Mercurial > docs > unix-phil
annotate unix-phil.ms @ 37:9282c4cea18c
more about uzbl design
author | meillo@marmaro.de |
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date | Sat, 03 Apr 2010 10:33:33 +0200 |
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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 |
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31 This paper discusses the importance of the Unix Philosophy in software design. |
0 | 32 Today, few software designers are aware of these concepts, |
3 | 33 and thus most modern software is limited and does not make use of software leverage. |
0 | 34 Knowing and following the tenets of the Unix Philosophy makes software more valuable. |
35 .AE | |
36 | |
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39 .FS |
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40 .ps -1 |
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41 This paper was prepared for the seminar ``Software Analysis'' at University Ulm. |
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42 Mentor was professor Schweiggert. 2010-02-05 |
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43 .br |
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44 You may get this document from my website |
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45 .CW \s-1http://marmaro.de/docs |
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46 .FE |
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47 |
0 | 48 .NH 1 |
49 Introduction | |
50 .LP | |
51 Building a software is a process from an idea of the purpose of the software | |
3 | 52 to its release. |
0 | 53 No matter \fIhow\fP the process is run, two things are common: |
54 the initial idea and the release. | |
9 | 55 The process in between can be of any shape. |
56 The the maintenance work after the release is ignored for the moment. | |
1 | 57 .PP |
0 | 58 The process of building splits mainly in two parts: |
59 the planning of what and how to build, and implementing the plan by writing code. | |
3 | 60 This paper focuses on the planning part \(en the designing of the software. |
61 .PP | |
62 Software design is the plan of how the internals and externals of the software should look like, | |
63 based on the requirements. | |
9 | 64 This paper discusses the recommendations of the Unix Philosophy about software design. |
3 | 65 .PP |
66 The here discussed ideas can get applied by any development process. | |
9 | 67 The Unix Philosophy does recommend how the software development process should look like, |
3 | 68 but this shall not be of matter here. |
0 | 69 Similar, the question of how to write the code is out of focus. |
1 | 70 .PP |
3 | 71 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet. |
1 | 72 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed. |
3 | 73 It is no limited set of rules, but what people see to be common to typical Unix software. |
1 | 74 Several people stated their view on the Unix Philosophy. |
75 Best known are: | |
76 .IP \(bu | |
77 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
78 .[ | |
79 %A M. D. McIlroy | |
80 %A E. N. Pinson | |
81 %A B. A. Taque | |
82 %T UNIX Time-Sharing System Forward | |
83 %J The Bell System Technical Journal | |
84 %D 1978 | |
85 %V 57 | |
86 %N 6 | |
87 %P 1902 | |
88 .] | |
89 .IP \(bu | |
90 Mike Gancarz' book ``The UNIX Philosophy''. | |
91 .[ | |
92 %A Mike Gancarz | |
93 %T The UNIX Philosophy | |
94 %D 1995 | |
95 %I Digital Press | |
96 .] | |
97 .IP \(bu | |
98 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
99 .[ | |
100 %A Eric S. Raymond | |
101 %T The Art of UNIX Programming | |
102 %D 2003 | |
103 %I Addison-Wesley | |
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104 %O .CW \s-1http://www.faqs.org/docs/artu/ |
1 | 105 .] |
0 | 106 .LP |
1 | 107 These different views on the Unix Philosophy have much in common. |
3 | 108 Especially, the main concepts are similar for all of them. |
1 | 109 But there are also points on which they differ. |
110 This only underlines what the Unix Philosophy is: | |
111 A retrospective view on the main concepts of Unix software; | |
9 | 112 especially those that were successful and unique to Unix. |
6 | 113 .\" really? |
1 | 114 .PP |
115 Before we will have a look at concrete concepts, | |
116 we discuss why software design is important | |
117 and what problems bad design introduces. | |
0 | 118 |
119 | |
120 .NH 1 | |
6 | 121 Importance of software design in general |
0 | 122 .LP |
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123 Why should we design software at all? |
6 | 124 It is general knowledge, that even a bad plan is better than no plan. |
125 Ignoring software design is programming without a plan. | |
126 This will lead pretty sure to horrible results. | |
127 .PP | |
128 The design of a software is its internal and external shape. | |
129 The design talked about here has nothing to do with visual appearance. | |
130 If we see a program as a car, then its color is of no matter. | |
131 Its design would be the car's size, its shape, the number and position of doors, | |
132 the ratio of passenger and cargo transport, and so forth. | |
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133 .PP |
6 | 134 A software's design is about quality properties. |
135 Each of the cars may be able to drive from A to B, | |
136 but it depends on its properties whether it is a good car for passenger transport or not. | |
137 It also depends on its properties if it is a good choice for a rough mountain area. | |
138 .PP | |
139 Requirements to a software are twofold: functional and non-functional. | |
140 Functional requirements are easier to define and to verify. | |
141 They are directly the software's functions. | |
142 Functional requirements are the reason why software gets written. | |
143 Someone has a problem and needs a tool to solve it. | |
144 Being able to solve the problem is the main functional requirement. | |
145 It is the driving force behind all programming effort. | |
146 .PP | |
147 On the other hand, there are also non-functional requirements. | |
148 They are called \fIquality\fP requirements, too. | |
149 The quality of a software is about properties that are not directly related to | |
150 the software's basic functions. | |
151 Quality aspects are about the properties that are overlooked at first sight. | |
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152 .PP |
6 | 153 Quality is of few matter when the software gets initially built, |
9 | 154 but it will be of matter in usage and maintenance of the software. |
6 | 155 A short-sighted might see in developing a software mainly building something up. |
156 Reality shows, that building the software the first time is only a small amount | |
157 of the overall work. | |
9 | 158 Bug fixing, extending, rebuilding of parts \(en short: maintenance work \(en |
6 | 159 does soon take over the major part of the time spent on a software. |
160 Not to forget the usage of the software. | |
161 These processes are highly influenced by the software's quality. | |
162 Thus, quality should never be neglected. | |
163 The problem is that you hardly ``stumble over'' bad quality during the first build, | |
164 but this is the time when you should care about good quality most. | |
165 .PP | |
166 Software design is not about the basic function of a software; | |
167 this requirement will get satisfied anyway, as it is the main driving force behind the development. | |
168 Software design is about quality aspects of the software. | |
169 Good design will lead to good quality, bad design to bad quality. | |
170 The primary functions of the software will be affected modestly by bad quality, | |
171 but good quality can provide a lot of additional gain from the software, | |
172 even at places where one never expected it. | |
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173 .PP |
6 | 174 The ISO/IEC 9126-1 standard, part 1, |
175 .[ | |
9 | 176 %I International Organization for Standardization |
6 | 177 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1 |
178 %C Geneve | |
179 %D 2001 | |
180 .] | |
181 defines the quality model as consisting out of: | |
182 .IP \(bu | |
183 .I Functionality | |
184 (suitability, accuracy, inter\%operability, security) | |
185 .IP \(bu | |
186 .I Reliability | |
187 (maturity, fault tolerance, recoverability) | |
188 .IP \(bu | |
189 .I Usability | |
190 (understandability, learnability, operability, attractiveness) | |
191 .IP \(bu | |
192 .I Efficiency | |
9 | 193 (time behavior, resource utilization) |
6 | 194 .IP \(bu |
195 .I Maintainability | |
23 | 196 (analyzability, changeability, stability, testability) |
6 | 197 .IP \(bu |
198 .I Portability | |
199 (adaptability, installability, co-existence, replaceability) | |
200 .LP | |
201 These goals are parts of a software's design. | |
202 Good design can give these properties to a software, | |
203 bad designed software will miss them. | |
7 | 204 .PP |
205 One further goal of software design is consistency. | |
206 Consistency eases understanding, working on, and using things. | |
207 Consistent internals and consistent interfaces to the outside can be provided by good design. | |
208 .PP | |
209 We should design software because good design avoids many problems during a software's lifetime. | |
210 And we should design software because good design can offer much gain, | |
211 that can be unrelated to the software main intend. | |
212 Indeed, we should spend much effort into good design to make the software more valuable. | |
213 The Unix Philosophy shows how to design software well. | |
214 It offers guidelines to achieve good quality and high gain for the effort spent. | |
0 | 215 |
216 | |
217 .NH 1 | |
218 The Unix Philosophy | |
4 | 219 .LP |
220 The origins of the Unix Philosophy were already introduced. | |
8 | 221 This chapter explains the philosophy, oriented on Gancarz, |
222 and shows concrete examples of its application. | |
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223 |
16 | 224 .NH 2 |
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225 Pipes |
0 | 226 .LP |
4 | 227 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
228 Knowledge of using the Unix shell is assumed. | |
229 .PP | |
230 Counting the number of files in the current directory: | |
9 | 231 .DS I 2n |
4 | 232 .CW |
9 | 233 .ps -1 |
4 | 234 ls | wc -l |
235 .DE | |
236 The | |
237 .CW ls | |
238 command lists all files in the current directory, one per line, | |
239 and | |
240 .CW "wc -l | |
8 | 241 counts the number of lines. |
4 | 242 .PP |
8 | 243 Counting the number of files that do not contain ``foo'' in their name: |
9 | 244 .DS I 2n |
4 | 245 .CW |
9 | 246 .ps -1 |
4 | 247 ls | grep -v foo | wc -l |
248 .DE | |
249 Here, the list of files is filtered by | |
250 .CW grep | |
251 to remove all that contain ``foo''. | |
252 The rest is the same as in the previous example. | |
253 .PP | |
254 Finding the five largest entries in the current directory. | |
9 | 255 .DS I 2n |
4 | 256 .CW |
9 | 257 .ps -1 |
4 | 258 du -s * | sort -nr | sed 5q |
259 .DE | |
260 .CW "du -s * | |
261 returns the recursively summed sizes of all files | |
8 | 262 \(en no matter if they are regular files or directories. |
4 | 263 .CW "sort -nr |
264 sorts the list numerically in reverse order. | |
265 Finally, | |
266 .CW "sed 5q | |
267 quits after it has printed the fifth line. | |
268 .PP | |
269 The presented command lines are examples of what Unix people would use | |
270 to get the desired output. | |
271 There are also other ways to get the same output. | |
272 It's a user's decision which way to go. | |
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273 .PP |
8 | 274 The examples show that many tasks on a Unix system |
4 | 275 are accomplished by combining several small programs. |
276 The connection between the single programs is denoted by the pipe operator `|'. | |
277 .PP | |
278 Pipes, and their extensive and easy use, are one of the great | |
279 achievements of the Unix system. | |
280 Pipes between programs have been possible in earlier operating systems, | |
281 but it has never been a so central part of the concept. | |
282 When, in the early seventies, Doug McIlroy introduced pipes for the | |
283 Unix system, | |
284 ``it was this concept and notation for linking several programs together | |
285 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
286 .[ | |
287 %T Unix: An Oral History | |
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288 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
4 | 289 .] |
290 .PP | |
291 Being able to specify pipelines in an easy way is, | |
292 however, not enough by itself. | |
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293 It is only one half. |
4 | 294 The other is the design of the programs that are used in the pipeline. |
8 | 295 They have to interfaces that allows them to be used in such a way. |
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296 |
16 | 297 .NH 2 |
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298 Interface design |
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299 .LP |
11 | 300 Unix is, first of all, simple \(en Everything is a file. |
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301 Files are sequences of bytes, without any special structure. |
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302 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin) |
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303 and write a stream of bytes to ``standard output'' (stdout). |
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304 .PP |
8 | 305 If the files \fIare\fP sequences of bytes, |
306 and the programs \fIare\fP filters on byte streams, | |
11 | 307 then there is exactly one standardized data interface. |
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308 Thus it is possible to combine them in any desired way. |
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309 .PP |
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310 Even a handful of small programs will yield a large set of combinations, |
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311 and thus a large set of different functions. |
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312 This is leverage! |
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313 If the programs are orthogonal to each other \(en the best case \(en |
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314 then the set of different functions is greatest. |
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315 .PP |
11 | 316 Programs might also have a separate control interface, |
317 besides their data interface. | |
318 The control interface is often called ``user interface'', | |
319 because it is usually designed to be used by humans. | |
320 The Unix Philosophy discourages to assume the user to be human. | |
321 Interactive use of software is slow use of software, | |
322 because the program waits for user input most of the time. | |
323 Interactive software requires the user to be in front of the computer | |
324 all the time. | |
325 Interactive software occupy the user's attention while they are running. | |
326 .PP | |
327 Now we come back to the idea of using several small programs, combined, | |
328 to have a more specific function. | |
329 If these single tools would all be interactive, | |
330 how would the user control them? | |
331 It is not only a problem to control several programs at once if they run at the same time, | |
332 it also very inefficient to have to control each of the single programs | |
333 that are intended to work as one large program. | |
334 Hence, the Unix Philosophy discourages programs to demand interactive use. | |
335 The behavior of programs should be defined at invocation. | |
336 This is done by specifying arguments (``command line switches'') to the program call. | |
337 Gancarz discusses this topic as ``avoid captive user interfaces''. | |
338 .[ | |
339 %A Mike Gancarz | |
340 %T The UNIX Philosophy | |
341 %I Digital Press | |
342 %D 1995 | |
343 %P 88 ff. | |
344 .] | |
345 .PP | |
346 Non-interactive use is, during development, also an advantage for testing. | |
347 Testing of interactive programs is much more complicated, | |
348 than testing of non-interactive programs. | |
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349 |
16 | 350 .NH 2 |
8 | 351 The toolchest approach |
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352 .LP |
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353 A toolchest is a set of tools. |
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354 Instead of having one big tool for all tasks, one has many small tools, |
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355 each for one task. |
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356 Difficult tasks are solved by combining several of the small, simple tools. |
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357 .PP |
11 | 358 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
359 that are filters on byte streams. | |
360 They are, to a large extend, unrelated in their function. | |
361 Hence, the Unix toolchest provides a large set of functions | |
362 that can be accessed by combining the programs in the desired way. | |
363 .PP | |
364 There are also advantages for developing small toolchest programs. | |
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365 It is easier and less error-prone to write small programs. |
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366 It is also easier and less error-prone to write a large set of small programs, |
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367 than to write one large program with all the functionality included. |
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368 If the small programs are combinable, then they offer even a larger set |
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369 of functions than the single large program. |
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370 Hence, one gets two advantages out of writing small, combinable programs. |
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371 .PP |
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372 There are two drawbacks of the toolchest approach. |
8 | 373 First, one simple, standardized, unidirectional interface has to be sufficient. |
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374 If one feels the need for more ``logic'' than a stream of bytes, |
8 | 375 then a different approach might be of need. |
13 | 376 But it is also possible, that he just can not imagine a design where |
8 | 377 a stream of bytes is sufficient. |
378 By becoming more familiar with the ``Unix style of thinking'', | |
379 developers will more often and easier find simple designs where | |
380 a stream of bytes is a sufficient interface. | |
381 .PP | |
382 The second drawback of a toolchest affects the users. | |
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383 A toolchest is often more difficult to use for novices. |
9 | 384 It is necessary to become familiar with each of the tools, |
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385 to be able to use the right one in a given situation. |
9 | 386 Additionally, one needs to combine the tools in a senseful way on its own. |
387 This is like a sharp knife \(en it is a powerful tool in the hand of a master, | |
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388 but of no good value in the hand of an unskilled. |
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389 .PP |
8 | 390 However, learning single, small tool of the toolchest is easier than |
391 learning a complex tool. | |
392 The user will have a basic understanding of a yet unknown tool, | |
393 if the several tools of the toolchest have a common style. | |
394 He will be able to transfer knowledge over one tool to another. | |
395 .PP | |
396 Moreover, the second drawback can be removed easily by adding wrappers | |
397 around the single tools. | |
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398 Novice users do not need to learn several tools if a professional wraps |
8 | 399 the single commands into a more high-level script. |
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400 Note that the wrapper script still calls the small tools; |
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401 the wrapper script is just like a skin around. |
8 | 402 No complexity is added this way, |
403 but new programs can get created out of existing one with very low effort. | |
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404 .PP |
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405 A wrapper script for finding the five largest entries in the current directory |
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406 could look like this: |
9 | 407 .DS I 2n |
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408 .CW |
9 | 409 .ps -1 |
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410 #!/bin/sh |
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411 du -s * | sort -nr | sed 5q |
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412 .DE |
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413 The script itself is just a text file that calls the command line |
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414 a professional user would type in directly. |
8 | 415 Making the program flexible on the number of entries it prints, |
416 is easily possible: | |
9 | 417 .DS I 2n |
8 | 418 .CW |
9 | 419 .ps -1 |
8 | 420 #!/bin/sh |
421 num=5 | |
422 [ $# -eq 1 ] && num="$1" | |
423 du -sh * | sort -nr | sed "${num}q" | |
424 .DE | |
425 This script acts like the one before, when called without an argument. | |
426 But one can also specify a numerical argument to define the number of lines to print. | |
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427 |
16 | 428 .NH 2 |
8 | 429 A powerful shell |
430 .LP | |
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431 It was already said, that the Unix shell provides the possibility to |
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432 combine small programs into large ones easily. |
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433 A powerful shell is a great feature in other ways, too. |
8 | 434 .PP |
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435 For instance by including a scripting language. |
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436 The control statements are build into the shell. |
8 | 437 The functions, however, are the normal programs, everyone can use on the system. |
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438 Thus, the programs are known, so learning to program in the shell is easy. |
8 | 439 Using normal programs as functions in the shell programming language |
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440 is only possible because they are small and combinable tools in a toolchest style. |
8 | 441 .PP |
442 The Unix shell encourages to write small scripts out of other programs, | |
443 because it is so easy to do. | |
444 This is a great step towards automation. | |
445 It is wonderful if the effort to automate a task equals the effort | |
446 it takes to do it the second time by hand. | |
447 If it is so, then the user will be happy to automate everything he does more than once. | |
448 .PP | |
449 Small programs that do one job well, standardized interfaces between them, | |
450 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
451 this will inevitably produce software leverage. | |
452 Getting multiple times the benefit of an investment is a great offer. | |
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453 .PP |
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454 The shell also encourages rapid prototyping. |
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455 Many well known programs started as quickly hacked shell scripts, |
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456 and turned into ``real'' programs, written in C, later. |
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457 Building a prototype first is a way to avoid the biggest problems |
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458 in application development. |
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459 Fred Brooks writes in ``No Silver Bullet'': |
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460 .[ |
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461 %A Frederick P. Brooks, Jr. |
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462 %T No Silver Bullet: Essence and Accidents of Software Engineering |
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463 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference |
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464 %E H.-J. Kugler |
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465 %D 1986 |
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466 %P 1069\(en1076 |
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467 %I Elsevier Science B.V. |
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468 %C Amsterdam, The Netherlands |
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469 .] |
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470 .QP |
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471 The hardest single part of building a software system is deciding precisely what to build. |
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472 No other part of the conceptual work is so difficult as establishing the detailed |
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473 technical requirements, [...]. |
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474 No other part of the work so cripples the resulting system if done wrong. |
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475 No other part is more difficult to rectify later. |
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476 .PP |
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477 Writing a prototype is a great method to become familiar with the requirements |
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478 and to actually run into real problems. |
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479 Today, prototyping is often seen as a first step in building a software. |
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480 This is, of course, good. |
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481 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
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482 After having built the prototype, one might notice, that the prototype is already |
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483 \fIgood enough\fP. |
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484 Hence, no reimplementation, in a more sophisticated programming language, might be of need, |
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485 for the moment. |
23 | 486 Maybe later, it might be necessary to rewrite the software, but not now. |
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487 .PP |
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488 By delaying further work, one keeps the flexibility to react easily on |
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489 changing requirements. |
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490 Software parts that are not written will not miss the requirements. |
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491 |
16 | 492 .NH 2 |
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493 Worse is better |
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494 .LP |
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495 The Unix Philosophy aims for the 80% solution; |
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496 others call it the ``Worse is better'' approach. |
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497 .PP |
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498 First, practical experience shows, that it is almost never possible to define the |
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499 requirements completely and correctly the first time. |
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500 Hence one should not try to; it will fail anyway. |
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501 Second, practical experience shows, that requirements change during time. |
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502 Hence it is best to delay requirement-based design decisions as long as possible. |
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503 Also, the software should be small and flexible as long as possible |
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504 to react on changing requirements. |
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505 Shell scripts, for example, are more easily adjusted as C programs. |
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506 Third, practical experience shows, that maintenance is hard work. |
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507 Hence, one should keep the amount of software as small as possible; |
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508 it should just fulfill the \fIcurrent\fP requirements. |
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509 Software parts that will be written later, do not need maintenance now. |
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510 .PP |
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511 Starting with a prototype in a scripting language has several advantages: |
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512 .IP \(bu |
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513 As the initial effort is low, one will likely start right away. |
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514 .IP \(bu |
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515 As working parts are available soon, the real requirements can get identified soon. |
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516 .IP \(bu |
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517 When a software is usable, it gets used, and thus tested. |
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518 Hence problems will be found at early stages of the development. |
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519 .IP \(bu |
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520 The prototype might be enough for the moment, |
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521 thus further work on the software can be delayed to a time |
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522 when one knows better about the requirements and problems, |
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523 than now. |
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524 .IP \(bu |
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525 Implementing now only the parts that are actually needed now, |
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526 requires fewer maintenance work. |
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527 .IP \(bu |
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528 If the global situation changes so that the software is not needed anymore, |
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529 then less effort was spent into the project, than it would have be |
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530 when a different approach had been used. |
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531 |
16 | 532 .NH 2 |
11 | 533 Upgrowth and survival of software |
534 .LP | |
12 | 535 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
13 | 536 Although these are just verbs, they do imply a specific view on the work process |
537 they describe. | |
12 | 538 The better verb, however, is to \fIgrow\fP. |
539 .PP | |
540 Creating software in the sense of the Unix Philosophy is an incremental process. | |
541 It starts with a first prototype, which evolves as requirements change. | |
542 A quickly hacked shell script might become a large, sophisticated, | |
13 | 543 compiled program this way. |
544 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
545 While being alive it will get extended, rearranged, rebuilt (from scratch). | |
12 | 546 Growing software matches the view that ``software is never finished. It is only released.'' |
547 .[ | |
13 | 548 %O FIXME |
549 %A Mike Gancarz | |
550 %T The UNIX Philosophy | |
551 %P 26 | |
12 | 552 .] |
553 .PP | |
13 | 554 Software can be seen as being controlled by evolutionary processes. |
555 Successful software is software that is used by many for a long time. | |
12 | 556 This implies that the software is needed, useful, and better than alternatives. |
557 Darwin talks about: ``The survival of the fittest.'' | |
558 .[ | |
13 | 559 %O FIXME |
560 %A Charles Darwin | |
12 | 561 .] |
562 Transferred to software: The most successful software, is the fittest, | |
563 is the one that survives. | |
13 | 564 (This may be at the level of one creature, or at the level of one species.) |
565 The fitness of software is affected mainly by four properties: | |
15 | 566 portability of code, portability of data, range of usability, and reusability of parts. |
567 .\" .IP \(bu | |
568 .\" portability of code | |
569 .\" .IP \(bu | |
570 .\" portability of data | |
571 .\" .IP \(bu | |
572 .\" range of usability | |
573 .\" .IP \(bu | |
574 .\" reuseability of parts | |
13 | 575 .PP |
15 | 576 (1) |
577 .I "Portability of code | |
578 means, using high-level programming languages, | |
13 | 579 sticking to the standard, |
580 and avoiding optimizations that introduce dependencies on specific hardware. | |
581 Hardware has a much lower lifetime than software. | |
582 By chaining software to a specific hardware, | |
583 the software's lifetime gets shortened to that of this hardware. | |
584 In contrast, software should be easy to port \(en | |
23 | 585 adaptation is the key to success. |
13 | 586 .\" cf. practice of prog: ch08 |
587 .PP | |
15 | 588 (2) |
589 .I "Portability of data | |
590 is best achieved by avoiding binary representations | |
13 | 591 to store data, because binary representations differ from machine to machine. |
23 | 592 Textual representation is favored. |
13 | 593 Historically, ASCII was the charset of choice. |
594 In the future, UTF-8 might be the better choice, however. | |
595 Important is that it is a plain text representation in a | |
596 very common charset encoding. | |
597 Apart from being able to transfer data between machines, | |
598 readable data has the great advantage, that humans are able | |
599 to directly edit it with text editors and other tools from the Unix toolchest. | |
600 .\" gancarz tenet 5 | |
12 | 601 .PP |
15 | 602 (3) |
603 A large | |
604 .I "range of usability | |
23 | 605 ensures good adaptation, and thus good survival. |
13 | 606 It is a special distinction if a software becomes used in fields of action, |
607 the original authors did never imagine. | |
608 Software that solves problems in a general way will likely be used | |
609 for all kinds of similar problems. | |
610 Being too specific limits the range of uses. | |
611 Requirements change through time, thus use cases change or even vanish. | |
612 A good example in this point is Allman's sendmail. | |
613 Allman identifies flexibility to be one major reason for sendmail's success: | |
614 .[ | |
615 %O FIXME | |
616 %A Allman | |
617 %T sendmail | |
618 .] | |
619 .QP | |
620 Second, I limited myself to the routing function [...]. | |
621 This was a departure from the dominant thought of the time, [...]. | |
622 .QP | |
623 Third, the sendmail configuration file was flexible enough to adopt | |
624 to a rapidly changing world [...]. | |
625 .LP | |
626 Successful software adopts itself to the changing world. | |
12 | 627 .PP |
15 | 628 (4) |
629 .I "Reuse of parts | |
630 is even one step further. | |
13 | 631 A software may completely lose its field of action, |
632 but parts of which the software is build may be general and independent enough | |
633 to survive this death. | |
634 If software is build by combining small independent programs, | |
635 then there are parts readily available for reuse. | |
636 Who cares if the large program is a failure, | |
637 but parts of it become successful instead? | |
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638 |
16 | 639 .NH 2 |
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640 Summary |
0 | 641 .LP |
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642 This chapter explained the central ideas of the Unix Philosophy. |
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643 For each of the ideas, it was exposed what advantages they introduce. |
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644 The Unix Philosophy are guidelines that help to write valuable software. |
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645 From the view point of a software developer or software designer, |
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646 the Unix Philosophy provides answers to many software design problem. |
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647 .PP |
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648 The various ideas of the Unix Philosophy are very interweaved |
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649 and can hardly be applied independently. |
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650 However, the probably most important messages are: |
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651 .I "``Do one thing well!''" , |
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652 .I "``Keep it simple!''" , |
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653 and |
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654 .I "``Use software leverage!'' |
0 | 655 |
8 | 656 |
657 | |
0 | 658 .NH 1 |
19 | 659 Case study: \s-1MH\s0 |
18 | 660 .LP |
30 | 661 The previous chapter introduced and explained the Unix Philosophy |
18 | 662 from a general point of view. |
30 | 663 The driving force were the guidelines; references to |
18 | 664 existing software were given only sparsely. |
665 In this and the next chapter, concrete software will be | |
666 the driving force in the discussion. | |
667 .PP | |
23 | 668 This first case study is about the mail user agents (\s-1MUA\s0) |
669 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP | |
670 (``new mail handler''). | |
671 \s-1MUA\s0s provide functions to read, compose, and organize mail, | |
672 but (ideally) not to transfer. | |
19 | 673 In this document, the name \s-1MH\s0 will be used for both of them. |
674 A distinction will only be made if differences between | |
675 them are described. | |
18 | 676 |
0 | 677 |
678 .NH 2 | |
19 | 679 Historical background |
0 | 680 .LP |
19 | 681 Electronic mail was available in Unix very early. |
30 | 682 The first \s-1MUA\s0 on Unix was \f(CWmail\fP, |
683 which was already present in the First Edition. | |
684 .[ | |
685 %A Peter H. Salus | |
686 %T A Quarter Century of UNIX | |
687 %D 1994 | |
688 %I Addison-Wesley | |
689 %P 41 f. | |
690 .] | |
691 It was a small program that either prints the user's mailbox file | |
19 | 692 or appends text to someone elses mailbox file, |
693 depending on the command line arguments. | |
694 .[ | |
695 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf | |
696 .] | |
697 It was a program that did one job well. | |
23 | 698 This job was emailing, which was very simple then. |
19 | 699 .PP |
23 | 700 Later, emailing became more powerful, and thus more complex. |
19 | 701 The simple \f(CWmail\fP, which knew nothing of subjects, |
702 independent handling of single messages, | |
703 and long-time storage of them, was not powerful enough anymore. | |
704 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') | |
705 in 1978 to provide additional functions for emailing. | |
706 Mail was still one program, but now it was large and did | |
707 several jobs. | |
23 | 708 Its user interface is modeled after the one of \fIed\fP. |
19 | 709 It is designed for humans, but is still scriptable. |
23 | 710 \fImailx\fP is the adaptation of Berkeley Mail into System V. |
19 | 711 .[ |
712 %A Gunnar Ritter | |
713 %O http://heirloom.sourceforge.net/mailx_history.html | |
714 .] | |
30 | 715 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s |
19 | 716 followed Mail's direction. |
717 They are large, monolithic programs which include all emailing functions. | |
718 .PP | |
23 | 719 A different way was taken by the people of \s-1RAND\s0 Corporation. |
19 | 720 In the beginning, they also had used a monolitic mail system, |
30 | 721 called \s-1MS\s0 (for ``mail system''). |
19 | 722 But in 1977, Stockton Gaines and Norman Shapiro |
723 came up with a proposal of a new email system concept \(en | |
724 one that honors the Unix Philosophy. | |
725 The concept was implemented by Bruce Borden in 1978 and 1979. | |
726 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
18 | 727 .PP |
728 Since then, \s-1RAND\s0, the University of California at Irvine and | |
19 | 729 at Berkeley, and several others have contributed to the software. |
18 | 730 However, it's core concepts remained the same. |
23 | 731 In the late 90s, when development of \s-1MH\s0 slowed down, |
19 | 732 Richard Coleman started with \fInmh\fP, the new mail handler. |
733 His goal was to improve \s-1MH\s0, especially in regard of | |
23 | 734 the requirements of modern emailing. |
19 | 735 Today, nmh is developed by various people on the Internet. |
18 | 736 .[ |
737 %T RAND and the Information Evolution: A History in Essays and Vignettes | |
738 %A Willis H. Ware | |
739 %D 2008 | |
740 %I The RAND Corporation | |
741 %P 128\(en137 | |
742 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/ | |
743 .] | |
744 .[ | |
745 %T MH & xmh: Email for Users & Programmers | |
746 %A Jerry Peek | |
747 %D 1991, 1992, 1995 | |
748 %I O'Reilly & Associates, Inc. | |
749 %P Appendix B | |
750 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP | |
751 .] | |
0 | 752 |
753 .NH 2 | |
20 | 754 Contrasts to monolithic mail systems |
0 | 755 .LP |
19 | 756 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
30 | 757 Although there might acutally exist further, very little known, |
758 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well. | |
19 | 759 .PP |
30 | 760 Monolithic \s-1MUA\s0s gather all their functions in one program. |
761 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
23 | 762 Following is a list of important programs of \s-1MH\s0's toolchest |
30 | 763 and their function. |
764 It gives a feeling of how the toolchest looks like. | |
19 | 765 .IP \(bu |
766 .CW inc : | |
30 | 767 incorporate new mail (this is how mail enters the system) |
19 | 768 .IP \(bu |
769 .CW scan : | |
770 list messages in folder | |
771 .IP \(bu | |
772 .CW show : | |
773 show message | |
774 .IP \(bu | |
775 .CW next\fR/\fPprev : | |
776 show next/previous message | |
777 .IP \(bu | |
778 .CW folder : | |
779 change current folder | |
780 .IP \(bu | |
781 .CW refile : | |
782 refile message into folder | |
783 .IP \(bu | |
784 .CW rmm : | |
785 remove message | |
786 .IP \(bu | |
787 .CW comp : | |
788 compose a new message | |
789 .IP \(bu | |
790 .CW repl : | |
791 reply to a message | |
792 .IP \(bu | |
793 .CW forw : | |
794 forward a message | |
795 .IP \(bu | |
796 .CW send : | |
30 | 797 send a prepared message (this is how mail leaves the system) |
0 | 798 .LP |
19 | 799 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
800 The user does not leave the shell to run \s-1MH\s0, | |
30 | 801 but he uses the various \s-1MH\s0 programs within the shell. |
23 | 802 Using a monolithic program with a captive user interface |
803 means ``entering'' the program, using it, and ``exiting'' the program. | |
804 Using toolchests like \s-1MH\s0 means running programs, | |
805 alone or in combinition with others, even from other toolchests, | |
806 without leaving the shell. | |
30 | 807 |
808 .NH 2 | |
809 Data storage | |
810 .LP | |
34 | 811 \s-1MH\s0's mail storage is a directory tree under the user's |
812 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP), | |
813 where mail folders are directories and mail messages are text files | |
814 within them. | |
815 Each mail folder contains a file \f(CW.mh_sequences\fP which lists | |
816 the public message sequences of that folder, for instance new messages. | |
817 Mail messages are text files located in a mail folder. | |
818 The files contain the messages as they were received. | |
819 They are numbered in ascending order in each folder. | |
19 | 820 .PP |
30 | 821 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. |
822 Alternatives are \fImbox\fP and \fImaildir\fP. | |
823 In the mbox format all messages are stored within one file. | |
824 This was a good solution in the early days, when messages | |
825 were only a few lines of text and were deleted soon. | |
826 Today, when single messages often include several megabytes | |
827 of attachments, it is a bad solution. | |
828 Another disadvantage of the mbox format is that it is | |
829 more difficult to write tools that work on mail messages, | |
830 because it is always necessary to first find and extract | |
831 the relevant message in the mbox file. | |
832 With the \s-1MH\s0 mailbox format, | |
833 each message is a self-standing item, by definition. | |
834 Also, the problem of concurrent access to one mailbox is | |
835 reduced to the problem of concurrent access to one message. | |
836 Maildir is generally similar to \s-1MH\s0's format, | |
837 but modified towards guaranteed reliability. | |
838 This involves some complexity, unfortunately. | |
34 | 839 .PP |
840 Working with \s-1MH\s0's toolchest on mailboxes is much like | |
841 working with Unix' toolchest on directory trees: | |
842 \f(CWscan\fP is like \f(CWls\fP, | |
843 \f(CWshow\fP is like \f(CWcat\fP, | |
844 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP, | |
845 \f(CWrefile\fP is like \f(CWmv\fP, | |
846 and \f(CWrmm\fP is like \f(CWrm\fP. | |
847 .PP | |
848 The context of tools in Unix consists mainly the current working directory, | |
849 the user identification, and the environment variables. | |
850 \s-1MH\s0 extends this context by two more items: | |
851 .IP \(bu | |
852 The current mail folder, which is similar to the current working directory. | |
853 For mail folders, \f(CWfolder\fP provides the corresponding functionality | |
854 of \f(CWcd\fP and \f(CWpwd\fP for directories. | |
855 .IP \(bu | |
856 Sequences, which are named sets of messages in a mail folder. | |
857 The current message, relative to a mail folder, is a special sequence. | |
858 It enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
859 .LP | |
860 In contrast to Unix' context, which is chained to the shell session, | |
861 \s-1MH\s0's context is independent. | |
862 Usually there is one context for each user, but a user can have many | |
863 contexts. | |
864 Public sequences are an exception, as they belong to the mail folder. | |
865 .[ | |
866 %O mh-profile(5) and mh-sequence(5) | |
867 .] | |
20 | 868 |
0 | 869 .NH 2 |
20 | 870 Discussion of the design |
871 .LP | |
872 The following paragraphs discuss \s-1MH\s0 in regard to the tenets | |
23 | 873 of the Unix Philosophy which Gancarz identified. |
20 | 874 |
875 .PP | |
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876 .B "Small is beautiful |
20 | 877 and |
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878 .B "do one thing well |
20 | 879 are two design goals that are directly visible in \s-1MH\s0. |
880 Gancarz actually presents \s-1MH\s0 as example under the headline | |
881 ``Making UNIX Do One Thing Well'': | |
882 .QP | |
883 [\s-1MH\s0] consists of a series of programs which | |
884 when combined give the user an enormous ability | |
885 to manipulate electronic mail messages. | |
886 A complex application, it shows that not only is it | |
887 possible to build large applications from smaller | |
888 components, but also that such designs are actually preferable. | |
889 .[ | |
890 %A Mike Gancarz | |
891 %T unix-phil | |
892 %P 125 | |
893 .] | |
0 | 894 .LP |
20 | 895 The various small programs of \s-1MH\s0 were relatively easy |
23 | 896 to write, because each of them is small, limited to one function, |
897 and has clear boundaries. | |
20 | 898 For the same reasons, they are also good to maintain. |
899 Further more, the system can easily get extended. | |
900 One only needs to put a new program into the toolchest. | |
23 | 901 This was done, for instance, when \s-1MIME\s0 support was added |
20 | 902 (e.g. \f(CWmhbuild\fP). |
903 Also, different programs can exist to do the basically same job | |
904 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
905 If someone needs a mail system with some additionally | |
23 | 906 functions that are available nowhere yet, he best takes a |
20 | 907 toolchest system like \s-1MH\s0 where he can add the |
908 functionality with little work. | |
909 | |
910 .PP | |
34 | 911 .B "Store data in flat text files |
912 is followed by \s-1MH\s0. | |
913 This is not surprising, because email messages are already plain text. | |
914 \s-1MH\s0 stores the messages as it receives them, | |
915 thus any other tool that works on RFC 2822 mail messages can operate | |
916 on the messages in an \s-1MH\s0 mailbox. | |
917 All other files \s-1MH\s0 uses are plain text too. | |
918 It is therefore possible and encouraged to use the text processing | |
919 tools of Unix' toolchest to extend \s-1MH\s0's toolchest. | |
20 | 920 |
921 .PP | |
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922 .B "Avoid captive user interfaces" . |
19 | 923 \s-1MH\s0 is perfectly suited for non-interactive use. |
924 It offers all functions directly and without captive user interfaces. | |
30 | 925 If, nonetheless, users want a graphical user interface, |
20 | 926 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
19 | 927 These are graphical frontends for the \s-1MH\s0 toolchest. |
928 This means, all email-related work is still done by \s-1MH\s0 tools, | |
20 | 929 but the frontend issues the appropriate calls when the user |
30 | 930 clicks on buttons. |
20 | 931 Providing easy-to-use user interfaces in form of frontends is a good |
19 | 932 approach, because it does not limit the power of the backend itself. |
20 | 933 The frontend will anyway only be able to make a subset of the |
23 | 934 backend's power and flexibility available to the user. |
20 | 935 But if it is a separate program, |
936 then the missing parts can still be accessed at the backend directly. | |
19 | 937 If it is integrated, then this will hardly be possible. |
30 | 938 Further more, it is possible to have different frontends to the same |
939 backend. | |
19 | 940 |
941 .PP | |
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942 .B "Choose portability over efficiency |
20 | 943 and |
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944 .B "use shell scripts to increase leverage and portability" . |
20 | 945 These two tenets are indirectly, but nicely, demonstrated by |
30 | 946 Bolsky and Korn in their book about the Korn Shell. |
20 | 947 .[ |
948 %T The KornShell: command and programming language | |
949 %A Morris I. Bolsky | |
950 %A David G. Korn | |
951 %I Prentice Hall | |
952 %D 1989 | |
30 | 953 %P 254\(en290 |
20 | 954 %O \s-1ISBN\s0: 0-13-516972-0 |
955 .] | |
30 | 956 They demonstrated, in chapter 18 of the book, a basic implementation |
20 | 957 of a subset of \s-1MH\s0 in ksh scripts. |
958 Of course, this was just a demonstration, but a brilliant one. | |
959 It shows how quickly one can implement such a prototype with shell scripts, | |
960 and how readable they are. | |
961 The implementation in the scripting language may not be very fast, | |
962 but it can be fast enough though, and this is all that matters. | |
963 By having the code in an interpreted language, like the shell, | |
964 portability becomes a minor issue, if we assume the interpreter | |
965 to be widespread. | |
966 This demonstration also shows how easy it is to create single programs | |
967 of a toolchest software. | |
30 | 968 There are eight tools (two of them have multiple names) and 16 functions |
969 with supporting code. | |
970 Each tool comprises between 12 and 38 lines of ksh, | |
971 in total about 200 lines. | |
972 The functions comprise between 3 and 78 lines of ksh, | |
973 in total about 450 lines. | |
20 | 974 Such small software is easy to write, easy to understand, |
975 and thus easy to maintain. | |
23 | 976 A toolchest improves the possibility to only write some parts |
20 | 977 and though create a working result. |
978 Expanding the toolchest without global changes will likely be | |
979 possible, too. | |
980 | |
981 .PP | |
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982 .B "Use software leverage to your advantage |
20 | 983 and the lesser tenet |
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984 .B "allow the user to tailor the environment |
20 | 985 are ideally followed in the design of \s-1MH\s0. |
21 | 986 Tailoring the environment is heavily encouraged by the ability to |
30 | 987 directly define default options to programs. |
988 It is even possible to define different default options | |
21 | 989 depending on the name under which the program was called. |
990 Software leverage is heavily encouraged by the ease it is to | |
991 create shell scripts that run a specific command line, | |
30 | 992 built of several \s-1MH\s0 programs. |
21 | 993 There is few software that so much wants users to tailor their |
994 environment and to leverage the use of the software, like \s-1MH\s0. | |
995 Just to make one example: | |
23 | 996 One might prefer a different listing format for the \f(CWscan\fP |
21 | 997 program. |
30 | 998 It is possible to take one of the distributed format files |
21 | 999 or to write one yourself. |
1000 To use the format as default for \f(CWscan\fP, a single line, | |
1001 reading | |
1002 .DS | |
1003 .CW | |
1004 scan: -form FORMATFILE | |
1005 .DE | |
1006 must be added to \f(CW.mh_profile\fP. | |
1007 If one wants this different format as an additional command, | |
23 | 1008 instead of changing the default, he needs to create a link to |
1009 \f(CWscan\fP, for instance titled \f(CWscan2\fP. | |
21 | 1010 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP, |
30 | 1011 as the option should only be in effect when scan is called as |
21 | 1012 \f(CWscan2\fP. |
20 | 1013 |
1014 .PP | |
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1015 .B "Make every program a filter |
21 | 1016 is hard to find in \s-1MH\s0. |
1017 The reason therefore is that most of \s-1MH\s0's tools provide | |
1018 basic file system operations for the mailboxes. | |
30 | 1019 The reason is the same because of which |
21 | 1020 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP |
1021 aren't filters neither. | |
23 | 1022 However, they build a basis on which filters can operate. |
1023 \s-1MH\s0 does not provide many filters itself, but it is a basis | |
1024 to write filters for. | |
30 | 1025 An example would be a mail message text highlighter, |
1026 that means a program that makes use of a color terminal to display | |
1027 header lines, quotations, and signatures in distinct colors. | |
1028 The author's version of this program, for instance, | |
1029 is a 25 line awk script. | |
21 | 1030 |
1031 .PP | |
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1032 .B "Build a prototype as soon as possible |
21 | 1033 was again well followed by \s-1MH\s0. |
1034 This tenet, of course, focuses on early development, which is | |
1035 long time ago for \s-1MH\s0. | |
1036 But without following this guideline at the very beginning, | |
23 | 1037 Bruce Borden may have not convinced the management of \s-1RAND\s0 |
1038 to ever create \s-1MH\s0. | |
1039 In Bruce' own words: | |
21 | 1040 .QP |
30 | 1041 [...] but they [Stockton Gaines and Norm Shapiro] were not able |
23 | 1042 to convince anyone that such a system would be fast enough to be usable. |
21 | 1043 I proposed a very short project to prove the basic concepts, |
1044 and my management agreed. | |
1045 Looking back, I realize that I had been very lucky with my first design. | |
1046 Without nearly enough design work, | |
1047 I built a working environment and some header files | |
1048 with key structures and wrote the first few \s-1MH\s0 commands: | |
1049 inc, show/next/prev, and comp. | |
1050 [...] | |
1051 With these three, I was able to convince people that the structure was viable. | |
1052 This took about three weeks. | |
1053 .[ | |
1054 %O FIXME | |
1055 .] | |
0 | 1056 |
1057 .NH 2 | |
1058 Problems | |
1059 .LP | |
22 | 1060 \s-1MH\s0, for sure is not without problems. |
30 | 1061 There are two main problems: one is technical, the other is about human behavior. |
22 | 1062 .PP |
1063 \s-1MH\s0 is old and email today is very different to email in the time | |
1064 when \s-1MH\s0 was designed. | |
1065 \s-1MH\s0 adopted to the changes pretty well, but it is limited. | |
1066 For example in development resources. | |
1067 \s-1MIME\s0 support and support for different character encodings | |
1068 is available, but only on a moderate level. | |
1069 More active developers could quickly improve there. | |
1070 It is also limited by design, which is the larger problem. | |
1071 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend. | |
1072 These design conflicts are not easily solvable. | |
1073 Possibly, they require a redesign. | |
30 | 1074 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers, |
1075 hence \s-1MH\s0 may never work well with \s-1IMAP\s0. | |
22 | 1076 .PP |
1077 The other kind of problem is human habits. | |
1078 When in this world almost all \s-1MUA\s0s are monolithic, | |
1079 it is very difficult to convince people to use a toolbox style \s-1MUA\s0 | |
1080 like \s-1MH\s0. | |
1081 The habits are so strong, that even people who understood the concept | |
30 | 1082 and advantages of \s-1MH\s0 do not like to switch, |
1083 simply because \s-1MH\s0 is different. | |
1084 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel, | |
1085 are quite outdated and thus not very appealing compared to the modern interfaces | |
1086 which monolithic \s-1MUA\s0s offer. | |
20 | 1087 |
1088 .NH 2 | |
1089 Summary \s-1MH\s0 | |
1090 .LP | |
31 | 1091 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design |
1092 and implementation. | |
1093 It consists of a toolchest of small tools, each of them does one job well. | |
1094 The tools are orthogonal to each other, to a large extend. | |
1095 However, for historical reasons, there also exist distinct tools | |
1096 that cover the same task. | |
1097 .PP | |
1098 The toolchest approach offers great flexibility to the user. | |
1099 He can use the complete power of the Unix shell with \s-1MH\s0. | |
1100 This makes \s-1MH\s0 a very powerful mail system. | |
1101 Extending and customizing \s-1MH\s0 is easy and encouraged, too. | |
1102 .PP | |
1103 Apart from the user's perspective, \s-1MH\s0 is development-friendly. | |
1104 Its overall design follows clear rules. | |
1105 The single tools do only one job, thus they are easy to understand, | |
1106 easy to write, and good to maintain. | |
1107 They are all independent and do not interfere with the others. | |
1108 Automated testing of their function is a straight forward task. | |
1109 .PP | |
1110 It is sad, that \s-1MH\s0's differentness is its largest problem, | |
1111 as its differentness is also its largest advantage. | |
1112 Unfortunately, for most people their habits are stronger | |
1113 than the attraction of the clear design and the power, \s-1MH\s0 offers. | |
0 | 1114 |
8 | 1115 |
1116 | |
0 | 1117 .NH 1 |
1118 Case study: uzbl | |
32 | 1119 .LP |
1120 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0, | |
1121 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy. | |
1122 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''. | |
1123 It is pronounced the identical. | |
0 | 1124 |
1125 .NH 2 | |
32 | 1126 Historical background |
0 | 1127 .LP |
32 | 1128 Uzbl was started by Dieter Plaetinck in April 2009. |
1129 The idea was born in a thread in the Arch Linux forum. | |
1130 .[ | |
1131 %O http://bbs.archlinux.org/viewtopic.php?id=67463 | |
1132 .] | |
1133 After some discussion about failures of well known web browsers, | |
1134 Plaetinck (alias Dieter@be) came up with a very sketchy proposal | |
1135 of how a better web browser could look like. | |
1136 To the question of another member, if Plaetinck would write that program, | |
1137 because it would sound fantastic, Plaetinck replied: | |
1138 ``Maybe, if I find the time ;-)''. | |
1139 .PP | |
1140 Fortunately, he found the time. | |
1141 One day later, the first prototype was out. | |
1142 One week later, uzbl had an own website. | |
1143 One month after the first code showed up, | |
1144 a mailing list was installed to coordinate and discuss further development. | |
1145 A wiki was set up to store documentation and scripts that showed up on the | |
1146 mailing list and elsewhere. | |
1147 .PP | |
1148 In the, now, one year of uzbl's existance, it was heavily developed in various branches. | |
1149 Plaetinck's task became more and more to only merge the best code from the | |
1150 different branches into his main branch, and to apply patches. | |
1151 About once a month, Plaetinck released a new version. | |
1152 In September 2009, he presented several forks of uzbl. | |
1153 Uzbl, acutally, opened the field for a whole family of web browsers with similar shape. | |
1154 .PP | |
1155 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl. | |
1156 In September 2009, the uzbl web browser was on \fISlashdot\fP. | |
0 | 1157 |
1158 .NH 2 | |
32 | 1159 Contrasts to other web browsers |
0 | 1160 .LP |
32 | 1161 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest, |
1162 most web browsers are monolithic, but uzbl is a frontend to a toolchest. | |
1163 .PP | |
1164 Today, uzbl is divided into uzbl-core and uzbl-browser. | |
1165 Uzbl-core is, how its name already indicates, the core of uzbl. | |
1166 It handles commands and events to interface other programs, | |
1167 and also displays webpages by using webkit as render engine. | |
1168 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar, | |
1169 an event manager, yanking, pasting, page searching, zooming, and more stuff, | |
1170 to form a ``complete'' web browser. | |
1171 In the following text, the term ``uzbl'' usually stands for uzbl-browser, | |
1172 so uzbl-core is included. | |
1173 .PP | |
1174 Unlike most other web browsers, uzbl is mainly the mediator between the | |
1175 various tools that cover single jobs of web browsing. | |
35 | 1176 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket, |
1177 and on stdin, and it writes events to a Unix socket and to stdout. | |
1178 The graphical rendering of the webpage is done by webkit, a web content engine. | |
1179 Uzbl-core is build around this library. | |
1180 Loading a webpage in a running uzbl instance requires only: | |
32 | 1181 .DS |
1182 .CW | |
1183 echo 'uri http://example.org' >/path/to/uzbl-fifo | |
1184 .DE | |
1185 .PP | |
1186 Downloads, browsing history, bookmarks, and thelike are not provided | |
1187 by uzbl-core itself, as they are in other web browsers. | |
35 | 1188 Uzbl-browser also only provides, so called, handler scripts that wrap |
1189 external applications which provide the actual functionality. | |
32 | 1190 For instance, \fIwget\fP is used to download files and uzbl-browser |
1191 includes a script that calls wget with appropriate options in | |
1192 a prepared environment. | |
1193 .PP | |
1194 Modern web browsers are proud to have addons, plugins, and modules, instead. | |
1195 This is their effort to achieve similar goals. | |
35 | 1196 But instead of using existing, external programs, modern web browsers |
1197 include these functions, although they might be loaded at runtime. | |
0 | 1198 |
1199 .NH 2 | |
32 | 1200 Discussion of the design |
0 | 1201 .LP |
32 | 1202 This section discusses uzbl in regard of the Unix Philosophy, |
1203 as identified by Gancarz. | |
1204 | |
1205 .PP | |
35 | 1206 .B "Make each program do one thing well" . |
1207 Uzbl tries to be a web browser and nothing else. | |
36
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1208 The common definition of a web browser is, of course, highly influenced by |
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1209 existing implementations of web browsers, although they are degenerated. |
35 | 1210 Web browsers should be programs to browse the web, and nothing more. |
1211 This is the one thing they should do, as demanded by the Unix Philosophy. | |
36
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1212 .PP |
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1213 Web browsers should, for instance, not manage downloads. |
35 | 1214 This is the job download managers exist for. |
1215 Download managers do primary care about being good in downloading files. | |
1216 Modern web browsers provide download management only as a secondary feature. | |
1217 How could they perform this job better, than programs that exist only for | |
1218 this very job? | |
1219 And how could anyone want less than the best download manager available? | |
32 | 1220 .PP |
35 | 1221 A web browser's job is to let the user browse the web. |
1222 This means, navigating through websites by following links. | |
36
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1223 Rendering the \s-1HTML\s0 sources is a different job, too. |
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1224 It is covered by the webkit render engine, in uzbl's case. |
35 | 1225 Audio and video content and files like PostScript, \s-1PDF\s0, and the like, |
36
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1226 are also not the job of a web browser. |
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1227 They should be handled by external applications \(en |
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1228 ones which's job is to handle such data. |
35 | 1229 Uzbl strives to do it this way. |
36
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1230 .PP |
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1231 Remember Doug McIlroy: |
35 | 1232 .I |
1233 ``Write programs that do one thing and do it well. | |
1234 Write programs to work together.'' | |
1235 .R | |
1236 .PP | |
1237 The lesser tenet | |
1238 .B "allow the user to tailor the environment | |
1239 matches good here. | |
1240 There was the question, how anyone could want anything less than the | |
1241 best program for the job. | |
36
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1242 But as personal preferences matter much, |
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1243 it is probably more important to ask: |
35 | 1244 How could anyone want something else than his preferred program for the job? |
36
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1245 .PP |
35 | 1246 Usually users want one program for one job. |
1247 Hence, whenever the task is, for instance, downloading, | |
36
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1248 exactly one download manager should be used. |
35 | 1249 More advanced users might want to have this download manager in this |
1250 situation and that one in that situation. | |
1251 They should be able to configure it this way. | |
1252 With uzbl, one can use any download manager the user wants. | |
36
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1253 To switch to a different one, only one line in a small handler script |
35 | 1254 needs to be changed. |
36
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1255 Alternatively it would be possible to query an entry in a global file |
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1256 or an environment variable, which specifies the download manager to use, |
35 | 1257 in the handler script. |
36
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1258 .PP |
35 | 1259 As uzbl does neither have its own download manager nor depends on a |
1260 specific one, thus uzbl's browsing abilities will not be lowered by having | |
1261 a bad download manager. | |
36
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1262 Uzbl's download capabilities will just as good as the ones of the best |
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1263 download manager available on the system. |
35 | 1264 Of course, this applies to all of the other supplimentary tools, too. |
32 | 1265 |
1266 .PP | |
36
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1267 .B "Use software leverage to your advantage" . |
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1268 Shell scripts are a good choice to extend uzbl. |
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1269 Uzbl is designed to be extended by external tools. |
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1270 These external tools are usually wrapped by small handler shell scripts. |
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1271 Shell scripts are the glue in this approach. |
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1272 They make the various parts fit together. |
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1273 .PP |
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1274 As an example, the history mechanism of uzbl shall be presented. |
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1275 Uzbl is configured to spawn a script to append an entry to the history |
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1276 whenever the event of a fully loaded page occurs. |
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1277 The script to append the entry to the history not much more than: |
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1278 .DS |
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1279 .CW |
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1280 #!/bin/sh |
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1281 file=/path/to/uzbl-history |
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1282 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file |
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1283 .DE |
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1284 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title. |
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1285 For loading an entry, a key is bound to spawn a load from history script. |
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1286 The script reverses the history to have newer entries first, |
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1287 then displays \fIdmenu\fP to select an item, |
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1288 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe. |
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1289 With error checking and corner cases removed, the script looks like this: |
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1290 .DS |
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1291 .CW |
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1292 #!/bin/sh |
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1293 file=/path/to/uzbl-history |
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1294 goto=`tac $file | dmenu | cut -d' ' -f 3` |
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1295 echo "uri $goto" > $4 |
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1296 .DE |
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1297 \f(CW$4\fP expands to the path of the command input pipe of the current |
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1298 uzbl instance. |
32 | 1299 |
1300 .PP | |
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1301 .B "Avoid captive user interfaces" . |
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1302 One could say, that uzbl, to a large extend, actually \fIis\fP |
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1303 a captive user interface. |
37 | 1304 But the difference to most other web browsers is, that uzbl is only |
1305 the captive user interface frontend and the core of the backend. | |
1306 Many parts of the backend are independed of uzbl. | |
1307 Some are distributed with uzbl, for some external programs, handler scripts | |
1308 are distributed, arbitrary additional functionality can be added if desired. | |
1309 .PP | |
1310 The frontend is captive \(en that is true. | |
1311 This is okay for the task of browsing the web, as this task is only relevant | |
1312 for humans. | |
1313 Automated programs would \fIcrawl\fP the web. | |
1314 That means, they read the source directly. | |
1315 The source includes all the semantics. | |
1316 The graphical representation is just for humans to transfer the semantics | |
1317 more intuitively. | |
32 | 1318 |
1319 .PP | |
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1320 .B "Make every program a filter" . |
37 | 1321 Graphical web browsers are almost dead ends in the chain of information flow. |
1322 Thus it is difficult to see what graphical web browsers should filter. | |
1323 Graphical web browsers exist almost only for interactive use by humans. | |
1324 The only case when one might want to automate the rendering function is | |
1325 to generate images of rendered webpages. | |
1326 | |
1327 .PP | |
1328 .B "Small is beautiful" | |
1329 is not easy to apply to a web browser, primary because the rendering task | |
1330 is very complex. | |
1331 Modern web browsers will always consist of many thousand lines of code, | |
1332 unfortunately. | |
1333 Using the toolchest approach and wrappers can split the browser into | |
1334 several small parts, tough. | |
1335 .PP | |
1336 Uzbl-core consists of about 3\,500 lines of C code. | |
1337 The distribution includes another 3\,500 lines of Shell and Python code, | |
1338 which are the handler scripts and plugins like a modal interface. | |
1339 Further more, uzbl uses external tools like \fIwget\fP, \fInetcat\fP. | |
1340 Up to this point, uzbl looks pretty neat and small. | |
1341 The ugly part of uzbl is the web content renderer webkit. | |
1342 Webkit consists of roughly 400\,000 (!) lines of code. | |
35 | 1343 |
1344 .PP | |
1345 .B "Build a prototype as soon as possible" . | |
1346 Plaetinck made his code public, right from the beginning. | |
1347 Discussion and development was open to everyone interessted. | |
1348 Within this first year of uzbl's existance, a new version was released, | |
1349 more often than once a month. | |
1350 Development version can be optained very simply from the code repository. | |
1351 Different forks and branches arose, new features were tested for suitability. | |
1352 The experiences of using prototypes influenced further development. | |
1353 Actually, all development was community driven. | |
1354 Plaetinck says: | |
1355 ``Right now I hardly code anything myself for Uzbl. | |
1356 I just merge in other people's code, ponder a lot, and lead the discussions.'' | |
1357 .[ | |
36
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1358 %A FIXME |
35 | 1359 %O http://lwn.net/Articles/341245/ |
1360 .] | |
32 | 1361 |
0 | 1362 |
1363 .NH 2 | |
1364 Problems | |
1365 .LP | |
1366 broken web | |
1367 | |
37 | 1368 .PP |
1369 But all functionality should be accessable at the backend too. | |
1370 Uzbl fails here, mainly because of webkit. | |
1371 Uzbl is not clearly separated into frontend and backend, | |
1372 especially the render engine is not an separate building part, | |
1373 like, for instance, the download manager is. | |
1374 This comes from the design of webkit. | |
1375 Webkit is not a self-standing program but a library to include. | |
1376 This might be of need for a graphical application to avoid complexity, | |
1377 but webkit has a lot of features included that do not belong to the | |
1378 webpage rendering job; a browsing history is just one example. | |
1379 .PP | |
1380 Ideally, webkit would just render the source of a webpage into a | |
1381 nice formated representation. | |
1382 .PP | |
1383 be a black box | |
1384 | |
1385 | |
8 | 1386 |
32 | 1387 .NH 2 |
1388 Summary uzbl | |
1389 .LP | |
1390 | |
1391 | |
8 | 1392 |
0 | 1393 .NH 1 |
1394 Final thoughts | |
1395 | |
1396 .NH 2 | |
1397 Quick summary | |
1398 .LP | |
1399 good design | |
1400 .LP | |
1401 unix phil | |
1402 .LP | |
1403 case studies | |
1404 | |
1405 .NH 2 | |
1406 Why people should choose | |
1407 .LP | |
1408 Make the right choice! | |
1409 | |
1410 .nr PI .5i | |
1411 .rm ]< | |
1412 .de ]< | |
1413 .LP | |
1414 .de FP | |
1415 .IP \\\\$1. | |
1416 \\.. | |
1417 .rm FS FE | |
1418 .. | |
1419 .SH | |
1420 References | |
1421 .[ | |
1422 $LIST$ | |
1423 .] | |
1424 .wh -1p |