Mercurial > docs > unix-phil
annotate unix-phil.ms @ 48:40caeb9e9b25
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| author | meillo@marmaro.de |
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| date | Mon, 12 Apr 2010 14:45:29 +0200 |
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8 . if !^\\$1^^ \&\\$1\f\\n(PQ\\$2 |
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10 .if n \{\ |
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11 . ie ^\\$1^^ .ul 999 |
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13 . if \\n(.$=1 \&\\$1 |
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14 . if \\n(.$>1 \&\\$1\c |
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15 . if \\n(.$>1 \&\\$2 |
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16 .\} |
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| 0 | 19 .ds [. \ [ |
| 20 .ds .] ] | |
| 42 | 21 |
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22 .de H |
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23 .if '\\$1'1' \{\ |
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24 . sp 2v |
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25 . nr PS +2 |
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26 . NH \\$1 |
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27 \\$2 |
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32 . B |
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33 \\*(SN \\$2 |
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34 . XE |
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35 .\} |
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36 .if '\\$1'2' \{\ |
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37 . NH \\$1 |
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38 \\$2 |
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39 . LP |
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41 \\*(SN \\$2 |
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42 . XE |
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43 .\} |
| 42 | 44 .. |
| 45 | |
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46 .am QP |
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47 .ps -1 |
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50 .am DS |
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51 .CW |
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52 .ps -1 |
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54 |
| 1 | 55 .\"---------------------------------------- |
| 42 | 56 |
| 0 | 57 .TL |
| 42 | 58 .ps +4 |
| 6 | 59 Why the Unix Philosophy still matters |
| 0 | 60 .AU |
| 61 markus schnalke <meillo@marmaro.de> | |
| 62 .AB | |
| 1 | 63 .ti \n(.iu |
| 39 | 64 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 65 Today, few software designers are aware of these concepts, |
| 39 | 66 and thus a lot of modern software is more limited than necessary |
| 67 and makes less use of software leverage than possible. | |
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68 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 69 .AE |
| 70 | |
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71 .FS |
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72 .ps -1 |
| 39 | 73 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
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74 Mentor was professor Franz Schweiggert. |
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75 Handed in on 2010-04-12. |
| 39 | 76 You may retrieve this document from |
| 77 .CW \s-1http://marmaro.de/docs \ . | |
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78 .FE |
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79 |
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80 .H 1 Introduction |
| 0 | 81 .LP |
| 40 | 82 The Unix Philosophy is the essence of how the Unix operating system, |
| 83 especially its toolchest, was designed. | |
| 84 It is no limited set of fixed rules, | |
| 85 but a loose set of guidelines which tell how to write software that | |
| 86 suites well into Unix. | |
| 87 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 88 The Wikipedia has an accurate definition: | |
| 89 .[ | |
| 44 | 90 wikipedia |
| 91 unix philosophy | |
| 40 | 92 .] |
| 93 .QP | |
| 94 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 95 approaches to developing software based on the experience of leading | |
| 96 developers of the Unix operating system. | |
| 3 | 97 .PP |
| 40 | 98 As there is no single definition of the Unix Philosophy, |
| 99 several people have stated their view on what it comprises. | |
| 1 | 100 Best known are: |
| 101 .IP \(bu | |
| 102 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 103 .[ | |
| 44 | 104 mahoney |
| 105 oral history | |
| 1 | 106 .] |
| 107 .IP \(bu | |
| 108 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 109 .[ | |
| 44 | 110 gancarz |
| 111 unix philosophy | |
| 1 | 112 .] |
| 113 .IP \(bu | |
| 114 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 115 .[ | |
| 44 | 116 raymond |
| 117 art of unix programming | |
| 1 | 118 .] |
| 0 | 119 .LP |
| 1 | 120 These different views on the Unix Philosophy have much in common. |
| 40 | 121 Especially, the main concepts are similar in all of them. |
| 122 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 123 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 124 | |
| 125 .PP | |
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126 The Unix Philosophy explains how to design good software for Unix. |
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127 Many concepts described here, base on facilities of Unix. |
| 40 | 128 Other operating systems may not offer such facilities, |
| 41 | 129 hence it may not be possible to design software in the way of the |
| 130 Unix Philosophy for them. | |
| 131 .PP | |
| 132 The Unix Philosophy has an idea of how the process of software development | |
| 133 should look like, but large parts of the philosophy are quite independent | |
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134 from a concrete development process. |
| 41 | 135 However, one will soon recognize that some development processes work well |
| 136 with the ideas of the Unix Philosophy and support them, while others are | |
| 137 at cross-purposes. | |
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138 Kent Beck's books about Extreme Programming are valuable supplemental |
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139 resources on this topic. |
| 40 | 140 .PP |
| 41 | 141 The question of how to actually write code and how the code should looks |
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142 like in detail, are out of focus here. |
| 41 | 143 ``The Practice of Programming'' by Kernighan and Pike, |
| 144 .[ | |
| 44 | 145 kernighan pike |
| 146 practice of programming | |
| 41 | 147 .] |
| 148 is a good book that covers this topic. | |
| 149 Its point of view matches to the one of this paper. | |
| 0 | 150 |
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151 .H 1 "Importance of software design in general |
| 0 | 152 .LP |
| 40 | 153 Software design is the planning of how the internal structure |
| 154 and external interfaces of a software should look like. | |
| 39 | 155 It has nothing to do with visual appearance. |
| 156 If we take a program as a car, then its color is of no matter. | |
| 157 Its design would be the car's size, its shape, the locations of doors, | |
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158 the passenger/space ratio, the available controls and instruments, |
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159 and so forth. |
| 39 | 160 .PP |
| 161 Why should software get designed at all? | |
| 6 | 162 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 163 Not designing software means programming without plan. |
| 164 This will pretty sure lead to horrible results. | |
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165 Software that is horrible to use and horrible to maintain. |
| 39 | 166 These two aspects are the visible ones. |
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167 Often invisible though, are the wasted possible gains. |
| 39 | 168 Good software design can make these gains available. |
| 6 | 169 .PP |
| 39 | 170 A software's design deals with quality properties. |
| 171 Good design leads to good quality, and quality is important. | |
| 172 Any car may be able to drive from A to B, | |
| 173 but it depends on the car's properties whether it is a good choice | |
| 174 for passenger transport or not. | |
| 175 It depends on its properties if it is a good choice | |
| 176 for a rough mountain area. | |
| 177 And it depends on its properties if the ride will be fun. | |
| 178 | |
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179 .PP |
| 39 | 180 Requirements for a software are twofold: |
| 181 functional and non-functional. | |
| 182 .IP \(bu | |
| 183 Functional requirements define directly the software's functions. | |
| 184 They are the reason why software gets written. | |
| 185 Someone has a problem and needs a tool to solve it. | |
| 186 Being able to solve the problem is the main functional goal. | |
| 187 It is the driving force behind all programming effort. | |
| 6 | 188 Functional requirements are easier to define and to verify. |
| 39 | 189 .IP \(bu |
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190 Non-functional requirements are called \fIquality\fP requirements, too. |
| 39 | 191 The quality of a software are the properties that are not directly related to |
| 192 the software's basic functions. | |
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193 Tools of bad quality often do solve the problems they were written for, |
| 39 | 194 but introduce problems and difficulties for usage and development, later on. |
| 195 Quality aspects are often overlooked at first sight, | |
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196 and are often difficult to define clearly and to verify. |
| 6 | 197 .PP |
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198 Quality is hardly interesting when the software gets built initially, |
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199 but it has a high impact on usability and maintenance of the software, later. |
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200 A short-sighted might see in developing a software, mainly building something up. |
| 39 | 201 But experience shows, that building the software the first time is |
| 202 only a small amount of the overall work. | |
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203 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en |
| 6 | 204 does soon take over the major part of the time spent on a software. |
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205 And of course, the time spent actually using the software. |
| 6 | 206 These processes are highly influenced by the software's quality. |
| 39 | 207 Thus, quality must not be neglected. |
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208 However, the problem with quality is that you hardly ``stumble over'' |
| 39 | 209 bad quality during the first build, |
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210 although this is the time when you should care about good quality most. |
| 6 | 211 .PP |
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212 Software design has little to do with the basic function of a software \(en |
| 39 | 213 this requirement will get satisfied anyway. |
| 214 Software design is more about quality aspects of the software. | |
| 215 Good design leads to good quality, bad design to bad quality. | |
| 6 | 216 The primary functions of the software will be affected modestly by bad quality, |
| 39 | 217 but good quality can provide a lot of additional gain, |
| 6 | 218 even at places where one never expected it. |
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219 .PP |
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220 The ISO/IEC\|9126-1 standard, part\|1, |
| 6 | 221 .[ |
| 44 | 222 iso product quality |
| 6 | 223 .] |
| 224 defines the quality model as consisting out of: | |
| 225 .IP \(bu | |
| 226 .I Functionality | |
| 227 (suitability, accuracy, inter\%operability, security) | |
| 228 .IP \(bu | |
| 229 .I Reliability | |
| 230 (maturity, fault tolerance, recoverability) | |
| 231 .IP \(bu | |
| 232 .I Usability | |
| 233 (understandability, learnability, operability, attractiveness) | |
| 234 .IP \(bu | |
| 235 .I Efficiency | |
| 9 | 236 (time behavior, resource utilization) |
| 6 | 237 .IP \(bu |
| 238 .I Maintainability | |
| 23 | 239 (analyzability, changeability, stability, testability) |
| 6 | 240 .IP \(bu |
| 241 .I Portability | |
| 242 (adaptability, installability, co-existence, replaceability) | |
| 243 .LP | |
| 39 | 244 Good design can improve these properties of a software, |
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245 bad designed software likely suffers in these points. |
| 7 | 246 .PP |
| 247 One further goal of software design is consistency. | |
| 248 Consistency eases understanding, working on, and using things. | |
| 39 | 249 Consistent internal structure and consistent interfaces to the outside |
| 250 can be provided by good design. | |
| 7 | 251 .PP |
| 39 | 252 Software should be well designed because good design avoids many |
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253 problems during a software's lifetime. |
| 39 | 254 And software should be well designed because good design can offer |
| 255 much additional gain. | |
| 256 Indeed, much effort should be spent into good design to make software more valuable. | |
| 257 The Unix Philosophy shows a way of how to design software well. | |
| 7 | 258 It offers guidelines to achieve good quality and high gain for the effort spent. |
| 0 | 259 |
| 260 | |
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261 .H 1 "The Unix Philosophy |
| 4 | 262 .LP |
| 263 The origins of the Unix Philosophy were already introduced. | |
| 8 | 264 This chapter explains the philosophy, oriented on Gancarz, |
| 265 and shows concrete examples of its application. | |
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267 .H 2 Pipes |
| 0 | 268 .LP |
| 4 | 269 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 270 Knowledge of using the Unix shell is assumed. | |
| 271 .PP | |
| 272 Counting the number of files in the current directory: | |
| 41 | 273 .DS |
| 4 | 274 ls | wc -l |
| 275 .DE | |
| 276 The | |
| 277 .CW ls | |
| 278 command lists all files in the current directory, one per line, | |
| 279 and | |
| 280 .CW "wc -l | |
| 8 | 281 counts the number of lines. |
| 4 | 282 .PP |
| 8 | 283 Counting the number of files that do not contain ``foo'' in their name: |
| 41 | 284 .DS |
| 4 | 285 ls | grep -v foo | wc -l |
| 286 .DE | |
| 287 Here, the list of files is filtered by | |
| 288 .CW grep | |
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289 to remove all lines that contain ``foo''. |
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290 The rest equals the previous example. |
| 4 | 291 .PP |
| 292 Finding the five largest entries in the current directory. | |
| 41 | 293 .DS |
| 4 | 294 du -s * | sort -nr | sed 5q |
| 295 .DE | |
| 296 .CW "du -s * | |
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297 returns the recursively summed sizes of all files in the current directory |
| 8 | 298 \(en no matter if they are regular files or directories. |
| 4 | 299 .CW "sort -nr |
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300 sorts the list numerically in reverse order (descending). |
| 4 | 301 Finally, |
| 302 .CW "sed 5q | |
| 303 quits after it has printed the fifth line. | |
| 304 .PP | |
| 305 The presented command lines are examples of what Unix people would use | |
| 306 to get the desired output. | |
| 307 There are also other ways to get the same output. | |
| 308 It's a user's decision which way to go. | |
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309 .PP |
| 8 | 310 The examples show that many tasks on a Unix system |
| 4 | 311 are accomplished by combining several small programs. |
| 312 The connection between the single programs is denoted by the pipe operator `|'. | |
| 313 .PP | |
| 314 Pipes, and their extensive and easy use, are one of the great | |
| 315 achievements of the Unix system. | |
| 316 Pipes between programs have been possible in earlier operating systems, | |
| 317 but it has never been a so central part of the concept. | |
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318 When, in the early seventies, Doug McIlroy introduced pipes into the |
| 4 | 319 Unix system, |
| 320 ``it was this concept and notation for linking several programs together | |
| 321 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 322 .[ | |
| 44 | 323 aughenbaugh |
| 324 unix oral history | |
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325 .] |
| 4 | 326 .PP |
| 327 Being able to specify pipelines in an easy way is, | |
| 328 however, not enough by itself. | |
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329 It is only one half. |
| 4 | 330 The other is the design of the programs that are used in the pipeline. |
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331 They need interfaces that allow them to be used in such a way. |
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332 |
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333 .H 2 "Interface design |
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334 .LP |
| 11 | 335 Unix is, first of all, simple \(en Everything is a file. |
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336 Files are sequences of bytes, without any special structure. |
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337 Programs should be filters, which read a stream of bytes from standard input (stdin) |
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338 and write a stream of bytes to standard output (stdout). |
| 8 | 339 If the files \fIare\fP sequences of bytes, |
| 340 and the programs \fIare\fP filters on byte streams, | |
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341 then there is exactly one data interface. |
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342 Hence it is possible to combine programs in any desired way. |
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343 .PP |
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344 Even a handful of small programs yields a large set of combinations, |
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345 and thus a large set of different functions. |
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346 This is leverage! |
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347 If the programs are orthogonal to each other \(en the best case \(en |
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348 then the set of different functions is greatest. |
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349 .PP |
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350 Programs can also have a separate control interface, |
| 11 | 351 besides their data interface. |
| 352 The control interface is often called ``user interface'', | |
| 353 because it is usually designed to be used by humans. | |
| 354 The Unix Philosophy discourages to assume the user to be human. | |
| 355 Interactive use of software is slow use of software, | |
| 356 because the program waits for user input most of the time. | |
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357 Interactive software requires the user to be in front of the computer. |
| 11 | 358 Interactive software occupy the user's attention while they are running. |
| 359 .PP | |
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360 Now to come back to the idea of combining several small programs, |
| 11 | 361 to have a more specific function. |
| 362 If these single tools would all be interactive, | |
| 363 how would the user control them? | |
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364 It is not only a problem to control several programs at once, |
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365 if they run at the same time, |
| 11 | 366 it also very inefficient to have to control each of the single programs |
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367 that are intended to act as one large program. |
| 11 | 368 Hence, the Unix Philosophy discourages programs to demand interactive use. |
| 369 The behavior of programs should be defined at invocation. | |
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370 This is done by specifying arguments to the program call |
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371 (command line switches). |
| 11 | 372 Gancarz discusses this topic as ``avoid captive user interfaces''. |
| 46 | 373 .[ [ |
| 44 | 374 gancarz unix philosophy |
| 46 | 375 .], page 88 ff.] |
| 11 | 376 .PP |
| 377 Non-interactive use is, during development, also an advantage for testing. | |
| 378 Testing of interactive programs is much more complicated, | |
| 379 than testing of non-interactive programs. | |
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380 |
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381 .H 2 "The toolchest approach |
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382 .LP |
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383 A toolchest is a set of tools. |
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384 Instead of having one big tool for all tasks, one has many small tools, |
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385 each for one task. |
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386 Difficult tasks are solved by combining several of the small, simple tools. |
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387 .PP |
| 11 | 388 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 389 that are filters on byte streams. | |
| 390 They are, to a large extend, unrelated in their function. | |
| 391 Hence, the Unix toolchest provides a large set of functions | |
| 392 that can be accessed by combining the programs in the desired way. | |
| 393 .PP | |
| 394 There are also advantages for developing small toolchest programs. | |
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395 It is easier and less error-prone to write small programs. |
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396 It is also easier and less error-prone to write a large set of small programs, |
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397 than to write one large program with all the functionality included. |
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398 If the small programs are combinable, then they offer even a larger set |
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399 of functions than the single large program. |
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400 Hence, one gets two advantages out of writing small, combinable programs: |
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401 They are easier to write and they offer a greater set of functions through |
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402 combination. |
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403 .PP |
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404 But there are also two main drawbacks of the toolchest approach. |
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405 First, one simple, standardized interface has to be sufficient. |
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406 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 407 then a different approach might be of need. |
| 13 | 408 But it is also possible, that he just can not imagine a design where |
| 8 | 409 a stream of bytes is sufficient. |
| 410 By becoming more familiar with the ``Unix style of thinking'', | |
| 411 developers will more often and easier find simple designs where | |
| 412 a stream of bytes is a sufficient interface. | |
| 413 .PP | |
| 414 The second drawback of a toolchest affects the users. | |
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415 A toolchest is often more difficult to use. |
| 9 | 416 It is necessary to become familiar with each of the tools, |
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417 to be able to use the right one in a given situation. |
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418 Additionally, one needs to combine the tools in a senseful way himself. |
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419 This is like a sharp knife \(en it is a powerful tool in the hand of a |
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420 master, but of no good value in the hand of an unskilled. |
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421 However, learning single, small tools of a toolchest is easier than |
| 8 | 422 learning a complex tool. |
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423 And the user will already have a basic understanding of a yet unknown tool, |
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424 if the tools of a toolchest have a common, consistent style. |
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425 He will be able to transfer knowledge over from one tool to another. |
| 8 | 426 .PP |
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427 Moreover, the second drawback can be removed to a large extend |
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428 by adding wrappers around the basic tools. |
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429 Novice users do not need to learn several tools, if a professional wraps |
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430 complete command lines into a higher-level script. |
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431 Note that the wrapper script still calls the small tools; |
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432 it is just like a skin around them. |
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433 No complexity is added this way. |
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434 But new programs can get created out of existing one with very low effort. |
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435 .PP |
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436 A wrapper script for finding the five largest entries in the current directory |
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437 could look like this: |
| 41 | 438 .DS |
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439 #!/bin/sh |
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440 du -s * | sort -nr | sed 5q |
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441 .DE |
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442 The script itself is just a text file that calls the command line, |
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443 which a professional user would type in directly. |
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444 It is probably worth to make the program flexible on the number of |
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445 entries it prints: |
| 41 | 446 .DS |
| 8 | 447 #!/bin/sh |
| 448 num=5 | |
| 449 [ $# -eq 1 ] && num="$1" | |
| 450 du -sh * | sort -nr | sed "${num}q" | |
| 451 .DE | |
| 452 This script acts like the one before, when called without an argument. | |
| 453 But one can also specify a numerical argument to define the number of lines to print. | |
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454 One can surely imagine even more flexible versions, however, |
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455 they will still relay on the external programs, |
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456 which do the actual work. |
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457 |
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458 .H 2 "A powerful shell |
| 8 | 459 .LP |
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460 The Unix shell provides the possibility to combine small programs into large ones. |
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461 But a powerful shell is a great feature in other ways, too. |
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462 For instance by being scriptable. |
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463 Control statements are build into the shell. |
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464 The functions, however, are the normal programs of the system. |
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465 Thus, as the programs are already known, |
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466 learning to program in the shell becomes easy. |
| 8 | 467 Using normal programs as functions in the shell programming language |
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468 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 469 .PP |
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470 The Unix shell encourages to write small scripts, |
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471 by combining existing programs, because it is so easy to do. |
| 8 | 472 This is a great step towards automation. |
| 473 It is wonderful if the effort to automate a task equals the effort | |
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474 to do the task a second time by hand. |
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475 If this holds, |
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476 then the user will be happy to automate everything he does more than once. |
| 8 | 477 .PP |
| 478 Small programs that do one job well, standardized interfaces between them, | |
| 479 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 480 this will inevitably produce software leverage. | |
| 481 Getting multiple times the benefit of an investment is a great offer. | |
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482 .PP |
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483 The shell also encourages rapid prototyping. |
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484 Many well known programs started as quickly hacked shell scripts, |
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485 and turned into ``real'' programs, written in C, later. |
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486 Building a prototype first, is a way to avoid the biggest problems |
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487 in application development. |
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488 Fred Brooks explains in ``No Silver Bullet'': |
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489 .[ |
| 44 | 490 brooks |
| 491 no silver bullet | |
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492 .] |
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493 .QP |
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494 The hardest single part of building a software system is deciding precisely what to build. |
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495 No other part of the conceptual work is so difficult as establishing the detailed |
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496 technical requirements, [...]. |
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497 No other part of the work so cripples the resulting system if done wrong. |
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498 No other part is more difficult to rectify later. |
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499 .PP |
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500 Writing a prototype is a great method for becoming familiar with the requirements |
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501 and to run into real problems early. |
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502 .[ [ |
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503 gancarz |
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504 unix philosophy |
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505 .], page 28 f.] |
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506 .PP |
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507 Prototyping is often seen as a first step in building a software. |
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508 This is, of course, good. |
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509 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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510 After having built the prototype, one might notice, that the prototype is already |
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511 \fIgood enough\fP. |
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512 Hence, no reimplementation, in a more sophisticated programming language, |
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513 might be of need, at least for the moment. |
| 23 | 514 Maybe later, it might be necessary to rewrite the software, but not now. |
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515 By delaying further work, one keeps the flexibility to react on |
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516 changing requirements. |
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517 Software parts that are not written will not miss the requirements. |
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518 |
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519 .H 2 "Worse is better |
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520 .LP |
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521 The Unix Philosophy aims for the 90% solution; |
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522 others call it the ``Worse is better'' approach. |
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523 Experience from real life projects shows: |
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524 .PP |
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525 (1) It is almost never possible to define the |
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526 requirements completely and correctly the first time. |
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527 Hence one should not try to; one will fail anyway. |
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528 .PP |
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529 (2) Requirements change during time. |
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530 Hence it is best to delay requirement-based design decisions as long as possible. |
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531 The software should be small and flexible as long as possible |
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532 to react on changing requirements. |
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533 Shell scripts, for example, are more easily adjusted as C programs. |
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534 .PP |
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535 (3) Maintenance work is hard work. |
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536 Hence, one should keep the amount of code as small as possible; |
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537 it should just fulfill the \fIcurrent\fP requirements. |
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538 Software parts that will be written in future, |
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539 do not need maintenance till then. |
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540 .PP |
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541 See Brooks' ``The Mythical Man-Month'' for reference. |
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542 .[ [ |
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543 brooks |
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544 mythical man-month |
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545 .], page 115 ff.] |
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546 .PP |
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547 Starting with a prototype in a scripting language has several advantages: |
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548 .IP \(bu |
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549 As the initial effort is low, one will likely start right away. |
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550 .IP \(bu |
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551 As working parts are available soon, the real requirements can get identified soon. |
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552 .IP \(bu |
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553 When a software is usable and valuable, it gets used, and thus tested. |
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554 Hence problems will be found at early stages of the development. |
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555 .IP \(bu |
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556 The prototype might be enough for the moment, |
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557 thus further work on the software can get delayed to a time |
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558 when one knows better about the requirements and problems, |
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559 than now. |
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560 .IP \(bu |
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561 Implementing now only the parts that are actually needed at the moment, |
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562 introduces fewer programming and maintenance work. |
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563 .IP \(bu |
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564 If the global situation changes so that the software is not needed anymore, |
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565 then less effort was spent into the project, than it would have be |
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566 when a different approach had been used. |
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567 |
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568 .H 2 "Upgrowth and survival of software |
| 11 | 569 .LP |
| 12 | 570 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 571 Although these are just verbs, they do imply a specific view on the work process |
| 572 they describe. | |
| 12 | 573 The better verb, however, is to \fIgrow\fP. |
| 574 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 575 It starts with a first prototype, which evolves as requirements change. | |
| 576 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 577 compiled program this way. |
| 578 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
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579 While being alive it will get extended, rearranged, rebuilt. |
| 12 | 580 Growing software matches the view that ``software is never finished. It is only released.'' |
| 46 | 581 .[ [ |
| 44 | 582 gancarz |
| 583 unix philosophy | |
| 46 | 584 .], page 26] |
| 12 | 585 .PP |
| 13 | 586 Software can be seen as being controlled by evolutionary processes. |
| 587 Successful software is software that is used by many for a long time. | |
| 12 | 588 This implies that the software is needed, useful, and better than alternatives. |
| 589 Darwin talks about: ``The survival of the fittest.'' | |
| 590 .[ | |
| 44 | 591 darwin |
| 592 origin of species | |
| 12 | 593 .] |
| 594 Transferred to software: The most successful software, is the fittest, | |
| 595 is the one that survives. | |
| 13 | 596 (This may be at the level of one creature, or at the level of one species.) |
| 597 The fitness of software is affected mainly by four properties: | |
| 15 | 598 portability of code, portability of data, range of usability, and reusability of parts. |
| 13 | 599 .PP |
| 15 | 600 (1) |
| 601 .I "Portability of code | |
| 602 means, using high-level programming languages, | |
| 13 | 603 sticking to the standard, |
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604 .[ [ |
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605 kernighan pike |
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606 practice of programming |
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607 .], chapter\|8] |
| 13 | 608 and avoiding optimizations that introduce dependencies on specific hardware. |
| 609 Hardware has a much lower lifetime than software. | |
| 610 By chaining software to a specific hardware, | |
| 611 the software's lifetime gets shortened to that of this hardware. | |
| 612 In contrast, software should be easy to port \(en | |
| 23 | 613 adaptation is the key to success. |
| 13 | 614 .PP |
| 15 | 615 (2) |
| 616 .I "Portability of data | |
| 617 is best achieved by avoiding binary representations | |
| 13 | 618 to store data, because binary representations differ from machine to machine. |
| 23 | 619 Textual representation is favored. |
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620 Historically, \s-1ASCII\s0 was the charset of choice. |
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621 For the future, \s-1UTF\s0-8 might be the better choice. |
| 13 | 622 Important is that it is a plain text representation in a |
| 623 very common charset encoding. | |
| 624 Apart from being able to transfer data between machines, | |
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625 readable data has the great advantage, that humans are able to directly |
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626 read and edit it with text editors and other tools from the Unix toolchest. |
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627 .[ [ |
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628 gancarz |
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629 unix philosophy |
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630 .], page 56 ff.] |
| 12 | 631 .PP |
| 15 | 632 (3) |
| 633 A large | |
| 634 .I "range of usability | |
| 23 | 635 ensures good adaptation, and thus good survival. |
| 13 | 636 It is a special distinction if a software becomes used in fields of action, |
| 637 the original authors did never imagine. | |
| 638 Software that solves problems in a general way will likely be used | |
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639 for many kinds of similar problems. |
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640 Being too specific limits the range of usability. |
| 13 | 641 Requirements change through time, thus use cases change or even vanish. |
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642 As a good example in this point, |
| 13 | 643 Allman identifies flexibility to be one major reason for sendmail's success: |
| 644 .[ | |
| 44 | 645 allman |
| 646 sendmail | |
| 13 | 647 .] |
| 648 .QP | |
| 649 Second, I limited myself to the routing function [...]. | |
| 650 This was a departure from the dominant thought of the time, [...]. | |
| 651 .QP | |
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652 Third, the sendmail configuration file was flexible enough to adapt |
| 13 | 653 to a rapidly changing world [...]. |
| 654 .LP | |
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655 Successful software adapts itself to the changing world. |
| 12 | 656 .PP |
| 15 | 657 (4) |
| 658 .I "Reuse of parts | |
| 659 is even one step further. | |
| 13 | 660 A software may completely lose its field of action, |
| 661 but parts of which the software is build may be general and independent enough | |
| 662 to survive this death. | |
| 663 If software is build by combining small independent programs, | |
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664 then these parts are readily available for reuse. |
| 13 | 665 Who cares if the large program is a failure, |
| 666 but parts of it become successful instead? | |
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667 |
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668 .H 2 "Summary |
| 0 | 669 .LP |
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670 This chapter explained central ideas of the Unix Philosophy. |
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671 For each of the ideas, the advantages they introduce were explained. |
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672 The Unix Philosophy are guidelines that help to write more valuable software. |
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673 From the view point of a software developer or software designer, |
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674 the Unix Philosophy provides answers to many software design problem. |
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675 .PP |
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676 The various ideas of the Unix Philosophy are very interweaved |
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677 and can hardly be applied independently. |
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678 However, the probably most important messages are: |
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679 .I "``Keep it simple!''" , |
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680 .I "``Do one thing well!''" , |
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681 and |
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682 .I "``Use software leverage!'' |
| 0 | 683 |
| 8 | 684 |
| 685 | |
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686 .H 1 "Case study: \s-1MH\s0 |
| 18 | 687 .LP |
| 30 | 688 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 689 from a general point of view. |
| 30 | 690 The driving force were the guidelines; references to |
| 18 | 691 existing software were given only sparsely. |
| 692 In this and the next chapter, concrete software will be | |
| 693 the driving force in the discussion. | |
| 694 .PP | |
| 23 | 695 This first case study is about the mail user agents (\s-1MUA\s0) |
| 696 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 697 (``new mail handler''). | |
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698 .[ |
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699 nmh website |
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700 .] |
| 23 | 701 \s-1MUA\s0s provide functions to read, compose, and organize mail, |
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702 but (ideally) not to transfer it. |
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703 In this document, the name \s-1MH\s0 will be used to include nmh. |
| 19 | 704 A distinction will only be made if differences between |
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705 \s-1MH\s0 and nmh are described. |
| 18 | 706 |
| 0 | 707 |
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708 .H 2 "Historical background |
| 0 | 709 .LP |
| 19 | 710 Electronic mail was available in Unix very early. |
| 30 | 711 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 712 which was already present in the First Edition. | |
| 46 | 713 .[ [ |
| 44 | 714 salus |
| 715 quarter century of unix | |
| 46 | 716 .], page 41 f.] |
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717 It was a small program that either printed the user's mailbox file |
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718 or appended text to someone elses mailbox file, |
| 19 | 719 depending on the command line arguments. |
| 720 .[ | |
| 44 | 721 manual mail(1) |
| 19 | 722 .] |
| 723 It was a program that did one job well. | |
| 23 | 724 This job was emailing, which was very simple then. |
| 19 | 725 .PP |
| 23 | 726 Later, emailing became more powerful, and thus more complex. |
| 19 | 727 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 728 independent handling of single messages, | |
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729 and long-time email storage, was not powerful enough anymore. |
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730 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') |
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731 to provide additional functions for emailing. |
| 19 | 732 Mail was still one program, but now it was large and did |
| 733 several jobs. | |
| 23 | 734 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 735 It is designed for humans, but is still scriptable. |
| 23 | 736 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 737 .[ |
| 44 | 738 ritter |
| 739 mailx history | |
| 19 | 740 .] |
| 30 | 741 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 742 followed Mail's direction. |
| 743 They are large, monolithic programs which include all emailing functions. | |
| 744 .PP | |
| 23 | 745 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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746 In the beginning, they also had used a monolithic mail system, |
| 30 | 747 called \s-1MS\s0 (for ``mail system''). |
| 19 | 748 But in 1977, Stockton Gaines and Norman Shapiro |
| 749 came up with a proposal of a new email system concept \(en | |
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750 one that honored the Unix Philosophy. |
| 19 | 751 The concept was implemented by Bruce Borden in 1978 and 1979. |
| 752 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 753 .PP |
| 754 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 755 at Berkeley, and several others have contributed to the software. |
| 18 | 756 However, it's core concepts remained the same. |
| 23 | 757 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 758 Richard Coleman started with \fInmh\fP, the new mail handler. |
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759 His goal was to improve \s-1MH\s0 especially in regard of |
| 23 | 760 the requirements of modern emailing. |
| 19 | 761 Today, nmh is developed by various people on the Internet. |
| 18 | 762 .[ |
| 44 | 763 ware |
| 764 rand history | |
| 18 | 765 .] |
| 766 .[ | |
| 44 | 767 peek |
| 768 mh | |
| 18 | 769 .] |
| 0 | 770 |
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771 .H 2 "Contrasts to monolithic mail systems |
| 0 | 772 .LP |
| 19 | 773 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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774 Although there might actually exist further, very little known, |
| 30 | 775 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 776 .PP |
| 30 | 777 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 778 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 779 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 780 and their function. |
| 781 It gives a feeling of how the toolchest looks like. | |
| 19 | 782 .IP \(bu |
| 783 .CW inc : | |
| 30 | 784 incorporate new mail (this is how mail enters the system) |
| 19 | 785 .IP \(bu |
| 786 .CW scan : | |
| 787 list messages in folder | |
| 788 .IP \(bu | |
| 789 .CW show : | |
| 790 show message | |
| 791 .IP \(bu | |
| 792 .CW next\fR/\fPprev : | |
| 793 show next/previous message | |
| 794 .IP \(bu | |
| 795 .CW folder : | |
| 796 change current folder | |
| 797 .IP \(bu | |
| 798 .CW refile : | |
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799 refile message into different folder |
| 19 | 800 .IP \(bu |
| 801 .CW rmm : | |
| 802 remove message | |
| 803 .IP \(bu | |
| 804 .CW comp : | |
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805 compose new message |
| 19 | 806 .IP \(bu |
| 807 .CW repl : | |
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808 reply to message |
| 19 | 809 .IP \(bu |
| 810 .CW forw : | |
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811 forward message |
| 19 | 812 .IP \(bu |
| 813 .CW send : | |
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814 send prepared message (this is how mail leaves the system) |
| 0 | 815 .LP |
| 19 | 816 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 817 The user does not leave the shell to run \s-1MH\s0, | |
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818 instead he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 819 Using a monolithic program with a captive user interface |
| 820 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 821 Using toolchests like \s-1MH\s0 means running programs, | |
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822 alone or in combination with others, also from other toolchests, |
| 23 | 823 without leaving the shell. |
| 30 | 824 |
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825 .H 2 "Data storage |
| 30 | 826 .LP |
| 34 | 827 \s-1MH\s0's mail storage is a directory tree under the user's |
| 828 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 829 where mail folders are directories and mail messages are text files | |
| 830 within them. | |
| 831 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
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832 the public message sequences of that folder, |
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833 for instance the \fIunseen\fP sequence for new messages. |
| 34 | 834 Mail messages are text files located in a mail folder. |
| 835 The files contain the messages as they were received. | |
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836 They are named by ascending numbers in each folder. |
| 19 | 837 .PP |
| 30 | 838 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 839 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 840 In the mbox format all messages are stored within one file. | |
| 841 This was a good solution in the early days, when messages | |
| 842 were only a few lines of text and were deleted soon. | |
| 843 Today, when single messages often include several megabytes | |
| 844 of attachments, it is a bad solution. | |
| 845 Another disadvantage of the mbox format is that it is | |
| 846 more difficult to write tools that work on mail messages, | |
| 847 because it is always necessary to first find and extract | |
| 848 the relevant message in the mbox file. | |
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849 With the \s-1MH\s0 mailbox format, each message is a separate file. |
| 30 | 850 Also, the problem of concurrent access to one mailbox is |
| 851 reduced to the problem of concurrent access to one message. | |
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852 The maildir format is generally similar to the \s-1MH\s0 format, |
| 30 | 853 but modified towards guaranteed reliability. |
| 854 This involves some complexity, unfortunately. | |
| 34 | 855 .PP |
| 856 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 857 working with Unix' toolchest on directory trees: | |
| 858 \f(CWscan\fP is like \f(CWls\fP, | |
| 859 \f(CWshow\fP is like \f(CWcat\fP, | |
| 860 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 861 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 862 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 863 .PP | |
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864 \s-1MH\s0 extends the context of processes in Unix by two more items, |
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865 for its tools: |
| 34 | 866 .IP \(bu |
| 867 The current mail folder, which is similar to the current working directory. | |
| 868 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 869 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 870 .IP \(bu | |
| 871 Sequences, which are named sets of messages in a mail folder. | |
| 872 The current message, relative to a mail folder, is a special sequence. | |
| 873 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 874 .LP | |
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875 In contrast to Unix' context, which is maintained by the kernel, |
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876 \s-1MH\s0's context must be maintained by the tools themselves. |
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877 Usually there is one context per user, which resides in his |
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878 \f(CWcontext\fP file in the \s-1MH\s0 directory, |
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879 but a user can have several contexts, too. |
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880 Public sequences are an exception, as they belong to a mail folder, |
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881 and reside in the \f(CW.mh_sequences\fP file there. |
| 34 | 882 .[ |
| 44 | 883 man page mh-profile mh-sequence |
| 34 | 884 .] |
| 20 | 885 |
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886 .H 2 "Discussion of the design |
| 20 | 887 .LP |
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888 This section discusses \s-1MH\s0 in regard to the tenets |
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889 of the Unix Philosophy that Gancarz identified. |
| 20 | 890 |
| 891 .PP | |
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892 .B "Small is beautiful |
| 20 | 893 and |
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894 .B "do one thing well |
| 20 | 895 are two design goals that are directly visible in \s-1MH\s0. |
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896 Gancarz actually presents \s-1MH\s0 in his book as example under the |
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897 headline ``Making \s-1UNIX\s0 Do One Thing Well'': |
| 46 | 898 .[ [ |
| 44 | 899 gancarz |
| 900 unix philosophy | |
| 46 | 901 .], page 125 ff.] |
| 20 | 902 .QP |
| 903 [\s-1MH\s0] consists of a series of programs which | |
| 904 when combined give the user an enormous ability | |
| 905 to manipulate electronic mail messages. | |
| 906 A complex application, it shows that not only is it | |
| 907 possible to build large applications from smaller | |
| 908 components, but also that such designs are actually preferable. | |
| 0 | 909 .LP |
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910 The various programs of \s-1MH\s0 were relatively easy to write, |
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911 because each of them is small, limited to one function, |
| 23 | 912 and has clear boundaries. |
| 20 | 913 For the same reasons, they are also good to maintain. |
| 914 Further more, the system can easily get extended. | |
| 915 One only needs to put a new program into the toolchest. | |
| 23 | 916 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 917 (e.g. \f(CWmhbuild\fP). |
| 918 Also, different programs can exist to do the basically same job | |
| 919 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
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920 .PP |
| 20 | 921 If someone needs a mail system with some additionally |
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922 functions that are not available anywhere yet, he best expands a |
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923 toolchest system like \s-1MH\s0. |
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924 There he can add new functionality by simply adding additional |
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925 programs to the toolchest. |
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926 There he does not risk to break existing functionality by doing so. |
| 20 | 927 |
| 928 .PP | |
| 34 | 929 .B "Store data in flat text files |
| 930 is followed by \s-1MH\s0. | |
| 931 This is not surprising, because email messages are already plain text. | |
| 932 \s-1MH\s0 stores the messages as it receives them, | |
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933 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate |
| 34 | 934 on the messages in an \s-1MH\s0 mailbox. |
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935 All other files \s-1MH\s0 uses are plain text, too. |
| 34 | 936 It is therefore possible and encouraged to use the text processing |
| 937 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 938 |
| 939 .PP | |
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940 .B "Avoid captive user interfaces" . |
| 19 | 941 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 942 It offers all functions directly and without captive user interfaces. | |
| 30 | 943 If, nonetheless, users want a graphical user interface, |
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944 they can have it with \fIxmh\fP or \fIexmh\fP. |
| 19 | 945 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 946 This means, all email-related work is still done by \s-1MH\s0 tools, | |
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947 but the frontend calls the appropriate commands when the user |
| 30 | 948 clicks on buttons. |
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949 .PP |
| 20 | 950 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 951 approach, because it does not limit the power of the backend itself. |
| 20 | 952 The frontend will anyway only be able to make a subset of the |
| 23 | 953 backend's power and flexibility available to the user. |
| 20 | 954 But if it is a separate program, |
| 955 then the missing parts can still be accessed at the backend directly. | |
| 19 | 956 If it is integrated, then this will hardly be possible. |
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957 An additional advantage is the possibility to have different frontends |
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958 to the same backend. |
| 19 | 959 |
| 960 .PP | |
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961 .B "Choose portability over efficiency |
| 20 | 962 and |
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963 .B "use shell scripts to increase leverage and portability" . |
| 20 | 964 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 965 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 966 .[ |
| 44 | 967 bolsky korn |
| 968 korn shell | |
| 20 | 969 .] |
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970 Chapter\|18 of the book shows a basic implementation |
| 20 | 971 of a subset of \s-1MH\s0 in ksh scripts. |
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972 Of course, this is just a demonstration, but a brilliant one. |
| 20 | 973 It shows how quickly one can implement such a prototype with shell scripts, |
| 974 and how readable they are. | |
| 975 The implementation in the scripting language may not be very fast, | |
| 976 but it can be fast enough though, and this is all that matters. | |
| 977 By having the code in an interpreted language, like the shell, | |
| 978 portability becomes a minor issue, if we assume the interpreter | |
| 979 to be widespread. | |
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980 .PP |
| 20 | 981 This demonstration also shows how easy it is to create single programs |
| 982 of a toolchest software. | |
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983 Eight tools (two of them have multiple names) and 16 functions |
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984 with supporting code are presented to the reader. |
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985 The tools comprise less than 40 lines of ksh each, |
| 30 | 986 in total about 200 lines. |
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987 The functions comprise less than 80 lines of ksh each, |
| 30 | 988 in total about 450 lines. |
| 20 | 989 Such small software is easy to write, easy to understand, |
| 990 and thus easy to maintain. | |
| 23 | 991 A toolchest improves the possibility to only write some parts |
| 20 | 992 and though create a working result. |
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993 Expanding the toolchest, even without global changes, |
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994 will likely be possible. |
| 20 | 995 |
| 996 .PP | |
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997 .B "Use software leverage to your advantage |
| 20 | 998 and the lesser tenet |
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999 .B "allow the user to tailor the environment |
| 20 | 1000 are ideally followed in the design of \s-1MH\s0. |
| 21 | 1001 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 1002 directly define default options to programs. |
| 1003 It is even possible to define different default options | |
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1004 depending on the name under which a program is called. |
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1005 Software leverage is heavily encouraged by the ease of |
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1006 creating shell scripts that run a specific command line, |
| 30 | 1007 built of several \s-1MH\s0 programs. |
| 21 | 1008 There is few software that so much wants users to tailor their |
| 1009 environment and to leverage the use of the software, like \s-1MH\s0. | |
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1010 .PP |
| 21 | 1011 Just to make one example: |
| 23 | 1012 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 1013 program. |
| 30 | 1014 It is possible to take one of the distributed format files |
| 21 | 1015 or to write one yourself. |
| 1016 To use the format as default for \f(CWscan\fP, a single line, | |
| 1017 reading | |
| 1018 .DS | |
| 1019 scan: -form FORMATFILE | |
| 1020 .DE | |
| 1021 must be added to \f(CW.mh_profile\fP. | |
| 1022 If one wants this different format as an additional command, | |
| 23 | 1023 instead of changing the default, he needs to create a link to |
| 1024 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1025 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
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1026 as the option should only be in effect for a program that is called as |
| 21 | 1027 \f(CWscan2\fP. |
| 20 | 1028 |
| 1029 .PP | |
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1030 .B "Make every program a filter |
| 21 | 1031 is hard to find in \s-1MH\s0. |
| 1032 The reason therefore is that most of \s-1MH\s0's tools provide | |
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1033 basic file system operations for mailboxes. |
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1034 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, |
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1035 and \f(CWrm\fP aren't filters neither. |
| 23 | 1036 \s-1MH\s0 does not provide many filters itself, but it is a basis |
| 1037 to write filters for. | |
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1038 An example would be a mail text highlighter, |
| 30 | 1039 that means a program that makes use of a color terminal to display |
| 1040 header lines, quotations, and signatures in distinct colors. | |
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1041 The author's version of such a program is an awk script with 25 lines. |
| 21 | 1042 |
| 1043 .PP | |
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1044 .B "Build a prototype as soon as possible |
| 21 | 1045 was again well followed by \s-1MH\s0. |
| 1046 This tenet, of course, focuses on early development, which is | |
| 1047 long time ago for \s-1MH\s0. | |
| 1048 But without following this guideline at the very beginning, | |
| 23 | 1049 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1050 to ever create \s-1MH\s0. | |
| 1051 In Bruce' own words: | |
| 46 | 1052 .[ [ |
| 44 | 1053 ware rand history |
| 46 | 1054 .], page 132] |
| 21 | 1055 .QP |
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1056 [...] but [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1057 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1058 I proposed a very short project to prove the basic concepts, |
| 1059 and my management agreed. | |
| 1060 Looking back, I realize that I had been very lucky with my first design. | |
| 1061 Without nearly enough design work, | |
| 1062 I built a working environment and some header files | |
| 1063 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1064 inc, show/next/prev, and comp. | |
| 1065 [...] | |
| 1066 With these three, I was able to convince people that the structure was viable. | |
| 1067 This took about three weeks. | |
| 0 | 1068 |
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1069 .H 2 "Problems |
| 0 | 1070 .LP |
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1071 \s-1MH\s0 is not without problems. |
| 30 | 1072 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1073 .PP |
| 1074 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1075 when \s-1MH\s0 was designed. | |
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1076 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though. |
| 22 | 1077 \s-1MIME\s0 support and support for different character encodings |
| 1078 is available, but only on a moderate level. | |
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1079 This comes from limited development resources. |
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1080 More active developers could quickly change this. |
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1081 But \s-1MH\s0 is also limited by design, which is the larger problem. |
| 22 | 1082 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. |
| 1083 These design conflicts are not easily solvable. | |
| 1084 Possibly, they require a redesign. | |
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1085 \s-1IMAP\s0 may be too different to the classic mail model, |
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1086 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well. |
| 22 | 1087 .PP |
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1088 The other kind of problem are human habits. |
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1089 In this world, where almost all \s-1MUA\s0s are monolithic, |
| 22 | 1090 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 |
| 1091 like \s-1MH\s0. | |
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1092 The habits are so strong, that even people who understand the concept |
| 30 | 1093 and advantages of \s-1MH\s0 do not like to switch, |
| 1094 simply because \s-1MH\s0 is different. | |
| 1095 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
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1096 are quite outdated and thus not very appealing, compared to the modern interfaces |
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1097 of many monolithic \s-1MUA\s0s. |
| 20 | 1098 |
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1099 NH 2 "Summary \s-1MH\s0 |
| 20 | 1100 .LP |
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1101 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design. |
| 31 | 1102 It consists of a toolchest of small tools, each of them does one job well. |
| 1103 The toolchest approach offers great flexibility to the user. | |
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1104 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0. |
| 31 | 1105 This makes \s-1MH\s0 a very powerful mail system. |
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1106 Extending and customizing \s-1MH\s0 is easy and encouraged. |
| 31 | 1107 .PP |
| 1108 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1109 Its overall design follows clear rules. | |
| 1110 The single tools do only one job, thus they are easy to understand, | |
| 1111 easy to write, and good to maintain. | |
| 1112 They are all independent and do not interfere with the others. | |
| 1113 Automated testing of their function is a straight forward task. | |
| 1114 .PP | |
| 1115 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1116 as its differentness is also its largest advantage. | |
| 1117 Unfortunately, for most people their habits are stronger | |
| 1118 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1119 |
| 8 | 1120 |
| 1121 | |
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1122 .H 1 "Case study: uzbl |
| 32 | 1123 .LP |
| 1124 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
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1125 which is an old and established software. |
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1126 This chapter covers uzbl, a fresh new project. |
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1127 Uzbl is a web browser that adheres to the Unix Philosophy. |
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1128 Its name comes from the \fILolspeak\fP word for ``usable''; |
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1129 it is pronounced identical. |
| 0 | 1130 |
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1131 .H 2 "Historical background |
| 0 | 1132 .LP |
| 32 | 1133 Uzbl was started by Dieter Plaetinck in April 2009. |
| 44 | 1134 The idea was born in a thread in the Arch Linux Forums. |
| 32 | 1135 .[ |
| 44 | 1136 arch linux forums |
| 1137 browser | |
| 32 | 1138 .] |
| 1139 After some discussion about failures of well known web browsers, | |
| 1140 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1141 of how a better web browser could look like. | |
| 1142 To the question of another member, if Plaetinck would write that program, | |
| 1143 because it would sound fantastic, Plaetinck replied: | |
| 1144 ``Maybe, if I find the time ;-)''. | |
| 1145 .PP | |
| 1146 Fortunately, he found the time. | |
| 1147 One day later, the first prototype was out. | |
| 1148 One week later, uzbl had an own website. | |
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1149 .[ |
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1150 uzbl website |
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1151 .] |
| 32 | 1152 One month after the first code showed up, |
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1153 a mailing list was installed to coordinate and discuss further development, |
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1154 and a wiki was added to store documentation and scripts that showed up on the |
| 32 | 1155 mailing list and elsewhere. |
| 1156 .PP | |
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1157 In the, now, one year of uzbl's existence, it was heavily developed on various branches. |
| 32 | 1158 Plaetinck's task became more and more to only merge the best code from the |
| 1159 different branches into his main branch, and to apply patches. | |
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1160 .[ |
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1161 lwn uzbl |
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1162 .] |
| 32 | 1163 About once a month, Plaetinck released a new version. |
| 1164 In September 2009, he presented several forks of uzbl. | |
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1165 .[ [ |
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1166 uzbl website |
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1167 .], news archive] |
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1168 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1169 .PP |
| 1170 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
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1171 .[ |
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1172 lwn uzbl |
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1173 .] |
| 32 | 1174 In September 2009, the uzbl web browser was on \fISlashdot\fP. |
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1175 .[ |
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1176 slashdot uzbl |
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1177 .] |
| 0 | 1178 |
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1179 .H 2 "Contrasts to other web browsers |
| 0 | 1180 .LP |
| 32 | 1181 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1182 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1183 .PP | |
| 1184 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1185 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1186 It handles commands and events to interface other programs, | |
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1187 and also displays webpages by using \fIwebkit\fP as render engine. |
| 32 | 1188 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, |
| 1189 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1190 to form a ``complete'' web browser. | |
| 1191 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1192 so uzbl-core is included. | |
| 1193 .PP | |
| 1194 Unlike most other web browsers, uzbl is mainly the mediator between the | |
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1195 various tools that cover single jobs. |
| 35 | 1196 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1197 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1198 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1199 .DS |
| 1200 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1201 .DE | |
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1202 The graphical rendering of the webpage is done by webkit, |
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1203 a web content engine. |
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1204 Uzbl-core is built around libwebkit. |
| 32 | 1205 .PP |
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1206 Downloads, browsing history, bookmarks, and the like are not provided |
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1207 by the core itself, like they are in other web browsers. |
| 35 | 1208 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1209 external applications which provide the actual functionality. | |
| 32 | 1210 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1211 includes a script that calls wget with appropriate options in | |
| 1212 a prepared environment. | |
| 1213 .PP | |
| 1214 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1215 This is their effort to achieve similar goals. | |
| 35 | 1216 But instead of using existing, external programs, modern web browsers |
|
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1217 include these functions. |
| 0 | 1218 |
|
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1219 .H 2 "Discussion of the design |
| 0 | 1220 .LP |
| 32 | 1221 This section discusses uzbl in regard of the Unix Philosophy, |
| 1222 as identified by Gancarz. | |
| 1223 | |
| 1224 .PP | |
| 35 | 1225 .B "Make each program do one thing well" . |
| 1226 Uzbl tries to be a web browser and nothing else. | |
|
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1227 The common definition of a web browser is, of course, highly influenced by |
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1228 existing implementations of web browsers, although they are degenerated. |
| 35 | 1229 Web browsers should be programs to browse the web, and nothing more. |
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1230 This is the one thing they should do. |
|
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1231 .PP |
|
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1232 Web browsers should not, for instance, manage downloads. |
| 35 | 1233 This is the job download managers exist for. |
| 1234 Download managers do primary care about being good in downloading files. | |
| 1235 Modern web browsers provide download management only as a secondary feature. | |
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1236 How could they do this job better, than programs that exist only for |
| 35 | 1237 this very job? |
| 1238 And how could anyone want less than the best download manager available? | |
| 32 | 1239 .PP |
| 35 | 1240 A web browser's job is to let the user browse the web. |
| 1241 This means, navigating through websites by following links. | |
|
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1242 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1243 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1244 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1245 are also not the job of a web browser. |
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1246 They should be handled by external applications \(en |
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1247 ones which's job is to handle such data. |
| 35 | 1248 Uzbl strives to do it this way. |
|
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1249 .PP |
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1250 Remember Doug McIlroy: |
| 35 | 1251 .I |
| 1252 ``Write programs that do one thing and do it well. | |
| 1253 Write programs to work together.'' | |
| 1254 .R | |
| 1255 .PP | |
| 1256 The lesser tenet | |
| 1257 .B "allow the user to tailor the environment | |
| 1258 matches good here. | |
| 1259 There was the question, how anyone could want anything less than the | |
| 1260 best program for the job. | |
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1261 But as personal preferences matter, it is probably more important to ask: |
| 35 | 1262 How could anyone want something else than his preferred program for the job? |
|
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1263 .PP |
|
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1264 Usually users want one program for a specific job. |
| 35 | 1265 Hence, whenever the task is, for instance, downloading, |
|
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1266 the same download manager should be used. |
| 35 | 1267 More advanced users might want to have this download manager in this |
| 1268 situation and that one in that situation. | |
| 1269 They should be able to configure it this way. | |
| 1270 With uzbl, one can use any download manager the user wants. | |
|
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1271 To switch to a different one, only one line in a small handler script |
| 35 | 1272 needs to be changed. |
|
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1273 Alternatively it would be possible to query the program to use by |
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1274 reading a global file or an environment variable, in the handler script. |
|
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1275 .PP |
|
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1276 Uzbl does neither have its own download manager nor depends on a |
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1277 specific one, hence uzbl's browsing abilities will not be lowered by having |
| 35 | 1278 a bad download manager. |
|
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1279 Uzbl's download capabilities will be just as good as the ones of the best |
|
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1280 download manager available on the system. |
|
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1281 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1282 |
| 1283 .PP | |
|
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1284 .B "Use software leverage to your advantage" . |
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1285 Uzbl is designed to be extended by external tools. |
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1286 These external tools are usually wrapped by small handler shell scripts. |
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1287 Shell scripts are the glue in this approach. |
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1288 They make the various parts fit together. |
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1289 .PP |
|
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1290 The history mechanism of uzbl shall be presented as an example. |
|
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1291 Uzbl is configured to spawn a script to append an entry to the history |
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1292 whenever the event of a fully loaded page occurs. |
|
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1293 The script to append the entry to the history is not much more than: |
|
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1294 .DS |
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1295 #!/bin/sh |
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1296 file=/path/to/uzbl-history |
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1297 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1298 .DE |
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1299 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1300 .PP |
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1301 For loading an entry, a key is bound to spawn a load-from-history script. |
|
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1302 The script reverses the history to have newer entries first, |
|
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1303 then displays \fIdmenu\fP to let the user select an item, |
|
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1304 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
|
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1305 With error checking and corner case handling removed, |
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1306 the script looks like this: |
|
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1307 .DS |
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1308 #!/bin/sh |
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1309 file=/path/to/uzbl-history |
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1310 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1311 echo "uri $goto" > $4 |
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1312 .DE |
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1313 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1314 uzbl instance. |
| 32 | 1315 |
| 1316 .PP | |
|
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1317 .B "Avoid captive user interfaces" . |
|
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1318 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1319 a captive user interface. |
| 37 | 1320 But the difference to most other web browsers is, that uzbl is only |
|
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1321 the captive user interface frontend (and the core of the backend). |
|
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1322 Many parts of the backend are independent of uzbl. |
|
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1323 Some are distributed with uzbl, for some external programs, |
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1324 handler scripts are distributed, |
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1325 but arbitrary additional functionality can be added if desired. |
| 37 | 1326 .PP |
| 1327 The frontend is captive \(en that is true. | |
| 1328 This is okay for the task of browsing the web, as this task is only relevant | |
| 1329 for humans. | |
| 1330 Automated programs would \fIcrawl\fP the web. | |
| 1331 That means, they read the source directly. | |
| 1332 The source includes all the semantics. | |
| 1333 The graphical representation is just for humans to transfer the semantics | |
| 1334 more intuitively. | |
| 32 | 1335 |
| 1336 .PP | |
|
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1337 .B "Make every program a filter" . |
| 37 | 1338 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1339 Thus it is difficult to see what graphical web browsers should filter. | |
|
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1340 Graphical web browsers exist almost only to be interactively used by humans. |
| 37 | 1341 The only case when one might want to automate the rendering function is |
| 1342 to generate images of rendered webpages. | |
| 1343 | |
| 1344 .PP | |
| 1345 .B "Small is beautiful" | |
|
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1346 is not easy to apply to a web browser, because modern web technology |
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1347 is very complex, hence the rendering task is very complex. |
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1348 Modern web browsers have to consist of many thousand lines of code, |
| 37 | 1349 unfortunately. |
| 1350 Using the toolchest approach and wrappers can split the browser into | |
| 1351 several small parts, tough. | |
| 1352 .PP | |
|
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1353 As of March 2010, uzbl-core consists of about 3\,500 lines of C code. |
| 37 | 1354 The distribution includes another 3\,500 lines of Shell and Python code, |
| 1355 which are the handler scripts and plugins like a modal interface. | |
|
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1356 Further more, uzbl uses functionality of external tools like |
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1357 \fIwget\fP and \fInetcat\fP. |
| 37 | 1358 Up to this point, uzbl looks pretty neat and small. |
|
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1359 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1360 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1361 Unfortunately, small web render engines are not possible anymore |
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1362 because of the modern web. |
| 35 | 1363 |
| 1364 .PP | |
| 1365 .B "Build a prototype as soon as possible" . | |
| 1366 Plaetinck made his code public, right from the beginning. | |
|
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1367 Discussion and development was, and still is, open to everyone interested. |
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1368 Development versions of uzbl can be obtained very simply from the code |
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1369 repository. |
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1370 Within the first year of uzbl's existence, a new version was released |
| 35 | 1371 more often than once a month. |
|
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1372 Different forks and branches arose. |
|
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1373 They introduced new features, which were tested for suitability |
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1374 for the main branch. |
| 35 | 1375 The experiences of using prototypes influenced further development. |
| 1376 Actually, all development was community driven. | |
|
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1377 Plaetinck says, three months after uzbl's birth: |
| 35 | 1378 ``Right now I hardly code anything myself for Uzbl. |
| 1379 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1380 .[ | |
| 44 | 1381 lwn |
| 1382 uzbl | |
| 35 | 1383 .] |
| 32 | 1384 |
| 0 | 1385 |
|
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1386 .H 2 "Problems |
| 0 | 1387 .LP |
|
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1388 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1389 It is sad, but people use what they know. |
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1390 Fortunately, uzbl's user interface can look and feel very much the |
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1391 same as the one of the well known web browsers, |
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1392 hiding the internal differences. |
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1393 But uzbl has to provide this similar look and feel to be accepted |
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1394 as a ``normal'' browser by ``normal'' users. |
| 37 | 1395 .PP |
|
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1396 Though, the more important problem is the modern web. |
|
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1397 The modern web is simply broken. |
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1398 It has state in a state-less protocol, |
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1399 it misuses technologies, |
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1400 and it is helplessly overloaded. |
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1401 The result are web content render engines that must consist |
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1402 of hundreds of thousands lines of code. |
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1403 They also must combine and integrate many different technologies, |
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1404 only to make our modern web accessible. |
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1405 Website to image converter are hardly possible to run without |
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1406 human interaction because of state in sessions, impossible |
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1407 deep-linking, and unautomatable technologies. |
| 37 | 1408 .PP |
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1409 The web was misused to provide all kinds of imaginable wishes. |
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1410 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1411 |
| 8 | 1412 |
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1413 .H 2 "Summary uzbl |
| 32 | 1414 .LP |
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1415 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1416 that is how uzbl is seen by its authors. |
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1417 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1418 It consists of independent parts that work together, |
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1419 while its core is mainly a mediator which glues the parts together. |
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1420 .PP |
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1421 Software leverage can excellently be seen in uzbl. |
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1422 External tools are used, independent tasks are separated |
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1423 in independent parts and glued together with small handler scripts. |
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1424 .PP |
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1425 As uzbl, more or less, consists of a set of tools and a bit |
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1426 of glue, anyone can put the parts together and expand it |
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1427 in any desired way. |
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1428 Uzbl is very flexible and customizable. |
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1429 These properties make it valuable for advanced users, |
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1430 but may keep novice users from using it. |
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1431 .PP |
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1432 But uzbl's main problem is the modern web, that makes it hard |
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1433 to design a sane web browser. |
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1434 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1435 |
| 8 | 1436 |
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1437 .H 1 "Final thoughts |
| 0 | 1438 |
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1439 .H 2 "Quick summary |
| 0 | 1440 .LP |
| 1441 good design | |
| 1442 .LP | |
| 1443 unix phil | |
| 1444 .LP | |
| 1445 case studies | |
| 1446 | |
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1447 .H 2 "Why people should choose |
| 0 | 1448 .LP |
| 1449 Make the right choice! | |
| 1450 | |
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1451 |
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1452 .bp |
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1453 .TL |
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1454 References |
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1455 .LP |
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1456 .XS |
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1457 .sp .5v |
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1458 .B |
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1459 References |
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1460 .XE |
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1461 .ev r |
| 0 | 1462 .rm ]< |
| 1463 .de ]< | |
| 1464 .LP | |
| 1465 .de FP | |
| 1466 .IP \\\\$1. | |
| 1467 \\.. | |
| 1468 .rm FS FE | |
| 1469 .. | |
| 42 | 1470 .nr PS -1 |
| 1471 .nr VS -1 | |
| 0 | 1472 .[ |
| 1473 $LIST$ | |
| 1474 .] | |
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1475 .nr PS +1 |
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1476 .nr VS +1 |
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1477 .ev |
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1478 |
| 42 | 1479 .bp |
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1480 .TL |
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1481 Table of Contents |
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1482 .LP |
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1483 .PX no |