other programs, | |
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1142 and also displays webpages by using \fIwebkit\fP as render engine. |
| 32 | 1143 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, |
| 1144 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1145 to form a ``complete'' web browser. | |
| 1146 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1147 so uzbl-core is included. | |
| 1148 .PP | |
| 1149 Unlike most other web browsers, uzbl is mainly the mediator between the | |
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1150 various tools that cover single jobs. |
| 35 | 1151 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1152 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1153 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1154 .DS |
| 1155 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1156 .DE | |
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1157 The graphical rendering of the webpage is done by webkit, |
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1158 a web content engine. |
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1159 Uzbl-core is built around libwebkit. |
| 32 | 1160 .PP |
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1161 Downloads, browsing history, bookmarks, and the like are not provided |
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1162 by the core itself, like they are in other web browsers. |
| 35 | 1163 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1164 external applications which provide the actual functionality. | |
| 32 | 1165 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1166 includes a script that calls wget with appropriate options in | |
| 1167 a prepared environment. | |
| 1168 .PP | |
| 1169 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1170 This is their effort to achieve similar goals. | |
| 35 | 1171 But instead of using existing, external programs, modern web browsers |
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1172 include these functions. |
| 0 | 1173 |
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1174 .H 2 "Discussion of the design |
| 0 | 1175 .LP |
| 32 | 1176 This section discusses uzbl in regard of the Unix Philosophy, |
| 1177 as identified by Gancarz. | |
| 1178 | |
| 1179 .PP | |
| 35 | 1180 .B "Make each program do one thing well" . |
| 1181 Uzbl tries to be a web browser and nothing else. | |
|
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1182 The common definition of a web browser is, of course, highly influenced by |
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1183 existing implementations of web browsers, although they are degenerated. |
| 35 | 1184 Web browsers should be programs to browse the web, and nothing more. |
|
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1185 This is the one thing they should do. |
|
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1186 .PP |
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1187 Web browsers should not, for instance, manage downloads. |
| 35 | 1188 This is the job download managers exist for. |
| 1189 Download managers do primary care about being good in downloading files. | |
| 1190 Modern web browsers provide download management only as a secondary feature. | |
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1191 How could they do this job better, than programs that exist only for |
| 35 | 1192 this very job? |
| 1193 And how could anyone want less than the best download manager available? | |
| 32 | 1194 .PP |
| 35 | 1195 A web browser's job is to let the user browse the web. |
| 1196 This means, navigating through websites by following links. | |
|
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1197 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1198 It is covered by the webkit render engine, in uzbl's case. |
|
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1199 Audio and video content and files like PostScript, \s-1PDF\s0, |
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1200 and the like, are also not the job of a web browser. |
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1201 Such content should be handled by external programs \(en |
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1202 programs that were written to handle such data. |
| 35 | 1203 Uzbl strives to do it this way. |
|
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1204 .PP |
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1205 Remember Doug McIlroy: |
| 35 | 1206 .I |
| 1207 ``Write programs that do one thing and do it well. | |
| 1208 Write programs to work together.'' | |
| 1209 .R | |
| 1210 .PP | |
| 1211 The lesser tenet | |
| 1212 .B "allow the user to tailor the environment | |
| 1213 matches good here. | |
| 1214 There was the question, how anyone could want anything less than the | |
| 1215 best program for the job. | |
|
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1216 But as personal preferences matter, it is probably more important to ask: |
| 35 | 1217 How could anyone want something else than his preferred program for the job? |
|
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1218 .PP |
|
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1219 Usually users want one program for a specific job. |
| 35 | 1220 Hence, whenever the task is, for instance, downloading, |
|
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1221 the same download manager should be used. |
| 35 | 1222 More advanced users might want to have this download manager in this |
| 1223 situation and that one in that situation. | |
| 1224 They should be able to configure it this way. | |
| 1225 With uzbl, one can use any download manager the user wants. | |
|
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1226 To switch to a different one, only one line in a small handler script |
| 35 | 1227 needs to be changed. |
|
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1228 Alternatively it would be possible to query the program to use by |
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1229 reading a global file or an environment variable, in the handler script. |
|
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1230 Of course, one can tell uzbl to use a different handler script, too. |
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1231 This requires a one line change in uzbl's config file. |
|
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1232 .PP |
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1233 Uzbl does neither have its own download manager nor depends on a |
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1234 specific one, hence uzbl's browsing abilities will not be lowered by having |
| 35 | 1235 a bad download manager. |
|
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1236 Uzbl's download capabilities will be just as good as the ones of the best |
|
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1237 download manager available on the system. |
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1238 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1239 |
| 1240 .PP | |
|
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1241 .B "Use software leverage to your advantage" . |
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1242 Uzbl is designed to be extended by external tools. |
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1243 These external tools are usually wrapped by small handler shell scripts. |
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1244 Shell scripts are the glue in this approach. |
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1245 They make the various parts fit together. |
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1246 .PP |
|
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1247 The history mechanism of uzbl shall be presented as an example. |
|
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1248 Uzbl is configured to spawn a script to append an entry to the history |
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1249 whenever the event of a fully loaded page occurs. |
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1250 The script to append the entry to the history is not much more than: |
|
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1251 .DS |
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1252 #!/bin/sh |
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1253 file=/path/to/uzbl-history |
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1254 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1255 .DE |
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1256 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1257 .PP |
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1258 For loading an entry, a key is bound to spawn a load-from-history script. |
|
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1259 The script reverses the history to have newer entries first, |
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1260 then displays \fIdmenu\fP to let the user select an item, |
|
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1261 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
|
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1262 With error checking and corner case handling removed, |
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1263 the script looks like this: |
|
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1264 .DS |
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1265 #!/bin/sh |
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1266 file=/path/to/uzbl-history |
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1267 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1268 echo "uri $goto" > $4 |
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1269 .DE |
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1270 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1271 uzbl instance. |
| 32 | 1272 |
| 1273 .PP | |
|
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1274 .B "Avoid captive user interfaces" . |
|
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1275 One could say, that uzbl, to a large extent, actually \fIis\fP |
|
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1276 a captive user interface. |
| 37 | 1277 But the difference to most other web browsers is, that uzbl is only |
|
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1278 the captive user interface frontend (and the core of the backend). |
|
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1279 Many parts of the backend are independent of uzbl. |
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1280 Some are distributed with uzbl, for some external programs, |
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1281 handler scripts are distributed, |
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1282 but arbitrary additional functionality can be added if desired. |
| 37 | 1283 .PP |
| 1284 The frontend is captive \(en that is true. | |
| 1285 This is okay for the task of browsing the web, as this task is only relevant | |
| 1286 for humans. | |
| 1287 Automated programs would \fIcrawl\fP the web. | |
| 1288 That means, they read the source directly. | |
| 1289 The source includes all the semantics. | |
| 1290 The graphical representation is just for humans to transfer the semantics | |
| 1291 more intuitively. | |
| 32 | 1292 |
| 1293 .PP | |
|
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1294 .B "Make every program a filter" . |
| 37 | 1295 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1296 Thus it is difficult to see what graphical web browsers should filter. | |
|
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1297 Graphical web browsers exist almost only to be interactively used by humans. |
| 37 | 1298 The only case when one might want to automate the rendering function is |
| 1299 to generate images of rendered webpages. | |
| 1300 | |
| 1301 .PP | |
| 1302 .B "Small is beautiful" | |
|
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1303 is not easy to apply to a web browser, because modern web technology |
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1304 is very complex, hence the rendering task is very complex. |
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1305 Modern web browsers have to consist of many thousand lines of code, |
| 37 | 1306 unfortunately. |
| 1307 Using the toolchest approach and wrappers can split the browser into | |
| 1308 several small parts, tough. | |
| 1309 .PP | |
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1310 As of March 2010, uzbl-core consists of about 3\,500 lines of C code. |
| 37 | 1311 The distribution includes another 3\,500 lines of Shell and Python code, |
| 1312 which are the handler scripts and plugins like a modal interface. | |
|
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1313 Further more, uzbl uses functionality of external tools like |
|
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1314 \fIwget\fP and \fIsocat\fP. |
| 37 | 1315 Up to this point, uzbl looks pretty neat and small. |
|
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1316 The ugly part of uzbl is the web content render engine, webkit. |
| 37 | 1317 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1318 Unfortunately, small web render engines are not possible anymore |
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1319 because of the modern web. |
| 35 | 1320 |
| 1321 .PP | |
| 1322 .B "Build a prototype as soon as possible" . | |
| 1323 Plaetinck made his code public, right from the beginning. | |
|
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1324 Discussion and development was, and still is, open to everyone interested. |
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1325 Development versions of uzbl can be obtained very simply from the code |
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1326 repository. |
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1327 Within the first year of uzbl's existence, a new version was released |
| 35 | 1328 more often than once a month. |
|
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1329 Different forks and branches arose. |
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1330 They introduced new features, which were tested for suitability |
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1331 for the main branch. |
| 35 | 1332 The experiences of using prototypes influenced further development. |
| 1333 Actually, all development was community driven. | |
|
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1334 Plaetinck says, three months after uzbl's birth: |
| 35 | 1335 ``Right now I hardly code anything myself for Uzbl. |
| 1336 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1337 .[ | |
| 44 | 1338 lwn |
| 1339 uzbl | |
| 35 | 1340 .] |
| 32 | 1341 |
| 0 | 1342 |
|
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1343 .H 2 "Problems |
| 0 | 1344 .LP |
|
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1345 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1346 It is sad, but people use what they know. |
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1347 Fortunately, uzbl's user interface can look and feel very much the |
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1348 same as the one of the well known web browsers, |
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1349 hiding the internal differences. |
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1350 But uzbl has to provide this similar look and feel to be accepted |
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1351 as a ``normal'' browser by ``normal'' users. |
| 37 | 1352 .PP |
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1353 Though, the more important problem is the modern web. |
|
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1354 The modern web is simply broken. |
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1355 It has state in a state-less protocol, |
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1356 it misuses technologies, |
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1357 and it is helplessly overloaded. |
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1358 The result are web content render engines that must consist |
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1359 of hundreds of thousands lines of code. |
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1360 They also must combine and integrate many different technologies, |
|
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1361 only to make our modern web accessible. |
|
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1362 Website to image converter are hardly possible to run without |
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1363 human interaction because of state in sessions, impossible |
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1364 deep-linking, and unautomatable technologies. |
| 37 | 1365 .PP |
|
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1366 The web was misused to provide all kinds of imaginable wishes. |
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1367 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1368 |
| 8 | 1369 |
| 51 | 1370 .H 2 "Summary |
| 32 | 1371 .LP |
|
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1372 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1373 that is how uzbl is seen by its authors. |
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1374 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1375 It consists of independent parts that work together, |
|
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1376 while its core is mainly a mediator which glues the parts together. |
|
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1377 .PP |
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1378 Software leverage can excellently be seen in uzbl. |
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1379 External tools are used, independent tasks are separated |
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1380 in independent parts and glued together with small handler scripts. |
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1381 .PP |
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1382 As uzbl, more or less, consists of a set of tools and a bit |
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1383 of glue, anyone can put the parts together and expand it |
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1384 in any desired way. |
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1385 Uzbl is very flexible and customizable. |
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1386 These properties make it valuable for advanced users, |
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1387 but may keep novice users from using it. |
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1388 .PP |
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1389 But uzbl's main problem is the modern web, that makes it hard |
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1390 to design a sane web browser. |
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1391 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1392 |
| 8 | 1393 |
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1394 .H 1 "Final thoughts |
| 0 | 1395 |
| 1396 .LP | |
| 50 | 1397 This paper explained why good design is important. |
| 1398 It introduced the Unix Philosophy as guidelines to good design, | |
| 1399 in order to create good quality software. | |
| 1400 Then, real life software, that was designed with the Unix Philosophy | |
| 1401 in mind, was discussed. | |
| 1402 .PP | |
| 1403 Throughout the paper, the aim was do explain \fIwhy\fP something | |
| 1404 should be done the Unix way. | |
| 1405 It was tried to give reasons that expose that the Unix Philosophy | |
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1406 is a preferable way for designing software. |
| 50 | 1407 .PP |
| 1408 The Unix Philosophy is close to the software developer's point of view. | |
| 1409 Its main goal is taming the beast ``software complexity''. | |
| 1410 Hence it strives first and foremost for simplicity, of software. | |
| 1411 It might appear, that usability for people is a minor goal. | |
| 1412 Actually, the Unix Philosophy sees usability as a result of sound design. | |
| 1413 Sound design does not need to be most intuitive, | |
| 1414 but it will provide a consistent way to access the enormous power | |
| 1415 of software leverage. | |
| 1416 .PP | |
| 1417 Being able to solve some concrete problem becomes less and less important, | |
| 1418 as there is software available for nearly every possible task today. | |
| 1419 But the quality of software matters. | |
| 1420 It is important that we have \fIgood\fP software. | |
| 1421 .sp | |
| 0 | 1422 .LP |
| 50 | 1423 .B "But why the Unix Philosophy? |
| 1424 .PP | |
| 1425 The largest problem of software development is the complexity involved. | |
| 1426 It is the only part of the job that computers cannot take over. | |
| 1427 The Unix Philosophy fights complexity as main enemy. | |
| 1428 .PP | |
| 1429 On the other hand, | |
| 1430 the most unique gain of software is its ability to leverage. | |
| 1431 Current software still fails to make the best possible use of this ability. | |
| 1432 The Unix Philosophy concentrates much on exploiting this great opportunity. | |
| 0 | 1433 |
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1434 |
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1435 .bp |
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1436 .TL |
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1437 References |
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1438 .LP |
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1439 .XS |
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1440 .sp .5v |
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1441 .B |
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1442 References |
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1443 .XE |
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1444 .ev r |
| 42 | 1445 .nr PS -1 |
| 1446 .nr VS -1 | |
| 0 | 1447 .[ |
| 1448 $LIST$ | |
| 1449 .] | |
|
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1450 .nr PS +1 |
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1451 .nr VS +1 |
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1452 .ev |
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1453 |
| 42 | 1454 .bp |
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1455 .TL |
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1456 Table of Contents |
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1457 .LP |
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1458 .PX no |