Mercurial > docs > unix-phil
annotate unix-phil.ms @ 46:98a1446744c7
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| author | meillo@marmaro.de |
|---|---|
| date | Mon, 12 Apr 2010 10:52:59 +0200 |
| parents | ade392f024aa |
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| 0 | 3 .nr lu 0 |
| 4 .de CW | |
| 5 .nr PQ \\n(.f | |
| 6 .if t .ft CW | |
| 17 | 7 .ie ^\\$1^^ .if n .ul 999 |
| 0 | 8 .el .if n .ul 1 |
| 17 | 9 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2 |
| 0 | 10 .if n .if \\n(.$=1 \&\\$1 |
| 11 .if n .if \\n(.$>1 \&\\$1\c | |
| 12 .if n .if \\n(.$>1 \&\\$2 | |
| 13 .. | |
| 14 .ds [. \ [ | |
| 15 .ds .] ] | |
| 42 | 16 |
| 17 .rn NH _N | |
| 18 .de NH | |
| 19 .if '\\$1'1' .sp 2v | |
| 20 .if '\\$1'1' .nr PS +2 | |
| 21 ._N \\$1 | |
| 22 .if '\\$1'1' .nr PS -2 | |
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25 .am QP |
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28 |
| 1 | 29 .\"---------------------------------------- |
| 42 | 30 |
| 0 | 31 .TL |
| 42 | 32 .ps +4 |
| 6 | 33 Why the Unix Philosophy still matters |
| 0 | 34 .AU |
| 35 markus schnalke <meillo@marmaro.de> | |
| 36 .AB | |
| 1 | 37 .ti \n(.iu |
| 39 | 38 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 39 Today, few software designers are aware of these concepts, |
| 39 | 40 and thus a lot of modern software is more limited than necessary |
| 41 and makes less use of software leverage than possible. | |
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42 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 43 .AE |
| 44 | |
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45 .FS |
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46 .ps -1 |
| 39 | 47 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
| 48 Mentor was professor Schweiggert. 2010-04-05 | |
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49 .br |
| 39 | 50 You may retrieve this document from |
| 51 .CW \s-1http://marmaro.de/docs \ . | |
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52 .FE |
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53 |
| 0 | 54 .NH 1 |
| 55 Introduction | |
| 42 | 56 .XS |
| 57 \*(SN Introduction | |
| 58 .XE | |
| 0 | 59 .LP |
| 40 | 60 The Unix Philosophy is the essence of how the Unix operating system, |
| 61 especially its toolchest, was designed. | |
| 62 It is no limited set of fixed rules, | |
| 63 but a loose set of guidelines which tell how to write software that | |
| 64 suites well into Unix. | |
| 65 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 66 The Wikipedia has an accurate definition: | |
| 67 .[ | |
| 44 | 68 wikipedia |
| 69 unix philosophy | |
| 40 | 70 .] |
| 71 .QP | |
| 72 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 73 approaches to developing software based on the experience of leading | |
| 74 developers of the Unix operating system. | |
| 3 | 75 .PP |
| 40 | 76 As there is no single definition of the Unix Philosophy, |
| 77 several people have stated their view on what it comprises. | |
| 1 | 78 Best known are: |
| 79 .IP \(bu | |
| 80 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 81 .[ | |
| 44 | 82 mahoney |
| 83 oral history | |
| 1 | 84 .] |
| 85 .IP \(bu | |
| 86 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 87 .[ | |
| 44 | 88 gancarz |
| 89 unix philosophy | |
| 1 | 90 .] |
| 91 .IP \(bu | |
| 92 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 93 .[ | |
| 44 | 94 raymond |
| 95 art of unix programming | |
| 1 | 96 .] |
| 0 | 97 .LP |
| 1 | 98 These different views on the Unix Philosophy have much in common. |
| 40 | 99 Especially, the main concepts are similar in all of them. |
| 100 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 101 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 102 | |
| 103 .PP | |
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104 The Unix Philosophy explains how to design good software for Unix. |
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105 Many concepts described here, base on facilities of Unix. |
| 40 | 106 Other operating systems may not offer such facilities, |
| 41 | 107 hence it may not be possible to design software in the way of the |
| 108 Unix Philosophy for them. | |
| 109 .PP | |
| 110 The Unix Philosophy has an idea of how the process of software development | |
| 111 should look like, but large parts of the philosophy are quite independent | |
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112 from a concrete development process. |
| 41 | 113 However, one will soon recognize that some development processes work well |
| 114 with the ideas of the Unix Philosophy and support them, while others are | |
| 115 at cross-purposes. | |
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116 Kent Beck's books about Extreme Programming are valuable supplemental |
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117 resources on this topic. |
| 40 | 118 .PP |
| 41 | 119 The question of how to actually write code and how the code should looks |
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120 like in detail, are out of focus here. |
| 41 | 121 ``The Practice of Programming'' by Kernighan and Pike, |
| 122 .[ | |
| 44 | 123 kernighan pike |
| 124 practice of programming | |
| 41 | 125 .] |
| 126 is a good book that covers this topic. | |
| 127 Its point of view matches to the one of this paper. | |
| 0 | 128 |
| 129 .NH 1 | |
| 6 | 130 Importance of software design in general |
| 42 | 131 .XS |
| 132 .sp .5v | |
| 133 \*(SN Importance of software design in general | |
| 134 .XE | |
| 0 | 135 .LP |
| 40 | 136 Software design is the planning of how the internal structure |
| 137 and external interfaces of a software should look like. | |
| 39 | 138 It has nothing to do with visual appearance. |
| 139 If we take a program as a car, then its color is of no matter. | |
| 140 Its design would be the car's size, its shape, the locations of doors, | |
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141 the passenger/space ratio, the available controls and instruments, |
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142 and so forth. |
| 39 | 143 .PP |
| 144 Why should software get designed at all? | |
| 6 | 145 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 146 Not designing software means programming without plan. |
| 147 This will pretty sure lead to horrible results. | |
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148 Software that is horrible to use and horrible to maintain. |
| 39 | 149 These two aspects are the visible ones. |
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150 Often invisible though, are the wasted possible gains. |
| 39 | 151 Good software design can make these gains available. |
| 6 | 152 .PP |
| 39 | 153 A software's design deals with quality properties. |
| 154 Good design leads to good quality, and quality is important. | |
| 155 Any car may be able to drive from A to B, | |
| 156 but it depends on the car's properties whether it is a good choice | |
| 157 for passenger transport or not. | |
| 158 It depends on its properties if it is a good choice | |
| 159 for a rough mountain area. | |
| 160 And it depends on its properties if the ride will be fun. | |
| 161 | |
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162 .PP |
| 39 | 163 Requirements for a software are twofold: |
| 164 functional and non-functional. | |
| 165 .IP \(bu | |
| 166 Functional requirements define directly the software's functions. | |
| 167 They are the reason why software gets written. | |
| 168 Someone has a problem and needs a tool to solve it. | |
| 169 Being able to solve the problem is the main functional goal. | |
| 170 It is the driving force behind all programming effort. | |
| 6 | 171 Functional requirements are easier to define and to verify. |
| 39 | 172 .IP \(bu |
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173 Non-functional requirements are called \fIquality\fP requirements, too. |
| 39 | 174 The quality of a software are the properties that are not directly related to |
| 175 the software's basic functions. | |
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176 Tools of bad quality often do solve the problems they were written for, |
| 39 | 177 but introduce problems and difficulties for usage and development, later on. |
| 178 Quality aspects are often overlooked at first sight, | |
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179 and are often difficult to define clearly and to verify. |
| 6 | 180 .PP |
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181 Quality is hardly interesting when the software gets built initially, |
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182 but it has a high impact on usability and maintenance of the software, later. |
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183 A short-sighted might see in developing a software, mainly building something up. |
| 39 | 184 But experience shows, that building the software the first time is |
| 185 only a small amount of the overall work. | |
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186 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en |
| 6 | 187 does soon take over the major part of the time spent on a software. |
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188 And of course, the time spent actually using the software. |
| 6 | 189 These processes are highly influenced by the software's quality. |
| 39 | 190 Thus, quality must not be neglected. |
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191 However, the problem with quality is that you hardly ``stumble over'' |
| 39 | 192 bad quality during the first build, |
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193 although this is the time when you should care about good quality most. |
| 6 | 194 .PP |
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195 Software design has little to do with the basic function of a software \(en |
| 39 | 196 this requirement will get satisfied anyway. |
| 197 Software design is more about quality aspects of the software. | |
| 198 Good design leads to good quality, bad design to bad quality. | |
| 6 | 199 The primary functions of the software will be affected modestly by bad quality, |
| 39 | 200 but good quality can provide a lot of additional gain, |
| 6 | 201 even at places where one never expected it. |
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202 .PP |
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203 The ISO/IEC\|9126-1 standard, part\|1, |
| 6 | 204 .[ |
| 44 | 205 iso product quality |
| 6 | 206 .] |
| 207 defines the quality model as consisting out of: | |
| 208 .IP \(bu | |
| 209 .I Functionality | |
| 210 (suitability, accuracy, inter\%operability, security) | |
| 211 .IP \(bu | |
| 212 .I Reliability | |
| 213 (maturity, fault tolerance, recoverability) | |
| 214 .IP \(bu | |
| 215 .I Usability | |
| 216 (understandability, learnability, operability, attractiveness) | |
| 217 .IP \(bu | |
| 218 .I Efficiency | |
| 9 | 219 (time behavior, resource utilization) |
| 6 | 220 .IP \(bu |
| 221 .I Maintainability | |
| 23 | 222 (analyzability, changeability, stability, testability) |
| 6 | 223 .IP \(bu |
| 224 .I Portability | |
| 225 (adaptability, installability, co-existence, replaceability) | |
| 226 .LP | |
| 39 | 227 Good design can improve these properties of a software, |
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228 bad designed software likely suffers in these points. |
| 7 | 229 .PP |
| 230 One further goal of software design is consistency. | |
| 231 Consistency eases understanding, working on, and using things. | |
| 39 | 232 Consistent internal structure and consistent interfaces to the outside |
| 233 can be provided by good design. | |
| 7 | 234 .PP |
| 39 | 235 Software should be well designed because good design avoids many |
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236 problems during a software's lifetime. |
| 39 | 237 And software should be well designed because good design can offer |
| 238 much additional gain. | |
| 239 Indeed, much effort should be spent into good design to make software more valuable. | |
| 240 The Unix Philosophy shows a way of how to design software well. | |
| 7 | 241 It offers guidelines to achieve good quality and high gain for the effort spent. |
| 0 | 242 |
| 243 | |
| 244 .NH 1 | |
| 245 The Unix Philosophy | |
| 42 | 246 .XS |
| 247 .sp .5v | |
| 248 \*(SN The Unix Philosophy | |
| 249 .XE | |
| 4 | 250 .LP |
| 251 The origins of the Unix Philosophy were already introduced. | |
| 8 | 252 This chapter explains the philosophy, oriented on Gancarz, |
| 253 and shows concrete examples of its application. | |
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254 |
| 16 | 255 .NH 2 |
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256 Pipes |
| 42 | 257 .XS |
| 258 \*(SN Pipes | |
| 259 .XE | |
| 0 | 260 .LP |
| 4 | 261 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 262 Knowledge of using the Unix shell is assumed. | |
| 263 .PP | |
| 264 Counting the number of files in the current directory: | |
| 41 | 265 .DS |
| 4 | 266 .CW |
| 9 | 267 .ps -1 |
| 4 | 268 ls | wc -l |
| 269 .DE | |
| 270 The | |
| 271 .CW ls | |
| 272 command lists all files in the current directory, one per line, | |
| 273 and | |
| 274 .CW "wc -l | |
| 8 | 275 counts the number of lines. |
| 4 | 276 .PP |
| 8 | 277 Counting the number of files that do not contain ``foo'' in their name: |
| 41 | 278 .DS |
| 4 | 279 .CW |
| 9 | 280 .ps -1 |
| 4 | 281 ls | grep -v foo | wc -l |
| 282 .DE | |
| 283 Here, the list of files is filtered by | |
| 284 .CW grep | |
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285 to remove all lines that contain ``foo''. |
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286 The rest equals the previous example. |
| 4 | 287 .PP |
| 288 Finding the five largest entries in the current directory. | |
| 41 | 289 .DS |
| 4 | 290 .CW |
| 9 | 291 .ps -1 |
| 4 | 292 du -s * | sort -nr | sed 5q |
| 293 .DE | |
| 294 .CW "du -s * | |
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295 returns the recursively summed sizes of all files in the current directory |
| 8 | 296 \(en no matter if they are regular files or directories. |
| 4 | 297 .CW "sort -nr |
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298 sorts the list numerically in reverse order (descending). |
| 4 | 299 Finally, |
| 300 .CW "sed 5q | |
| 301 quits after it has printed the fifth line. | |
| 302 .PP | |
| 303 The presented command lines are examples of what Unix people would use | |
| 304 to get the desired output. | |
| 305 There are also other ways to get the same output. | |
| 306 It's a user's decision which way to go. | |
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307 .PP |
| 8 | 308 The examples show that many tasks on a Unix system |
| 4 | 309 are accomplished by combining several small programs. |
| 310 The connection between the single programs is denoted by the pipe operator `|'. | |
| 311 .PP | |
| 312 Pipes, and their extensive and easy use, are one of the great | |
| 313 achievements of the Unix system. | |
| 314 Pipes between programs have been possible in earlier operating systems, | |
| 315 but it has never been a so central part of the concept. | |
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316 When, in the early seventies, Doug McIlroy introduced pipes into the |
| 4 | 317 Unix system, |
| 318 ``it was this concept and notation for linking several programs together | |
| 319 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 320 .[ | |
| 44 | 321 aughenbaugh |
| 322 unix oral history | |
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323 .] |
| 4 | 324 .PP |
| 325 Being able to specify pipelines in an easy way is, | |
| 326 however, not enough by itself. | |
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327 It is only one half. |
| 4 | 328 The other is the design of the programs that are used in the pipeline. |
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329 They need interfaces that allow them to be used in such a way. |
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330 |
| 16 | 331 .NH 2 |
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332 Interface design |
| 42 | 333 .XS |
| 334 \*(SN Interface design | |
| 335 .XE | |
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336 .LP |
| 11 | 337 Unix is, first of all, simple \(en Everything is a file. |
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338 Files are sequences of bytes, without any special structure. |
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339 Programs should be filters, which read a stream of bytes from standard input (stdin) |
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340 and write a stream of bytes to standard output (stdout). |
| 8 | 341 If the files \fIare\fP sequences of bytes, |
| 342 and the programs \fIare\fP filters on byte streams, | |
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343 then there is exactly one data interface. |
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344 Hence it is possible to combine programs in any desired way. |
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345 .PP |
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346 Even a handful of small programs yields a large set of combinations, |
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347 and thus a large set of different functions. |
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348 This is leverage! |
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349 If the programs are orthogonal to each other \(en the best case \(en |
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350 then the set of different functions is greatest. |
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351 .PP |
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352 Programs can also have a separate control interface, |
| 11 | 353 besides their data interface. |
| 354 The control interface is often called ``user interface'', | |
| 355 because it is usually designed to be used by humans. | |
| 356 The Unix Philosophy discourages to assume the user to be human. | |
| 357 Interactive use of software is slow use of software, | |
| 358 because the program waits for user input most of the time. | |
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359 Interactive software requires the user to be in front of the computer. |
| 11 | 360 Interactive software occupy the user's attention while they are running. |
| 361 .PP | |
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362 Now to come back to the idea of combining several small programs, |
| 11 | 363 to have a more specific function. |
| 364 If these single tools would all be interactive, | |
| 365 how would the user control them? | |
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366 It is not only a problem to control several programs at once, |
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367 if they run at the same time, |
| 11 | 368 it also very inefficient to have to control each of the single programs |
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369 that are intended to act as one large program. |
| 11 | 370 Hence, the Unix Philosophy discourages programs to demand interactive use. |
| 371 The behavior of programs should be defined at invocation. | |
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372 This is done by specifying arguments to the program call |
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373 (command line switches). |
| 11 | 374 Gancarz discusses this topic as ``avoid captive user interfaces''. |
| 46 | 375 .[ [ |
| 44 | 376 gancarz unix philosophy |
| 46 | 377 .], page 88 ff.] |
| 11 | 378 .PP |
| 379 Non-interactive use is, during development, also an advantage for testing. | |
| 380 Testing of interactive programs is much more complicated, | |
| 381 than testing of non-interactive programs. | |
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382 |
| 16 | 383 .NH 2 |
| 8 | 384 The toolchest approach |
| 42 | 385 .XS |
| 386 \*(SN The toolchest approach | |
| 387 .XE | |
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388 .LP |
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389 A toolchest is a set of tools. |
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390 Instead of having one big tool for all tasks, one has many small tools, |
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391 each for one task. |
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392 Difficult tasks are solved by combining several of the small, simple tools. |
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393 .PP |
| 11 | 394 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 395 that are filters on byte streams. | |
| 396 They are, to a large extend, unrelated in their function. | |
| 397 Hence, the Unix toolchest provides a large set of functions | |
| 398 that can be accessed by combining the programs in the desired way. | |
| 399 .PP | |
| 400 There are also advantages for developing small toolchest programs. | |
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401 It is easier and less error-prone to write small programs. |
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402 It is also easier and less error-prone to write a large set of small programs, |
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403 than to write one large program with all the functionality included. |
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404 If the small programs are combinable, then they offer even a larger set |
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405 of functions than the single large program. |
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406 Hence, one gets two advantages out of writing small, combinable programs: |
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407 They are easier to write and they offer a greater set of functions through |
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408 combination. |
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409 .PP |
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410 But there are also two main drawbacks of the toolchest approach. |
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411 First, one simple, standardized interface has to be sufficient. |
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412 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 413 then a different approach might be of need. |
| 13 | 414 But it is also possible, that he just can not imagine a design where |
| 8 | 415 a stream of bytes is sufficient. |
| 416 By becoming more familiar with the ``Unix style of thinking'', | |
| 417 developers will more often and easier find simple designs where | |
| 418 a stream of bytes is a sufficient interface. | |
| 419 .PP | |
| 420 The second drawback of a toolchest affects the users. | |
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421 A toolchest is often more difficult to use. |
| 9 | 422 It is necessary to become familiar with each of the tools, |
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423 to be able to use the right one in a given situation. |
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424 Additionally, one needs to combine the tools in a senseful way himself. |
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425 This is like a sharp knife \(en it is a powerful tool in the hand of a |
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426 master, but of no good value in the hand of an unskilled. |
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427 However, learning single, small tools of a toolchest is easier than |
| 8 | 428 learning a complex tool. |
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429 And the user will already have a basic understanding of a yet unknown tool, |
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430 if the tools of a toolchest have a common, consistent style. |
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431 He will be able to transfer knowledge over from one tool to another. |
| 8 | 432 .PP |
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433 Moreover, the second drawback can be removed to a large extend |
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434 by adding wrappers around the basic tools. |
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435 Novice users do not need to learn several tools, if a professional wraps |
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436 complete command lines into a higher-level script. |
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437 Note that the wrapper script still calls the small tools; |
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438 it is just like a skin around them. |
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439 No complexity is added this way. |
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440 But new programs can get created out of existing one with very low effort. |
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441 .PP |
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442 A wrapper script for finding the five largest entries in the current directory |
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443 could look like this: |
| 41 | 444 .DS |
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445 .CW |
| 9 | 446 .ps -1 |
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447 #!/bin/sh |
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448 du -s * | sort -nr | sed 5q |
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449 .DE |
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450 The script itself is just a text file that calls the command line, |
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451 which a professional user would type in directly. |
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452 It is probably worth to make the program flexible on the number of |
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453 entries it prints: |
| 41 | 454 .DS |
| 8 | 455 .CW |
| 9 | 456 .ps -1 |
| 8 | 457 #!/bin/sh |
| 458 num=5 | |
| 459 [ $# -eq 1 ] && num="$1" | |
| 460 du -sh * | sort -nr | sed "${num}q" | |
| 461 .DE | |
| 462 This script acts like the one before, when called without an argument. | |
| 463 But one can also specify a numerical argument to define the number of lines to print. | |
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464 One can surely imagine even more flexible versions, however, |
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465 they will still relay on the external programs, |
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466 which do the actual work. |
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467 |
| 16 | 468 .NH 2 |
| 8 | 469 A powerful shell |
| 42 | 470 .XS |
| 471 \*(SN A powerful shell | |
| 472 .XE | |
| 8 | 473 .LP |
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474 The Unix shell provides the possibility to combine small programs into large ones. |
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475 But a powerful shell is a great feature in other ways, too. |
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476 For instance by being scriptable. |
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477 Control statements are build into the shell. |
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478 The functions, however, are the normal programs of the system. |
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479 Thus, as the programs are already known, |
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480 learning to program in the shell becomes easy. |
| 8 | 481 Using normal programs as functions in the shell programming language |
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482 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 483 .PP |
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484 The Unix shell encourages to write small scripts, |
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485 by combining existing programs, because it is so easy to do. |
| 8 | 486 This is a great step towards automation. |
| 487 It is wonderful if the effort to automate a task equals the effort | |
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488 to do the task a second time by hand. |
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489 If this holds, |
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490 then the user will be happy to automate everything he does more than once. |
| 8 | 491 .PP |
| 492 Small programs that do one job well, standardized interfaces between them, | |
| 493 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 494 this will inevitably produce software leverage. | |
| 495 Getting multiple times the benefit of an investment is a great offer. | |
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496 .PP |
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497 The shell also encourages rapid prototyping. |
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498 Many well known programs started as quickly hacked shell scripts, |
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499 and turned into ``real'' programs, written in C, later. |
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500 Building a prototype first, is a way to avoid the biggest problems |
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501 in application development. |
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502 Fred Brooks explains in ``No Silver Bullet'': |
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503 .[ |
| 44 | 504 brooks |
| 505 no silver bullet | |
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506 .] |
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507 .QP |
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508 The hardest single part of building a software system is deciding precisely what to build. |
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509 No other part of the conceptual work is so difficult as establishing the detailed |
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510 technical requirements, [...]. |
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511 No other part of the work so cripples the resulting system if done wrong. |
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512 No other part is more difficult to rectify later. |
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513 .PP |
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514 Writing a prototype is a great method for becoming familiar with the requirements |
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515 and to run into real problems early. |
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516 .PP |
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517 Prototyping is often seen as a first step in building a software. |
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518 This is, of course, good. |
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519 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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520 After having built the prototype, one might notice, that the prototype is already |
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521 \fIgood enough\fP. |
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522 Hence, no reimplementation, in a more sophisticated programming language, |
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523 might be of need, at least for the moment. |
| 23 | 524 Maybe later, it might be necessary to rewrite the software, but not now. |
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525 By delaying further work, one keeps the flexibility to react on |
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526 changing requirements. |
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527 Software parts that are not written will not miss the requirements. |
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528 |
| 16 | 529 .NH 2 |
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530 Worse is better |
| 42 | 531 .XS |
| 532 \*(SN Worse is better | |
| 533 .XE | |
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534 .LP |
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535 The Unix Philosophy aims for the 90% solution; |
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536 others call it the ``Worse is better'' approach. |
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537 Practical experience shows, that: |
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538 .PP |
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539 (1) It is almost never possible to define the |
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540 requirements completely and correctly the first time. |
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541 Hence one should not try to; one will fail anyway. |
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542 .PP |
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543 (2) Requirements change during time. |
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544 Hence it is best to delay requirement-based design decisions as long as possible. |
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545 The software should be small and flexible as long as possible |
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546 to react on changing requirements. |
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547 Shell scripts, for example, are more easily adjusted as C programs. |
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548 .PP |
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549 (3) Maintenance work is hard work. |
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550 Hence, one should keep the amount of code as small as possible; |
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551 it should just fulfill the \fIcurrent\fP requirements. |
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552 Software parts that will be written in future, |
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553 do not need maintenance till then. |
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554 .PP |
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555 Starting with a prototype in a scripting language has several advantages: |
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556 .IP \(bu |
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557 As the initial effort is low, one will likely start right away. |
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558 .IP \(bu |
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559 As working parts are available soon, the real requirements can get identified soon. |
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560 .IP \(bu |
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561 When a software is usable and valuable, it gets used, and thus tested. |
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562 Hence problems will be found at early stages of the development. |
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563 .IP \(bu |
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564 The prototype might be enough for the moment, |
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565 thus further work on the software can get delayed to a time |
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566 when one knows better about the requirements and problems, |
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567 than now. |
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568 .IP \(bu |
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569 Implementing now only the parts that are actually needed at the moment, |
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570 introduces fewer programming and maintenance work. |
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571 .IP \(bu |
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572 If the global situation changes so that the software is not needed anymore, |
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573 then less effort was spent into the project, than it would have be |
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574 when a different approach had been used. |
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575 |
| 16 | 576 .NH 2 |
| 11 | 577 Upgrowth and survival of software |
| 42 | 578 .XS |
| 579 \*(SN Upgrowth and survival of software | |
| 580 .XE | |
| 11 | 581 .LP |
| 12 | 582 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 583 Although these are just verbs, they do imply a specific view on the work process |
| 584 they describe. | |
| 12 | 585 The better verb, however, is to \fIgrow\fP. |
| 586 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 587 It starts with a first prototype, which evolves as requirements change. | |
| 588 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 589 compiled program this way. |
| 590 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
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591 While being alive it will get extended, rearranged, rebuilt. |
| 12 | 592 Growing software matches the view that ``software is never finished. It is only released.'' |
| 46 | 593 .[ [ |
| 44 | 594 gancarz |
| 595 unix philosophy | |
| 46 | 596 .], page 26] |
| 12 | 597 .PP |
| 13 | 598 Software can be seen as being controlled by evolutionary processes. |
| 599 Successful software is software that is used by many for a long time. | |
| 12 | 600 This implies that the software is needed, useful, and better than alternatives. |
| 601 Darwin talks about: ``The survival of the fittest.'' | |
| 602 .[ | |
| 44 | 603 darwin |
| 604 origin of species | |
| 12 | 605 .] |
| 606 Transferred to software: The most successful software, is the fittest, | |
| 607 is the one that survives. | |
| 13 | 608 (This may be at the level of one creature, or at the level of one species.) |
| 609 The fitness of software is affected mainly by four properties: | |
| 15 | 610 portability of code, portability of data, range of usability, and reusability of parts. |
| 611 .\" .IP \(bu | |
| 612 .\" portability of code | |
| 613 .\" .IP \(bu | |
| 614 .\" portability of data | |
| 615 .\" .IP \(bu | |
| 616 .\" range of usability | |
| 617 .\" .IP \(bu | |
| 618 .\" reuseability of parts | |
| 13 | 619 .PP |
| 15 | 620 (1) |
| 621 .I "Portability of code | |
| 622 means, using high-level programming languages, | |
| 13 | 623 sticking to the standard, |
| 624 and avoiding optimizations that introduce dependencies on specific hardware. | |
| 625 Hardware has a much lower lifetime than software. | |
| 626 By chaining software to a specific hardware, | |
| 627 the software's lifetime gets shortened to that of this hardware. | |
| 628 In contrast, software should be easy to port \(en | |
| 23 | 629 adaptation is the key to success. |
| 13 | 630 .\" cf. practice of prog: ch08 |
| 631 .PP | |
| 15 | 632 (2) |
| 633 .I "Portability of data | |
| 634 is best achieved by avoiding binary representations | |
| 13 | 635 to store data, because binary representations differ from machine to machine. |
| 23 | 636 Textual representation is favored. |
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637 Historically, \s-1ASCII\s0 was the charset of choice. |
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638 For the future, \s-1UTF\s0-8 might be the better choice. |
| 13 | 639 Important is that it is a plain text representation in a |
| 640 very common charset encoding. | |
| 641 Apart from being able to transfer data between machines, | |
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642 readable data has the great advantage, that humans are able to directly |
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643 read and edit it with text editors and other tools from the Unix toolchest. |
| 13 | 644 .\" gancarz tenet 5 |
| 12 | 645 .PP |
| 15 | 646 (3) |
| 647 A large | |
| 648 .I "range of usability | |
| 23 | 649 ensures good adaptation, and thus good survival. |
| 13 | 650 It is a special distinction if a software becomes used in fields of action, |
| 651 the original authors did never imagine. | |
| 652 Software that solves problems in a general way will likely be used | |
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653 for many kinds of similar problems. |
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654 Being too specific limits the range of usability. |
| 13 | 655 Requirements change through time, thus use cases change or even vanish. |
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656 As a good example in this point, |
| 13 | 657 Allman identifies flexibility to be one major reason for sendmail's success: |
| 658 .[ | |
| 44 | 659 allman |
| 660 sendmail | |
| 13 | 661 .] |
| 662 .QP | |
| 663 Second, I limited myself to the routing function [...]. | |
| 664 This was a departure from the dominant thought of the time, [...]. | |
| 665 .QP | |
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666 Third, the sendmail configuration file was flexible enough to adapt |
| 13 | 667 to a rapidly changing world [...]. |
| 668 .LP | |
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669 Successful software adapts itself to the changing world. |
| 12 | 670 .PP |
| 15 | 671 (4) |
| 672 .I "Reuse of parts | |
| 673 is even one step further. | |
| 13 | 674 A software may completely lose its field of action, |
| 675 but parts of which the software is build may be general and independent enough | |
| 676 to survive this death. | |
| 677 If software is build by combining small independent programs, | |
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678 then these parts are readily available for reuse. |
| 13 | 679 Who cares if the large program is a failure, |
| 680 but parts of it become successful instead? | |
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681 |
| 16 | 682 .NH 2 |
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683 Summary |
| 42 | 684 .XS |
| 685 \*(SN Summary | |
| 686 .XE | |
| 0 | 687 .LP |
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688 This chapter explained central ideas of the Unix Philosophy. |
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689 For each of the ideas, the advantages they introduce were explained. |
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690 The Unix Philosophy are guidelines that help to write more valuable software. |
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691 From the view point of a software developer or software designer, |
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692 the Unix Philosophy provides answers to many software design problem. |
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693 .PP |
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694 The various ideas of the Unix Philosophy are very interweaved |
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695 and can hardly be applied independently. |
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696 However, the probably most important messages are: |
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697 .I "``Keep it simple!''" , |
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698 .I "``Do one thing well!''" , |
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699 and |
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700 .I "``Use software leverage!'' |
| 0 | 701 |
| 8 | 702 |
| 703 | |
| 0 | 704 .NH 1 |
| 19 | 705 Case study: \s-1MH\s0 |
| 42 | 706 .XS |
| 707 .sp .5v | |
| 708 \*(SN Case study: \s-1MH\s0 | |
| 709 .XE | |
| 18 | 710 .LP |
| 30 | 711 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 712 from a general point of view. |
| 30 | 713 The driving force were the guidelines; references to |
| 18 | 714 existing software were given only sparsely. |
| 715 In this and the next chapter, concrete software will be | |
| 716 the driving force in the discussion. | |
| 717 .PP | |
| 23 | 718 This first case study is about the mail user agents (\s-1MUA\s0) |
| 719 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 720 (``new mail handler''). | |
| 721 \s-1MUA\s0s provide functions to read, compose, and organize mail, | |
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722 but (ideally) not to transfer it. |
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723 In this document, the name \s-1MH\s0 will be used to include nmh. |
| 19 | 724 A distinction will only be made if differences between |
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725 \s-1MH\s0 and nmh are described. |
| 18 | 726 |
| 0 | 727 |
| 728 .NH 2 | |
| 19 | 729 Historical background |
| 42 | 730 .XS |
| 731 \*(SN Historical background | |
| 732 .XE | |
| 0 | 733 .LP |
| 19 | 734 Electronic mail was available in Unix very early. |
| 30 | 735 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 736 which was already present in the First Edition. | |
| 46 | 737 .[ [ |
| 44 | 738 salus |
| 739 quarter century of unix | |
| 46 | 740 .], page 41 f.] |
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741 It was a small program that either printed the user's mailbox file |
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742 or appended text to someone elses mailbox file, |
| 19 | 743 depending on the command line arguments. |
| 744 .[ | |
| 44 | 745 manual mail(1) |
| 19 | 746 .] |
| 747 It was a program that did one job well. | |
| 23 | 748 This job was emailing, which was very simple then. |
| 19 | 749 .PP |
| 23 | 750 Later, emailing became more powerful, and thus more complex. |
| 19 | 751 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 752 independent handling of single messages, | |
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753 and long-time email storage, was not powerful enough anymore. |
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754 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') |
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755 to provide additional functions for emailing. |
| 19 | 756 Mail was still one program, but now it was large and did |
| 757 several jobs. | |
| 23 | 758 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 759 It is designed for humans, but is still scriptable. |
| 23 | 760 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 761 .[ |
| 44 | 762 ritter |
| 763 mailx history | |
| 19 | 764 .] |
| 30 | 765 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 766 followed Mail's direction. |
| 767 They are large, monolithic programs which include all emailing functions. | |
| 768 .PP | |
| 23 | 769 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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770 In the beginning, they also had used a monolithic mail system, |
| 30 | 771 called \s-1MS\s0 (for ``mail system''). |
| 19 | 772 But in 1977, Stockton Gaines and Norman Shapiro |
| 773 came up with a proposal of a new email system concept \(en | |
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774 one that honored the Unix Philosophy. |
| 19 | 775 The concept was implemented by Bruce Borden in 1978 and 1979. |
| 776 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 777 .PP |
| 778 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 779 at Berkeley, and several others have contributed to the software. |
| 18 | 780 However, it's core concepts remained the same. |
| 23 | 781 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 782 Richard Coleman started with \fInmh\fP, the new mail handler. |
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783 His goal was to improve \s-1MH\s0 especially in regard of |
| 23 | 784 the requirements of modern emailing. |
| 19 | 785 Today, nmh is developed by various people on the Internet. |
| 18 | 786 .[ |
| 44 | 787 ware |
| 788 rand history | |
| 18 | 789 .] |
| 790 .[ | |
| 44 | 791 peek |
| 792 mh | |
| 18 | 793 .] |
| 0 | 794 |
| 795 .NH 2 | |
| 20 | 796 Contrasts to monolithic mail systems |
| 42 | 797 .XS |
| 798 \*(SN Contrasts to monolithic mail systems | |
| 799 .XE | |
| 0 | 800 .LP |
| 19 | 801 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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802 Although there might actually exist further, very little known, |
| 30 | 803 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 804 .PP |
| 30 | 805 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 806 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 807 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 808 and their function. |
| 809 It gives a feeling of how the toolchest looks like. | |
| 19 | 810 .IP \(bu |
| 811 .CW inc : | |
| 30 | 812 incorporate new mail (this is how mail enters the system) |
| 19 | 813 .IP \(bu |
| 814 .CW scan : | |
| 815 list messages in folder | |
| 816 .IP \(bu | |
| 817 .CW show : | |
| 818 show message | |
| 819 .IP \(bu | |
| 820 .CW next\fR/\fPprev : | |
| 821 show next/previous message | |
| 822 .IP \(bu | |
| 823 .CW folder : | |
| 824 change current folder | |
| 825 .IP \(bu | |
| 826 .CW refile : | |
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827 refile message into different folder |
| 19 | 828 .IP \(bu |
| 829 .CW rmm : | |
| 830 remove message | |
| 831 .IP \(bu | |
| 832 .CW comp : | |
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833 compose new message |
| 19 | 834 .IP \(bu |
| 835 .CW repl : | |
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836 reply to message |
| 19 | 837 .IP \(bu |
| 838 .CW forw : | |
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839 forward message |
| 19 | 840 .IP \(bu |
| 841 .CW send : | |
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842 send prepared message (this is how mail leaves the system) |
| 0 | 843 .LP |
| 19 | 844 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 845 The user does not leave the shell to run \s-1MH\s0, | |
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846 instead he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 847 Using a monolithic program with a captive user interface |
| 848 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 849 Using toolchests like \s-1MH\s0 means running programs, | |
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850 alone or in combination with others, also from other toolchests, |
| 23 | 851 without leaving the shell. |
| 30 | 852 |
| 853 .NH 2 | |
| 854 Data storage | |
| 42 | 855 .XS |
| 856 \*(SN Data storage | |
| 857 .XE | |
| 30 | 858 .LP |
| 34 | 859 \s-1MH\s0's mail storage is a directory tree under the user's |
| 860 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 861 where mail folders are directories and mail messages are text files | |
| 862 within them. | |
| 863 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
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864 the public message sequences of that folder, |
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865 for instance the \fIunseen\fP sequence for new messages. |
| 34 | 866 Mail messages are text files located in a mail folder. |
| 867 The files contain the messages as they were received. | |
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868 They are named by ascending numbers in each folder. |
| 19 | 869 .PP |
| 30 | 870 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 871 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 872 In the mbox format all messages are stored within one file. | |
| 873 This was a good solution in the early days, when messages | |
| 874 were only a few lines of text and were deleted soon. | |
| 875 Today, when single messages often include several megabytes | |
| 876 of attachments, it is a bad solution. | |
| 877 Another disadvantage of the mbox format is that it is | |
| 878 more difficult to write tools that work on mail messages, | |
| 879 because it is always necessary to first find and extract | |
| 880 the relevant message in the mbox file. | |
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881 With the \s-1MH\s0 mailbox format, each message is a separate file. |
| 30 | 882 Also, the problem of concurrent access to one mailbox is |
| 883 reduced to the problem of concurrent access to one message. | |
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884 The maildir format is generally similar to the \s-1MH\s0 format, |
| 30 | 885 but modified towards guaranteed reliability. |
| 886 This involves some complexity, unfortunately. | |
| 34 | 887 .PP |
| 888 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 889 working with Unix' toolchest on directory trees: | |
| 890 \f(CWscan\fP is like \f(CWls\fP, | |
| 891 \f(CWshow\fP is like \f(CWcat\fP, | |
| 892 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 893 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 894 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 895 .PP | |
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896 \s-1MH\s0 extends the context of processes in Unix by two more items, |
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897 for its tools: |
| 34 | 898 .IP \(bu |
| 899 The current mail folder, which is similar to the current working directory. | |
| 900 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 901 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 902 .IP \(bu | |
| 903 Sequences, which are named sets of messages in a mail folder. | |
| 904 The current message, relative to a mail folder, is a special sequence. | |
| 905 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 906 .LP | |
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907 In contrast to Unix' context, which is maintained by the kernel, |
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908 \s-1MH\s0's context must be maintained by the tools themselves. |
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909 Usually there is one context per user, which resides in his |
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910 \f(CWcontext\fP file in the \s-1MH\s0 directory, |
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911 but a user can have several contexts, too. |
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912 Public sequences are an exception, as they belong to a mail folder, |
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913 and reside in the \f(CW.mh_sequences\fP file there. |
| 34 | 914 .[ |
| 44 | 915 man page mh-profile mh-sequence |
| 34 | 916 .] |
| 20 | 917 |
| 0 | 918 .NH 2 |
| 20 | 919 Discussion of the design |
| 42 | 920 .XS |
| 921 \*(SN Discussion of the design | |
| 922 .XE | |
| 20 | 923 .LP |
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924 This section discusses \s-1MH\s0 in regard to the tenets |
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925 of the Unix Philosophy that Gancarz identified. |
| 20 | 926 |
| 927 .PP | |
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928 .B "Small is beautiful |
| 20 | 929 and |
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930 .B "do one thing well |
| 20 | 931 are two design goals that are directly visible in \s-1MH\s0. |
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932 Gancarz actually presents \s-1MH\s0 in his book as example under the |
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933 headline ``Making \s-1UNIX\s0 Do One Thing Well'': |
| 46 | 934 .[ [ |
| 44 | 935 gancarz |
| 936 unix philosophy | |
| 46 | 937 .], page 125 ff.] |
| 20 | 938 .QP |
| 939 [\s-1MH\s0] consists of a series of programs which | |
| 940 when combined give the user an enormous ability | |
| 941 to manipulate electronic mail messages. | |
| 942 A complex application, it shows that not only is it | |
| 943 possible to build large applications from smaller | |
| 944 components, but also that such designs are actually preferable. | |
| 0 | 945 .LP |
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946 The various programs of \s-1MH\s0 were relatively easy to write, |
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947 because each of them is small, limited to one function, |
| 23 | 948 and has clear boundaries. |
| 20 | 949 For the same reasons, they are also good to maintain. |
| 950 Further more, the system can easily get extended. | |
| 951 One only needs to put a new program into the toolchest. | |
| 23 | 952 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 953 (e.g. \f(CWmhbuild\fP). |
| 954 Also, different programs can exist to do the basically same job | |
| 955 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
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956 .PP |
| 20 | 957 If someone needs a mail system with some additionally |
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958 functions that are not available anywhere yet, he best expands a |
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959 toolchest system like \s-1MH\s0. |
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960 There he can add new functionality by simply adding additional |
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961 programs to the toolchest. |
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962 There he does not risk to break existing functionality by doing so. |
| 20 | 963 |
| 964 .PP | |
| 34 | 965 .B "Store data in flat text files |
| 966 is followed by \s-1MH\s0. | |
| 967 This is not surprising, because email messages are already plain text. | |
| 968 \s-1MH\s0 stores the messages as it receives them, | |
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969 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate |
| 34 | 970 on the messages in an \s-1MH\s0 mailbox. |
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971 All other files \s-1MH\s0 uses are plain text, too. |
| 34 | 972 It is therefore possible and encouraged to use the text processing |
| 973 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 974 |
| 975 .PP | |
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976 .B "Avoid captive user interfaces" . |
| 19 | 977 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 978 It offers all functions directly and without captive user interfaces. | |
| 30 | 979 If, nonetheless, users want a graphical user interface, |
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980 they can have it with \fIxmh\fP or \fIexmh\fP. |
| 19 | 981 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 982 This means, all email-related work is still done by \s-1MH\s0 tools, | |
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983 but the frontend calls the appropriate commands when the user |
| 30 | 984 clicks on buttons. |
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985 .PP |
| 20 | 986 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 987 approach, because it does not limit the power of the backend itself. |
| 20 | 988 The frontend will anyway only be able to make a subset of the |
| 23 | 989 backend's power and flexibility available to the user. |
| 20 | 990 But if it is a separate program, |
| 991 then the missing parts can still be accessed at the backend directly. | |
| 19 | 992 If it is integrated, then this will hardly be possible. |
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993 An additional advantage is the possibility to have different frontends |
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994 to the same backend. |
| 19 | 995 |
| 996 .PP | |
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997 .B "Choose portability over efficiency |
| 20 | 998 and |
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999 .B "use shell scripts to increase leverage and portability" . |
| 20 | 1000 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 1001 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 1002 .[ |
| 44 | 1003 bolsky korn |
| 1004 korn shell | |
| 20 | 1005 .] |
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1006 Chapter\|18 of the book shows a basic implementation |
| 20 | 1007 of a subset of \s-1MH\s0 in ksh scripts. |
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1008 Of course, this is just a demonstration, but a brilliant one. |
| 20 | 1009 It shows how quickly one can implement such a prototype with shell scripts, |
| 1010 and how readable they are. | |
| 1011 The implementation in the scripting language may not be very fast, | |
| 1012 but it can be fast enough though, and this is all that matters. | |
| 1013 By having the code in an interpreted language, like the shell, | |
| 1014 portability becomes a minor issue, if we assume the interpreter | |
| 1015 to be widespread. | |
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1016 .PP |
| 20 | 1017 This demonstration also shows how easy it is to create single programs |
| 1018 of a toolchest software. | |
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1019 Eight tools (two of them have multiple names) and 16 functions |
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1020 with supporting code are presented to the reader. |
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1021 The tools comprise less than 40 lines of ksh each, |
| 30 | 1022 in total about 200 lines. |
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1023 The functions comprise less than 80 lines of ksh each, |
| 30 | 1024 in total about 450 lines. |
| 20 | 1025 Such small software is easy to write, easy to understand, |
| 1026 and thus easy to maintain. | |
| 23 | 1027 A toolchest improves the possibility to only write some parts |
| 20 | 1028 and though create a working result. |
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1029 Expanding the toolchest, even without global changes, |
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1030 will likely be possible. |
| 20 | 1031 |
| 1032 .PP | |
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1033 .B "Use software leverage to your advantage |
| 20 | 1034 and the lesser tenet |
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1035 .B "allow the user to tailor the environment |
| 20 | 1036 are ideally followed in the design of \s-1MH\s0. |
| 21 | 1037 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 1038 directly define default options to programs. |
| 1039 It is even possible to define different default options | |
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1040 depending on the name under which a program is called. |
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1041 Software leverage is heavily encouraged by the ease of |
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1042 creating shell scripts that run a specific command line, |
| 30 | 1043 built of several \s-1MH\s0 programs. |
| 21 | 1044 There is few software that so much wants users to tailor their |
| 1045 environment and to leverage the use of the software, like \s-1MH\s0. | |
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1046 .PP |
| 21 | 1047 Just to make one example: |
| 23 | 1048 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 1049 program. |
| 30 | 1050 It is possible to take one of the distributed format files |
| 21 | 1051 or to write one yourself. |
| 1052 To use the format as default for \f(CWscan\fP, a single line, | |
| 1053 reading | |
| 1054 .DS | |
| 1055 .CW | |
| 1056 scan: -form FORMATFILE | |
| 1057 .DE | |
| 1058 must be added to \f(CW.mh_profile\fP. | |
| 1059 If one wants this different format as an additional command, | |
| 23 | 1060 instead of changing the default, he needs to create a link to |
| 1061 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1062 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
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1063 as the option should only be in effect for a program that is called as |
| 21 | 1064 \f(CWscan2\fP. |
| 20 | 1065 |
| 1066 .PP | |
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1067 .B "Make every program a filter |
| 21 | 1068 is hard to find in \s-1MH\s0. |
| 1069 The reason therefore is that most of \s-1MH\s0's tools provide | |
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1070 basic file system operations for mailboxes. |
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1071 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, |
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1072 and \f(CWrm\fP aren't filters neither. |
| 23 | 1073 \s-1MH\s0 does not provide many filters itself, but it is a basis |
| 1074 to write filters for. | |
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1075 An example would be a mail text highlighter, |
| 30 | 1076 that means a program that makes use of a color terminal to display |
| 1077 header lines, quotations, and signatures in distinct colors. | |
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1078 The author's version of such a program is an awk script with 25 lines. |
| 21 | 1079 |
| 1080 .PP | |
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1081 .B "Build a prototype as soon as possible |
| 21 | 1082 was again well followed by \s-1MH\s0. |
| 1083 This tenet, of course, focuses on early development, which is | |
| 1084 long time ago for \s-1MH\s0. | |
| 1085 But without following this guideline at the very beginning, | |
| 23 | 1086 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1087 to ever create \s-1MH\s0. | |
| 1088 In Bruce' own words: | |
| 46 | 1089 .[ [ |
| 44 | 1090 ware rand history |
| 46 | 1091 .], page 132] |
| 21 | 1092 .QP |
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1093 [...] but [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1094 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1095 I proposed a very short project to prove the basic concepts, |
| 1096 and my management agreed. | |
| 1097 Looking back, I realize that I had been very lucky with my first design. | |
| 1098 Without nearly enough design work, | |
| 1099 I built a working environment and some header files | |
| 1100 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1101 inc, show/next/prev, and comp. | |
| 1102 [...] | |
| 1103 With these three, I was able to convince people that the structure was viable. | |
| 1104 This took about three weeks. | |
| 0 | 1105 |
| 1106 .NH 2 | |
| 1107 Problems | |
| 42 | 1108 .XS |
| 1109 \*(SN Problems | |
| 1110 .XE | |
| 0 | 1111 .LP |
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1112 \s-1MH\s0 is not without problems. |
| 30 | 1113 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1114 .PP |
| 1115 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1116 when \s-1MH\s0 was designed. | |
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1117 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though. |
| 22 | 1118 \s-1MIME\s0 support and support for different character encodings |
| 1119 is available, but only on a moderate level. | |
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1120 This comes from limited development resources. |
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1121 More active developers could quickly change this. |
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1122 But \s-1MH\s0 is also limited by design, which is the larger problem. |
| 22 | 1123 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. |
| 1124 These design conflicts are not easily solvable. | |
| 1125 Possibly, they require a redesign. | |
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1126 \s-1IMAP\s0 may be too different to the classic mail model, |
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1127 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well. |
| 22 | 1128 .PP |
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1129 The other kind of problem are human habits. |
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1130 In this world, where almost all \s-1MUA\s0s are monolithic, |
| 22 | 1131 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 |
| 1132 like \s-1MH\s0. | |
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1133 The habits are so strong, that even people who understand the concept |
| 30 | 1134 and advantages of \s-1MH\s0 do not like to switch, |
| 1135 simply because \s-1MH\s0 is different. | |
| 1136 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
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1137 are quite outdated and thus not very appealing, compared to the modern interfaces |
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1138 of many monolithic \s-1MUA\s0s. |
| 20 | 1139 |
| 1140 .NH 2 | |
| 1141 Summary \s-1MH\s0 | |
| 42 | 1142 .XS |
| 1143 \*(SN Summary \s-1MH\s0 | |
| 1144 .XE | |
| 20 | 1145 .LP |
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1146 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design. |
| 31 | 1147 It consists of a toolchest of small tools, each of them does one job well. |
| 1148 The toolchest approach offers great flexibility to the user. | |
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1149 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0. |
| 31 | 1150 This makes \s-1MH\s0 a very powerful mail system. |
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1151 Extending and customizing \s-1MH\s0 is easy and encouraged. |
| 31 | 1152 .PP |
| 1153 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1154 Its overall design follows clear rules. | |
| 1155 The single tools do only one job, thus they are easy to understand, | |
| 1156 easy to write, and good to maintain. | |
| 1157 They are all independent and do not interfere with the others. | |
| 1158 Automated testing of their function is a straight forward task. | |
| 1159 .PP | |
| 1160 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1161 as its differentness is also its largest advantage. | |
| 1162 Unfortunately, for most people their habits are stronger | |
| 1163 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1164 |
| 8 | 1165 |
| 1166 | |
| 0 | 1167 .NH 1 |
| 1168 Case study: uzbl | |
| 42 | 1169 .XS |
| 1170 .sp .5v | |
| 1171 \*(SN Case study: uzbl | |
| 1172 .XE | |
| 32 | 1173 .LP |
| 1174 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
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1175 which is an old and established software. |
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1176 This chapter covers uzbl, a fresh new project. |
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1177 Uzbl is a web browser that adheres to the Unix Philosophy. |
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1178 Its name comes from the \fILolspeak\fP word for ``usable''; |
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1179 it is pronounced identical. |
| 0 | 1180 |
| 1181 .NH 2 | |
| 32 | 1182 Historical background |
| 42 | 1183 .XS |
| 1184 \*(SN Historical background | |
| 1185 .XE | |
| 0 | 1186 .LP |
| 32 | 1187 Uzbl was started by Dieter Plaetinck in April 2009. |
| 44 | 1188 The idea was born in a thread in the Arch Linux Forums. |
| 32 | 1189 .[ |
| 44 | 1190 arch linux forums |
| 1191 browser | |
| 32 | 1192 .] |
| 1193 After some discussion about failures of well known web browsers, | |
| 1194 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1195 of how a better web browser could look like. | |
| 1196 To the question of another member, if Plaetinck would write that program, | |
| 1197 because it would sound fantastic, Plaetinck replied: | |
| 1198 ``Maybe, if I find the time ;-)''. | |
| 1199 .PP | |
| 1200 Fortunately, he found the time. | |
| 1201 One day later, the first prototype was out. | |
| 1202 One week later, uzbl had an own website. | |
| 1203 One month after the first code showed up, | |
| 1204 a mailing list was installed to coordinate and discuss further development. | |
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1205 Then a wiki followed to store documentation and scripts that showed up on the |
| 32 | 1206 mailing list and elsewhere. |
| 1207 .PP | |
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1208 In the, now, one year of uzbl's existence, it was heavily developed on various branches. |
| 32 | 1209 Plaetinck's task became more and more to only merge the best code from the |
| 1210 different branches into his main branch, and to apply patches. | |
| 1211 About once a month, Plaetinck released a new version. | |
| 1212 In September 2009, he presented several forks of uzbl. | |
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1213 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1214 .PP |
| 1215 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
| 1216 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
| 0 | 1217 |
| 1218 .NH 2 | |
| 32 | 1219 Contrasts to other web browsers |
| 42 | 1220 .XS |
| 1221 \*(SN Contrasts to other web browsers | |
| 1222 .XE | |
| 0 | 1223 .LP |
| 32 | 1224 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1225 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1226 .PP | |
| 1227 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1228 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1229 It handles commands and events to interface other programs, | |
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1230 and also displays webpages by using \fIwebkit\fP as render engine. |
| 32 | 1231 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, |
| 1232 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1233 to form a ``complete'' web browser. | |
| 1234 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1235 so uzbl-core is included. | |
| 1236 .PP | |
| 1237 Unlike most other web browsers, uzbl is mainly the mediator between the | |
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1238 various tools that cover single jobs. |
| 35 | 1239 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1240 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1241 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1242 .DS |
| 1243 .CW | |
| 1244 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1245 .DE | |
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1246 The graphical rendering of the webpage is done by webkit, |
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1247 a web content engine. |
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1248 Uzbl-core is built around libwebkit. |
| 32 | 1249 .PP |
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1250 Downloads, browsing history, bookmarks, and the like are not provided |
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1251 by the core itself, like they are in other web browsers. |
| 35 | 1252 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1253 external applications which provide the actual functionality. | |
| 32 | 1254 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1255 includes a script that calls wget with appropriate options in | |
| 1256 a prepared environment. | |
| 1257 .PP | |
| 1258 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1259 This is their effort to achieve similar goals. | |
| 35 | 1260 But instead of using existing, external programs, modern web browsers |
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1261 include these functions. |
| 0 | 1262 |
| 1263 .NH 2 | |
| 32 | 1264 Discussion of the design |
| 42 | 1265 .XS |
| 1266 \*(SN Discussion of the design | |
| 1267 .XE | |
| 0 | 1268 .LP |
| 32 | 1269 This section discusses uzbl in regard of the Unix Philosophy, |
| 1270 as identified by Gancarz. | |
| 1271 | |
| 1272 .PP | |
| 35 | 1273 .B "Make each program do one thing well" . |
| 1274 Uzbl tries to be a web browser and nothing else. | |
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1275 The common definition of a web browser is, of course, highly influenced by |
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1276 existing implementations of web browsers, although they are degenerated. |
| 35 | 1277 Web browsers should be programs to browse the web, and nothing more. |
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1278 This is the one thing they should do. |
|
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1279 .PP |
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1280 Web browsers should not, for instance, manage downloads. |
| 35 | 1281 This is the job download managers exist for. |
| 1282 Download managers do primary care about being good in downloading files. | |
| 1283 Modern web browsers provide download management only as a secondary feature. | |
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1284 How could they do this job better, than programs that exist only for |
| 35 | 1285 this very job? |
| 1286 And how could anyone want less than the best download manager available? | |
| 32 | 1287 .PP |
| 35 | 1288 A web browser's job is to let the user browse the web. |
| 1289 This means, navigating through websites by following links. | |
|
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1290 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1291 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1292 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1293 are also not the job of a web browser. |
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1294 They should be handled by external applications \(en |
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1295 ones which's job is to handle such data. |
| 35 | 1296 Uzbl strives to do it this way. |
|
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1297 .PP |
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1298 Remember Doug McIlroy: |
| 35 | 1299 .I |
| 1300 ``Write programs that do one thing and do it well. | |
| 1301 Write programs to work together.'' | |
| 1302 .R | |
| 1303 .PP | |
| 1304 The lesser tenet | |
| 1305 .B "allow the user to tailor the environment | |
| 1306 matches good here. | |
| 1307 There was the question, how anyone could want anything less than the | |
| 1308 best program for the job. | |
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1309 But as personal preferences matter, it is probably more important to ask: |
| 35 | 1310 How could anyone want something else than his preferred program for the job? |
|
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1311 .PP |
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1312 Usually users want one program for a specific job. |
| 35 | 1313 Hence, whenever the task is, for instance, downloading, |
|
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1314 the same download manager should be used. |
| 35 | 1315 More advanced users might want to have this download manager in this |
| 1316 situation and that one in that situation. | |
| 1317 They should be able to configure it this way. | |
| 1318 With uzbl, one can use any download manager the user wants. | |
|
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1319 To switch to a different one, only one line in a small handler script |
| 35 | 1320 needs to be changed. |
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1321 Alternatively it would be possible to query the program to use by |
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1322 reading a global file or an environment variable, in the handler script. |
|
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1323 .PP |
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1324 Uzbl does neither have its own download manager nor depends on a |
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1325 specific one, hence uzbl's browsing abilities will not be lowered by having |
| 35 | 1326 a bad download manager. |
|
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1327 Uzbl's download capabilities will be just as good as the ones of the best |
|
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1328 download manager available on the system. |
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1329 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1330 |
| 1331 .PP | |
|
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1332 .B "Use software leverage to your advantage" . |
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1333 Uzbl is designed to be extended by external tools. |
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1334 These external tools are usually wrapped by small handler shell scripts. |
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1335 Shell scripts are the glue in this approach. |
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1336 They make the various parts fit together. |
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1337 .PP |
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1338 The history mechanism of uzbl shall be presented as an example. |
|
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1339 Uzbl is configured to spawn a script to append an entry to the history |
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1340 whenever the event of a fully loaded page occurs. |
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1341 The script to append the entry to the history is not much more than: |
|
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1342 .DS |
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1343 .CW |
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1344 #!/bin/sh |
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1345 file=/path/to/uzbl-history |
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1346 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1347 .DE |
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1348 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1349 .PP |
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1350 For loading an entry, a key is bound to spawn a load-from-history script. |
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1351 The script reverses the history to have newer entries first, |
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1352 then displays \fIdmenu\fP to let the user select an item, |
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1353 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
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1354 With error checking and corner case handling removed, |
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1355 the script looks like this: |
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1356 .DS |
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1357 .CW |
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1358 #!/bin/sh |
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1359 file=/path/to/uzbl-history |
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1360 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1361 echo "uri $goto" > $4 |
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1362 .DE |
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1363 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1364 uzbl instance. |
| 32 | 1365 |
| 1366 .PP | |
|
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1367 .B "Avoid captive user interfaces" . |
|
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1368 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1369 a captive user interface. |
| 37 | 1370 But the difference to most other web browsers is, that uzbl is only |
|
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1371 the captive user interface frontend (and the core of the backend). |
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1372 Many parts of the backend are independent of uzbl. |
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1373 Some are distributed with uzbl, for some external programs, |
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1374 handler scripts are distributed, |
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1375 but arbitrary additional functionality can be added if desired. |
| 37 | 1376 .PP |
| 1377 The frontend is captive \(en that is true. | |
| 1378 This is okay for the task of browsing the web, as this task is only relevant | |
| 1379 for humans. | |
| 1380 Automated programs would \fIcrawl\fP the web. | |
| 1381 That means, they read the source directly. | |
| 1382 The source includes all the semantics. | |
| 1383 The graphical representation is just for humans to transfer the semantics | |
| 1384 more intuitively. | |
| 32 | 1385 |
| 1386 .PP | |
|
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1387 .B "Make every program a filter" . |
| 37 | 1388 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1389 Thus it is difficult to see what graphical web browsers should filter. | |
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1390 Graphical web browsers exist almost only to be interactively used by humans. |
| 37 | 1391 The only case when one might want to automate the rendering function is |
| 1392 to generate images of rendered webpages. | |
| 1393 | |
| 1394 .PP | |
| 1395 .B "Small is beautiful" | |
|
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1396 is not easy to apply to a web browser, because modern web technology |
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1397 is very complex, hence the rendering task is very complex. |
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1398 Modern web browsers have to consist of many thousand lines of code, |
| 37 | 1399 unfortunately. |
| 1400 Using the toolchest approach and wrappers can split the browser into | |
| 1401 several small parts, tough. | |
| 1402 .PP | |
|
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1403 As of March 2010, uzbl-core consists of about 3\,500 lines of C code. |
| 37 | 1404 The distribution includes another 3\,500 lines of Shell and Python code, |
| 1405 which are the handler scripts and plugins like a modal interface. | |
|
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1406 Further more, uzbl uses functionality of external tools like |
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1407 \fIwget\fP and \fInetcat\fP. |
| 37 | 1408 Up to this point, uzbl looks pretty neat and small. |
|
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1409 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1410 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1411 Unfortunately, small web render engines are not possible anymore |
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1412 because of the modern web. |
| 35 | 1413 |
| 1414 .PP | |
| 1415 .B "Build a prototype as soon as possible" . | |
| 1416 Plaetinck made his code public, right from the beginning. | |
|
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1417 Discussion and development was, and still is, open to everyone interested. |
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1418 Development versions of uzbl can be obtained very simply from the code |
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1419 repository. |
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1420 Within the first year of uzbl's existence, a new version was released |
| 35 | 1421 more often than once a month. |
|
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1422 Different forks and branches arose. |
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1423 They introduced new features, which were tested for suitability |
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1424 for the main branch. |
| 35 | 1425 The experiences of using prototypes influenced further development. |
| 1426 Actually, all development was community driven. | |
|
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1427 Plaetinck says, three months after uzbl's birth: |
| 35 | 1428 ``Right now I hardly code anything myself for Uzbl. |
| 1429 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1430 .[ | |
| 44 | 1431 lwn |
| 1432 uzbl | |
| 35 | 1433 .] |
| 32 | 1434 |
| 0 | 1435 |
| 1436 .NH 2 | |
| 1437 Problems | |
| 42 | 1438 .XS |
| 1439 \*(SN Problems | |
| 1440 .XE | |
| 0 | 1441 .LP |
|
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1442 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1443 It is sad, but people use what they know. |
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1444 Fortunately, uzbl's user interface can look and feel very much the |
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1445 same as the one of the well known web browsers, |
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1446 hiding the internal differences. |
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1447 But uzbl has to provide this similar look and feel to be accepted |
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1448 as a ``normal'' browser by ``normal'' users. |
| 37 | 1449 .PP |
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1450 Though, the more important problem is the modern web. |
|
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1451 The modern web is simply broken. |
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1452 It has state in a state-less protocol, |
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1453 it misuses technologies, |
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1454 and it is helplessly overloaded. |
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1455 The result are web content render engines that must consist |
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1456 of hundreds of thousands lines of code. |
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1457 They also must combine and integrate many different technologies, |
|
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1458 only to make our modern web accessible. |
|
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1459 Website to image converter are hardly possible to run without |
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1460 human interaction because of state in sessions, impossible |
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1461 deep-linking, and unautomatable technologies. |
| 37 | 1462 .PP |
|
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1463 The web was misused to provide all kinds of imaginable wishes. |
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1464 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1465 |
| 8 | 1466 |
| 32 | 1467 .NH 2 |
| 1468 Summary uzbl | |
| 42 | 1469 .XS |
| 1470 \*(SN Summary uzbl | |
| 1471 .XE | |
| 32 | 1472 .LP |
|
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1473 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1474 that is how uzbl is seen by its authors. |
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1475 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1476 It consists of independent parts that work together, |
|
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1477 while its core is mainly a mediator which glues the parts together. |
|
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1478 .PP |
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1479 Software leverage can excellently be seen in uzbl. |
|
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1480 External tools are used, independent tasks are separated |
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1481 in independent parts and glued together with small handler scripts. |
|
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1482 .PP |
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1483 As uzbl, more or less, consists of a set of tools and a bit |
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1484 of glue, anyone can put the parts together and expand it |
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1485 in any desired way. |
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1486 Uzbl is very flexible and customizable. |
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1487 These properties make it valuable for advanced users, |
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1488 but may keep novice users from using it. |
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1489 .PP |
|
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1490 But uzbl's main problem is the modern web, that makes it hard |
|
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1491 to design a sane web browser. |
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1492 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1493 |
| 8 | 1494 |
| 0 | 1495 .NH 1 |
| 1496 Final thoughts | |
| 42 | 1497 .XS |
| 1498 .sp .5v | |
| 1499 \*(SN Final thoughts | |
| 1500 .XE | |
| 0 | 1501 |
| 1502 .NH 2 | |
| 1503 Quick summary | |
| 42 | 1504 .XS |
| 1505 \*(SN Quick summary | |
| 1506 .XE | |
| 0 | 1507 .LP |
| 1508 good design | |
| 1509 .LP | |
| 1510 unix phil | |
| 1511 .LP | |
| 1512 case studies | |
| 1513 | |
| 1514 .NH 2 | |
| 1515 Why people should choose | |
| 42 | 1516 .XS |
| 1517 \*(SN Why people should choose | |
| 1518 .XE | |
| 0 | 1519 .LP |
| 1520 Make the right choice! | |
| 1521 | |
| 42 | 1522 .nr PI .3i |
| 0 | 1523 .rm ]< |
| 1524 .de ]< | |
| 1525 .LP | |
| 1526 .de FP | |
| 1527 .IP \\\\$1. | |
| 1528 \\.. | |
| 1529 .rm FS FE | |
| 1530 .. | |
| 42 | 1531 .ds CH " |
| 1532 .bp | |
| 1533 .rs | |
| 1534 .sp .3i | |
| 1535 .TL | |
| 0 | 1536 References |
| 42 | 1537 .LP |
| 1538 .XS | |
| 1539 .sp .5v | |
| 1540 References | |
| 1541 .XE | |
| 1542 .sp 2v | |
| 1543 .nr PS -1 | |
| 1544 .nr VS -1 | |
| 0 | 1545 .[ |
| 1546 $LIST$ | |
| 1547 .] | |
| 42 | 1548 .\".wh -1p |
| 1549 .bp | |
| 1550 .PX |