Mercurial > docs > unix-phil
annotate unix-phil.ms @ 53:14f5ff66ad8a
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| author | meillo@marmaro.de |
|---|---|
| date | Thu, 15 Apr 2010 12:30:25 +0200 |
| parents | a41320ca9ab6 |
| children | 0a435d76b868 |
| rev | line source |
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| 49 | 1 .so style |
| 42 | 2 |
| 0 | 3 .TL |
| 42 | 4 .ps +4 |
| 6 | 5 Why the Unix Philosophy still matters |
| 0 | 6 .AU |
| 7 markus schnalke <meillo@marmaro.de> | |
| 8 .AB | |
| 1 | 9 .ti \n(.iu |
| 39 | 10 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 11 Today, few software designers are aware of these concepts, |
| 39 | 12 and thus a lot of modern software is more limited than necessary |
| 13 and makes less use of software leverage than possible. | |
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14 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 15 .AE |
| 16 | |
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17 .FS |
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18 .ps -1 |
| 39 | 19 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
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20 Mentor was professor Franz Schweiggert. |
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21 Handed in on 2010-04-12. |
| 39 | 22 You may retrieve this document from |
| 23 .CW \s-1http://marmaro.de/docs \ . | |
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26 .H 1 Introduction |
| 0 | 27 .LP |
| 40 | 28 The Unix Philosophy is the essence of how the Unix operating system, |
| 29 especially its toolchest, was designed. | |
| 30 It is no limited set of fixed rules, | |
| 31 but a loose set of guidelines which tell how to write software that | |
| 32 suites well into Unix. | |
| 33 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 34 The Wikipedia has an accurate definition: | |
| 35 .[ | |
| 44 | 36 wikipedia |
| 37 unix philosophy | |
| 40 | 38 .] |
| 39 .QP | |
| 40 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 41 approaches to developing software based on the experience of leading | |
| 42 developers of the Unix operating system. | |
| 3 | 43 .PP |
| 40 | 44 As there is no single definition of the Unix Philosophy, |
| 45 several people have stated their view on what it comprises. | |
| 1 | 46 Best known are: |
| 47 .IP \(bu | |
| 48 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 49 .[ | |
| 44 | 50 mahoney |
| 51 oral history | |
| 1 | 52 .] |
| 53 .IP \(bu | |
| 54 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 55 .[ | |
| 44 | 56 gancarz |
| 57 unix philosophy | |
| 1 | 58 .] |
| 59 .IP \(bu | |
| 60 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 61 .[ | |
| 44 | 62 raymond |
| 63 art of unix programming | |
| 1 | 64 .] |
| 0 | 65 .LP |
| 1 | 66 These different views on the Unix Philosophy have much in common. |
| 40 | 67 Especially, the main concepts are similar in all of them. |
| 68 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 69 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 70 | |
| 71 .PP | |
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72 The Unix Philosophy explains how to design good software for Unix. |
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73 Many concepts described here, base on facilities of Unix. |
| 40 | 74 Other operating systems may not offer such facilities, |
| 41 | 75 hence it may not be possible to design software in the way of the |
| 76 Unix Philosophy for them. | |
| 77 .PP | |
| 78 The Unix Philosophy has an idea of how the process of software development | |
| 79 should look like, but large parts of the philosophy are quite independent | |
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80 from a concrete development process. |
| 41 | 81 However, one will soon recognize that some development processes work well |
| 82 with the ideas of the Unix Philosophy and support them, while others are | |
| 83 at cross-purposes. | |
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84 Kent Beck's books about Extreme Programming are valuable supplemental |
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85 resources on this topic. |
| 40 | 86 .PP |
| 41 | 87 The question of how to actually write code and how the code should looks |
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88 like in detail, are out of focus here. |
| 41 | 89 ``The Practice of Programming'' by Kernighan and Pike, |
| 90 .[ | |
| 44 | 91 kernighan pike |
| 92 practice of programming | |
| 41 | 93 .] |
| 94 is a good book that covers this topic. | |
| 95 Its point of view matches to the one of this paper. | |
| 0 | 96 |
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97 .H 1 "Importance of software design in general |
| 0 | 98 .LP |
| 40 | 99 Software design is the planning of how the internal structure |
| 100 and external interfaces of a software should look like. | |
| 39 | 101 It has nothing to do with visual appearance. |
| 102 If we take a program as a car, then its color is of no matter. | |
| 103 Its design would be the car's size, its shape, the locations of doors, | |
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104 the passenger/space ratio, the available controls and instruments, |
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105 and so forth. |
| 39 | 106 .PP |
| 107 Why should software get designed at all? | |
| 6 | 108 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 109 Not designing software means programming without plan. |
| 110 This will pretty sure lead to horrible results. | |
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111 Software that is horrible to use and horrible to maintain. |
| 39 | 112 These two aspects are the visible ones. |
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113 Often invisible though, are the wasted possible gains. |
| 39 | 114 Good software design can make these gains available. |
| 6 | 115 .PP |
| 39 | 116 A software's design deals with quality properties. |
| 117 Good design leads to good quality, and quality is important. | |
| 118 Any car may be able to drive from A to B, | |
| 119 but it depends on the car's properties whether it is a good choice | |
| 120 for passenger transport or not. | |
| 121 It depends on its properties if it is a good choice | |
| 122 for a rough mountain area. | |
| 123 And it depends on its properties if the ride will be fun. | |
| 124 | |
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125 .PP |
| 39 | 126 Requirements for a software are twofold: |
| 127 functional and non-functional. | |
| 128 .IP \(bu | |
| 129 Functional requirements define directly the software's functions. | |
| 130 They are the reason why software gets written. | |
| 131 Someone has a problem and needs a tool to solve it. | |
| 132 Being able to solve the problem is the main functional goal. | |
| 133 It is the driving force behind all programming effort. | |
| 6 | 134 Functional requirements are easier to define and to verify. |
| 39 | 135 .IP \(bu |
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136 Non-functional requirements are called \fIquality\fP requirements, too. |
| 39 | 137 The quality of a software are the properties that are not directly related to |
| 138 the software's basic functions. | |
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139 Tools of bad quality often do solve the problems they were written for, |
| 39 | 140 but introduce problems and difficulties for usage and development, later on. |
| 141 Quality aspects are often overlooked at first sight, | |
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142 and are often difficult to define clearly and to verify. |
| 6 | 143 .PP |
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144 Quality is hardly interesting when the software gets built initially, |
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145 but it has a high impact on usability and maintenance of the software, later. |
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146 A short-sighted might see in developing a software, mainly building something up. |
| 39 | 147 But experience shows, that building the software the first time is |
| 148 only a small amount of the overall work. | |
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149 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en |
| 6 | 150 does soon take over the major part of the time spent on a software. |
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151 And of course, the time spent actually using the software. |
| 6 | 152 These processes are highly influenced by the software's quality. |
| 39 | 153 Thus, quality must not be neglected. |
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154 However, the problem with quality is that you hardly ``stumble over'' |
| 39 | 155 bad quality during the first build, |
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156 although this is the time when you should care about good quality most. |
| 6 | 157 .PP |
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158 Software design has little to do with the basic function of a software \(en |
| 39 | 159 this requirement will get satisfied anyway. |
| 160 Software design is more about quality aspects of the software. | |
| 161 Good design leads to good quality, bad design to bad quality. | |
| 6 | 162 The primary functions of the software will be affected modestly by bad quality, |
| 39 | 163 but good quality can provide a lot of additional gain, |
| 6 | 164 even at places where one never expected it. |
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165 .PP |
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166 The ISO/IEC\|9126-1 standard, part\|1, |
| 6 | 167 .[ |
| 44 | 168 iso product quality |
| 6 | 169 .] |
| 170 defines the quality model as consisting out of: | |
| 171 .IP \(bu | |
| 172 .I Functionality | |
| 173 (suitability, accuracy, inter\%operability, security) | |
| 174 .IP \(bu | |
| 175 .I Reliability | |
| 176 (maturity, fault tolerance, recoverability) | |
| 177 .IP \(bu | |
| 178 .I Usability | |
| 179 (understandability, learnability, operability, attractiveness) | |
| 180 .IP \(bu | |
| 181 .I Efficiency | |
| 9 | 182 (time behavior, resource utilization) |
| 6 | 183 .IP \(bu |
| 184 .I Maintainability | |
| 23 | 185 (analyzability, changeability, stability, testability) |
| 6 | 186 .IP \(bu |
| 187 .I Portability | |
| 188 (adaptability, installability, co-existence, replaceability) | |
| 189 .LP | |
| 39 | 190 Good design can improve these properties of a software, |
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191 bad designed software likely suffers in these points. |
| 7 | 192 .PP |
| 193 One further goal of software design is consistency. | |
| 194 Consistency eases understanding, working on, and using things. | |
| 39 | 195 Consistent internal structure and consistent interfaces to the outside |
| 196 can be provided by good design. | |
| 7 | 197 .PP |
| 39 | 198 Software should be well designed because good design avoids many |
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199 problems during a software's lifetime. |
| 39 | 200 And software should be well designed because good design can offer |
| 201 much additional gain. | |
| 202 Indeed, much effort should be spent into good design to make software more valuable. | |
| 203 The Unix Philosophy shows a way of how to design software well. | |
| 7 | 204 It offers guidelines to achieve good quality and high gain for the effort spent. |
| 0 | 205 |
| 206 | |
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207 .H 1 "The Unix Philosophy |
| 4 | 208 .LP |
| 209 The origins of the Unix Philosophy were already introduced. | |
| 8 | 210 This chapter explains the philosophy, oriented on Gancarz, |
| 211 and shows concrete examples of its application. | |
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212 |
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213 .H 2 Pipes |
| 0 | 214 .LP |
| 4 | 215 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 216 Knowledge of using the Unix shell is assumed. | |
| 217 .PP | |
| 218 Counting the number of files in the current directory: | |
| 41 | 219 .DS |
| 4 | 220 ls | wc -l |
| 221 .DE | |
| 222 The | |
| 223 .CW ls | |
| 224 command lists all files in the current directory, one per line, | |
| 225 and | |
| 226 .CW "wc -l | |
| 8 | 227 counts the number of lines. |
| 4 | 228 .PP |
| 8 | 229 Counting the number of files that do not contain ``foo'' in their name: |
| 41 | 230 .DS |
| 4 | 231 ls | grep -v foo | wc -l |
| 232 .DE | |
| 233 Here, the list of files is filtered by | |
| 234 .CW grep | |
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235 to remove all lines that contain ``foo''. |
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236 The rest equals the previous example. |
| 4 | 237 .PP |
| 238 Finding the five largest entries in the current directory. | |
| 41 | 239 .DS |
| 4 | 240 du -s * | sort -nr | sed 5q |
| 241 .DE | |
| 242 .CW "du -s * | |
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243 returns the recursively summed sizes of all files in the current directory |
| 8 | 244 \(en no matter if they are regular files or directories. |
| 4 | 245 .CW "sort -nr |
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246 sorts the list numerically in reverse order (descending). |
| 4 | 247 Finally, |
| 248 .CW "sed 5q | |
| 249 quits after it has printed the fifth line. | |
| 250 .PP | |
| 251 The presented command lines are examples of what Unix people would use | |
| 252 to get the desired output. | |
| 253 There are also other ways to get the same output. | |
| 254 It's a user's decision which way to go. | |
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255 .PP |
| 8 | 256 The examples show that many tasks on a Unix system |
| 4 | 257 are accomplished by combining several small programs. |
| 258 The connection between the single programs is denoted by the pipe operator `|'. | |
| 259 .PP | |
| 260 Pipes, and their extensive and easy use, are one of the great | |
| 261 achievements of the Unix system. | |
| 262 Pipes between programs have been possible in earlier operating systems, | |
| 263 but it has never been a so central part of the concept. | |
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264 When, in the early seventies, Doug McIlroy introduced pipes into the |
| 4 | 265 Unix system, |
| 266 ``it was this concept and notation for linking several programs together | |
| 267 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 268 .[ | |
| 44 | 269 aughenbaugh |
| 270 unix oral history | |
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271 .] |
| 4 | 272 .PP |
| 273 Being able to specify pipelines in an easy way is, | |
| 274 however, not enough by itself. | |
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275 It is only one half. |
| 4 | 276 The other is the design of the programs that are used in the pipeline. |
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277 They need interfaces that allow them to be used in such a way. |
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278 |
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279 .H 2 "Interface design |
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280 .LP |
| 11 | 281 Unix is, first of all, simple \(en Everything is a file. |
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282 Files are sequences of bytes, without any special structure. |
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283 Programs should be filters, which read a stream of bytes from standard input (stdin) |
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284 and write a stream of bytes to standard output (stdout). |
| 8 | 285 If the files \fIare\fP sequences of bytes, |
| 286 and the programs \fIare\fP filters on byte streams, | |
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287 then there is exactly one data interface. |
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288 Hence it is possible to combine programs in any desired way. |
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289 .PP |
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290 Even a handful of small programs yields a large set of combinations, |
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291 and thus a large set of different functions. |
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292 This is leverage! |
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293 If the programs are orthogonal to each other \(en the best case \(en |
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294 then the set of different functions is greatest. |
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295 .PP |
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296 Programs can also have a separate control interface, |
| 11 | 297 besides their data interface. |
| 298 The control interface is often called ``user interface'', | |
| 299 because it is usually designed to be used by humans. | |
| 300 The Unix Philosophy discourages to assume the user to be human. | |
| 301 Interactive use of software is slow use of software, | |
| 302 because the program waits for user input most of the time. | |
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303 Interactive software requires the user to be in front of the computer. |
| 11 | 304 Interactive software occupy the user's attention while they are running. |
| 305 .PP | |
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306 Now to come back to the idea of combining several small programs, |
| 11 | 307 to have a more specific function. |
| 308 If these single tools would all be interactive, | |
| 309 how would the user control them? | |
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310 It is not only a problem to control several programs at once, |
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311 if they run at the same time, |
| 11 | 312 it also very inefficient to have to control each of the single programs |
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313 that are intended to act as one large program. |
| 11 | 314 Hence, the Unix Philosophy discourages programs to demand interactive use. |
| 315 The behavior of programs should be defined at invocation. | |
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316 This is done by specifying arguments to the program call |
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317 (command line switches). |
| 11 | 318 Gancarz discusses this topic as ``avoid captive user interfaces''. |
| 46 | 319 .[ [ |
| 44 | 320 gancarz unix philosophy |
| 46 | 321 .], page 88 ff.] |
| 11 | 322 .PP |
| 323 Non-interactive use is, during development, also an advantage for testing. | |
| 324 Testing of interactive programs is much more complicated, | |
| 325 than testing of non-interactive programs. | |
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326 |
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327 .H 2 "The toolchest approach |
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328 .LP |
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329 A toolchest is a set of tools. |
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330 Instead of having one big tool for all tasks, one has many small tools, |
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331 each for one task. |
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332 Difficult tasks are solved by combining several of the small, simple tools. |
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333 .PP |
| 11 | 334 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 335 that are filters on byte streams. | |
| 336 They are, to a large extend, unrelated in their function. | |
| 337 Hence, the Unix toolchest provides a large set of functions | |
| 338 that can be accessed by combining the programs in the desired way. | |
| 339 .PP | |
| 340 There are also advantages for developing small toolchest programs. | |
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341 It is easier and less error-prone to write small programs. |
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342 It is also easier and less error-prone to write a large set of small programs, |
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343 than to write one large program with all the functionality included. |
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344 If the small programs are combinable, then they offer even a larger set |
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345 of functions than the single large program. |
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346 Hence, one gets two advantages out of writing small, combinable programs: |
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347 They are easier to write and they offer a greater set of functions through |
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348 combination. |
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349 .PP |
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350 But there are also two main drawbacks of the toolchest approach. |
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351 First, one simple, standardized interface has to be sufficient. |
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352 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 353 then a different approach might be of need. |
| 13 | 354 But it is also possible, that he just can not imagine a design where |
| 8 | 355 a stream of bytes is sufficient. |
| 356 By becoming more familiar with the ``Unix style of thinking'', | |
| 357 developers will more often and easier find simple designs where | |
| 358 a stream of bytes is a sufficient interface. | |
| 359 .PP | |
| 360 The second drawback of a toolchest affects the users. | |
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361 A toolchest is often more difficult to use. |
| 9 | 362 It is necessary to become familiar with each of the tools, |
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363 to be able to use the right one in a given situation. |
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364 Additionally, one needs to combine the tools in a senseful way himself. |
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365 This is like a sharp knife \(en it is a powerful tool in the hand of a |
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366 master, but of no good value in the hand of an unskilled. |
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367 However, learning single, small tools of a toolchest is easier than |
| 8 | 368 learning a complex tool. |
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369 And the user will already have a basic understanding of a yet unknown tool, |
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370 if the tools of a toolchest have a common, consistent style. |
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371 He will be able to transfer knowledge over from one tool to another. |
| 8 | 372 .PP |
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373 Moreover, the second drawback can be removed to a large extend |
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374 by adding wrappers around the basic tools. |
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375 Novice users do not need to learn several tools, if a professional wraps |
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376 complete command lines into a higher-level script. |
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377 Note that the wrapper script still calls the small tools; |
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378 it is just like a skin around them. |
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379 No complexity is added this way. |
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380 But new programs can get created out of existing one with very low effort. |
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381 .PP |
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382 A wrapper script for finding the five largest entries in the current directory |
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383 could look like this: |
| 41 | 384 .DS |
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385 #!/bin/sh |
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386 du -s * | sort -nr | sed 5q |
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387 .DE |
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388 The script itself is just a text file that calls the command line, |
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389 which a professional user would type in directly. |
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390 It is probably worth to make the program flexible on the number of |
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391 entries it prints: |
| 41 | 392 .DS |
| 8 | 393 #!/bin/sh |
| 394 num=5 | |
| 395 [ $# -eq 1 ] && num="$1" | |
| 396 du -sh * | sort -nr | sed "${num}q" | |
| 397 .DE | |
| 398 This script acts like the one before, when called without an argument. | |
| 399 But one can also specify a numerical argument to define the number of lines to print. | |
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400 One can surely imagine even more flexible versions, however, |
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401 they will still relay on the external programs, |
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402 which do the actual work. |
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403 |
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404 .H 2 "A powerful shell |
| 8 | 405 .LP |
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406 The Unix shell provides the possibility to combine small programs into large ones. |
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407 But a powerful shell is a great feature in other ways, too. |
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408 For instance by being scriptable. |
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409 Control statements are build into the shell. |
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410 The functions, however, are the normal programs of the system. |
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411 Thus, as the programs are already known, |
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412 learning to program in the shell becomes easy. |
| 8 | 413 Using normal programs as functions in the shell programming language |
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414 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 415 .PP |
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416 The Unix shell encourages to write small scripts, |
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417 by combining existing programs, because it is so easy to do. |
| 8 | 418 This is a great step towards automation. |
| 419 It is wonderful if the effort to automate a task equals the effort | |
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420 to do the task a second time by hand. |
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421 If this holds, |
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422 then the user will be happy to automate everything he does more than once. |
| 8 | 423 .PP |
| 424 Small programs that do one job well, standardized interfaces between them, | |
| 425 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 426 this will inevitably produce software leverage. | |
| 427 Getting multiple times the benefit of an investment is a great offer. | |
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428 .PP |
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429 The shell also encourages rapid prototyping. |
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430 Many well known programs started as quickly hacked shell scripts, |
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431 and turned into ``real'' programs, written in C, later. |
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432 Building a prototype first, is a way to avoid the biggest problems |
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433 in application development. |
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434 Fred Brooks explains in ``No Silver Bullet'': |
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435 .[ |
| 44 | 436 brooks |
| 437 no silver bullet | |
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438 .] |
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439 .QP |
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440 The hardest single part of building a software system is deciding precisely what to build. |
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441 No other part of the conceptual work is so difficult as establishing the detailed |
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442 technical requirements, [...]. |
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443 No other part of the work so cripples the resulting system if done wrong. |
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444 No other part is more difficult to rectify later. |
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445 .PP |
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446 Writing a prototype is a great method for becoming familiar with the requirements |
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447 and to run into real problems early. |
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448 .[ [ |
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449 gancarz |
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450 unix philosophy |
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451 .], page 28 f.] |
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452 .PP |
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453 Prototyping is often seen as a first step in building a software. |
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454 This is, of course, good. |
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455 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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456 After having built the prototype, one might notice, that the prototype is already |
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457 \fIgood enough\fP. |
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458 Hence, no reimplementation, in a more sophisticated programming language, |
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459 might be of need, at least for the moment. |
| 23 | 460 Maybe later, it might be necessary to rewrite the software, but not now. |
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461 By delaying further work, one keeps the flexibility to react on |
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462 changing requirements. |
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463 Software parts that are not written will not miss the requirements. |
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464 |
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465 .H 2 "Worse is better |
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466 .LP |
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467 The Unix Philosophy aims for the 90% solution; |
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468 others call it the ``Worse is better'' approach. |
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469 Experience from real life projects shows: |
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470 .PP |
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471 (1) It is almost never possible to define the |
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472 requirements completely and correctly the first time. |
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473 Hence one should not try to; one will fail anyway. |
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474 .PP |
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475 (2) Requirements change during time. |
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476 Hence it is best to delay requirement-based design decisions as long as possible. |
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477 The software should be small and flexible as long as possible |
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478 to react on changing requirements. |
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479 Shell scripts, for example, are more easily adjusted as C programs. |
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480 .PP |
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481 (3) Maintenance work is hard work. |
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482 Hence, one should keep the amount of code as small as possible; |
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483 it should just fulfill the \fIcurrent\fP requirements. |
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484 Software parts that will be written in future, |
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485 do not need maintenance till then. |
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486 .PP |
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487 See Brooks' ``The Mythical Man-Month'' for reference. |
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488 .[ [ |
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489 brooks |
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490 mythical man-month |
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491 .], page 115 ff.] |
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492 .PP |
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493 Starting with a prototype in a scripting language has several advantages: |
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494 .IP \(bu |
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495 As the initial effort is low, one will likely start right away. |
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496 .IP \(bu |
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497 As working parts are available soon, the real requirements can get identified soon. |
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498 .IP \(bu |
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499 When a software is usable and valuable, it gets used, and thus tested. |
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500 Hence problems will be found at early stages of the development. |
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501 .IP \(bu |
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502 The prototype might be enough for the moment, |
| 51 | 503 thus further work can get delayed to a time |
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504 when one knows better about the requirements and problems, |
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505 than now. |
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506 .IP \(bu |
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507 Implementing now only the parts that are actually needed at the moment, |
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508 introduces fewer programming and maintenance work. |
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509 .IP \(bu |
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510 If the global situation changes so that the software is not needed anymore, |
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511 then less effort was spent into the project, than it would have be |
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512 when a different approach had been used. |
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513 |
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514 .H 2 "Upgrowth and survival of software |
| 11 | 515 .LP |
| 12 | 516 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 517 Although these are just verbs, they do imply a specific view on the work process |
| 518 they describe. | |
| 12 | 519 The better verb, however, is to \fIgrow\fP. |
| 520 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 521 It starts with a first prototype, which evolves as requirements change. | |
| 522 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 523 compiled program this way. |
| 524 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
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525 While being alive it will get extended, rearranged, rebuilt. |
| 12 | 526 Growing software matches the view that ``software is never finished. It is only released.'' |
| 46 | 527 .[ [ |
| 44 | 528 gancarz |
| 529 unix philosophy | |
| 46 | 530 .], page 26] |
| 12 | 531 .PP |
| 13 | 532 Software can be seen as being controlled by evolutionary processes. |
| 533 Successful software is software that is used by many for a long time. | |
| 12 | 534 This implies that the software is needed, useful, and better than alternatives. |
| 535 Darwin talks about: ``The survival of the fittest.'' | |
| 536 .[ | |
| 44 | 537 darwin |
| 538 origin of species | |
| 12 | 539 .] |
| 540 Transferred to software: The most successful software, is the fittest, | |
| 541 is the one that survives. | |
| 13 | 542 (This may be at the level of one creature, or at the level of one species.) |
| 543 The fitness of software is affected mainly by four properties: | |
| 15 | 544 portability of code, portability of data, range of usability, and reusability of parts. |
| 13 | 545 .PP |
| 15 | 546 (1) |
| 547 .I "Portability of code | |
| 548 means, using high-level programming languages, | |
| 13 | 549 sticking to the standard, |
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550 .[ [ |
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551 kernighan pike |
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552 practice of programming |
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553 .], chapter\|8] |
| 13 | 554 and avoiding optimizations that introduce dependencies on specific hardware. |
| 555 Hardware has a much lower lifetime than software. | |
| 556 By chaining software to a specific hardware, | |
| 557 the software's lifetime gets shortened to that of this hardware. | |
| 558 In contrast, software should be easy to port \(en | |
| 23 | 559 adaptation is the key to success. |
| 13 | 560 .PP |
| 15 | 561 (2) |
| 562 .I "Portability of data | |
| 563 is best achieved by avoiding binary representations | |
| 13 | 564 to store data, because binary representations differ from machine to machine. |
| 23 | 565 Textual representation is favored. |
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566 Historically, \s-1ASCII\s0 was the charset of choice. |
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567 For the future, \s-1UTF\s0-8 might be the better choice. |
| 13 | 568 Important is that it is a plain text representation in a |
| 569 very common charset encoding. | |
| 570 Apart from being able to transfer data between machines, | |
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571 readable data has the great advantage, that humans are able to directly |
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572 read and edit it with text editors and other tools from the Unix toolchest. |
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573 .[ [ |
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574 gancarz |
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575 unix philosophy |
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576 .], page 56 ff.] |
| 12 | 577 .PP |
| 15 | 578 (3) |
| 579 A large | |
| 580 .I "range of usability | |
| 23 | 581 ensures good adaptation, and thus good survival. |
| 13 | 582 It is a special distinction if a software becomes used in fields of action, |
| 583 the original authors did never imagine. | |
| 584 Software that solves problems in a general way will likely be used | |
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585 for many kinds of similar problems. |
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586 Being too specific limits the range of usability. |
| 13 | 587 Requirements change through time, thus use cases change or even vanish. |
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588 As a good example in this point, |
| 13 | 589 Allman identifies flexibility to be one major reason for sendmail's success: |
| 590 .[ | |
| 44 | 591 allman |
| 592 sendmail | |
| 13 | 593 .] |
| 594 .QP | |
| 595 Second, I limited myself to the routing function [...]. | |
| 596 This was a departure from the dominant thought of the time, [...]. | |
| 597 .QP | |
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598 Third, the sendmail configuration file was flexible enough to adapt |
| 13 | 599 to a rapidly changing world [...]. |
| 600 .LP | |
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601 Successful software adapts itself to the changing world. |
| 12 | 602 .PP |
| 15 | 603 (4) |
| 604 .I "Reuse of parts | |
| 605 is even one step further. | |
| 13 | 606 A software may completely lose its field of action, |
| 607 but parts of which the software is build may be general and independent enough | |
| 608 to survive this death. | |
| 609 If software is build by combining small independent programs, | |
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610 then these parts are readily available for reuse. |
| 13 | 611 Who cares if the large program is a failure, |
| 612 but parts of it become successful instead? | |
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613 |
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614 .H 2 "Summary |
| 0 | 615 .LP |
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616 This chapter explained central ideas of the Unix Philosophy. |
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617 For each of the ideas, the advantages they introduce were explained. |
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618 The Unix Philosophy are guidelines that help to write more valuable software. |
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619 From the view point of a software developer or software designer, |
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620 the Unix Philosophy provides answers to many software design problem. |
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621 .PP |
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622 The various ideas of the Unix Philosophy are very interweaved |
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623 and can hardly be applied independently. |
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624 However, the probably most important messages are: |
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625 .I "``Keep it simple!''" , |
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626 .I "``Do one thing well!''" , |
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627 and |
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628 .I "``Use software leverage!'' |
| 0 | 629 |
| 8 | 630 |
| 631 | |
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632 .H 1 "Case study: \s-1MH\s0 |
| 18 | 633 .LP |
| 30 | 634 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 635 from a general point of view. |
| 30 | 636 The driving force were the guidelines; references to |
| 18 | 637 existing software were given only sparsely. |
| 638 In this and the next chapter, concrete software will be | |
| 639 the driving force in the discussion. | |
| 640 .PP | |
| 23 | 641 This first case study is about the mail user agents (\s-1MUA\s0) |
| 642 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 643 (``new mail handler''). | |
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644 .[ |
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645 nmh website |
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646 .] |
| 23 | 647 \s-1MUA\s0s provide functions to read, compose, and organize mail, |
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648 but (ideally) not to transfer it. |
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649 In this document, the name \s-1MH\s0 will be used to include nmh. |
| 19 | 650 A distinction will only be made if differences between |
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651 \s-1MH\s0 and nmh are described. |
| 18 | 652 |
| 0 | 653 |
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654 .H 2 "Historical background |
| 0 | 655 .LP |
| 19 | 656 Electronic mail was available in Unix very early. |
| 30 | 657 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 658 which was already present in the First Edition. | |
| 46 | 659 .[ [ |
| 44 | 660 salus |
| 661 quarter century of unix | |
| 46 | 662 .], page 41 f.] |
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663 It was a small program that either printed the user's mailbox file |
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664 or appended text to someone elses mailbox file, |
| 19 | 665 depending on the command line arguments. |
| 666 .[ | |
| 44 | 667 manual mail(1) |
| 19 | 668 .] |
| 669 It was a program that did one job well. | |
| 23 | 670 This job was emailing, which was very simple then. |
| 19 | 671 .PP |
| 23 | 672 Later, emailing became more powerful, and thus more complex. |
| 19 | 673 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 674 independent handling of single messages, | |
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675 and long-time email storage, was not powerful enough anymore. |
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676 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') |
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677 to provide additional functions for emailing. |
| 19 | 678 Mail was still one program, but now it was large and did |
| 679 several jobs. | |
| 23 | 680 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 681 It is designed for humans, but is still scriptable. |
| 23 | 682 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 683 .[ |
| 44 | 684 ritter |
| 685 mailx history | |
| 19 | 686 .] |
| 30 | 687 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 688 followed Mail's direction. |
| 689 They are large, monolithic programs which include all emailing functions. | |
| 690 .PP | |
| 23 | 691 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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692 In the beginning, they also had used a monolithic mail system, |
| 30 | 693 called \s-1MS\s0 (for ``mail system''). |
| 19 | 694 But in 1977, Stockton Gaines and Norman Shapiro |
| 695 came up with a proposal of a new email system concept \(en | |
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696 one that honored the Unix Philosophy. |
| 19 | 697 The concept was implemented by Bruce Borden in 1978 and 1979. |
| 698 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 699 .PP |
| 700 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 701 at Berkeley, and several others have contributed to the software. |
| 18 | 702 However, it's core concepts remained the same. |
| 23 | 703 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 704 Richard Coleman started with \fInmh\fP, the new mail handler. |
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705 His goal was to improve \s-1MH\s0 especially in regard of |
| 23 | 706 the requirements of modern emailing. |
| 19 | 707 Today, nmh is developed by various people on the Internet. |
| 18 | 708 .[ |
| 44 | 709 ware |
| 710 rand history | |
| 18 | 711 .] |
| 712 .[ | |
| 44 | 713 peek |
| 714 mh | |
| 18 | 715 .] |
| 0 | 716 |
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717 .H 2 "Contrasts to monolithic mail systems |
| 0 | 718 .LP |
| 19 | 719 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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720 Although there might actually exist further, very little known, |
| 30 | 721 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 722 .PP |
| 30 | 723 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 724 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 725 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 726 and their function. |
| 727 It gives a feeling of how the toolchest looks like. | |
| 19 | 728 .IP \(bu |
| 729 .CW inc : | |
| 30 | 730 incorporate new mail (this is how mail enters the system) |
| 19 | 731 .IP \(bu |
| 732 .CW scan : | |
| 733 list messages in folder | |
| 734 .IP \(bu | |
| 735 .CW show : | |
| 736 show message | |
| 737 .IP \(bu | |
| 738 .CW next\fR/\fPprev : | |
| 739 show next/previous message | |
| 740 .IP \(bu | |
| 741 .CW folder : | |
| 742 change current folder | |
| 743 .IP \(bu | |
| 744 .CW refile : | |
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745 refile message into different folder |
| 19 | 746 .IP \(bu |
| 747 .CW rmm : | |
| 748 remove message | |
| 749 .IP \(bu | |
| 750 .CW comp : | |
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751 compose new message |
| 19 | 752 .IP \(bu |
| 753 .CW repl : | |
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754 reply to message |
| 19 | 755 .IP \(bu |
| 756 .CW forw : | |
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757 forward message |
| 19 | 758 .IP \(bu |
| 759 .CW send : | |
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760 send prepared message (this is how mail leaves the system) |
| 0 | 761 .LP |
| 19 | 762 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 763 The user does not leave the shell to run \s-1MH\s0, | |
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764 instead he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 765 Using a monolithic program with a captive user interface |
| 766 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 767 Using toolchests like \s-1MH\s0 means running programs, | |
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768 alone or in combination with others, also from other toolchests, |
| 23 | 769 without leaving the shell. |
| 30 | 770 |
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771 .H 2 "Data storage |
| 30 | 772 .LP |
| 34 | 773 \s-1MH\s0's mail storage is a directory tree under the user's |
| 774 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 775 where mail folders are directories and mail messages are text files | |
| 776 within them. | |
| 777 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
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778 the public message sequences of that folder, |
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779 for instance the \fIunseen\fP sequence for new messages. |
| 34 | 780 Mail messages are text files located in a mail folder. |
| 781 The files contain the messages as they were received. | |
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782 They are named by ascending numbers in each folder. |
| 19 | 783 .PP |
| 30 | 784 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 785 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 786 In the mbox format all messages are stored within one file. | |
| 787 This was a good solution in the early days, when messages | |
| 788 were only a few lines of text and were deleted soon. | |
| 789 Today, when single messages often include several megabytes | |
| 790 of attachments, it is a bad solution. | |
| 791 Another disadvantage of the mbox format is that it is | |
| 792 more difficult to write tools that work on mail messages, | |
| 793 because it is always necessary to first find and extract | |
| 794 the relevant message in the mbox file. | |
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795 With the \s-1MH\s0 mailbox format, each message is a separate file. |
| 30 | 796 Also, the problem of concurrent access to one mailbox is |
| 797 reduced to the problem of concurrent access to one message. | |
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798 The maildir format is generally similar to the \s-1MH\s0 format, |
| 30 | 799 but modified towards guaranteed reliability. |
| 800 This involves some complexity, unfortunately. | |
| 34 | 801 .PP |
| 802 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 803 working with Unix' toolchest on directory trees: | |
| 804 \f(CWscan\fP is like \f(CWls\fP, | |
| 805 \f(CWshow\fP is like \f(CWcat\fP, | |
| 806 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 807 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 808 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 809 .PP | |
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810 \s-1MH\s0 extends the context of processes in Unix by two more items, |
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811 for its tools: |
| 34 | 812 .IP \(bu |
| 813 The current mail folder, which is similar to the current working directory. | |
| 814 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 815 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 816 .IP \(bu | |
| 817 Sequences, which are named sets of messages in a mail folder. | |
| 818 The current message, relative to a mail folder, is a special sequence. | |
| 819 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 820 .LP | |
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821 In contrast to Unix' context, which is maintained by the kernel, |
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822 \s-1MH\s0's context must be maintained by the tools themselves. |
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823 Usually there is one context per user, which resides in his |
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824 \f(CWcontext\fP file in the \s-1MH\s0 directory, |
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825 but a user can have several contexts, too. |
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826 Public sequences are an exception, as they belong to a mail folder, |
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827 and reside in the \f(CW.mh_sequences\fP file there. |
| 34 | 828 .[ |
| 44 | 829 man page mh-profile mh-sequence |
| 34 | 830 .] |
| 20 | 831 |
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832 .H 2 "Discussion of the design |
| 20 | 833 .LP |
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834 This section discusses \s-1MH\s0 in regard to the tenets |
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835 of the Unix Philosophy that Gancarz identified. |
| 20 | 836 |
| 837 .PP | |
|
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838 .B "Small is beautiful |
| 20 | 839 and |
|
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840 .B "do one thing well |
| 20 | 841 are two design goals that are directly visible in \s-1MH\s0. |
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842 Gancarz actually presents \s-1MH\s0 in his book as example under the |
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843 headline ``Making \s-1UNIX\s0 Do One Thing Well'': |
| 46 | 844 .[ [ |
| 44 | 845 gancarz |
| 846 unix philosophy | |
| 46 | 847 .], page 125 ff.] |
| 20 | 848 .QP |
| 849 [\s-1MH\s0] consists of a series of programs which | |
| 850 when combined give the user an enormous ability | |
| 851 to manipulate electronic mail messages. | |
| 852 A complex application, it shows that not only is it | |
| 853 possible to build large applications from smaller | |
| 854 components, but also that such designs are actually preferable. | |
| 0 | 855 .LP |
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856 The various programs of \s-1MH\s0 were relatively easy to write, |
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857 because each of them is small, limited to one function, |
| 23 | 858 and has clear boundaries. |
| 20 | 859 For the same reasons, they are also good to maintain. |
| 860 Further more, the system can easily get extended. | |
| 861 One only needs to put a new program into the toolchest. | |
| 23 | 862 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 863 (e.g. \f(CWmhbuild\fP). |
| 864 Also, different programs can exist to do the basically same job | |
| 865 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
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866 .PP |
| 20 | 867 If someone needs a mail system with some additionally |
|
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868 functions that are not available anywhere yet, he best expands a |
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869 toolchest system like \s-1MH\s0. |
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870 There he can add new functionality by simply adding additional |
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871 programs to the toolchest. |
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872 There he does not risk to break existing functionality by doing so. |
| 20 | 873 |
| 874 .PP | |
| 34 | 875 .B "Store data in flat text files |
| 876 is followed by \s-1MH\s0. | |
| 877 This is not surprising, because email messages are already plain text. | |
| 878 \s-1MH\s0 stores the messages as it receives them, | |
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879 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate |
| 34 | 880 on the messages in an \s-1MH\s0 mailbox. |
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881 All other files \s-1MH\s0 uses are plain text, too. |
| 34 | 882 It is therefore possible and encouraged to use the text processing |
| 883 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 884 |
| 885 .PP | |
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886 .B "Avoid captive user interfaces" . |
| 19 | 887 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 888 It offers all functions directly and without captive user interfaces. | |
| 30 | 889 If, nonetheless, users want a graphical user interface, |
|
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890 they can have it with \fIxmh\fP, \fIexmh\fP, |
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891 or with the Emacs interface \fImh-e\fP. |
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892 These are frontends for the \s-1MH\s0 toolchest. |
| 19 | 893 This means, all email-related work is still done by \s-1MH\s0 tools, |
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894 but the frontend calls the appropriate commands when the user |
|
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895 clicks on buttons or pushes a key. |
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896 .PP |
| 20 | 897 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 898 approach, because it does not limit the power of the backend itself. |
| 20 | 899 The frontend will anyway only be able to make a subset of the |
| 23 | 900 backend's power and flexibility available to the user. |
| 20 | 901 But if it is a separate program, |
| 902 then the missing parts can still be accessed at the backend directly. | |
| 19 | 903 If it is integrated, then this will hardly be possible. |
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904 An additional advantage is the possibility to have different frontends |
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905 to the same backend. |
| 19 | 906 |
| 907 .PP | |
|
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908 .B "Choose portability over efficiency |
| 20 | 909 and |
|
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910 .B "use shell scripts to increase leverage and portability" . |
| 20 | 911 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 912 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 913 .[ |
| 44 | 914 bolsky korn |
| 915 korn shell | |
| 20 | 916 .] |
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917 Chapter\|18 of the book shows a basic implementation |
| 20 | 918 of a subset of \s-1MH\s0 in ksh scripts. |
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919 Of course, this is just a demonstration, but a brilliant one. |
| 20 | 920 It shows how quickly one can implement such a prototype with shell scripts, |
| 921 and how readable they are. | |
| 922 The implementation in the scripting language may not be very fast, | |
| 923 but it can be fast enough though, and this is all that matters. | |
| 924 By having the code in an interpreted language, like the shell, | |
| 925 portability becomes a minor issue, if we assume the interpreter | |
| 926 to be widespread. | |
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927 .PP |
| 20 | 928 This demonstration also shows how easy it is to create single programs |
| 929 of a toolchest software. | |
|
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930 Eight tools (two of them have multiple names) and 16 functions |
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931 with supporting code are presented to the reader. |
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932 The tools comprise less than 40 lines of ksh each, |
| 30 | 933 in total about 200 lines. |
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934 The functions comprise less than 80 lines of ksh each, |
| 30 | 935 in total about 450 lines. |
| 20 | 936 Such small software is easy to write, easy to understand, |
| 937 and thus easy to maintain. | |
| 23 | 938 A toolchest improves the possibility to only write some parts |
| 20 | 939 and though create a working result. |
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940 Expanding the toolchest, even without global changes, |
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941 will likely be possible. |
| 20 | 942 |
| 943 .PP | |
|
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944 .B "Use software leverage to your advantage |
| 20 | 945 and the lesser tenet |
|
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946 .B "allow the user to tailor the environment |
| 20 | 947 are ideally followed in the design of \s-1MH\s0. |
| 21 | 948 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 949 directly define default options to programs. |
| 950 It is even possible to define different default options | |
|
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951 depending on the name under which a program is called. |
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952 Software leverage is heavily encouraged by the ease of |
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953 creating shell scripts that run a specific command line, |
| 30 | 954 built of several \s-1MH\s0 programs. |
| 21 | 955 There is few software that so much wants users to tailor their |
| 956 environment and to leverage the use of the software, like \s-1MH\s0. | |
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957 .PP |
| 21 | 958 Just to make one example: |
| 23 | 959 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 960 program. |
| 30 | 961 It is possible to take one of the distributed format files |
| 21 | 962 or to write one yourself. |
| 963 To use the format as default for \f(CWscan\fP, a single line, | |
| 964 reading | |
| 965 .DS | |
| 966 scan: -form FORMATFILE | |
| 967 .DE | |
| 968 must be added to \f(CW.mh_profile\fP. | |
| 969 If one wants this different format as an additional command, | |
| 23 | 970 instead of changing the default, he needs to create a link to |
| 971 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 972 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
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973 as the option should only be in effect for a program that is called as |
| 21 | 974 \f(CWscan2\fP. |
| 20 | 975 |
| 976 .PP | |
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977 .B "Make every program a filter |
| 21 | 978 is hard to find in \s-1MH\s0. |
| 979 The reason therefore is that most of \s-1MH\s0's tools provide | |
|
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980 basic file system operations for mailboxes. |
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981 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, |
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982 and \f(CWrm\fP aren't filters neither. |
| 23 | 983 \s-1MH\s0 does not provide many filters itself, but it is a basis |
| 984 to write filters for. | |
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985 An example would be a mail text highlighter, |
| 30 | 986 that means a program that makes use of a color terminal to display |
| 987 header lines, quotations, and signatures in distinct colors. | |
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988 The author's version of such a program is an awk script with 25 lines. |
| 21 | 989 |
| 990 .PP | |
|
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991 .B "Build a prototype as soon as possible |
| 21 | 992 was again well followed by \s-1MH\s0. |
| 993 This tenet, of course, focuses on early development, which is | |
| 994 long time ago for \s-1MH\s0. | |
| 995 But without following this guideline at the very beginning, | |
| 23 | 996 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 997 to ever create \s-1MH\s0. | |
| 998 In Bruce' own words: | |
| 46 | 999 .[ [ |
| 44 | 1000 ware rand history |
| 46 | 1001 .], page 132] |
| 21 | 1002 .QP |
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1003 [...] but [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1004 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1005 I proposed a very short project to prove the basic concepts, |
| 1006 and my management agreed. | |
| 1007 Looking back, I realize that I had been very lucky with my first design. | |
| 1008 Without nearly enough design work, | |
| 1009 I built a working environment and some header files | |
| 1010 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1011 inc, show/next/prev, and comp. | |
| 1012 [...] | |
| 1013 With these three, I was able to convince people that the structure was viable. | |
| 1014 This took about three weeks. | |
| 0 | 1015 |
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1016 .H 2 "Problems |
| 0 | 1017 .LP |
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1018 \s-1MH\s0 is not without problems. |
| 30 | 1019 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1020 .PP |
| 1021 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1022 when \s-1MH\s0 was designed. | |
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1023 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though. |
| 22 | 1024 \s-1MIME\s0 support and support for different character encodings |
| 1025 is available, but only on a moderate level. | |
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1026 This comes from limited development resources. |
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1027 More active developers could quickly change this. |
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1028 But \s-1MH\s0 is also limited by design, which is the larger problem. |
| 22 | 1029 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. |
| 1030 These design conflicts are not easily solvable. | |
| 1031 Possibly, they require a redesign. | |
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1032 \s-1IMAP\s0 may be too different to the classic mail model, |
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1033 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well. |
| 22 | 1034 .PP |
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1035 The other kind of problem are human habits. |
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1036 In this world, where almost all \s-1MUA\s0s are monolithic, |
| 22 | 1037 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 |
| 1038 like \s-1MH\s0. | |
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1039 The habits are so strong, that even people who understand the concept |
| 30 | 1040 and advantages of \s-1MH\s0 do not like to switch, |
| 1041 simply because \s-1MH\s0 is different. | |
| 1042 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
|
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1043 are quite outdated and thus not very appealing, compared to the modern interfaces |
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1044 of many monolithic \s-1MUA\s0s. |
|
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1045 One notable exception is \fImh-e\fP which provides an Emacs interface |
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1046 to \s-1MH\s0. |
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1047 \fIMh-e\fP looks much like \fImutt\fP or \fIpine\fP, |
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1048 but it has buttons, menus, and graphical display capabilities. |
| 20 | 1049 |
|
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1050 .H 2 "Summary |
| 20 | 1051 .LP |
|
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1052 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design. |
| 31 | 1053 It consists of a toolchest of small tools, each of them does one job well. |
| 1054 The toolchest approach offers great flexibility to the user. | |
|
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1055 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0. |
| 31 | 1056 This makes \s-1MH\s0 a very powerful mail system. |
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1057 Extending and customizing \s-1MH\s0 is easy and encouraged. |
| 31 | 1058 .PP |
| 1059 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1060 Its overall design follows clear rules. | |
| 1061 The single tools do only one job, thus they are easy to understand, | |
| 1062 easy to write, and good to maintain. | |
| 1063 They are all independent and do not interfere with the others. | |
| 1064 Automated testing of their function is a straight forward task. | |
| 1065 .PP | |
| 1066 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1067 as its differentness is also its largest advantage. | |
| 1068 Unfortunately, for most people their habits are stronger | |
| 1069 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1070 |
| 8 | 1071 |
| 1072 | |
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1073 .H 1 "Case study: uzbl |
| 32 | 1074 .LP |
| 1075 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
|
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1076 which is an old and established software. |
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1077 This chapter covers uzbl, a fresh new project. |
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1078 Uzbl is a web browser that adheres to the Unix Philosophy. |
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1079 Its name comes from the \fILolspeak\fP word for ``usable''; |
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1080 it is pronounced identical. |
| 0 | 1081 |
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1082 .H 2 "Historical background |
| 0 | 1083 .LP |
| 32 | 1084 Uzbl was started by Dieter Plaetinck in April 2009. |
| 44 | 1085 The idea was born in a thread in the Arch Linux Forums. |
| 32 | 1086 .[ |
| 44 | 1087 arch linux forums |
| 1088 browser | |
| 32 | 1089 .] |
| 1090 After some discussion about failures of well known web browsers, | |
| 1091 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1092 of how a better web browser could look like. | |
| 1093 To the question of another member, if Plaetinck would write that program, | |
| 1094 because it would sound fantastic, Plaetinck replied: | |
| 1095 ``Maybe, if I find the time ;-)''. | |
| 1096 .PP | |
| 1097 Fortunately, he found the time. | |
| 1098 One day later, the first prototype was out. | |
| 1099 One week later, uzbl had an own website. | |
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1100 .[ |
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1101 uzbl website |
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1102 .] |
| 32 | 1103 One month after the first code showed up, |
|
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1104 a mailing list was installed to coordinate and discuss further development, |
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1105 and a wiki was added to store documentation and scripts that showed up on the |
| 32 | 1106 mailing list and elsewhere. |
| 1107 .PP | |
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1108 In the, now, one year of uzbl's existence, it was heavily developed on various branches. |
| 32 | 1109 Plaetinck's task became more and more to only merge the best code from the |
| 1110 different branches into his main branch, and to apply patches. | |
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1111 .[ |
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1112 lwn uzbl |
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1113 .] |
| 32 | 1114 About once a month, Plaetinck released a new version. |
| 1115 In September 2009, he presented several forks of uzbl. | |
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1116 .[ [ |
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1117 uzbl website |
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1118 .], news archive] |
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1119 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1120 .PP |
| 1121 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
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1122 .[ |
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1123 lwn uzbl |
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1124 .] |
| 32 | 1125 In September 2009, the uzbl web browser was on \fISlashdot\fP. |
|
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1126 .[ |
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1127 slashdot uzbl |
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1128 .] |
| 0 | 1129 |
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1130 .H 2 "Contrasts to other web browsers |
| 0 | 1131 .LP |
| 32 | 1132 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1133 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1134 .PP | |
| 1135 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1136 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1137 It handles commands and events to interface other programs, | |
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1138 and also displays webpages by using \fIwebkit\fP as render engine. |
| 32 | 1139 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, |
| 1140 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1141 to form a ``complete'' web browser. | |
| 1142 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1143 so uzbl-core is included. | |
| 1144 .PP | |
| 1145 Unlike most other web browsers, uzbl is mainly the mediator between the | |
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1146 various tools that cover single jobs. |
| 35 | 1147 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1148 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1149 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1150 .DS |
| 1151 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1152 .DE | |
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1153 The graphical rendering of the webpage is done by webkit, |
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1154 a web content engine. |
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1155 Uzbl-core is built around libwebkit. |
| 32 | 1156 .PP |
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1157 Downloads, browsing history, bookmarks, and the like are not provided |
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1158 by the core itself, like they are in other web browsers. |
| 35 | 1159 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1160 external applications which provide the actual functionality. | |
| 32 | 1161 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1162 includes a script that calls wget with appropriate options in | |
| 1163 a prepared environment. | |
| 1164 .PP | |
| 1165 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1166 This is their effort to achieve similar goals. | |
| 35 | 1167 But instead of using existing, external programs, modern web browsers |
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1168 include these functions. |
| 0 | 1169 |
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1170 .H 2 "Discussion of the design |
| 0 | 1171 .LP |
| 32 | 1172 This section discusses uzbl in regard of the Unix Philosophy, |
| 1173 as identified by Gancarz. | |
| 1174 | |
| 1175 .PP | |
| 35 | 1176 .B "Make each program do one thing well" . |
| 1177 Uzbl tries to be a web browser and nothing else. | |
|
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1178 The common definition of a web browser is, of course, highly influenced by |
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1179 existing implementations of web browsers, although they are degenerated. |
| 35 | 1180 Web browsers should be programs to browse the web, and nothing more. |
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1181 This is the one thing they should do. |
|
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1182 .PP |
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1183 Web browsers should not, for instance, manage downloads. |
| 35 | 1184 This is the job download managers exist for. |
| 1185 Download managers do primary care about being good in downloading files. | |
| 1186 Modern web browsers provide download management only as a secondary feature. | |
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1187 How could they do this job better, than programs that exist only for |
| 35 | 1188 this very job? |
| 1189 And how could anyone want less than the best download manager available? | |
| 32 | 1190 .PP |
| 35 | 1191 A web browser's job is to let the user browse the web. |
| 1192 This means, navigating through websites by following links. | |
|
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1193 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1194 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1195 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1196 are also not the job of a web browser. |
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1197 They should be handled by external applications \(en |
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1198 ones which's job is to handle such data. |
| 35 | 1199 Uzbl strives to do it this way. |
|
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1200 .PP |
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1201 Remember Doug McIlroy: |
| 35 | 1202 .I |
| 1203 ``Write programs that do one thing and do it well. | |
| 1204 Write programs to work together.'' | |
| 1205 .R | |
| 1206 .PP | |
| 1207 The lesser tenet | |
| 1208 .B "allow the user to tailor the environment | |
| 1209 matches good here. | |
| 1210 There was the question, how anyone could want anything less than the | |
| 1211 best program for the job. | |
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1212 But as personal preferences matter, it is probably more important to ask: |
| 35 | 1213 How could anyone want something else than his preferred program for the job? |
|
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1214 .PP |
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1215 Usually users want one program for a specific job. |
| 35 | 1216 Hence, whenever the task is, for instance, downloading, |
|
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1217 the same download manager should be used. |
| 35 | 1218 More advanced users might want to have this download manager in this |
| 1219 situation and that one in that situation. | |
| 1220 They should be able to configure it this way. | |
| 1221 With uzbl, one can use any download manager the user wants. | |
|
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1222 To switch to a different one, only one line in a small handler script |
| 35 | 1223 needs to be changed. |
|
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1224 Alternatively it would be possible to query the program to use by |
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1225 reading a global file or an environment variable, in the handler script. |
|
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1226 .PP |
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1227 Uzbl does neither have its own download manager nor depends on a |
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1228 specific one, hence uzbl's browsing abilities will not be lowered by having |
| 35 | 1229 a bad download manager. |
|
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1230 Uzbl's download capabilities will be just as good as the ones of the best |
|
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1231 download manager available on the system. |
|
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1232 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1233 |
| 1234 .PP | |
|
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1235 .B "Use software leverage to your advantage" . |
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1236 Uzbl is designed to be extended by external tools. |
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1237 These external tools are usually wrapped by small handler shell scripts. |
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1238 Shell scripts are the glue in this approach. |
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1239 They make the various parts fit together. |
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1240 .PP |
|
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1241 The history mechanism of uzbl shall be presented as an example. |
|
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1242 Uzbl is configured to spawn a script to append an entry to the history |
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1243 whenever the event of a fully loaded page occurs. |
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1244 The script to append the entry to the history is not much more than: |
|
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1245 .DS |
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1246 #!/bin/sh |
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1247 file=/path/to/uzbl-history |
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1248 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1249 .DE |
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1250 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1251 .PP |
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1252 For loading an entry, a key is bound to spawn a load-from-history script. |
|
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1253 The script reverses the history to have newer entries first, |
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1254 then displays \fIdmenu\fP to let the user select an item, |
|
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1255 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
|
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1256 With error checking and corner case handling removed, |
|
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1257 the script looks like this: |
|
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1258 .DS |
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1259 #!/bin/sh |
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1260 file=/path/to/uzbl-history |
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1261 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1262 echo "uri $goto" > $4 |
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1263 .DE |
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1264 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1265 uzbl instance. |
| 32 | 1266 |
| 1267 .PP | |
|
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1268 .B "Avoid captive user interfaces" . |
|
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1269 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1270 a captive user interface. |
| 37 | 1271 But the difference to most other web browsers is, that uzbl is only |
|
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1272 the captive user interface frontend (and the core of the backend). |
|
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1273 Many parts of the backend are independent of uzbl. |
|
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1274 Some are distributed with uzbl, for some external programs, |
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1275 handler scripts are distributed, |
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1276 but arbitrary additional functionality can be added if desired. |
| 37 | 1277 .PP |
| 1278 The frontend is captive \(en that is true. | |
| 1279 This is okay for the task of browsing the web, as this task is only relevant | |
| 1280 for humans. | |
| 1281 Automated programs would \fIcrawl\fP the web. | |
| 1282 That means, they read the source directly. | |
| 1283 The source includes all the semantics. | |
| 1284 The graphical representation is just for humans to transfer the semantics | |
| 1285 more intuitively. | |
| 32 | 1286 |
| 1287 .PP | |
|
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1288 .B "Make every program a filter" . |
| 37 | 1289 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1290 Thus it is difficult to see what graphical web browsers should filter. | |
|
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1291 Graphical web browsers exist almost only to be interactively used by humans. |
| 37 | 1292 The only case when one might want to automate the rendering function is |
| 1293 to generate images of rendered webpages. | |
| 1294 | |
| 1295 .PP | |
| 1296 .B "Small is beautiful" | |
|
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1297 is not easy to apply to a web browser, because modern web technology |
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1298 is very complex, hence the rendering task is very complex. |
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1299 Modern web browsers have to consist of many thousand lines of code, |
| 37 | 1300 unfortunately. |
| 1301 Using the toolchest approach and wrappers can split the browser into | |
| 1302 several small parts, tough. | |
| 1303 .PP | |
|
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1304 As of March 2010, uzbl-core consists of about 3\,500 lines of C code. |
| 37 | 1305 The distribution includes another 3\,500 lines of Shell and Python code, |
| 1306 which are the handler scripts and plugins like a modal interface. | |
|
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1307 Further more, uzbl uses functionality of external tools like |
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1308 \fIwget\fP and \fInetcat\fP. |
| 37 | 1309 Up to this point, uzbl looks pretty neat and small. |
|
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1310 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1311 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1312 Unfortunately, small web render engines are not possible anymore |
|
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1313 because of the modern web. |
| 35 | 1314 |
| 1315 .PP | |
| 1316 .B "Build a prototype as soon as possible" . | |
| 1317 Plaetinck made his code public, right from the beginning. | |
|
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1318 Discussion and development was, and still is, open to everyone interested. |
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1319 Development versions of uzbl can be obtained very simply from the code |
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1320 repository. |
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1321 Within the first year of uzbl's existence, a new version was released |
| 35 | 1322 more often than once a month. |
|
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1323 Different forks and branches arose. |
|
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1324 They introduced new features, which were tested for suitability |
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1325 for the main branch. |
| 35 | 1326 The experiences of using prototypes influenced further development. |
| 1327 Actually, all development was community driven. | |
|
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1328 Plaetinck says, three months after uzbl's birth: |
| 35 | 1329 ``Right now I hardly code anything myself for Uzbl. |
| 1330 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1331 .[ | |
| 44 | 1332 lwn |
| 1333 uzbl | |
| 35 | 1334 .] |
| 32 | 1335 |
| 0 | 1336 |
|
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1337 .H 2 "Problems |
| 0 | 1338 .LP |
|
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1339 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1340 It is sad, but people use what they know. |
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1341 Fortunately, uzbl's user interface can look and feel very much the |
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1342 same as the one of the well known web browsers, |
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1343 hiding the internal differences. |
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1344 But uzbl has to provide this similar look and feel to be accepted |
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1345 as a ``normal'' browser by ``normal'' users. |
| 37 | 1346 .PP |
|
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1347 Though, the more important problem is the modern web. |
|
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1348 The modern web is simply broken. |
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1349 It has state in a state-less protocol, |
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1350 it misuses technologies, |
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1351 and it is helplessly overloaded. |
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1352 The result are web content render engines that must consist |
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1353 of hundreds of thousands lines of code. |
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1354 They also must combine and integrate many different technologies, |
|
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1355 only to make our modern web accessible. |
|
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1356 Website to image converter are hardly possible to run without |
|
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1357 human interaction because of state in sessions, impossible |
|
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1358 deep-linking, and unautomatable technologies. |
| 37 | 1359 .PP |
|
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1360 The web was misused to provide all kinds of imaginable wishes. |
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1361 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1362 |
| 8 | 1363 |
| 51 | 1364 .H 2 "Summary |
| 32 | 1365 .LP |
|
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1366 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1367 that is how uzbl is seen by its authors. |
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1368 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1369 It consists of independent parts that work together, |
|
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1370 while its core is mainly a mediator which glues the parts together. |
|
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1371 .PP |
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1372 Software leverage can excellently be seen in uzbl. |
|
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1373 External tools are used, independent tasks are separated |
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1374 in independent parts and glued together with small handler scripts. |
|
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1375 .PP |
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1376 As uzbl, more or less, consists of a set of tools and a bit |
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1377 of glue, anyone can put the parts together and expand it |
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1378 in any desired way. |
|
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1379 Uzbl is very flexible and customizable. |
|
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1380 These properties make it valuable for advanced users, |
|
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1381 but may keep novice users from using it. |
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1382 .PP |
|
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1383 But uzbl's main problem is the modern web, that makes it hard |
|
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1384 to design a sane web browser. |
|
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1385 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1386 |
| 8 | 1387 |
|
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1388 .H 1 "Final thoughts |
| 0 | 1389 |
| 1390 .LP | |
| 50 | 1391 This paper explained why good design is important. |
| 1392 It introduced the Unix Philosophy as guidelines to good design, | |
| 1393 in order to create good quality software. | |
| 1394 Then, real life software, that was designed with the Unix Philosophy | |
| 1395 in mind, was discussed. | |
| 1396 .PP | |
| 1397 Throughout the paper, the aim was do explain \fIwhy\fP something | |
| 1398 should be done the Unix way. | |
| 1399 It was tried to give reasons that expose that the Unix Philosophy | |
| 1400 is a preferrable way for designing software. | |
| 1401 .PP | |
| 1402 The Unix Philosophy is close to the software developer's point of view. | |
| 1403 Its main goal is taming the beast ``software complexity''. | |
| 1404 Hence it strives first and foremost for simplicity, of software. | |
| 1405 It might appear, that usability for people is a minor goal. | |
| 1406 Actually, the Unix Philosophy sees usability as a result of sound design. | |
| 1407 Sound design does not need to be most intuitive, | |
| 1408 but it will provide a consistent way to access the enormous power | |
| 1409 of software leverage. | |
| 1410 .PP | |
| 1411 Being able to solve some concrete problem becomes less and less important, | |
| 1412 as there is software available for nearly every possible task today. | |
| 1413 But the quality of software matters. | |
| 1414 It is important that we have \fIgood\fP software. | |
| 1415 .sp | |
| 0 | 1416 .LP |
| 50 | 1417 .B "But why the Unix Philosophy? |
| 1418 .PP | |
| 1419 The largest problem of software development is the complexity involved. | |
| 1420 It is the only part of the job that computers cannot take over. | |
| 1421 The Unix Philosophy fights complexity as main enemy. | |
| 1422 .PP | |
| 1423 On the other hand, | |
| 1424 the most unique gain of software is its ability to leverage. | |
| 1425 Current software still fails to make the best possible use of this ability. | |
| 1426 The Unix Philosophy concentrates much on exploiting this great opportunity. | |
| 0 | 1427 |
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1428 |
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1429 .bp |
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1430 .TL |
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1431 References |
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1432 .LP |
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1433 .XS |
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1434 .sp .5v |
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1435 .B |
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1436 References |
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1437 .XE |
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1438 .ev r |
| 42 | 1439 .nr PS -1 |
| 1440 .nr VS -1 | |
| 0 | 1441 .[ |
| 1442 $LIST$ | |
| 1443 .] | |
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1444 .nr PS +1 |
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1445 .nr VS +1 |
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1446 .ev |
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1447 |
| 42 | 1448 .bp |
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1449 .TL |
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1450 Table of Contents |
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1451 .LP |
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1452 .PX no |