Mercurial > docs > unix-phil
annotate unix-phil.ms @ 41:13ef7042fa28
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| author | meillo@marmaro.de |
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| date | Fri, 09 Apr 2010 12:44:08 +0200 |
| parents | 422679bdf384 |
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2 .nr VS 13 |
| 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 .] ] | |
| 1 | 16 .\"---------------------------------------- |
| 0 | 17 .TL |
| 6 | 18 Why the Unix Philosophy still matters |
| 0 | 19 .AU |
| 20 markus schnalke <meillo@marmaro.de> | |
| 21 .AB | |
| 1 | 22 .ti \n(.iu |
| 39 | 23 This paper explains the importance of the Unix Philosophy for software design. |
| 0 | 24 Today, few software designers are aware of these concepts, |
| 39 | 25 and thus a lot of modern software is more limited than necessary |
| 26 and makes less use of software leverage than possible. | |
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27 Knowing and following the guidelines of the Unix Philosophy makes software more valuable. |
| 0 | 28 .AE |
| 29 | |
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30 .FS |
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31 .ps -1 |
| 39 | 32 This paper was prepared for the ``Software Analysis'' seminar at University Ulm. |
| 33 Mentor was professor Schweiggert. 2010-04-05 | |
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34 .br |
| 39 | 35 You may retrieve this document from |
| 36 .CW \s-1http://marmaro.de/docs \ . | |
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37 .FE |
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38 |
| 0 | 39 .NH 1 |
| 40 Introduction | |
| 41 .LP | |
| 40 | 42 The Unix Philosophy is the essence of how the Unix operating system, |
| 43 especially its toolchest, was designed. | |
| 44 It is no limited set of fixed rules, | |
| 45 but a loose set of guidelines which tell how to write software that | |
| 46 suites well into Unix. | |
| 47 Actually, the Unix Philosophy describes what is common to typical Unix software. | |
| 48 The Wikipedia has an accurate definition: | |
| 49 .[ | |
| 50 %A Wikipedia | |
| 51 %T Unix philosophy | |
| 52 %P Wikipedia, The Free Encyclopedia | |
| 53 %D 2010-03-21 17:20 UTC | |
| 54 %O .CW \s-1http://en.wikipedia.org/w/index.php?title=Unix_philosophy&oldid=351189719 | |
| 55 .] | |
| 56 .QP | |
| 41 | 57 .ps -1 |
| 40 | 58 The \fIUnix philosophy\fP is a set of cultural norms and philosophical |
| 59 approaches to developing software based on the experience of leading | |
| 60 developers of the Unix operating system. | |
| 3 | 61 .PP |
| 40 | 62 As there is no single definition of the Unix Philosophy, |
| 63 several people have stated their view on what it comprises. | |
| 1 | 64 Best known are: |
| 65 .IP \(bu | |
| 66 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 67 .[ | |
| 68 %A M. D. McIlroy | |
| 69 %A E. N. Pinson | |
| 70 %A B. A. Taque | |
| 71 %T UNIX Time-Sharing System Forward | |
| 72 %J The Bell System Technical Journal | |
| 73 %D 1978 | |
| 74 %V 57 | |
| 75 %N 6 | |
| 76 %P 1902 | |
| 77 .] | |
| 78 .IP \(bu | |
| 79 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 80 .[ | |
| 81 %A Mike Gancarz | |
| 82 %T The UNIX Philosophy | |
| 83 %D 1995 | |
| 84 %I Digital Press | |
| 85 .] | |
| 86 .IP \(bu | |
| 87 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 88 .[ | |
| 89 %A Eric S. Raymond | |
| 90 %T The Art of UNIX Programming | |
| 91 %D 2003 | |
| 92 %I Addison-Wesley | |
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93 %O .CW \s-1http://www.faqs.org/docs/artu/ |
| 1 | 94 .] |
| 0 | 95 .LP |
| 1 | 96 These different views on the Unix Philosophy have much in common. |
| 40 | 97 Especially, the main concepts are similar in all of them. |
| 98 McIlroy's definition can surely be called the core of the Unix Philosophy, | |
| 99 but the fundamental idea behind it all, is ``small is beautiful''. | |
| 100 | |
| 101 .PP | |
| 102 The Unix Philosophy tells how to design and write good software for Unix. | |
| 103 Many concepts described here base on facilities of Unix. | |
| 104 Other operating systems may not offer such facilities, | |
| 41 | 105 hence it may not be possible to design software in the way of the |
| 106 Unix Philosophy for them. | |
| 107 .PP | |
| 108 The Unix Philosophy has an idea of how the process of software development | |
| 109 should look like, but large parts of the philosophy are quite independent | |
| 110 from the development process used. | |
| 111 However, one will soon recognize that some development processes work well | |
| 112 with the ideas of the Unix Philosophy and support them, while others are | |
| 113 at cross-purposes. | |
| 114 Kent Beck's books about Extreme Programming are valuable supplimental | |
| 115 resources. | |
| 40 | 116 .PP |
| 41 | 117 The question of how to actually write code and how the code should looks |
| 118 like internally, are out of focus here. | |
| 119 ``The Practice of Programming'' by Kernighan and Pike, | |
| 120 .[ | |
| 121 %A Brian W. Kernighan | |
| 122 %A Rob Pike | |
| 123 %T The Practice of Programming | |
| 124 %I Addison-Wesley | |
| 125 %D 1999 | |
| 126 .] | |
| 127 is a good book that covers this topic. | |
| 128 Its point of view matches to the one of this paper. | |
| 0 | 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: | |
| 41 | 258 .DS |
| 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: |
| 41 | 271 .DS |
| 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. | |
| 41 | 282 .DS |
| 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: |
| 41 | 434 .DS |
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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: | |
| 41 | 444 .DS |
| 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 |
| 41 | 498 .ps -1 |
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499 The hardest single part of building a software system is deciding precisely what to build. |
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500 No other part of the conceptual work is so difficult as establishing the detailed |
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501 technical requirements, [...]. |
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502 No other part of the work so cripples the resulting system if done wrong. |
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503 No other part is more difficult to rectify later. |
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504 .PP |
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505 Writing a prototype is a great method to become familiar with the requirements |
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506 and to actually run into real problems. |
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507 Today, prototyping is often seen as a first step in building a software. |
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508 This is, of course, good. |
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509 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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510 After having built the prototype, one might notice, that the prototype is already |
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511 \fIgood enough\fP. |
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512 Hence, no reimplementation, in a more sophisticated programming language, might be of need, |
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513 for the moment. |
| 23 | 514 Maybe later, it might be necessary to rewrite the software, but not now. |
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515 .PP |
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516 By delaying further work, one keeps the flexibility to react easily on |
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517 changing requirements. |
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518 Software parts that are not written will not miss the requirements. |
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519 |
| 16 | 520 .NH 2 |
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521 Worse is better |
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522 .LP |
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523 The Unix Philosophy aims for the 80% solution; |
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524 others call it the ``Worse is better'' approach. |
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525 .PP |
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526 First, practical experience shows, that it is almost never possible to define the |
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527 requirements completely and correctly the first time. |
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528 Hence one should not try to; it will fail anyway. |
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529 Second, practical experience shows, that requirements change during time. |
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530 Hence it is best to delay requirement-based design decisions as long as possible. |
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531 Also, the software should be small and flexible as long as possible |
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532 to react on changing requirements. |
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533 Shell scripts, for example, are more easily adjusted as C programs. |
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534 Third, practical experience shows, that maintenance is hard work. |
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535 Hence, one should keep the amount of software as small as possible; |
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536 it should just fulfill the \fIcurrent\fP requirements. |
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537 Software parts that will be written later, do not need maintenance now. |
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538 .PP |
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539 Starting with a prototype in a scripting language has several advantages: |
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540 .IP \(bu |
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541 As the initial effort is low, one will likely start right away. |
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542 .IP \(bu |
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543 As working parts are available soon, the real requirements can get identified soon. |
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544 .IP \(bu |
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545 When a software is usable, it gets used, and thus tested. |
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546 Hence problems will be found at early stages of the development. |
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547 .IP \(bu |
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548 The prototype might be enough for the moment, |
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549 thus further work on the software can be delayed to a time |
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550 when one knows better about the requirements and problems, |
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551 than now. |
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552 .IP \(bu |
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553 Implementing now only the parts that are actually needed now, |
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554 requires fewer maintenance work. |
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555 .IP \(bu |
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556 If the global situation changes so that the software is not needed anymore, |
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557 then less effort was spent into the project, than it would have be |
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558 when a different approach had been used. |
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559 |
| 16 | 560 .NH 2 |
| 11 | 561 Upgrowth and survival of software |
| 562 .LP | |
| 12 | 563 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 564 Although these are just verbs, they do imply a specific view on the work process |
| 565 they describe. | |
| 12 | 566 The better verb, however, is to \fIgrow\fP. |
| 567 .PP | |
| 568 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 569 It starts with a first prototype, which evolves as requirements change. | |
| 570 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 571 compiled program this way. |
| 572 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
| 573 While being alive it will get extended, rearranged, rebuilt (from scratch). | |
| 12 | 574 Growing software matches the view that ``software is never finished. It is only released.'' |
| 575 .[ | |
| 13 | 576 %O FIXME |
| 577 %A Mike Gancarz | |
| 578 %T The UNIX Philosophy | |
| 579 %P 26 | |
| 12 | 580 .] |
| 581 .PP | |
| 13 | 582 Software can be seen as being controlled by evolutionary processes. |
| 583 Successful software is software that is used by many for a long time. | |
| 12 | 584 This implies that the software is needed, useful, and better than alternatives. |
| 585 Darwin talks about: ``The survival of the fittest.'' | |
| 586 .[ | |
| 13 | 587 %O FIXME |
| 588 %A Charles Darwin | |
| 12 | 589 .] |
| 590 Transferred to software: The most successful software, is the fittest, | |
| 591 is the one that survives. | |
| 13 | 592 (This may be at the level of one creature, or at the level of one species.) |
| 593 The fitness of software is affected mainly by four properties: | |
| 15 | 594 portability of code, portability of data, range of usability, and reusability of parts. |
| 595 .\" .IP \(bu | |
| 596 .\" portability of code | |
| 597 .\" .IP \(bu | |
| 598 .\" portability of data | |
| 599 .\" .IP \(bu | |
| 600 .\" range of usability | |
| 601 .\" .IP \(bu | |
| 602 .\" reuseability of parts | |
| 13 | 603 .PP |
| 15 | 604 (1) |
| 605 .I "Portability of code | |
| 606 means, using high-level programming languages, | |
| 13 | 607 sticking to the standard, |
| 608 and avoiding optimizations that introduce dependencies on specific hardware. | |
| 609 Hardware has a much lower lifetime than software. | |
| 610 By chaining software to a specific hardware, | |
| 611 the software's lifetime gets shortened to that of this hardware. | |
| 612 In contrast, software should be easy to port \(en | |
| 23 | 613 adaptation is the key to success. |
| 13 | 614 .\" cf. practice of prog: ch08 |
| 615 .PP | |
| 15 | 616 (2) |
| 617 .I "Portability of data | |
| 618 is best achieved by avoiding binary representations | |
| 13 | 619 to store data, because binary representations differ from machine to machine. |
| 23 | 620 Textual representation is favored. |
| 13 | 621 Historically, ASCII was the charset of choice. |
| 622 In the future, UTF-8 might be the better choice, however. | |
| 623 Important is that it is a plain text representation in a | |
| 624 very common charset encoding. | |
| 625 Apart from being able to transfer data between machines, | |
| 626 readable data has the great advantage, that humans are able | |
| 627 to directly edit it with text editors and other tools from the Unix toolchest. | |
| 628 .\" gancarz tenet 5 | |
| 12 | 629 .PP |
| 15 | 630 (3) |
| 631 A large | |
| 632 .I "range of usability | |
| 23 | 633 ensures good adaptation, and thus good survival. |
| 13 | 634 It is a special distinction if a software becomes used in fields of action, |
| 635 the original authors did never imagine. | |
| 636 Software that solves problems in a general way will likely be used | |
| 637 for all kinds of similar problems. | |
| 638 Being too specific limits the range of uses. | |
| 639 Requirements change through time, thus use cases change or even vanish. | |
| 640 A good example in this point is Allman's sendmail. | |
| 641 Allman identifies flexibility to be one major reason for sendmail's success: | |
| 642 .[ | |
| 643 %O FIXME | |
| 644 %A Allman | |
| 645 %T sendmail | |
| 646 .] | |
| 647 .QP | |
| 41 | 648 .ps -1 |
| 13 | 649 Second, I limited myself to the routing function [...]. |
| 650 This was a departure from the dominant thought of the time, [...]. | |
| 651 .QP | |
| 41 | 652 .ps -1 |
| 13 | 653 Third, the sendmail configuration file was flexible enough to adopt |
| 654 to a rapidly changing world [...]. | |
| 655 .LP | |
| 656 Successful software adopts itself to the changing world. | |
| 12 | 657 .PP |
| 15 | 658 (4) |
| 659 .I "Reuse of parts | |
| 660 is even one step further. | |
| 13 | 661 A software may completely lose its field of action, |
| 662 but parts of which the software is build may be general and independent enough | |
| 663 to survive this death. | |
| 664 If software is build by combining small independent programs, | |
| 665 then there are parts readily available for reuse. | |
| 666 Who cares if the large program is a failure, | |
| 667 but parts of it become successful instead? | |
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668 |
| 16 | 669 .NH 2 |
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670 Summary |
| 0 | 671 .LP |
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672 This chapter explained the central ideas of the Unix Philosophy. |
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673 For each of the ideas, it was exposed what advantages they introduce. |
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674 The Unix Philosophy are guidelines that help to write valuable software. |
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675 From the view point of a software developer or software designer, |
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676 the Unix Philosophy provides answers to many software design problem. |
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677 .PP |
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678 The various ideas of the Unix Philosophy are very interweaved |
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679 and can hardly be applied independently. |
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680 However, the probably most important messages are: |
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681 .I "``Do one thing well!''" , |
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682 .I "``Keep it simple!''" , |
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683 and |
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684 .I "``Use software leverage!'' |
| 0 | 685 |
| 8 | 686 |
| 687 | |
| 0 | 688 .NH 1 |
| 19 | 689 Case study: \s-1MH\s0 |
| 18 | 690 .LP |
| 30 | 691 The previous chapter introduced and explained the Unix Philosophy |
| 18 | 692 from a general point of view. |
| 30 | 693 The driving force were the guidelines; references to |
| 18 | 694 existing software were given only sparsely. |
| 695 In this and the next chapter, concrete software will be | |
| 696 the driving force in the discussion. | |
| 697 .PP | |
| 23 | 698 This first case study is about the mail user agents (\s-1MUA\s0) |
| 699 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
| 700 (``new mail handler''). | |
| 701 \s-1MUA\s0s provide functions to read, compose, and organize mail, | |
| 702 but (ideally) not to transfer. | |
| 19 | 703 In this document, the name \s-1MH\s0 will be used for both of them. |
| 704 A distinction will only be made if differences between | |
| 705 them are described. | |
| 18 | 706 |
| 0 | 707 |
| 708 .NH 2 | |
| 19 | 709 Historical background |
| 0 | 710 .LP |
| 19 | 711 Electronic mail was available in Unix very early. |
| 30 | 712 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
| 713 which was already present in the First Edition. | |
| 714 .[ | |
| 715 %A Peter H. Salus | |
| 716 %T A Quarter Century of UNIX | |
| 717 %D 1994 | |
| 718 %I Addison-Wesley | |
| 719 %P 41 f. | |
| 720 .] | |
| 721 It was a small program that either prints the user's mailbox file | |
| 19 | 722 or appends text to someone elses mailbox file, |
| 723 depending on the command line arguments. | |
| 724 .[ | |
| 725 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf | |
| 726 .] | |
| 727 It was a program that did one job well. | |
| 23 | 728 This job was emailing, which was very simple then. |
| 19 | 729 .PP |
| 23 | 730 Later, emailing became more powerful, and thus more complex. |
| 19 | 731 The simple \f(CWmail\fP, which knew nothing of subjects, |
| 732 independent handling of single messages, | |
| 733 and long-time storage of them, was not powerful enough anymore. | |
| 734 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') | |
| 735 in 1978 to provide additional functions for emailing. | |
| 736 Mail was still one program, but now it was large and did | |
| 737 several jobs. | |
| 23 | 738 Its user interface is modeled after the one of \fIed\fP. |
| 19 | 739 It is designed for humans, but is still scriptable. |
| 23 | 740 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
| 19 | 741 .[ |
| 742 %A Gunnar Ritter | |
| 743 %O http://heirloom.sourceforge.net/mailx_history.html | |
| 744 .] | |
| 30 | 745 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
| 19 | 746 followed Mail's direction. |
| 747 They are large, monolithic programs which include all emailing functions. | |
| 748 .PP | |
| 23 | 749 A different way was taken by the people of \s-1RAND\s0 Corporation. |
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750 In the beginning, they also had used a monolithic mail system, |
| 30 | 751 called \s-1MS\s0 (for ``mail system''). |
| 19 | 752 But in 1977, Stockton Gaines and Norman Shapiro |
| 753 came up with a proposal of a new email system concept \(en | |
| 754 one that honors the Unix Philosophy. | |
| 755 The concept was implemented by Bruce Borden in 1978 and 1979. | |
| 756 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 757 .PP |
| 758 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 759 at Berkeley, and several others have contributed to the software. |
| 18 | 760 However, it's core concepts remained the same. |
| 23 | 761 In the late 90s, when development of \s-1MH\s0 slowed down, |
| 19 | 762 Richard Coleman started with \fInmh\fP, the new mail handler. |
| 763 His goal was to improve \s-1MH\s0, especially in regard of | |
| 23 | 764 the requirements of modern emailing. |
| 19 | 765 Today, nmh is developed by various people on the Internet. |
| 18 | 766 .[ |
| 767 %T RAND and the Information Evolution: A History in Essays and Vignettes | |
| 768 %A Willis H. Ware | |
| 769 %D 2008 | |
| 770 %I The RAND Corporation | |
| 771 %P 128\(en137 | |
| 772 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/ | |
| 773 .] | |
| 774 .[ | |
| 775 %T MH & xmh: Email for Users & Programmers | |
| 776 %A Jerry Peek | |
| 777 %D 1991, 1992, 1995 | |
| 778 %I O'Reilly & Associates, Inc. | |
| 779 %P Appendix B | |
| 780 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP | |
| 781 .] | |
| 0 | 782 |
| 783 .NH 2 | |
| 20 | 784 Contrasts to monolithic mail systems |
| 0 | 785 .LP |
| 19 | 786 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
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787 Although there might actually exist further, very little known, |
| 30 | 788 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. |
| 19 | 789 .PP |
| 30 | 790 Monolithic \s-1MUA\s0s gather all their functions in one program. |
| 791 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 23 | 792 Following is a list of important programs of \s-1MH\s0's toolchest |
| 30 | 793 and their function. |
| 794 It gives a feeling of how the toolchest looks like. | |
| 19 | 795 .IP \(bu |
| 796 .CW inc : | |
| 30 | 797 incorporate new mail (this is how mail enters the system) |
| 19 | 798 .IP \(bu |
| 799 .CW scan : | |
| 800 list messages in folder | |
| 801 .IP \(bu | |
| 802 .CW show : | |
| 803 show message | |
| 804 .IP \(bu | |
| 805 .CW next\fR/\fPprev : | |
| 806 show next/previous message | |
| 807 .IP \(bu | |
| 808 .CW folder : | |
| 809 change current folder | |
| 810 .IP \(bu | |
| 811 .CW refile : | |
| 812 refile message into folder | |
| 813 .IP \(bu | |
| 814 .CW rmm : | |
| 815 remove message | |
| 816 .IP \(bu | |
| 817 .CW comp : | |
| 818 compose a new message | |
| 819 .IP \(bu | |
| 820 .CW repl : | |
| 821 reply to a message | |
| 822 .IP \(bu | |
| 823 .CW forw : | |
| 824 forward a message | |
| 825 .IP \(bu | |
| 826 .CW send : | |
| 30 | 827 send a prepared message (this is how mail leaves the system) |
| 0 | 828 .LP |
| 19 | 829 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 830 The user does not leave the shell to run \s-1MH\s0, | |
| 30 | 831 but he uses the various \s-1MH\s0 programs within the shell. |
| 23 | 832 Using a monolithic program with a captive user interface |
| 833 means ``entering'' the program, using it, and ``exiting'' the program. | |
| 834 Using toolchests like \s-1MH\s0 means running programs, | |
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835 alone or in combination with others, even from other toolchests, |
| 23 | 836 without leaving the shell. |
| 30 | 837 |
| 838 .NH 2 | |
| 839 Data storage | |
| 840 .LP | |
| 34 | 841 \s-1MH\s0's mail storage is a directory tree under the user's |
| 842 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
| 843 where mail folders are directories and mail messages are text files | |
| 844 within them. | |
| 845 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
| 846 the public message sequences of that folder, for instance new messages. | |
| 847 Mail messages are text files located in a mail folder. | |
| 848 The files contain the messages as they were received. | |
| 849 They are numbered in ascending order in each folder. | |
| 19 | 850 .PP |
| 30 | 851 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
| 852 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 853 In the mbox format all messages are stored within one file. | |
| 854 This was a good solution in the early days, when messages | |
| 855 were only a few lines of text and were deleted soon. | |
| 856 Today, when single messages often include several megabytes | |
| 857 of attachments, it is a bad solution. | |
| 858 Another disadvantage of the mbox format is that it is | |
| 859 more difficult to write tools that work on mail messages, | |
| 860 because it is always necessary to first find and extract | |
| 861 the relevant message in the mbox file. | |
| 862 With the \s-1MH\s0 mailbox format, | |
| 863 each message is a self-standing item, by definition. | |
| 864 Also, the problem of concurrent access to one mailbox is | |
| 865 reduced to the problem of concurrent access to one message. | |
| 866 Maildir is generally similar to \s-1MH\s0's format, | |
| 867 but modified towards guaranteed reliability. | |
| 868 This involves some complexity, unfortunately. | |
| 34 | 869 .PP |
| 870 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
| 871 working with Unix' toolchest on directory trees: | |
| 872 \f(CWscan\fP is like \f(CWls\fP, | |
| 873 \f(CWshow\fP is like \f(CWcat\fP, | |
| 874 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
| 875 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 876 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 877 .PP | |
| 878 The context of tools in Unix consists mainly the current working directory, | |
| 879 the user identification, and the environment variables. | |
| 880 \s-1MH\s0 extends this context by two more items: | |
| 881 .IP \(bu | |
| 882 The current mail folder, which is similar to the current working directory. | |
| 883 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
| 884 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
| 885 .IP \(bu | |
| 886 Sequences, which are named sets of messages in a mail folder. | |
| 887 The current message, relative to a mail folder, is a special sequence. | |
| 888 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 889 .LP | |
| 890 In contrast to Unix' context, which is chained to the shell session, | |
| 891 \s-1MH\s0's context is independent. | |
| 892 Usually there is one context for each user, but a user can have many | |
| 893 contexts. | |
| 894 Public sequences are an exception, as they belong to the mail folder. | |
| 895 .[ | |
| 896 %O mh-profile(5) and mh-sequence(5) | |
| 897 .] | |
| 20 | 898 |
| 0 | 899 .NH 2 |
| 20 | 900 Discussion of the design |
| 901 .LP | |
| 902 The following paragraphs discuss \s-1MH\s0 in regard to the tenets | |
| 23 | 903 of the Unix Philosophy which Gancarz identified. |
| 20 | 904 |
| 905 .PP | |
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906 .B "Small is beautiful |
| 20 | 907 and |
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908 .B "do one thing well |
| 20 | 909 are two design goals that are directly visible in \s-1MH\s0. |
| 910 Gancarz actually presents \s-1MH\s0 as example under the headline | |
| 911 ``Making UNIX Do One Thing Well'': | |
| 41 | 912 .[ |
| 913 %A Mike Gancarz | |
| 914 %T unix-phil | |
| 915 %P 125 | |
| 916 .] | |
| 20 | 917 .QP |
| 41 | 918 .ps -1 |
| 20 | 919 [\s-1MH\s0] consists of a series of programs which |
| 920 when combined give the user an enormous ability | |
| 921 to manipulate electronic mail messages. | |
| 922 A complex application, it shows that not only is it | |
| 923 possible to build large applications from smaller | |
| 924 components, but also that such designs are actually preferable. | |
| 0 | 925 .LP |
| 20 | 926 The various small programs of \s-1MH\s0 were relatively easy |
| 23 | 927 to write, because each of them is small, limited to one function, |
| 928 and has clear boundaries. | |
| 20 | 929 For the same reasons, they are also good to maintain. |
| 930 Further more, the system can easily get extended. | |
| 931 One only needs to put a new program into the toolchest. | |
| 23 | 932 This was done, for instance, when \s-1MIME\s0 support was added |
| 20 | 933 (e.g. \f(CWmhbuild\fP). |
| 934 Also, different programs can exist to do the basically same job | |
| 935 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
| 936 If someone needs a mail system with some additionally | |
| 23 | 937 functions that are available nowhere yet, he best takes a |
| 20 | 938 toolchest system like \s-1MH\s0 where he can add the |
| 939 functionality with little work. | |
| 940 | |
| 941 .PP | |
| 34 | 942 .B "Store data in flat text files |
| 943 is followed by \s-1MH\s0. | |
| 944 This is not surprising, because email messages are already plain text. | |
| 945 \s-1MH\s0 stores the messages as it receives them, | |
| 946 thus any other tool that works on RFC 2822 mail messages can operate | |
| 947 on the messages in an \s-1MH\s0 mailbox. | |
| 948 All other files \s-1MH\s0 uses are plain text too. | |
| 949 It is therefore possible and encouraged to use the text processing | |
| 950 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
| 20 | 951 |
| 952 .PP | |
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953 .B "Avoid captive user interfaces" . |
| 19 | 954 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 955 It offers all functions directly and without captive user interfaces. | |
| 30 | 956 If, nonetheless, users want a graphical user interface, |
| 20 | 957 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
| 19 | 958 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 959 This means, all email-related work is still done by \s-1MH\s0 tools, | |
| 20 | 960 but the frontend issues the appropriate calls when the user |
| 30 | 961 clicks on buttons. |
| 20 | 962 Providing easy-to-use user interfaces in form of frontends is a good |
| 19 | 963 approach, because it does not limit the power of the backend itself. |
| 20 | 964 The frontend will anyway only be able to make a subset of the |
| 23 | 965 backend's power and flexibility available to the user. |
| 20 | 966 But if it is a separate program, |
| 967 then the missing parts can still be accessed at the backend directly. | |
| 19 | 968 If it is integrated, then this will hardly be possible. |
| 30 | 969 Further more, it is possible to have different frontends to the same |
| 970 backend. | |
| 19 | 971 |
| 972 .PP | |
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973 .B "Choose portability over efficiency |
| 20 | 974 and |
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975 .B "use shell scripts to increase leverage and portability" . |
| 20 | 976 These two tenets are indirectly, but nicely, demonstrated by |
| 30 | 977 Bolsky and Korn in their book about the Korn Shell. |
| 20 | 978 .[ |
| 979 %T The KornShell: command and programming language | |
| 980 %A Morris I. Bolsky | |
| 981 %A David G. Korn | |
| 982 %I Prentice Hall | |
| 983 %D 1989 | |
| 30 | 984 %P 254\(en290 |
| 20 | 985 %O \s-1ISBN\s0: 0-13-516972-0 |
| 986 .] | |
| 30 | 987 They demonstrated, in chapter 18 of the book, a basic implementation |
| 20 | 988 of a subset of \s-1MH\s0 in ksh scripts. |
| 989 Of course, this was just a demonstration, but a brilliant one. | |
| 990 It shows how quickly one can implement such a prototype with shell scripts, | |
| 991 and how readable they are. | |
| 992 The implementation in the scripting language may not be very fast, | |
| 993 but it can be fast enough though, and this is all that matters. | |
| 994 By having the code in an interpreted language, like the shell, | |
| 995 portability becomes a minor issue, if we assume the interpreter | |
| 996 to be widespread. | |
| 997 This demonstration also shows how easy it is to create single programs | |
| 998 of a toolchest software. | |
| 30 | 999 There are eight tools (two of them have multiple names) and 16 functions |
| 1000 with supporting code. | |
| 1001 Each tool comprises between 12 and 38 lines of ksh, | |
| 1002 in total about 200 lines. | |
| 1003 The functions comprise between 3 and 78 lines of ksh, | |
| 1004 in total about 450 lines. | |
| 20 | 1005 Such small software is easy to write, easy to understand, |
| 1006 and thus easy to maintain. | |
| 23 | 1007 A toolchest improves the possibility to only write some parts |
| 20 | 1008 and though create a working result. |
| 1009 Expanding the toolchest without global changes will likely be | |
| 1010 possible, too. | |
| 1011 | |
| 1012 .PP | |
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1013 .B "Use software leverage to your advantage |
| 20 | 1014 and the lesser tenet |
|
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1015 .B "allow the user to tailor the environment |
| 20 | 1016 are ideally followed in the design of \s-1MH\s0. |
| 21 | 1017 Tailoring the environment is heavily encouraged by the ability to |
| 30 | 1018 directly define default options to programs. |
| 1019 It is even possible to define different default options | |
| 21 | 1020 depending on the name under which the program was called. |
| 1021 Software leverage is heavily encouraged by the ease it is to | |
| 1022 create shell scripts that run a specific command line, | |
| 30 | 1023 built of several \s-1MH\s0 programs. |
| 21 | 1024 There is few software that so much wants users to tailor their |
| 1025 environment and to leverage the use of the software, like \s-1MH\s0. | |
| 1026 Just to make one example: | |
| 23 | 1027 One might prefer a different listing format for the \f(CWscan\fP |
| 21 | 1028 program. |
| 30 | 1029 It is possible to take one of the distributed format files |
| 21 | 1030 or to write one yourself. |
| 1031 To use the format as default for \f(CWscan\fP, a single line, | |
| 1032 reading | |
| 1033 .DS | |
| 1034 .CW | |
| 1035 scan: -form FORMATFILE | |
| 1036 .DE | |
| 1037 must be added to \f(CW.mh_profile\fP. | |
| 1038 If one wants this different format as an additional command, | |
| 23 | 1039 instead of changing the default, he needs to create a link to |
| 1040 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
| 21 | 1041 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
| 30 | 1042 as the option should only be in effect when scan is called as |
| 21 | 1043 \f(CWscan2\fP. |
| 20 | 1044 |
| 1045 .PP | |
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1046 .B "Make every program a filter |
| 21 | 1047 is hard to find in \s-1MH\s0. |
| 1048 The reason therefore is that most of \s-1MH\s0's tools provide | |
| 1049 basic file system operations for the mailboxes. | |
| 30 | 1050 The reason is the same because of which |
| 21 | 1051 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP |
| 1052 aren't filters neither. | |
| 23 | 1053 However, they build a basis on which filters can operate. |
| 1054 \s-1MH\s0 does not provide many filters itself, but it is a basis | |
| 1055 to write filters for. | |
| 30 | 1056 An example would be a mail message text highlighter, |
| 1057 that means a program that makes use of a color terminal to display | |
| 1058 header lines, quotations, and signatures in distinct colors. | |
| 1059 The author's version of this program, for instance, | |
| 1060 is a 25 line awk script. | |
| 21 | 1061 |
| 1062 .PP | |
|
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1063 .B "Build a prototype as soon as possible |
| 21 | 1064 was again well followed by \s-1MH\s0. |
| 1065 This tenet, of course, focuses on early development, which is | |
| 1066 long time ago for \s-1MH\s0. | |
| 1067 But without following this guideline at the very beginning, | |
| 23 | 1068 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
| 1069 to ever create \s-1MH\s0. | |
| 1070 In Bruce' own words: | |
| 41 | 1071 .[ |
| 1072 %O FIXME | |
| 1073 .] | |
| 21 | 1074 .QP |
| 41 | 1075 .ps -1 |
| 30 | 1076 [...] but they [Stockton Gaines and Norm Shapiro] were not able |
| 23 | 1077 to convince anyone that such a system would be fast enough to be usable. |
| 21 | 1078 I proposed a very short project to prove the basic concepts, |
| 1079 and my management agreed. | |
| 1080 Looking back, I realize that I had been very lucky with my first design. | |
| 1081 Without nearly enough design work, | |
| 1082 I built a working environment and some header files | |
| 1083 with key structures and wrote the first few \s-1MH\s0 commands: | |
| 1084 inc, show/next/prev, and comp. | |
| 1085 [...] | |
| 1086 With these three, I was able to convince people that the structure was viable. | |
| 1087 This took about three weeks. | |
| 0 | 1088 |
| 1089 .NH 2 | |
| 1090 Problems | |
| 1091 .LP | |
| 22 | 1092 \s-1MH\s0, for sure is not without problems. |
| 30 | 1093 There are two main problems: one is technical, the other is about human behavior. |
| 22 | 1094 .PP |
| 1095 \s-1MH\s0 is old and email today is very different to email in the time | |
| 1096 when \s-1MH\s0 was designed. | |
| 1097 \s-1MH\s0 adopted to the changes pretty well, but it is limited. | |
| 1098 For example in development resources. | |
| 1099 \s-1MIME\s0 support and support for different character encodings | |
| 1100 is available, but only on a moderate level. | |
| 1101 More active developers could quickly improve there. | |
| 1102 It is also limited by design, which is the larger problem. | |
| 1103 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. | |
| 1104 These design conflicts are not easily solvable. | |
| 1105 Possibly, they require a redesign. | |
| 30 | 1106 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers, |
| 1107 hence \s-1MH\s0 may never work well with \s-1IMAP\s0. | |
| 22 | 1108 .PP |
| 1109 The other kind of problem is human habits. | |
| 1110 When in this world almost all \s-1MUA\s0s are monolithic, | |
| 1111 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 | |
| 1112 like \s-1MH\s0. | |
| 1113 The habits are so strong, that even people who understood the concept | |
| 30 | 1114 and advantages of \s-1MH\s0 do not like to switch, |
| 1115 simply because \s-1MH\s0 is different. | |
| 1116 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
| 1117 are quite outdated and thus not very appealing compared to the modern interfaces | |
| 1118 which monolithic \s-1MUA\s0s offer. | |
| 20 | 1119 |
| 1120 .NH 2 | |
| 1121 Summary \s-1MH\s0 | |
| 1122 .LP | |
| 31 | 1123 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design |
| 1124 and implementation. | |
| 1125 It consists of a toolchest of small tools, each of them does one job well. | |
| 1126 The tools are orthogonal to each other, to a large extend. | |
| 1127 However, for historical reasons, there also exist distinct tools | |
| 1128 that cover the same task. | |
| 1129 .PP | |
| 1130 The toolchest approach offers great flexibility to the user. | |
| 1131 He can use the complete power of the Unix shell with \s-1MH\s0. | |
| 1132 This makes \s-1MH\s0 a very powerful mail system. | |
| 1133 Extending and customizing \s-1MH\s0 is easy and encouraged, too. | |
| 1134 .PP | |
| 1135 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
| 1136 Its overall design follows clear rules. | |
| 1137 The single tools do only one job, thus they are easy to understand, | |
| 1138 easy to write, and good to maintain. | |
| 1139 They are all independent and do not interfere with the others. | |
| 1140 Automated testing of their function is a straight forward task. | |
| 1141 .PP | |
| 1142 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
| 1143 as its differentness is also its largest advantage. | |
| 1144 Unfortunately, for most people their habits are stronger | |
| 1145 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
| 0 | 1146 |
| 8 | 1147 |
| 1148 | |
| 0 | 1149 .NH 1 |
| 1150 Case study: uzbl | |
| 32 | 1151 .LP |
| 1152 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
| 1153 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy. | |
| 1154 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''. | |
| 1155 It is pronounced the identical. | |
| 0 | 1156 |
| 1157 .NH 2 | |
| 32 | 1158 Historical background |
| 0 | 1159 .LP |
| 32 | 1160 Uzbl was started by Dieter Plaetinck in April 2009. |
| 1161 The idea was born in a thread in the Arch Linux forum. | |
| 1162 .[ | |
| 1163 %O http://bbs.archlinux.org/viewtopic.php?id=67463 | |
| 1164 .] | |
| 1165 After some discussion about failures of well known web browsers, | |
| 1166 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
| 1167 of how a better web browser could look like. | |
| 1168 To the question of another member, if Plaetinck would write that program, | |
| 1169 because it would sound fantastic, Plaetinck replied: | |
| 1170 ``Maybe, if I find the time ;-)''. | |
| 1171 .PP | |
| 1172 Fortunately, he found the time. | |
| 1173 One day later, the first prototype was out. | |
| 1174 One week later, uzbl had an own website. | |
| 1175 One month after the first code showed up, | |
| 1176 a mailing list was installed to coordinate and discuss further development. | |
| 1177 A wiki was set up to store documentation and scripts that showed up on the | |
| 1178 mailing list and elsewhere. | |
| 1179 .PP | |
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1180 In the, now, one year of uzbl's existence, it was heavily developed in various branches. |
| 32 | 1181 Plaetinck's task became more and more to only merge the best code from the |
| 1182 different branches into his main branch, and to apply patches. | |
| 1183 About once a month, Plaetinck released a new version. | |
| 1184 In September 2009, he presented several forks of uzbl. | |
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1185 Uzbl, actually, opened the field for a whole family of web browsers with similar shape. |
| 32 | 1186 .PP |
| 1187 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
| 1188 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
| 0 | 1189 |
| 1190 .NH 2 | |
| 32 | 1191 Contrasts to other web browsers |
| 0 | 1192 .LP |
| 32 | 1193 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
| 1194 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
| 1195 .PP | |
| 1196 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
| 1197 Uzbl-core is, how its name already indicates, the core of uzbl. | |
| 1198 It handles commands and events to interface other programs, | |
| 1199 and also displays webpages by using webkit as render engine. | |
| 1200 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, | |
| 1201 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
| 1202 to form a ``complete'' web browser. | |
| 1203 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
| 1204 so uzbl-core is included. | |
| 1205 .PP | |
| 1206 Unlike most other web browsers, uzbl is mainly the mediator between the | |
| 1207 various tools that cover single jobs of web browsing. | |
| 35 | 1208 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
| 1209 and on stdin, and it writes events to a Unix socket and to stdout. | |
| 1210 The graphical rendering of the webpage is done by webkit, a web content engine. | |
| 1211 Uzbl-core is build around this library. | |
| 1212 Loading a webpage in a running uzbl instance requires only: | |
| 32 | 1213 .DS |
| 1214 .CW | |
| 1215 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
| 1216 .DE | |
| 1217 .PP | |
| 1218 Downloads, browsing history, bookmarks, and thelike are not provided | |
| 1219 by uzbl-core itself, as they are in other web browsers. | |
| 35 | 1220 Uzbl-browser also only provides, so called, handler scripts that wrap |
| 1221 external applications which provide the actual functionality. | |
| 32 | 1222 For instance, \fIwget\fP is used to download files and uzbl-browser |
| 1223 includes a script that calls wget with appropriate options in | |
| 1224 a prepared environment. | |
| 1225 .PP | |
| 1226 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
| 1227 This is their effort to achieve similar goals. | |
| 35 | 1228 But instead of using existing, external programs, modern web browsers |
| 1229 include these functions, although they might be loaded at runtime. | |
| 0 | 1230 |
| 1231 .NH 2 | |
| 32 | 1232 Discussion of the design |
| 0 | 1233 .LP |
| 32 | 1234 This section discusses uzbl in regard of the Unix Philosophy, |
| 1235 as identified by Gancarz. | |
| 1236 | |
| 1237 .PP | |
| 35 | 1238 .B "Make each program do one thing well" . |
| 1239 Uzbl tries to be a web browser and nothing else. | |
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1240 The common definition of a web browser is, of course, highly influenced by |
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1241 existing implementations of web browsers, although they are degenerated. |
| 35 | 1242 Web browsers should be programs to browse the web, and nothing more. |
| 1243 This is the one thing they should do, as demanded by the Unix Philosophy. | |
|
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1244 .PP |
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1245 Web browsers should, for instance, not manage downloads. |
| 35 | 1246 This is the job download managers exist for. |
| 1247 Download managers do primary care about being good in downloading files. | |
| 1248 Modern web browsers provide download management only as a secondary feature. | |
| 1249 How could they perform this job better, than programs that exist only for | |
| 1250 this very job? | |
| 1251 And how could anyone want less than the best download manager available? | |
| 32 | 1252 .PP |
| 35 | 1253 A web browser's job is to let the user browse the web. |
| 1254 This means, navigating through websites by following links. | |
|
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1255 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1256 It is covered by the webkit render engine, in uzbl's case. |
| 35 | 1257 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
|
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1258 are also not the job of a web browser. |
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1259 They should be handled by external applications \(en |
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1260 ones which's job is to handle such data. |
| 35 | 1261 Uzbl strives to do it this way. |
|
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1262 .PP |
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1263 Remember Doug McIlroy: |
| 35 | 1264 .I |
| 1265 ``Write programs that do one thing and do it well. | |
| 1266 Write programs to work together.'' | |
| 1267 .R | |
| 1268 .PP | |
| 1269 The lesser tenet | |
| 1270 .B "allow the user to tailor the environment | |
| 1271 matches good here. | |
| 1272 There was the question, how anyone could want anything less than the | |
| 1273 best program for the job. | |
|
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1274 But as personal preferences matter much, |
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1275 it is probably more important to ask: |
| 35 | 1276 How could anyone want something else than his preferred program for the job? |
|
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1277 .PP |
| 35 | 1278 Usually users want one program for one job. |
| 1279 Hence, whenever the task is, for instance, downloading, | |
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1280 exactly one download manager should be used. |
| 35 | 1281 More advanced users might want to have this download manager in this |
| 1282 situation and that one in that situation. | |
| 1283 They should be able to configure it this way. | |
| 1284 With uzbl, one can use any download manager the user wants. | |
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1285 To switch to a different one, only one line in a small handler script |
| 35 | 1286 needs to be changed. |
|
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1287 Alternatively it would be possible to query an entry in a global file |
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1288 or an environment variable, which specifies the download manager to use, |
| 35 | 1289 in the handler script. |
|
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1290 .PP |
| 35 | 1291 As uzbl does neither have its own download manager nor depends on a |
| 1292 specific one, thus uzbl's browsing abilities will not be lowered by having | |
| 1293 a bad download manager. | |
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1294 Uzbl's download capabilities will just as good as the ones of the best |
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1295 download manager available on the system. |
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1296 Of course, this applies to all of the other supplementary tools, too. |
| 32 | 1297 |
| 1298 .PP | |
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1299 .B "Use software leverage to your advantage" . |
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1300 Shell scripts are a good choice to extend uzbl. |
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1301 Uzbl is designed to be extended by external tools. |
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1302 These external tools are usually wrapped by small handler shell scripts. |
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1303 Shell scripts are the glue in this approach. |
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1304 They make the various parts fit together. |
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1305 .PP |
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1306 As an example, the history mechanism of uzbl shall be presented. |
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1307 Uzbl is configured to spawn a script to append an entry to the history |
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1308 whenever the event of a fully loaded page occurs. |
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1309 The script to append the entry to the history not much more than: |
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1310 .DS |
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1311 .CW |
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1312 #!/bin/sh |
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1313 file=/path/to/uzbl-history |
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1314 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1315 .DE |
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1316 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1317 For loading an entry, a key is bound to spawn a load from history script. |
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1318 The script reverses the history to have newer entries first, |
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1319 then displays \fIdmenu\fP to select an item, |
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1320 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
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1321 With error checking and corner cases removed, the script looks like this: |
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1322 .DS |
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1323 .CW |
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1324 #!/bin/sh |
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1325 file=/path/to/uzbl-history |
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1326 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1327 echo "uri $goto" > $4 |
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1328 .DE |
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1329 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1330 uzbl instance. |
| 32 | 1331 |
| 1332 .PP | |
|
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1333 .B "Avoid captive user interfaces" . |
|
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1334 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1335 a captive user interface. |
| 37 | 1336 But the difference to most other web browsers is, that uzbl is only |
| 1337 the captive user interface frontend and the core of the backend. | |
|
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1338 Many parts of the backend are independent of uzbl. |
| 37 | 1339 Some are distributed with uzbl, for some external programs, handler scripts |
| 1340 are distributed, arbitrary additional functionality can be added if desired. | |
| 1341 .PP | |
| 1342 The frontend is captive \(en that is true. | |
| 1343 This is okay for the task of browsing the web, as this task is only relevant | |
| 1344 for humans. | |
| 1345 Automated programs would \fIcrawl\fP the web. | |
| 1346 That means, they read the source directly. | |
| 1347 The source includes all the semantics. | |
| 1348 The graphical representation is just for humans to transfer the semantics | |
| 1349 more intuitively. | |
| 32 | 1350 |
| 1351 .PP | |
|
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1352 .B "Make every program a filter" . |
| 37 | 1353 Graphical web browsers are almost dead ends in the chain of information flow. |
| 1354 Thus it is difficult to see what graphical web browsers should filter. | |
| 1355 Graphical web browsers exist almost only for interactive use by humans. | |
| 1356 The only case when one might want to automate the rendering function is | |
| 1357 to generate images of rendered webpages. | |
| 1358 | |
| 1359 .PP | |
| 1360 .B "Small is beautiful" | |
|
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1361 is not easy to apply to a web browser, primary because modern web technology |
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1362 is very complex; hence the rendering task is very complex. |
| 37 | 1363 Modern web browsers will always consist of many thousand lines of code, |
| 1364 unfortunately. | |
| 1365 Using the toolchest approach and wrappers can split the browser into | |
| 1366 several small parts, tough. | |
| 1367 .PP | |
| 1368 Uzbl-core consists of about 3\,500 lines of C code. | |
| 1369 The distribution includes another 3\,500 lines of Shell and Python code, | |
| 1370 which are the handler scripts and plugins like a modal interface. | |
|
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1371 Further more, uzbl uses functionality of external tools like |
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1372 \fIwget\fP and \fInetcat\fP. |
| 37 | 1373 Up to this point, uzbl looks pretty neat and small. |
|
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1374 The ugly part of uzbl is the web content renderer, webkit. |
| 37 | 1375 Webkit consists of roughly 400\,000 (!) lines of code. |
|
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1376 Unfortunately, small web render engines are not possible anymore |
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1377 because of the modern web. |
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1378 The problems section will explain this in more detail. |
| 35 | 1379 |
| 1380 .PP | |
| 1381 .B "Build a prototype as soon as possible" . | |
| 1382 Plaetinck made his code public, right from the beginning. | |
|
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1383 Discussion and development was, and still is, open to everyone interested. |
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1384 Development versions of uzbl can be obtained very simply from the code |
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1385 repository. |
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1386 Within the first year of uzbl's existence, a new version was released |
| 35 | 1387 more often than once a month. |
|
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1388 Different forks and branches arose. |
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1389 They introduced new features, which were tested for suitability. |
| 35 | 1390 The experiences of using prototypes influenced further development. |
| 1391 Actually, all development was community driven. | |
|
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1392 Plaetinck says, three months after uzbl's birth: |
| 35 | 1393 ``Right now I hardly code anything myself for Uzbl. |
| 1394 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
| 1395 .[ | |
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1396 %A FIXME |
| 35 | 1397 %O http://lwn.net/Articles/341245/ |
| 1398 .] | |
| 32 | 1399 |
| 0 | 1400 |
| 1401 .NH 2 | |
| 1402 Problems | |
| 1403 .LP | |
|
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1404 Similar to \s-1MH\s0, uzbl, too suffers from being different. |
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1405 It is sad, but people use what they know. |
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1406 Fortunately, uzbl's user interface can look and feel very much the |
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1407 same as the one of the well known web browsers, |
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1408 hiding the internal differences. |
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1409 But uzbl has to provide this similar look and feel to be accepted |
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1410 as a ``normal'' browser by ``normal'' users. |
| 37 | 1411 .PP |
|
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1412 The more important problem is the modern web. |
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1413 The modern web is simply broken. |
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1414 It has state in a state-less protocol, |
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1415 it misuses technologies, |
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1416 and it is helplessly overloaded. |
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1417 The result are web content render engines that must consist |
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1418 of hundreds of thousands lines of code. |
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1419 They also must combine and integrate many different technologies, |
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1420 only to make our modern web usable. |
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1421 Website to image converter are hardly possible to run without |
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1422 human interaction because of state in sessions, impossible |
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1423 deep-linking, and unautomatable technologies. |
| 37 | 1424 .PP |
|
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1425 The web was misused to provide all kinds of imaginable wishes. |
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1426 Now web browsers, and eventually the users, suffer from it. |
| 37 | 1427 |
| 8 | 1428 |
| 32 | 1429 .NH 2 |
| 1430 Summary uzbl | |
| 1431 .LP | |
|
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1432 ``Uzbl is a browser that adheres to the Unix Philosophy'', |
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1433 that is how uzbl is seen by its authors. |
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1434 Indeed, uzbl follows the Unix Philosophy in many ways. |
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1435 It consists of independent parts that work together, |
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1436 its core is mainly a mediator which glues the parts together. |
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1437 .PP |
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1438 Software leverage can excellently be seen in uzbl. |
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1439 It makes use of external tools, separates independent tasks |
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1440 in independent parts, and glues them together with small |
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1441 handler scripts, around uzbl-core. |
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1442 .PP |
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1443 As uzbl, more or less, consists of a set of tools and a bit |
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1444 of glue, anyone can put the parts together and expand it |
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1445 in any desired way. |
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1446 Uzbl is very flexible and customizable. |
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1447 These properties make it valuable for advanced users, |
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1448 but may keep novice users from using it. |
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1449 .PP |
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1450 Uzbl's main problem is the modern web, that makes it hard |
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1451 to design a sane web browser. |
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1452 Despite this bad situation, uzbl does a fairly good job. |
| 32 | 1453 |
| 8 | 1454 |
| 0 | 1455 .NH 1 |
| 1456 Final thoughts | |
| 1457 | |
| 1458 .NH 2 | |
| 1459 Quick summary | |
| 1460 .LP | |
| 1461 good design | |
| 1462 .LP | |
| 1463 unix phil | |
| 1464 .LP | |
| 1465 case studies | |
| 1466 | |
| 1467 .NH 2 | |
| 1468 Why people should choose | |
| 1469 .LP | |
| 1470 Make the right choice! | |
| 1471 | |
| 1472 .nr PI .5i | |
| 1473 .rm ]< | |
| 1474 .de ]< | |
| 1475 .LP | |
| 1476 .de FP | |
| 1477 .IP \\\\$1. | |
| 1478 \\.. | |
| 1479 .rm FS FE | |
| 1480 .. | |
| 1481 .SH | |
| 1482 References | |
| 1483 .[ | |
| 1484 $LIST$ | |
| 1485 .] | |
| 1486 .wh -1p |