Mercurial > docs > unix-phil
annotate unix-phil.ms @ 40:422679bdf384
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| author | meillo@marmaro.de |
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| date | Thu, 08 Apr 2010 23:11:28 +0200 |
| parents | c87143793d82 |
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| 23 .ds .] ] | |
| 1 | 24 .\"---------------------------------------- |
| 0 | 25 .TL |
| 6 | 26 Why the Unix Philosophy still matters |
| 0 | 27 .AU |
| 28 markus schnalke <meillo@marmaro.de> | |
| 29 .AB | |
| 1 | 30 .ti \n(.iu |
| 39 | 31 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 32 Today, few software designers are aware of these concepts, |
| 39 | 33 and thus a lot of modern software is more limited than necessary |
| 34 and makes less use of software leverage than possible. | |
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35 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 36 .AE |
| 37 | |
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41 .ps -1 |
| 39 | 42 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
| 43 Mentor was professor Schweiggert. 2010-04-05 | |
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44 .br |
| 39 | 45 You may retrieve this document from |
| 46 .CW \s-1http://marmaro.de/docs \ . | |
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48 |
| 0 | 49 .NH 1 |
| 50 Introduction | |
| 51 .LP | |
| 40 | 52 The Unix Philosophy is the essence of how the Unix operating system, |
| 53 especially its toolchest, was designed. | |
| 54 It is no limited set of fixed rules, | |
| 55 but a loose set of guidelines which tell how to write software that | |
| 56 suites well into Unix. | |
| 57 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 58 The Wikipedia has an accurate definition: | |
| 59 .[ | |
| 60 %A Wikipedia | |
| 61 %T Unix philosophy | |
| 62 %P Wikipedia, The Free Encyclopedia | |
| 63 %D 2010-03-21 17:20 UTC | |
| 64 %O .CW \s-1http://en.wikipedia.org/w/index.php?title=Unix_philosophy&oldid=351189719 | |
| 65 .] | |
| 66 .QP | |
| 67 The \fIUnix philosophy\fP is a set of cultural norms and philosophical | |
| 68 approaches to developing software based on the experience of leading | |
| 69 developers of the Unix operating system. | |
| 3 | 70 .PP |
| 40 | 71 As there is no single definition of the Unix Philosophy, |
| 72 several people have stated their view on what it comprises. | |
| 1 | 73 Best known are: |
| 74 .IP \(bu | |
| 75 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 76 .[ | |
| 77 %A M. D. McIlroy | |
| 78 %A E. N. Pinson | |
| 79 %A B. A. Taque | |
| 80 %T UNIX Time-Sharing System Forward | |
| 81 %J The Bell System Technical Journal | |
| 82 %D 1978 | |
| 83 %V 57 | |
| 84 %N 6 | |
| 85 %P 1902 | |
| 86 .] | |
| 87 .IP \(bu | |
| 88 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 89 .[ | |
| 90 %A Mike Gancarz | |
| 91 %T The UNIX Philosophy | |
| 92 %D 1995 | |
| 93 %I Digital Press | |
| 94 .] | |
| 95 .IP \(bu | |
| 96 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 97 .[ | |
| 98 %A Eric S. Raymond | |
| 99 %T The Art of UNIX Programming | |
| 100 %D 2003 | |
| 101 %I Addison-Wesley | |
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102 %O .CW \s-1http://www.faqs.org/docs/artu/ |
| 1 | 103 .] |
| 0 | 104 .LP |
| 1 | 105 These different views on the Unix Philosophy have much in common. |
| 40 | 106 Especially, the main concepts are similar in all of them. |
| 107 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 108 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 109 | |
| 110 .PP | |
| 111 The Unix Philosophy tells how to design and write good software for Unix. | |
| 112 Many concepts described here base on facilities of Unix. | |
| 113 Other operating systems may not offer such facilities, | |
| 114 hence it may not be possible to design software is the way of the Unix Philosophy. | |
| 115 | |
| 116 FIXME | |
| 117 | |
| 118 This paper discusses the recommendations of the Unix Philosophy about software design. | |
| 119 .PP | |
| 120 The here discussed ideas can get applied by any development process. | |
| 121 The Unix Philosophy does recommend how the software development process should look like, | |
| 122 but this shall not be of matter here. | |
| 123 Similar, the question of how to write the code is out of focus. | |
| 1 | 124 .PP |
| 125 Before we will have a look at concrete concepts, | |
| 126 we discuss why software design is important | |
| 127 and what problems bad design introduces. | |
| 0 | 128 |
| 129 | |
| 130 .NH 1 | |
| 6 | 131 Importance of software design in general |
| 0 | 132 .LP |
| 40 | 133 Software design is the planning of how the internal structure |
| 134 and external interfaces of a software should look like. | |
| 39 | 135 It has nothing to do with visual appearance. |
| 136 If we take a program as a car, then its color is of no matter. | |
| 137 Its design would be the car's size, its shape, the locations of doors, | |
| 138 the passenger/space ratio, the luggage capacity, and so forth. | |
| 139 .PP | |
| 140 Why should software get designed at all? | |
| 6 | 141 It is general knowledge, that even a bad plan is better than no plan. |
| 39 | 142 Not designing software means programming without plan. |
| 143 This will pretty sure lead to horrible results. | |
| 144 Horrible to use and horrible to maintain. | |
| 145 These two aspects are the visible ones. | |
| 146 Often invisible are the wasted possible gains. | |
| 147 Good software design can make these gains available. | |
| 6 | 148 .PP |
| 39 | 149 A software's design deals with quality properties. |
| 150 Good design leads to good quality, and quality is important. | |
| 151 Any car may be able to drive from A to B, | |
| 152 but it depends on the car's properties whether it is a good choice | |
| 153 for passenger transport or not. | |
| 154 It depends on its properties if it is a good choice | |
| 155 for a rough mountain area. | |
| 156 And it depends on its properties if the ride will be fun. | |
| 157 | |
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158 .PP |
| 39 | 159 Requirements for a software are twofold: |
| 160 functional and non-functional. | |
| 161 .IP \(bu | |
| 162 Functional requirements define directly the software's functions. | |
| 163 They are the reason why software gets written. | |
| 164 Someone has a problem and needs a tool to solve it. | |
| 165 Being able to solve the problem is the main functional goal. | |
| 166 It is the driving force behind all programming effort. | |
| 6 | 167 Functional requirements are easier to define and to verify. |
| 39 | 168 .IP \(bu |
| 169 Non-functional requirements are also called \fIquality\fP requirements. | |
| 170 The quality of a software are the properties that are not directly related to | |
| 171 the software's basic functions. | |
| 172 Tools of bad quality often solve the problems they were written for, | |
| 173 but introduce problems and difficulties for usage and development, later on. | |
| 174 Quality aspects are often overlooked at first sight, | |
| 175 and they are often difficult to define clearly and to verify. | |
| 6 | 176 .PP |
| 39 | 177 Quality is of few matter when the software gets built initially, |
| 178 but it is of matter for usage and maintenance of the software. | |
| 6 | 179 A short-sighted might see in developing a software mainly building something up. |
| 39 | 180 But experience shows, that building the software the first time is |
| 181 only a small amount of the overall work. | |
| 182 Bug fixing, extending, rebuilding of parts | |
| 183 \(en maintenance work, for short \(en | |
| 6 | 184 does soon take over the major part of the time spent on a software. |
| 185 Not to forget the usage of the software. | |
| 186 These processes are highly influenced by the software's quality. | |
| 39 | 187 Thus, quality must not be neglected. |
| 188 The problem with quality is that you hardly ``stumble over'' | |
| 189 bad quality during the first build, | |
| 6 | 190 but this is the time when you should care about good quality most. |
| 191 .PP | |
| 39 | 192 Software design is less the basic function of a software \(en |
| 193 this requirement will get satisfied anyway. | |
| 194 Software design is more about quality aspects of the software. | |
| 195 Good design leads to good quality, bad design to bad quality. | |
| 6 | 196 The primary functions of the software will be affected modestly by bad quality, |
| 39 | 197 but good quality can provide a lot of additional gain, |
| 6 | 198 even at places where one never expected it. |
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199 .PP |
| 6 | 200 The ISO/IEC 9126-1 standard, part 1, |
| 201 .[ | |
| 9 | 202 %I International Organization for Standardization |
| 6 | 203 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1 |
| 204 %C Geneve | |
| 205 %D 2001 | |
| 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, |
| 228 bad designed software probably suffers from not having them. | |
| 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 |
| 236 problems during the software's lifetime. | |
| 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 | |
| 4 | 246 .LP |
| 247 The origins of the Unix Philosophy were already introduced. | |
| 8 | 248 This chapter explains the philosophy, oriented on Gancarz, |
| 249 and shows concrete examples of its application. | |
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250 |
| 16 | 251 .NH 2 |
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252 Pipes |
| 0 | 253 .LP |
| 4 | 254 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 255 Knowledge of using the Unix shell is assumed. | |
| 256 .PP | |
| 257 Counting the number of files in the current directory: | |
| 9 | 258 .DS I 2n |
| 4 | 259 .CW |
| 9 | 260 .ps -1 |
| 4 | 261 ls | wc -l |
| 262 .DE | |
| 263 The | |
| 264 .CW ls | |
| 265 command lists all files in the current directory, one per line, | |
| 266 and | |
| 267 .CW "wc -l | |
| 8 | 268 counts the number of lines. |
| 4 | 269 .PP |
| 8 | 270 Counting the number of files that do not contain ``foo'' in their name: |
| 9 | 271 .DS I 2n |
| 4 | 272 .CW |
| 9 | 273 .ps -1 |
| 4 | 274 ls | grep -v foo | wc -l |
| 275 .DE | |
| 276 Here, the list of files is filtered by | |
| 277 .CW grep | |
| 278 to remove all that contain ``foo''. | |
| 279 The rest is the same as in the previous example. | |
| 280 .PP | |
| 281 Finding the five largest entries in the current directory. | |
| 9 | 282 .DS I 2n |
| 4 | 283 .CW |
| 9 | 284 .ps -1 |
| 4 | 285 du -s * | sort -nr | sed 5q |
| 286 .DE | |
| 287 .CW "du -s * | |
| 288 returns the recursively summed sizes of all files | |
| 8 | 289 \(en no matter if they are regular files or directories. |
| 4 | 290 .CW "sort -nr |
| 291 sorts the list numerically in reverse order. | |
| 292 Finally, | |
| 293 .CW "sed 5q | |
| 294 quits after it has printed the fifth line. | |
| 295 .PP | |
| 296 The presented command lines are examples of what Unix people would use | |
| 297 to get the desired output. | |
| 298 There are also other ways to get the same output. | |
| 299 It's a user's decision which way to go. | |
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300 .PP |
| 8 | 301 The examples show that many tasks on a Unix system |
| 4 | 302 are accomplished by combining several small programs. |
| 303 The connection between the single programs is denoted by the pipe operator `|'. | |
| 304 .PP | |
| 305 Pipes, and their extensive and easy use, are one of the great | |
| 306 achievements of the Unix system. | |
| 307 Pipes between programs have been possible in earlier operating systems, | |
| 308 but it has never been a so central part of the concept. | |
| 309 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 310 Unix system, | |
| 311 ``it was this concept and notation for linking several programs together | |
| 312 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 313 .[ | |
| 314 %T Unix: An Oral History | |
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315 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
| 4 | 316 .] |
| 317 .PP | |
| 318 Being able to specify pipelines in an easy way is, | |
| 319 however, not enough by itself. | |
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320 It is only one half. |
| 4 | 321 The other is the design of the programs that are used in the pipeline. |
| 8 | 322 They have to interfaces that allows them to be used in such a way. |
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323 |
| 16 | 324 .NH 2 |
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325 Interface design |
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326 .LP |
| 11 | 327 Unix is, first of all, simple \(en Everything is a file. |
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328 Files are sequences of bytes, without any special structure. |
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329 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin) |
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330 and write a stream of bytes to ``standard output'' (stdout). |
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331 .PP |
| 8 | 332 If the files \fIare\fP sequences of bytes, |
| 333 and the programs \fIare\fP filters on byte streams, | |
| 11 | 334 then there is exactly one standardized data interface. |
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335 Thus it is possible to combine them in any desired way. |
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336 .PP |
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337 Even a handful of small programs will yield a large set of combinations, |
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338 and thus a large set of different functions. |
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339 This is leverage! |
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340 If the programs are orthogonal to each other \(en the best case \(en |
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341 then the set of different functions is greatest. |
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342 .PP |
| 11 | 343 Programs might also have a separate control interface, |
| 344 besides their data interface. | |
| 345 The control interface is often called ``user interface'', | |
| 346 because it is usually designed to be used by humans. | |
| 347 The Unix Philosophy discourages to assume the user to be human. | |
| 348 Interactive use of software is slow use of software, | |
| 349 because the program waits for user input most of the time. | |
| 350 Interactive software requires the user to be in front of the computer | |
| 351 all the time. | |
| 352 Interactive software occupy the user's attention while they are running. | |
| 353 .PP | |
| 354 Now we come back to the idea of using several small programs, combined, | |
| 355 to have a more specific function. | |
| 356 If these single tools would all be interactive, | |
| 357 how would the user control them? | |
| 358 It is not only a problem to control several programs at once if they run at the same time, | |
| 359 it also very inefficient to have to control each of the single programs | |
| 360 that are intended to work as one large program. | |
| 361 Hence, the Unix Philosophy discourages programs to demand interactive use. | |
| 362 The behavior of programs should be defined at invocation. | |
| 363 This is done by specifying arguments (``command line switches'') to the program call. | |
| 364 Gancarz discusses this topic as ``avoid captive user interfaces''. | |
| 365 .[ | |
| 366 %A Mike Gancarz | |
| 367 %T The UNIX Philosophy | |
| 368 %I Digital Press | |
| 369 %D 1995 | |
| 370 %P 88 ff. | |
| 371 .] | |
| 372 .PP | |
| 373 Non-interactive use is, during development, also an advantage for testing. | |
| 374 Testing of interactive programs is much more complicated, | |
| 375 than testing of non-interactive programs. | |
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376 |
| 16 | 377 .NH 2 |
| 8 | 378 The toolchest approach |
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379 .LP |
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380 A toolchest is a set of tools. |
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381 Instead of having one big tool for all tasks, one has many small tools, |
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382 each for one task. |
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383 Difficult tasks are solved by combining several of the small, simple tools. |
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384 .PP |
| 11 | 385 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 386 that are filters on byte streams. | |
| 387 They are, to a large extend, unrelated in their function. | |
| 388 Hence, the Unix toolchest provides a large set of functions | |
| 389 that can be accessed by combining the programs in the desired way. | |
| 390 .PP | |
| 391 There are also advantages for developing small toolchest programs. | |
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392 It is easier and less error-prone to write small programs. |
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393 It is also easier and less error-prone to write a large set of small programs, |
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394 than to write one large program with all the functionality included. |
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395 If the small programs are combinable, then they offer even a larger set |
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396 of functions than the single large program. |
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397 Hence, one gets two advantages out of writing small, combinable programs. |
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398 .PP |
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399 There are two drawbacks of the toolchest approach. |
| 8 | 400 First, one simple, standardized, unidirectional interface has to be sufficient. |
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401 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 402 then a different approach might be of need. |
| 13 | 403 But it is also possible, that he just can not imagine a design where |
| 8 | 404 a stream of bytes is sufficient. |
| 405 By becoming more familiar with the ``Unix style of thinking'', | |
| 406 developers will more often and easier find simple designs where | |
| 407 a stream of bytes is a sufficient interface. | |
| 408 .PP | |
| 409 The second drawback of a toolchest affects the users. | |
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410 A toolchest is often more difficult to use for novices. |
| 9 | 411 It is necessary to become familiar with each of the tools, |
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412 to be able to use the right one in a given situation. |
| 9 | 413 Additionally, one needs to combine the tools in a senseful way on its own. |
| 414 This is like a sharp knife \(en it is a powerful tool in the hand of a master, | |
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415 but of no good value in the hand of an unskilled. |
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416 .PP |
| 8 | 417 However, learning single, small tool of the toolchest is easier than |
| 418 learning a complex tool. | |
| 419 The user will have a basic understanding of a yet unknown tool, | |
| 420 if the several tools of the toolchest have a common style. | |
| 421 He will be able to transfer knowledge over one tool to another. | |
| 422 .PP | |
| 423 Moreover, the second drawback can be removed easily by adding wrappers | |
| 424 around the single tools. | |
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425 Novice users do not need to learn several tools if a professional wraps |
| 8 | 426 the single commands into a more high-level script. |
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427 Note that the wrapper script still calls the small tools; |
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428 the wrapper script is just like a skin around. |
| 8 | 429 No complexity is added this way, |
| 430 but new programs can get created out of existing one with very low effort. | |
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431 .PP |
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432 A wrapper script for finding the five largest entries in the current directory |
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433 could look like this: |
| 9 | 434 .DS I 2n |
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435 .CW |
| 9 | 436 .ps -1 |
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437 #!/bin/sh |
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438 du -s * | sort -nr | sed 5q |
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439 .DE |
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440 The script itself is just a text file that calls the command line |
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441 a professional user would type in directly. |
| 8 | 442 Making the program flexible on the number of entries it prints, |
| 443 is easily possible: | |
| 9 | 444 .DS I 2n |
| 8 | 445 .CW |
| 9 | 446 .ps -1 |
| 8 | 447 #!/bin/sh |
| 448 num=5 | |
| 449 [ $# -eq 1 ] && num="$1" | |
| 450 du -sh * | sort -nr | sed "${num}q" | |
| 451 .DE | |
| 452 This script acts like the one before, when called without an argument. | |
| 453 But one can also specify a numerical argument to define the number of lines to print. | |
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454 |
| 16 | 455 .NH 2 |
| 8 | 456 A powerful shell |
| 457 .LP | |
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458 It was already said, that the Unix shell provides the possibility to |
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459 combine small programs into large ones easily. |
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460 A powerful shell is a great feature in other ways, too. |
| 8 | 461 .PP |
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462 For instance by including a scripting language. |
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463 The control statements are build into the shell. |
| 8 | 464 The functions, however, are the normal programs, everyone can use on the system. |
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465 Thus, the programs are known, so learning to program in the shell is easy. |
| 8 | 466 Using normal programs as functions in the shell programming language |
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467 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 468 .PP |
| 469 The Unix shell encourages to write small scripts out of other programs, | |
| 470 because it is so easy to do. | |
| 471 This is a great step towards automation. | |
| 472 It is wonderful if the effort to automate a task equals the effort | |
| 473 it takes to do it the second time by hand. | |
| 474 If it is so, then the user will be happy to automate everything he does more than once. | |
| 475 .PP | |
| 476 Small programs that do one job well, standardized interfaces between them, | |
| 477 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 478 this will inevitably produce software leverage. | |
| 479 Getting multiple times the benefit of an investment is a great offer. | |
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480 .PP |
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481 The shell also encourages rapid prototyping. |
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482 Many well known programs started as quickly hacked shell scripts, |
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483 and turned into ``real'' programs, written in C, later. |
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484 Building a prototype first is a way to avoid the biggest problems |
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485 in application development. |
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486 Fred Brooks writes in ``No Silver Bullet'': |
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487 .[ |
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488 %A Frederick P. Brooks, Jr. |
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489 %T No Silver Bullet: Essence and Accidents of Software Engineering |
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490 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference |
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491 %E H.-J. Kugler |
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492 %D 1986 |
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493 %P 1069\(en1076 |
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494 %I Elsevier Science B.V. |
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495 %C Amsterdam, The Netherlands |
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496 .] |
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497 .QP |
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498 The hardest single part of building a software system is deciding precisely what to build. |
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499 No other part of the conceptual work is so difficult as establishing the detailed |
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500 technical requirements, [...]. |
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501 No other part of the work so cripples the resulting system if done wrong. |
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502 No other part is more difficult to rectify later. |
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503 .PP |
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504 Writing a prototype is a great method to become familiar with the requirements |
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505 and to actually run into real problems. |
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506 Today, prototyping is often seen as a first step in building a software. |
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507 This is, of course, good. |
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508 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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509 After having built the prototype, one might notice, that the prototype is already |
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510 \fIgood enough\fP. |
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511 Hence, no reimplementation, in a more sophisticated programming language, might be of need, |
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512 for the moment. |
| 23 | 513 Maybe later, it might be necessary to rewrite the software, but not now. |
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514 .PP |
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515 By delaying further work, one keeps the flexibility to react easily on |
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516 changing requirements. |
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517 Software parts that are not written will not miss the requirements. |
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518 |
| 16 | 519 .NH 2 |
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520 Worse is better |
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521 .LP |
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522 The Unix Philosophy aims for the 80% solution; |
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523 others call it the ``Worse is better'' approach. |
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524 .PP |
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525 First, practical experience shows, that it is almost never possible to define the |
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526 requirements completely and correctly the first time. |
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527 Hence one should not try to; it will fail anyway. |
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528 Second, practical experience shows, that requirements change during time. |
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529 Hence it is best to delay requirement-based design decisions as long as possible. |
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530 Also, the software should be small and flexible as long as possible |
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531 to react on changing requirements. |
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532 Shell scripts, for example, are more easily adjusted as C programs. |
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533 Third, practical experience shows, that maintenance is hard work. |
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534 Hence, one should keep the amount of software as small as possible; |
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535 it should just fulfill the \fIcurrent\fP requirements. |
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536 Software parts that will be written later, do not need maintenance now. |
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537 .PP |
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538 Starting with a prototype in a scripting language has several advantages: |
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539 .IP \(bu |
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540 As the initial effort is low, one will likely start right away. |
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541 .IP \(bu |
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542 As working parts are available soon, the real requirements can get identified soon. |
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543 .IP \(bu |
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544 When a software is usable, it gets used, and thus tested. |
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545 Hence problems will be found at early stages of the development. |
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546 .IP \(bu |
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547 The prototype might be enough for the moment, |
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548 thus further work on the software can be delayed to a time |
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549 when one knows better about the requirements and problems, |
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550 than now. |
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551 .IP \(bu |
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552 Implementing now only the parts that are actually needed now, |
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553 requires fewer maintenance work. |
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554 .IP \(bu |
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555 If the global situation changes so that the software is not needed anymore, |
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556 then less effort was spent into the project, than it would have be |
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557 when a different approach had been used. |
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558 |
| 16 | 559 .NH 2 |
| 11 | 560 Upgrowth and survival of software |
| 561 .LP | |
| 12 | 562 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 563 Although these are just verbs, they do imply a specific view on the work process |
| 564 they describe. | |
| 12 | 565 The better verb, however, is to \fIgrow\fP. |
| 566 .PP | |
| 567 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 568 It starts with a first prototype, which evolves as requirements change. | |
| 569 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 570 compiled program this way. |
| 571 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
| 572 While being alive it will get extended, rearranged, rebuilt (from scratch). | |
| 12 | 573 Growing software matches the view that ``software is never finished. It is only released.'' |
| 574 .[ | |
| 13 | 575 %O FIXME |
| 576 %A Mike Gancarz | |
| 577 %T The UNIX Philosophy | |
| 578 %P 26 | |
| 12 | 579 .] |
| 580 .PP | |
| 13 | 581 Software can be seen as being controlled by evolutionary processes. |
| 582 Successful software is software that is used by many for a long time. | |
| 12 | 583 This implies that the software is needed, useful, and better than alternatives. |
| 584 Darwin talks about: ``The survival of the fittest.'' | |
| 585 .[ | |
| 13 | 586 %O FIXME |
| 587 %A Charles Darwin | |
| 12 | 588 .] |
| 589 Transferred to software: The most successful software, is the fittest, | |
| 590 is the one that survives. | |
| 13 | 591 (This may be at the level of one creature, or at the level of one species.) |
| 592 The fitness of software is affected mainly by four properties: | |
| 15 | 593 portability of code, portability of data, range of usability, and reusability of parts. |
| 594 .\" .IP \(bu | |
| 595 .\" portability of code | |
| 596 .\" .IP \(bu | |
| 597 .\" portability of data | |
| 598 .\" .IP \(bu | |
| 599 .\" range of usability | |
| 600 .\" .IP \(bu | |
| 601 .\" reuseability of parts | |
| 13 | 602 .PP |
| 15 | 603 (1) |
| 604 .I "Portability of code | |
| 605 means, using high-level programming languages, | |
| 13 | 606 sticking to the standard, |
| 607 and avoiding optimizations that introduce dependencies on specific hardware. | |
| 608 Hardware has a much lower lifetime than software. | |
| 609 By chaining software to a specific hardware, | |
| 610 the software's lifetime gets shortened to that of this hardware. | |
| 611 In contrast, software should be easy to port \(en | |
| 23 | 612 adaptation is the key to success. |
| 13 | 613 .\" cf. practice of prog: ch08 |
| 614 .PP | |
| 15 | 615 (2) |
| 616 .I "Portability of data | |
| 617 is best achieved by avoiding binary representations | |
| 13 | 618 to store data, because binary representations differ from machine to machine. |
| 23 | 619 Textual representation is favored. |
| 13 | 620 Historically, ASCII was the charset of choice. |
| 621 In the future, UTF-8 might be the better choice, however. | |
| 622 Important is that it is a plain text representation in a | |
| 623 very common charset encoding. | |
| 624 Apart from being able to transfer data between machines, | |
| 625 readable data has the great advantage, that humans are able | |
| 626 to directly edit it with text editors and other tools from the Unix toolchest. | |
| 627 .\" gancarz tenet 5 | |
| 12 | 628 .PP |
| 15 | 629 (3) |
| 630 A large | |
| 631 .I "range of usability | |
| 23 | 632 ensures good adaptation, and thus good survival. |
| 13 | 633 It is a special distinction if a software becomes used in fields of action, |
| 634 the original authors did never imagine. | |
| 635 Software that solves problems in a general way will likely be used | |
| 636 for all kinds of similar problems. | |
| 637 Being too specific limits the range of uses. | |
| 638 Requirements change through time, thus use cases change or even vanish. | |
| 639 A good example in this point is Allman's sendmail. | |
| 640 Allman identifies flexibility to be one major reason for sendmail's success: | |
| 641 .[ | |
| 642 %O FIXME | |
| 643 %A Allman | |
| 644 %T sendmail | |
| 645 .] | |
| 646 .QP | |
| 647 Second, I limited myself to the routing function [...]. | |
| 648 This was a departure from the dominant thought of the time, [...]. | |
| 649 .QP | |
| 650 Third, the sendmail configuration file was flexible enough to adopt | |
| 651 to a rapidly changing world [...]. | |
| 652 .LP | |
| 653 Successful software adopts itself to the changing world. | |
| 12 | 654 .PP |
| 15 | 655 (4) |
| 656 .I "Reuse of parts | |
| 657 is even one step further. | |
| 13 | 658 A software may completely lose its field of action, |
| 659 but parts of which the software is build may be general and independent enough | |
| 660 to survive this death. | |
| 661 If software is build by combining small independent programs, | |
| 662 then there are parts readily available for reuse. | |
| 663 Who cares if the large program is a failure, | |
| 664 but parts of it become successful instead? | |
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665 |
| 16 | 666 .NH 2 |
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667 Summary |
| 0 | 668 .LP |
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669 This chapter explained the central ideas of the Unix Philosophy. |
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670 For each of the ideas, it was exposed what advantages they introduce. |
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671 The Unix Philosophy are guidelines that help to write valuable software. |
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672 From the view point of a software developer or software designer, |
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673 the Unix Philosophy provides answers to many software design problem. |
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674 .PP |
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675 The various ideas of the Unix Philosophy are very interweaved |
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676 and can hardly be applied independently. |
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677 However, the probably most important messages are: |
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678 .I "``Do one thing well!''" , |
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679 .I "``Keep it simple!''" , |
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680 and |
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681 .I "``Use software leverage!'' |
| 0 | 682 |
| 8 | 683 |
| 684 | |
| 0 | 685 .NH 1 |
| 19 | 686 Case study: \s-1MH\s0 |
| 18 | 687 .LP |
| 30 | 688 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 689 from a general point of view. |
| 30 | 690 The driving force were the guidelines; references to |
| 18 | 691 existing software were given only sparsely. |
| 692 In this and the next chapter, concrete software will be | |
| 693 the driving force in the discussion. | |
| 694 .PP | |
| 23 | 695 This first case study is about the mail user agents (\s-1MUA\s0) |
| 696 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 697 (``new mail handler''). | |
| 698 \s-1MUA\s0s provide functions to read, compose, and organize mail, | |
| 699 but (ideally) not to transfer. | |
| 19 | 700 In this document, the name \s-1MH\s0 will be used for both of them. |
| 701 A distinction will only be made if differences between | |
| 702 them are described. | |
| 18 | 703 |
| 0 | 704 |
| 705 .NH 2 | |
| 19 | 706 Historical background |
| 0 | 707 .LP |
| 19 | 708 Electronic mail was available in Unix very early. |
| 30 | 709 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 710 which was already present in the First Edition. | |
| 711 .[ | |
| 712 %A Peter H. Salus | |
| 713 %T A Quarter Century of UNIX | |
| 714 %D 1994 | |
| 715 %I Addison-Wesley | |
| 716 %P 41 f. | |
| 717 .] | |
| 718 It was a small program that either prints the user's mailbox file | |
| 19 | 719 or appends text to someone elses mailbox file, |
| 720 depending on the command line arguments. | |
| 721 .[ | |
| 722 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf | |
| 723 .] | |
| 724 It was a program that did one job well. | |
| 23 | 725 This job was emailing, which was very simple then. |
| 19 | 726 .PP |
| 23 | 727 Later, emailing became more powerful, and thus more complex. |
| 19 | 728 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 729 independent handling of single messages, | |
| 730 and long-time storage of them, was not powerful enough anymore. | |
| 731 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') | |
| 732 in 1978 to provide additional functions for emailing. | |
| 733 Mail was still one program, but now it was large and did | |
| 734 several jobs. | |
| 23 | 735 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 736 It is designed for humans, but is still scriptable. |
| 23 | 737 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 738 .[ |
| 739 %A Gunnar Ritter | |
| 740 %O http://heirloom.sourceforge.net/mailx_history.html | |
| 741 .] | |
| 30 | 742 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 743 followed Mail's direction. |
| 744 They are large, monolithic programs which include all emailing functions. | |
| 745 .PP | |
| 23 | 746 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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747 In the beginning, they also had used a monolithic mail system, |
| 30 | 748 called \s-1MS\s0 (for ``mail system''). |
| 19 | 749 But in 1977, Stockton Gaines and Norman Shapiro |
| 750 came up with a proposal of a new email system concept \(en | |
| 751 one that honors the Unix Philosophy. | |
| 752 The concept was implemented by Bruce Borden in 1978 and 1979. | |
| 753 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 754 .PP |
| 755 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 756 at Berkeley, and several others have contributed to the software. |
| 18 | 757 However, it's core concepts remained the same. |
| 23 | 758 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 759 Richard Coleman started with \fInmh\fP, the new mail handler. |
| 760 His goal was to improve \s-1MH\s0, especially in regard of | |
| 23 | 761 the requirements of modern emailing. |
| 19 | 762 Today, nmh is developed by various people on the Internet. |
| 18 | 763 .[ |
| 764 %T RAND and the Information Evolution: A History in Essays and Vignettes | |
| 765 %A Willis H. Ware | |
| 766 %D 2008 | |
| 767 %I The RAND Corporation | |
| 768 %P 128\(en137 | |
| 769 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/ | |
| 770 .] | |
| 771 .[ | |
| 772 %T MH & xmh: Email for Users & Programmers | |
| 773 %A Jerry Peek | |
| 774 %D 1991, 1992, 1995 | |
| 775 %I O'Reilly & Associates, Inc. | |
| 776 %P Appendix B | |
| 777 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP | |
| 778 .] | |
| 0 | 779 |
| 780 .NH 2 | |
| 20 | 781 Contrasts to monolithic mail systems |
| 0 | 782 .LP |
| 19 | 783 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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784 Although there might actually exist further, very little known, |
| 30 | 785 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 786 .PP |
| 30 | 787 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 788 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 789 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 790 and their function. |
| 791 It gives a feeling of how the toolchest looks like. | |
| 19 | 792 .IP \(bu |
| 793 .CW inc : | |
| 30 | 794 incorporate new mail (this is how mail enters the system) |
| 19 | 795 .IP \(bu |
| 796 .CW scan : | |
| 797 list messages in folder | |
| 798 .IP \(bu | |
| 799 .CW show : | |
| 800 show message | |
| 801 .IP \(bu | |
| 802 .CW next\fR/\fPprev : | |
| 803 show next/previous message | |
| 804 .IP \(bu | |
| 805 .CW folder : | |
| 806 change current folder | |
| 807 .IP \(bu | |
| 808 .CW refile : | |
| 809 refile message into folder | |
| 810 .IP \(bu | |
| 811 .CW rmm : | |
| 812 remove message | |
| 813 .IP \(bu | |
| 814 .CW comp : | |
| 815 compose a new message | |
| 816 .IP \(bu | |
| 817 .CW repl : | |
| 818 reply to a message | |
| 819 .IP \(bu | |
| 820 .CW forw : | |
| 821 forward a message | |
| 822 .IP \(bu | |
| 823 .CW send : | |
| 30 | 824 send a prepared message (this is how mail leaves the system) |
| 0 | 825 .LP |
| 19 | 826 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 827 The user does not leave the shell to run \s-1MH\s0, | |
| 30 | 828 but he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 829 Using a monolithic program with a captive user interface |
| 830 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 831 Using toolchests like \s-1MH\s0 means running programs, | |
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832 alone or in combination with others, even from other toolchests, |
| 23 | 833 without leaving the shell. |
| 30 | 834 |
| 835 .NH 2 | |
| 836 Data storage | |
| 837 .LP | |
| 34 | 838 \s-1MH\s0's mail storage is a directory tree under the user's |
| 839 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 840 where mail folders are directories and mail messages are text files | |
| 841 within them. | |
| 842 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
| 843 the public message sequences of that folder, for instance new messages. | |
| 844 Mail messages are text files located in a mail folder. | |
| 845 The files contain the messages as they were received. | |
| 846 They are numbered in ascending order in each folder. | |
| 19 | 847 .PP |
| 30 | 848 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 849 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 850 In the mbox format all messages are stored within one file. | |
| 851 This was a good solution in the early days, when messages | |
| 852 were only a few lines of text and were deleted soon. | |
| 853 Today, when single messages often include several megabytes | |
| 854 of attachments, it is a bad solution. | |
| 855 Another disadvantage of the mbox format is that it is | |
| 856 more difficult to write tools that work on mail messages, | |
| 857 because it is always necessary to first find and extract | |
| 858 the relevant message in the mbox file. | |
| 859 With the \s-1MH\s0 mailbox format, | |
| 860 each message is a self-standing item, by definition. | |
| 861 Also, the problem of concurrent access to one mailbox is | |
| 862 reduced to the problem of concurrent access to one message. | |
| 863 Maildir is generally similar to \s-1MH\s0's format, | |
| 864 but modified towards guaranteed reliability. | |
| 865 This involves some complexity, unfortunately. | |
| 34 | 866 .PP |
| 867 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 868 working with Unix' toolchest on directory trees: | |
| 869 \f(CWscan\fP is like \f(CWls\fP, | |
| 870 \f(CWshow\fP is like \f(CWcat\fP, | |
| 871 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 872 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 873 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 874 .PP | |
| 875 The context of tools in Unix consists mainly the current working directory, | |
| 876 the user identification, and the environment variables. | |
| 877 \s-1MH\s0 extends this context by two more items: | |
| 878 .IP \(bu | |
| 879 The current mail folder, which is similar to the current working directory. | |
| 880 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 881 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 882 .IP \(bu | |
| 883 Sequences, which are named sets of messages in a mail folder. | |
| 884 The current message, relative to a mail folder, is a special sequence. | |
| 885 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 886 .LP | |
| 887 In contrast to Unix' context, which is chained to the shell session, | |
| 888 \s-1MH\s0's context is independent. | |
| 889 Usually there is one context for each user, but a user can have many | |
| 890 contexts. | |
| 891 Public sequences are an exception, as they belong to the mail folder. | |
| 892 .[ | |
| 893 %O mh-profile(5) and mh-sequence(5) | |
| 894 .] | |
| 20 | 895 |
| 0 | 896 .NH 2 |
| 20 | 897 Discussion of the design |
| 898 .LP | |
| 899 The following paragraphs discuss \s-1MH\s0 in regard to the tenets | |
| 23 | 900 of the Unix Philosophy which Gancarz identified. |
| 20 | 901 |
| 902 .PP | |
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903 .B "Small is beautiful |
| 20 | 904 and |
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905 .B "do one thing well |
| 20 | 906 are two design goals that are directly visible in \s-1MH\s0. |
| 907 Gancarz actually presents \s-1MH\s0 as example under the headline | |
| 908 ``Making UNIX Do One Thing Well'': | |
| 909 .QP | |
| 910 [\s-1MH\s0] consists of a series of programs which | |
| 911 when combined give the user an enormous ability | |
| 912 to manipulate electronic mail messages. | |
| 913 A complex application, it shows that not only is it | |
| 914 possible to build large applications from smaller | |
| 915 components, but also that such designs are actually preferable. | |
| 916 .[ | |
| 917 %A Mike Gancarz | |
| 918 %T unix-phil | |
| 919 %P 125 | |
| 920 .] | |
| 0 | 921 .LP |
| 20 | 922 The various small programs of \s-1MH\s0 were relatively easy |
| 23 | 923 to write, because each of them is small, limited to one function, |
| 924 and has clear boundaries. | |
| 20 | 925 For the same reasons, they are also good to maintain. |
| 926 Further more, the system can easily get extended. | |
| 927 One only needs to put a new program into the toolchest. | |
| 23 | 928 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 929 (e.g. \f(CWmhbuild\fP). |
| 930 Also, different programs can exist to do the basically same job | |
| 931 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
| 932 If someone needs a mail system with some additionally | |
| 23 | 933 functions that are available nowhere yet, he best takes a |
| 20 | 934 toolchest system like \s-1MH\s0 where he can add the |
| 935 functionality with little work. | |
| 936 | |
| 937 .PP | |
| 34 | 938 .B "Store data in flat text files |
| 939 is followed by \s-1MH\s0. | |
| 940 This is not surprising, because email messages are already plain text. | |
| 941 \s-1MH\s0 stores the messages as it receives them, | |
| 942 thus any other tool that works on RFC 2822 mail messages can operate | |
| 943 on the messages in an \s-1MH\s0 mailbox. | |
| 944 All other files \s-1MH\s0 uses are plain text too. | |
| 945 It is therefore possible and encouraged to use the text processing | |
| 946 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 947 |
| 948 .PP | |
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949 .B "Avoid captive user interfaces" . |
| 19 | 950 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 951 It offers all functions directly and without captive user interfaces. | |
| 30 | 952 If, nonetheless, users want a graphical user interface, |
| 20 | 953 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
| 19 | 954 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 955 This means, all email-related work is still done by \s-1MH\s0 tools, | |
| 20 | 956 but the frontend issues the appropriate calls when the user |
| 30 | 957 clicks on buttons. |
| 20 | 958 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 959 approach, because it does not limit the power of the backend itself. |
| 20 | 960 The frontend will anyway only be able to make a subset of the |
| 23 | 961 backend's power and flexibility available to the user. |
| 20 | 962 But if it is a separate program, |
| 963 then the missing parts can still be accessed at the backend directly. | |
| 19 | 964 If it is integrated, then this will hardly be possible. |
| 30 | 965 Further more, it is possible to have different frontends to the same |
| 966 backend. | |
| 19 | 967 |
| 968 .PP | |
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969 .B "Choose portability over efficiency |
| 20 | 970 and |
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971 .B "use shell scripts to increase leverage and portability" . |
| 20 | 972 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 973 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 974 .[ |
| 975 %T The KornShell: command and programming language | |
| 976 %A Morris I. Bolsky | |
| 977 %A David G. Korn | |
| 978 %I Prentice Hall | |
| 979 %D 1989 | |
| 30 | 980 %P 254\(en290 |
| 20 | 981 %O \s-1ISBN\s0: 0-13-516972-0 |
| 982 .] | |
| 30 | 983 They demonstrated, in chapter 18 of the book, a basic implementation |
| 20 | 984 of a subset of \s-1MH\s0 in ksh scripts. |
| 985 Of course, this was just a demonstration, but a brilliant one. | |
| 986 It shows how quickly one can implement such a prototype with shell scripts, | |
| 987 and how readable they are. | |
| 988 The implementation in the scripting language may not be very fast, | |
| 989 but it can be fast enough though, and this is all that matters. | |
| 990 By having the code in an interpreted language, like the shell, | |
| 991 portability becomes a minor issue, if we assume the interpreter | |
| 992 to be widespread. | |
| 993 This demonstration also shows how easy it is to create single programs | |
| 994 of a toolchest software. | |
| 30 | 995 There are eight tools (two of them have multiple names) and 16 functions |
| 996 with supporting code. | |
| 997 Each tool comprises between 12 and 38 lines of ksh, | |
| 998 in total about 200 lines. | |
| 999 The functions comprise between 3 and 78 lines of ksh, | |
| 1000 in total about 450 lines. | |
| 20 | 1001 Such small software is easy to write, easy to understand, |
| 1002 and thus easy to maintain. | |
| 23 | 1003 A toolchest improves the possibility to only write some parts |
| 20 | 1004 and though create a working result. |
| 1005 Expanding the toolchest without global changes will likely be | |
| 1006 possible, too. | |
| 1007 | |
| 1008 .PP | |
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1009 .B "Use software leverage to your advantage |
| 20 | 1010 and the lesser tenet |
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1011 .B "allow the user to tailor the environment |
| 20 | 1012 are ideally followed in the design of \s-1MH\s0. |
| 21 | 1013 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 1014 directly define default options to programs. |
| 1015 It is even possible to define different default options | |
| 21 | 1016 depending on the name under which the program was called. |
| 1017 Software leverage is heavily encouraged by the ease it is to | |
| 1018 create shell scripts that run a specific command line, | |
| 30 | 1019 built of several \s-1MH\s0 programs. |
| 21 | 1020 There is few software that so much wants users to tailor their |
| 1021 environment and to leverage the use of the software, like \s-1MH\s0. | |
| 1022 Just to make one example: | |
| 23 | 1023 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 1024 program. |
| 30 | 1025 It is possible to take one of the distributed format files |
| 21 | 1026 or to write one yourself. |
| 1027 To use the format as default for \f(CWscan\fP, a single line, | |
| 1028 reading | |
| 1029 .DS | |
| 1030 .CW | |
| 1031 scan: -form FORMATFILE | |
| 1032 .DE | |
| 1033 must be added to \f(CW.mh_profile\fP. | |
| 1034 If one wants this different format as an additional command, | |
| 23 | 1035 instead of changing the default, he needs to create a link to |
| 1036 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1037 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
| 30 | 1038 as the option should only be in effect when scan is called as |
| 21 | 1039 \f(CWscan2\fP. |
| 20 | 1040 |
| 1041 .PP | |
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1042 .B "Make every program a filter |
| 21 | 1043 is hard to find in \s-1MH\s0. |
| 1044 The reason therefore is that most of \s-1MH\s0's tools provide | |
| 1045 basic file system operations for the mailboxes. | |
| 30 | 1046 The reason is the same because of which |
| 21 | 1047 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP |
| 1048 aren't filters neither. | |
| 23 | 1049 However, they build a basis on which filters can operate. |
| 1050 \s-1MH\s0 does not provide many filters itself, but it is a basis | |
| 1051 to write filters for. | |
| 30 | 1052 An example would be a mail message text highlighter, |
| 1053 that means a program that makes use of a color terminal to display | |
| 1054 header lines, quotations, and signatures in distinct colors. | |
| 1055 The author's version of this program, for instance, | |
| 1056 is a 25 line awk script. | |
| 21 | 1057 |
| 1058 .PP | |
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1059 .B "Build a prototype as soon as possible |
| 21 | 1060 was again well followed by \s-1MH\s0. |
| 1061 This tenet, of course, focuses on early development, which is | |
| 1062 long time ago for \s-1MH\s0. | |
| 1063 But without following this guideline at the very beginning, | |
| 23 | 1064 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1065 to ever create \s-1MH\s0. | |
| 1066 In Bruce' own words: | |
| 21 | 1067 .QP |
| 30 | 1068 [...] but they [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1069 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1070 I proposed a very short project to prove the basic concepts, |
| 1071 and my management agreed. | |
| 1072 Looking back, I realize that I had been very lucky with my first design. | |
| 1073 Without nearly enough design work, | |
| 1074 I built a working environment and some header files | |
| 1075 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1076 inc, show/next/prev, and comp. | |
| 1077 [...] | |
| 1078 With these three, I was able to convince people that the structure was viable. | |
| 1079 This took about three weeks. | |
| 1080 .[ | |
| 1081 %O FIXME | |
| 1082 .] | |
| 0 | 1083 |
| 1084 .NH 2 | |
| 1085 Problems | |
| 1086 .LP | |
| 22 | 1087 \s-1MH\s0, for sure is not without problems. |
| 30 | 1088 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1089 .PP |
| 1090 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1091 when \s-1MH\s0 was designed. | |
| 1092 \s-1MH\s0 adopted to the changes pretty well, but it is limited. | |
| 1093 For example in development resources. | |
| 1094 \s-1MIME\s0 support and support for different character encodings | |
| 1095 is available, but only on a moderate level. | |
| 1096 More active developers could quickly improve there. | |
| 1097 It is also limited by design, which is the larger problem. | |
| 1098 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. | |
| 1099 These design conflicts are not easily solvable. | |
| 1100 Possibly, they require a redesign. | |
| 30 | 1101 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers, |
| 1102 hence \s-1MH\s0 may never work well with \s-1IMAP\s0. | |
| 22 | 1103 .PP |
| 1104 The other kind of problem is human habits. | |
| 1105 When in this world almost all \s-1MUA\s0s are monolithic, | |
| 1106 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 | |
| 1107 like \s-1MH\s0. | |
| 1108 The habits are so strong, that even people who understood the concept | |
| 30 | 1109 and advantages of \s-1MH\s0 do not like to switch, |
| 1110 simply because \s-1MH\s0 is different. | |
| 1111 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
| 1112 are quite outdated and thus not very appealing compared to the modern interfaces | |
| 1113 which monolithic \s-1MUA\s0s offer. | |
| 20 | 1114 |
| 1115 .NH 2 | |
| 1116 Summary \s-1MH\s0 | |
| 1117 .LP | |
| 31 | 1118 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design |
| 1119 and implementation. | |
| 1120 It consists of a toolchest of small tools, each of them does one job well. | |
| 1121 The tools are orthogonal to each other, to a large extend. | |
| 1122 However, for historical reasons, there also exist distinct tools | |
| 1123 that cover the same task. | |
| 1124 .PP | |
| 1125 The toolchest approach offers great flexibility to the user. | |
| 1126 He can use the complete power of the Unix shell with \s-1MH\s0. | |
| 1127 This makes \s-1MH\s0 a very powerful mail system. | |
| 1128 Extending and customizing \s-1MH\s0 is easy and encouraged, too. | |
| 1129 .PP | |
| 1130 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1131 Its overall design follows clear rules. | |
| 1132 The single tools do only one job, thus they are easy to understand, | |
| 1133 easy to write, and good to maintain. | |
| 1134 They are all independent and do not interfere with the others. | |
| 1135 Automated testing of their function is a straight forward task. | |
| 1136 .PP | |
| 1137 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1138 as its differentness is also its largest advantage. | |
| 1139 Unfortunately, for most people their habits are stronger | |
| 1140 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1141 |
| 8 | 1142 |
| 1143 | |
| 0 | 1144 .NH 1 |
| 1145 Case study: uzbl | |
| 32 | 1146 .LP |
| 1147 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
| 1148 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy. | |
| 1149 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''. | |
| 1150 It is pronounced the identical. | |
| 0 | 1151 |
| 1152 .NH 2 | |
| 32 | 1153 Historical background |
| 0 | 1154 .LP |
| 32 | 1155 Uzbl was started by Dieter Plaetinck in April 2009. |
| 1156 The idea was born in a thread in the Arch Linux forum. | |
| 1157 .[ | |
| 1158 %O http://bbs.archlinux.org/viewtopic.php?id=67463 | |
| 1159 .] | |
| 1160 After some discussion about failures of well known web browsers, | |
| 1161 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1162 of how a better web browser could look like. | |
| 1163 To the question of another member, if Plaetinck would write that program, | |
| 1164 because it would sound fantastic, Plaetinck replied: | |
| 1165 ``Maybe, if I find the time ;-)''. | |
| 1166 .PP | |
| 1167 Fortunately, he found the time. | |
| 1168 One day later, the first prototype was out. | |
| 1169 One week later, uzbl had an own website. | |
| 1170 One month after the first code showed up, | |
| 1171 a mailing list was installed to coordinate and discuss further development. | |
| 1172 A wiki was set up to store documentation and scripts that showed up on the | |
| 1173 mailing list and elsewhere. | |
| 1174 .PP | |
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1175 In the, now, one year of uzbl's existence, it was heavily developed in various branches. |
| 32 | 1176 Plaetinck's task became more and more to only merge the best code from the |
| 1177 different branches into his main branch, and to apply patches. | |
| 1178 About once a month, Plaetinck released a new version. | |
| 1179 In September 2009, he presented several forks of uzbl. | |
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1180 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1181 .PP |
| 1182 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
| 1183 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
| 0 | 1184 |
| 1185 .NH 2 | |
| 32 | 1186 Contrasts to other web browsers |
| 0 | 1187 .LP |
| 32 | 1188 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1189 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1190 .PP | |
| 1191 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1192 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1193 It handles commands and events to interface other programs, | |
| 1194 and also displays webpages by using webkit as render engine. | |
| 1195 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, | |
| 1196 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1197 to form a ``complete'' web browser. | |
| 1198 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1199 so uzbl-core is included. | |
| 1200 .PP | |
| 1201 Unlike most other web browsers, uzbl is mainly the mediator between the | |
| 1202 various tools that cover single jobs of web browsing. | |
| 35 | 1203 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1204 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1205 The graphical rendering of the webpage is done by webkit, a web content engine. | |
| 1206 Uzbl-core is build around this library. | |
| 1207 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1208 .DS |
| 1209 .CW | |
| 1210 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1211 .DE | |
| 1212 .PP | |
| 1213 Downloads, browsing history, bookmarks, and thelike are not provided | |
| 1214 by uzbl-core itself, as they are in other web browsers. | |
| 35 | 1215 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1216 external applications which provide the actual functionality. | |
| 32 | 1217 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1218 includes a script that calls wget with appropriate options in | |
| 1219 a prepared environment. | |
| 1220 .PP | |
| 1221 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1222 This is their effort to achieve similar goals. | |
| 35 | 1223 But instead of using existing, external programs, modern web browsers |
| 1224 include these functions, although they might be loaded at runtime. | |
| 0 | 1225 |
| 1226 .NH 2 | |
| 32 | 1227 Discussion of the design |
| 0 | 1228 .LP |
| 32 | 1229 This section discusses uzbl in regard of the Unix Philosophy, |
| 1230 as identified by Gancarz. | |
| 1231 | |
| 1232 .PP | |
| 35 | 1233 .B "Make each program do one thing well" . |
| 1234 Uzbl tries to be a web browser and nothing else. | |
|
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1235 The common definition of a web browser is, of course, highly influenced by |
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1236 existing implementations of web browsers, although they are degenerated. |
| 35 | 1237 Web browsers should be programs to browse the web, and nothing more. |
| 1238 This is the one thing they should do, as demanded by the Unix Philosophy. | |
|
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1239 .PP |
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1240 Web browsers should, for instance, not manage downloads. |
| 35 | 1241 This is the job download managers exist for. |
| 1242 Download managers do primary care about being good in downloading files. | |
| 1243 Modern web browsers provide download management only as a secondary feature. | |
| 1244 How could they perform this job better, than programs that exist only for | |
| 1245 this very job? | |
| 1246 And how could anyone want less than the best download manager available? | |
| 32 | 1247 .PP |
| 35 | 1248 A web browser's job is to let the user browse the web. |
| 1249 This means, navigating through websites by following links. | |
|
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1250 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1251 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1252 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1253 are also not the job of a web browser. |
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1254 They should be handled by external applications \(en |
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1255 ones which's job is to handle such data. |
| 35 | 1256 Uzbl strives to do it this way. |
|
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1257 .PP |
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1258 Remember Doug McIlroy: |
| 35 | 1259 .I |
| 1260 ``Write programs that do one thing and do it well. | |
| 1261 Write programs to work together.'' | |
| 1262 .R | |
| 1263 .PP | |
| 1264 The lesser tenet | |
| 1265 .B "allow the user to tailor the environment | |
| 1266 matches good here. | |
| 1267 There was the question, how anyone could want anything less than the | |
| 1268 best program for the job. | |
|
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1269 But as personal preferences matter much, |
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1270 it is probably more important to ask: |
| 35 | 1271 How could anyone want something else than his preferred program for the job? |
|
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1272 .PP |
| 35 | 1273 Usually users want one program for one job. |
| 1274 Hence, whenever the task is, for instance, downloading, | |
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1275 exactly one download manager should be used. |
| 35 | 1276 More advanced users might want to have this download manager in this |
| 1277 situation and that one in that situation. | |
| 1278 They should be able to configure it this way. | |
| 1279 With uzbl, one can use any download manager the user wants. | |
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1280 To switch to a different one, only one line in a small handler script |
| 35 | 1281 needs to be changed. |
|
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1282 Alternatively it would be possible to query an entry in a global file |
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1283 or an environment variable, which specifies the download manager to use, |
| 35 | 1284 in the handler script. |
|
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1285 .PP |
| 35 | 1286 As uzbl does neither have its own download manager nor depends on a |
| 1287 specific one, thus uzbl's browsing abilities will not be lowered by having | |
| 1288 a bad download manager. | |
|
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1289 Uzbl's download capabilities will just as good as the ones of the best |
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1290 download manager available on the system. |
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1291 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1292 |
| 1293 .PP | |
|
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1294 .B "Use software leverage to your advantage" . |
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1295 Shell scripts are a good choice to extend uzbl. |
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1296 Uzbl is designed to be extended by external tools. |
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1297 These external tools are usually wrapped by small handler shell scripts. |
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1298 Shell scripts are the glue in this approach. |
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1299 They make the various parts fit together. |
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1300 .PP |
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1301 As an example, the history mechanism of uzbl shall be presented. |
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1302 Uzbl is configured to spawn a script to append an entry to the history |
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1303 whenever the event of a fully loaded page occurs. |
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1304 The script to append the entry to the history not much more than: |
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1305 .DS |
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1306 .CW |
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1307 #!/bin/sh |
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1308 file=/path/to/uzbl-history |
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1309 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1310 .DE |
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1311 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1312 For loading an entry, a key is bound to spawn a load from history script. |
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1313 The script reverses the history to have newer entries first, |
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1314 then displays \fIdmenu\fP to select an item, |
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1315 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
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1316 With error checking and corner cases removed, the script looks like this: |
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1317 .DS |
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1318 .CW |
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1319 #!/bin/sh |
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1320 file=/path/to/uzbl-history |
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1321 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1322 echo "uri $goto" > $4 |
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1323 .DE |
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1324 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1325 uzbl instance. |
| 32 | 1326 |
| 1327 .PP | |
|
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1328 .B "Avoid captive user interfaces" . |
|
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1329 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1330 a captive user interface. |
| 37 | 1331 But the difference to most other web browsers is, that uzbl is only |
| 1332 the captive user interface frontend and the core of the backend. | |
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1333 Many parts of the backend are independent of uzbl. |
| 37 | 1334 Some are distributed with uzbl, for some external programs, handler scripts |
| 1335 are distributed, arbitrary additional functionality can be added if desired. | |
| 1336 .PP | |
| 1337 The frontend is captive \(en that is true. | |
| 1338 This is okay for the task of browsing the web, as this task is only relevant | |
| 1339 for humans. | |
| 1340 Automated programs would \fIcrawl\fP the web. | |
| 1341 That means, they read the source directly. | |
| 1342 The source includes all the semantics. | |
| 1343 The graphical representation is just for humans to transfer the semantics | |
| 1344 more intuitively. | |
| 32 | 1345 |
| 1346 .PP | |
|
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1347 .B "Make every program a filter" . |
| 37 | 1348 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1349 Thus it is difficult to see what graphical web browsers should filter. | |
| 1350 Graphical web browsers exist almost only for interactive use by humans. | |
| 1351 The only case when one might want to automate the rendering function is | |
| 1352 to generate images of rendered webpages. | |
| 1353 | |
| 1354 .PP | |
| 1355 .B "Small is beautiful" | |
|
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1356 is not easy to apply to a web browser, primary because modern web technology |
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1357 is very complex; hence the rendering task is very complex. |
| 37 | 1358 Modern web browsers will always consist of many thousand lines of code, |
| 1359 unfortunately. | |
| 1360 Using the toolchest approach and wrappers can split the browser into | |
| 1361 several small parts, tough. | |
| 1362 .PP | |
| 1363 Uzbl-core consists of about 3\,500 lines of C code. | |
| 1364 The distribution includes another 3\,500 lines of Shell and Python code, | |
| 1365 which are the handler scripts and plugins like a modal interface. | |
|
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1366 Further more, uzbl uses functionality of external tools like |
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1367 \fIwget\fP and \fInetcat\fP. |
| 37 | 1368 Up to this point, uzbl looks pretty neat and small. |
|
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1369 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1370 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1371 Unfortunately, small web render engines are not possible anymore |
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1372 because of the modern web. |
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1373 The problems section will explain this in more detail. |
| 35 | 1374 |
| 1375 .PP | |
| 1376 .B "Build a prototype as soon as possible" . | |
| 1377 Plaetinck made his code public, right from the beginning. | |
|
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1378 Discussion and development was, and still is, open to everyone interested. |
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1379 Development versions of uzbl can be obtained very simply from the code |
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1380 repository. |
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1381 Within the first year of uzbl's existence, a new version was released |
| 35 | 1382 more often than once a month. |
|
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1383 Different forks and branches arose. |
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1384 They introduced new features, which were tested for suitability. |
| 35 | 1385 The experiences of using prototypes influenced further development. |
| 1386 Actually, all development was community driven. | |
|
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1387 Plaetinck says, three months after uzbl's birth: |
| 35 | 1388 ``Right now I hardly code anything myself for Uzbl. |
| 1389 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1390 .[ | |
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1391 %A FIXME |
| 35 | 1392 %O http://lwn.net/Articles/341245/ |
| 1393 .] | |
| 32 | 1394 |
| 0 | 1395 |
| 1396 .NH 2 | |
| 1397 Problems | |
| 1398 .LP | |
|
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1399 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1400 It is sad, but people use what they know. |
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1401 Fortunately, uzbl's user interface can look and feel very much the |
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1402 same as the one of the well known web browsers, |
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1403 hiding the internal differences. |
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1404 But uzbl has to provide this similar look and feel to be accepted |
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1405 as a ``normal'' browser by ``normal'' users. |
| 37 | 1406 .PP |
|
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1407 The more important problem is the modern web. |
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1408 The modern web is simply broken. |
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1409 It has state in a state-less protocol, |
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1410 it misuses technologies, |
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1411 and it is helplessly overloaded. |
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1412 The result are web content render engines that must consist |
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1413 of hundreds of thousands lines of code. |
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1414 They also must combine and integrate many different technologies, |
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1415 only to make our modern web usable. |
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1416 Website to image converter are hardly possible to run without |
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1417 human interaction because of state in sessions, impossible |
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1418 deep-linking, and unautomatable technologies. |
| 37 | 1419 .PP |
|
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1420 The web was misused to provide all kinds of imaginable wishes. |
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1421 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1422 |
| 8 | 1423 |
| 32 | 1424 .NH 2 |
| 1425 Summary uzbl | |
| 1426 .LP | |
|
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1427 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1428 that is how uzbl is seen by its authors. |
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1429 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1430 It consists of independent parts that work together, |
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1431 its core is mainly a mediator which glues the parts together. |
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1432 .PP |
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1433 Software leverage can excellently be seen in uzbl. |
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1434 It makes use of external tools, separates independent tasks |
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1435 in independent parts, and glues them together with small |
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1436 handler scripts, around uzbl-core. |
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1437 .PP |
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1438 As uzbl, more or less, consists of a set of tools and a bit |
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1439 of glue, anyone can put the parts together and expand it |
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1440 in any desired way. |
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1441 Uzbl is very flexible and customizable. |
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1442 These properties make it valuable for advanced users, |
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1443 but may keep novice users from using it. |
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1444 .PP |
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1445 Uzbl's main problem is the modern web, that makes it hard |
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1446 to design a sane web browser. |
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1447 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1448 |
| 8 | 1449 |
| 0 | 1450 .NH 1 |
| 1451 Final thoughts | |
| 1452 | |
| 1453 .NH 2 | |
| 1454 Quick summary | |
| 1455 .LP | |
| 1456 good design | |
| 1457 .LP | |
| 1458 unix phil | |
| 1459 .LP | |
| 1460 case studies | |
| 1461 | |
| 1462 .NH 2 | |
| 1463 Why people should choose | |
| 1464 .LP | |
| 1465 Make the right choice! | |
| 1466 | |
| 1467 .nr PI .5i | |
| 1468 .rm ]< | |
| 1469 .de ]< | |
| 1470 .LP | |
| 1471 .de FP | |
| 1472 .IP \\\\$1. | |
| 1473 \\.. | |
| 1474 .rm FS FE | |
| 1475 .. | |
| 1476 .SH | |
| 1477 References | |
| 1478 .[ | |
| 1479 $LIST$ | |
| 1480 .] | |
| 1481 .wh -1p |