Mercurial > docs > unix-phil
annotate unix-phil.ms @ 20:578d5c84e5c0
a lot about mh (ch04)
| author | meillo@marmaro.de |
|---|---|
| date | Fri, 26 Feb 2010 00:57:37 +0100 |
| parents | d8f428cee0d1 |
| children | ca929b042039 |
| rev | line source |
|---|---|
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
1 .\".if n .pl 1000i |
| 0 | 2 .de XX |
| 3 .pl 1v | |
| 4 .. | |
| 5 .em XX | |
| 1 | 6 .\".nr PI 0 |
| 7 .\".if t .nr PD .5v | |
| 8 .\".if n .nr PD 1v | |
| 0 | 9 .nr lu 0 |
| 10 .de CW | |
| 11 .nr PQ \\n(.f | |
| 12 .if t .ft CW | |
| 17 | 13 .ie ^\\$1^^ .if n .ul 999 |
| 0 | 14 .el .if n .ul 1 |
| 17 | 15 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2 |
| 0 | 16 .if n .if \\n(.$=1 \&\\$1 |
| 17 .if n .if \\n(.$>1 \&\\$1\c | |
| 18 .if n .if \\n(.$>1 \&\\$2 | |
| 19 .. | |
| 20 .ds [. \ [ | |
| 21 .ds .] ] | |
| 1 | 22 .\"---------------------------------------- |
| 0 | 23 .TL |
| 6 | 24 Why the Unix Philosophy still matters |
| 0 | 25 .AU |
| 26 markus schnalke <meillo@marmaro.de> | |
| 27 .AB | |
| 1 | 28 .ti \n(.iu |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
29 This paper discusses the importance of the Unix Philosophy in software design. |
| 0 | 30 Today, few software designers are aware of these concepts, |
| 3 | 31 and thus most modern software is limited and does not make use of software leverage. |
| 0 | 32 Knowing and following the tenets of the Unix Philosophy makes software more valuable. |
| 33 .AE | |
| 34 | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
35 .\".if t .2C |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
36 |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
37 .FS |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
38 .ps -1 |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
39 This paper was prepared for the seminar ``Software Analysis'' at University Ulm. |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
40 Mentor was professor Schweiggert. 2010-02-05 |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
41 .br |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
42 You may get this document from my website |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
43 .CW \s-1http://marmaro.de/docs |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
44 .FE |
|
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
45 |
| 0 | 46 .NH 1 |
| 47 Introduction | |
| 48 .LP | |
| 49 Building a software is a process from an idea of the purpose of the software | |
| 3 | 50 to its release. |
| 0 | 51 No matter \fIhow\fP the process is run, two things are common: |
| 52 the initial idea and the release. | |
| 9 | 53 The process in between can be of any shape. |
| 54 The the maintenance work after the release is ignored for the moment. | |
| 1 | 55 .PP |
| 0 | 56 The process of building splits mainly in two parts: |
| 57 the planning of what and how to build, and implementing the plan by writing code. | |
| 3 | 58 This paper focuses on the planning part \(en the designing of the software. |
| 59 .PP | |
| 60 Software design is the plan of how the internals and externals of the software should look like, | |
| 61 based on the requirements. | |
| 9 | 62 This paper discusses the recommendations of the Unix Philosophy about software design. |
| 3 | 63 .PP |
| 64 The here discussed ideas can get applied by any development process. | |
| 9 | 65 The Unix Philosophy does recommend how the software development process should look like, |
| 3 | 66 but this shall not be of matter here. |
| 0 | 67 Similar, the question of how to write the code is out of focus. |
| 1 | 68 .PP |
| 3 | 69 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet. |
| 1 | 70 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed. |
| 3 | 71 It is no limited set of rules, but what people see to be common to typical Unix software. |
| 1 | 72 Several people stated their view on the Unix Philosophy. |
| 73 Best known are: | |
| 74 .IP \(bu | |
| 75 Doug McIlroy's summary: ``Write programs that do one thing and do it well.'' | |
| 76 .[ | |
| 77 %A M. D. McIlroy | |
| 78 %A E. N. Pinson | |
| 79 %A B. A. Taque | |
| 80 %T UNIX Time-Sharing System Forward | |
| 81 %J The Bell System Technical Journal | |
| 82 %D 1978 | |
| 83 %V 57 | |
| 84 %N 6 | |
| 85 %P 1902 | |
| 86 .] | |
| 87 .IP \(bu | |
| 88 Mike Gancarz' book ``The UNIX Philosophy''. | |
| 89 .[ | |
| 90 %A Mike Gancarz | |
| 91 %T The UNIX Philosophy | |
| 92 %D 1995 | |
| 93 %I Digital Press | |
| 94 .] | |
| 95 .IP \(bu | |
| 96 Eric S. Raymond's book ``The Art of UNIX Programming''. | |
| 97 .[ | |
| 98 %A Eric S. Raymond | |
| 99 %T The Art of UNIX Programming | |
| 100 %D 2003 | |
| 101 %I Addison-Wesley | |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
102 %O .CW \s-1http://www.faqs.org/docs/artu/ |
| 1 | 103 .] |
| 0 | 104 .LP |
| 1 | 105 These different views on the Unix Philosophy have much in common. |
| 3 | 106 Especially, the main concepts are similar for all of them. |
| 1 | 107 But there are also points on which they differ. |
| 108 This only underlines what the Unix Philosophy is: | |
| 109 A retrospective view on the main concepts of Unix software; | |
| 9 | 110 especially those that were successful and unique to Unix. |
| 6 | 111 .\" really? |
| 1 | 112 .PP |
| 113 Before we will have a look at concrete concepts, | |
| 114 we discuss why software design is important | |
| 115 and what problems bad design introduces. | |
| 0 | 116 |
| 117 | |
| 118 .NH 1 | |
| 6 | 119 Importance of software design in general |
| 0 | 120 .LP |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
121 Why should we design software at all? |
| 6 | 122 It is general knowledge, that even a bad plan is better than no plan. |
| 123 Ignoring software design is programming without a plan. | |
| 124 This will lead pretty sure to horrible results. | |
| 125 .PP | |
| 126 The design of a software is its internal and external shape. | |
| 127 The design talked about here has nothing to do with visual appearance. | |
| 128 If we see a program as a car, then its color is of no matter. | |
| 129 Its design would be the car's size, its shape, the number and position of doors, | |
| 130 the ratio of passenger and cargo transport, and so forth. | |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
131 .PP |
| 6 | 132 A software's design is about quality properties. |
| 133 Each of the cars may be able to drive from A to B, | |
| 134 but it depends on its properties whether it is a good car for passenger transport or not. | |
| 135 It also depends on its properties if it is a good choice for a rough mountain area. | |
| 136 .PP | |
| 137 Requirements to a software are twofold: functional and non-functional. | |
| 138 Functional requirements are easier to define and to verify. | |
| 139 They are directly the software's functions. | |
| 140 Functional requirements are the reason why software gets written. | |
| 141 Someone has a problem and needs a tool to solve it. | |
| 142 Being able to solve the problem is the main functional requirement. | |
| 143 It is the driving force behind all programming effort. | |
| 144 .PP | |
| 145 On the other hand, there are also non-functional requirements. | |
| 146 They are called \fIquality\fP requirements, too. | |
| 147 The quality of a software is about properties that are not directly related to | |
| 148 the software's basic functions. | |
| 149 Quality aspects are about the properties that are overlooked at first sight. | |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
150 .PP |
| 6 | 151 Quality is of few matter when the software gets initially built, |
| 9 | 152 but it will be of matter in usage and maintenance of the software. |
| 6 | 153 A short-sighted might see in developing a software mainly building something up. |
| 154 Reality shows, that building the software the first time is only a small amount | |
| 155 of the overall work. | |
| 9 | 156 Bug fixing, extending, rebuilding of parts \(en short: maintenance work \(en |
| 6 | 157 does soon take over the major part of the time spent on a software. |
| 158 Not to forget the usage of the software. | |
| 159 These processes are highly influenced by the software's quality. | |
| 160 Thus, quality should never be neglected. | |
| 161 The problem is that you hardly ``stumble over'' bad quality during the first build, | |
| 162 but this is the time when you should care about good quality most. | |
| 163 .PP | |
| 164 Software design is not about the basic function of a software; | |
| 165 this requirement will get satisfied anyway, as it is the main driving force behind the development. | |
| 166 Software design is about quality aspects of the software. | |
| 167 Good design will lead to good quality, bad design to bad quality. | |
| 168 The primary functions of the software will be affected modestly by bad quality, | |
| 169 but good quality can provide a lot of additional gain from the software, | |
| 170 even at places where one never expected it. | |
|
2
fbd7baf6a61f
added content about sw design; some formating
meillo@marmaro.de
parents:
1
diff
changeset
|
171 .PP |
| 6 | 172 The ISO/IEC 9126-1 standard, part 1, |
| 173 .[ | |
| 9 | 174 %I International Organization for Standardization |
| 6 | 175 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1 |
| 176 %C Geneve | |
| 177 %D 2001 | |
| 178 .] | |
| 179 defines the quality model as consisting out of: | |
| 180 .IP \(bu | |
| 181 .I Functionality | |
| 182 (suitability, accuracy, inter\%operability, security) | |
| 183 .IP \(bu | |
| 184 .I Reliability | |
| 185 (maturity, fault tolerance, recoverability) | |
| 186 .IP \(bu | |
| 187 .I Usability | |
| 188 (understandability, learnability, operability, attractiveness) | |
| 189 .IP \(bu | |
| 190 .I Efficiency | |
| 9 | 191 (time behavior, resource utilization) |
| 6 | 192 .IP \(bu |
| 193 .I Maintainability | |
| 194 (analysability, changeability, stability, testability) | |
| 195 .IP \(bu | |
| 196 .I Portability | |
| 197 (adaptability, installability, co-existence, replaceability) | |
| 198 .LP | |
| 199 These goals are parts of a software's design. | |
| 200 Good design can give these properties to a software, | |
| 201 bad designed software will miss them. | |
| 7 | 202 .PP |
| 203 One further goal of software design is consistency. | |
| 204 Consistency eases understanding, working on, and using things. | |
| 205 Consistent internals and consistent interfaces to the outside can be provided by good design. | |
| 206 .PP | |
| 207 We should design software because good design avoids many problems during a software's lifetime. | |
| 208 And we should design software because good design can offer much gain, | |
| 209 that can be unrelated to the software main intend. | |
| 210 Indeed, we should spend much effort into good design to make the software more valuable. | |
| 211 The Unix Philosophy shows how to design software well. | |
| 212 It offers guidelines to achieve good quality and high gain for the effort spent. | |
| 0 | 213 |
| 214 | |
| 215 .NH 1 | |
| 216 The Unix Philosophy | |
| 4 | 217 .LP |
| 218 The origins of the Unix Philosophy were already introduced. | |
| 8 | 219 This chapter explains the philosophy, oriented on Gancarz, |
| 220 and shows concrete examples of its application. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
221 |
| 16 | 222 .NH 2 |
|
14
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
223 Pipes |
| 0 | 224 .LP |
| 4 | 225 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 226 Knowledge of using the Unix shell is assumed. | |
| 227 .PP | |
| 228 Counting the number of files in the current directory: | |
| 9 | 229 .DS I 2n |
| 4 | 230 .CW |
| 9 | 231 .ps -1 |
| 4 | 232 ls | wc -l |
| 233 .DE | |
| 234 The | |
| 235 .CW ls | |
| 236 command lists all files in the current directory, one per line, | |
| 237 and | |
| 238 .CW "wc -l | |
| 8 | 239 counts the number of lines. |
| 4 | 240 .PP |
| 8 | 241 Counting the number of files that do not contain ``foo'' in their name: |
| 9 | 242 .DS I 2n |
| 4 | 243 .CW |
| 9 | 244 .ps -1 |
| 4 | 245 ls | grep -v foo | wc -l |
| 246 .DE | |
| 247 Here, the list of files is filtered by | |
| 248 .CW grep | |
| 249 to remove all that contain ``foo''. | |
| 250 The rest is the same as in the previous example. | |
| 251 .PP | |
| 252 Finding the five largest entries in the current directory. | |
| 9 | 253 .DS I 2n |
| 4 | 254 .CW |
| 9 | 255 .ps -1 |
| 4 | 256 du -s * | sort -nr | sed 5q |
| 257 .DE | |
| 258 .CW "du -s * | |
| 259 returns the recursively summed sizes of all files | |
| 8 | 260 \(en no matter if they are regular files or directories. |
| 4 | 261 .CW "sort -nr |
| 262 sorts the list numerically in reverse order. | |
| 263 Finally, | |
| 264 .CW "sed 5q | |
| 265 quits after it has printed the fifth line. | |
| 266 .PP | |
| 267 The presented command lines are examples of what Unix people would use | |
| 268 to get the desired output. | |
| 269 There are also other ways to get the same output. | |
| 270 It's a user's decision which way to go. | |
|
14
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
271 .PP |
| 8 | 272 The examples show that many tasks on a Unix system |
| 4 | 273 are accomplished by combining several small programs. |
| 274 The connection between the single programs is denoted by the pipe operator `|'. | |
| 275 .PP | |
| 276 Pipes, and their extensive and easy use, are one of the great | |
| 277 achievements of the Unix system. | |
| 278 Pipes between programs have been possible in earlier operating systems, | |
| 279 but it has never been a so central part of the concept. | |
| 280 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 281 Unix system, | |
| 282 ``it was this concept and notation for linking several programs together | |
| 283 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 284 .[ | |
| 285 %T Unix: An Oral History | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
286 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
| 4 | 287 .] |
| 288 .PP | |
| 289 Being able to specify pipelines in an easy way is, | |
| 290 however, not enough by itself. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
291 It is only one half. |
| 4 | 292 The other is the design of the programs that are used in the pipeline. |
| 8 | 293 They have to interfaces that allows them to be used in such a way. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
294 |
| 16 | 295 .NH 2 |
|
14
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
296 Interface design |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
297 .LP |
| 11 | 298 Unix is, first of all, simple \(en Everything is a file. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
299 Files are sequences of bytes, without any special structure. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
300 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin) |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
301 and write a stream of bytes to ``standard output'' (stdout). |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
302 .PP |
| 8 | 303 If the files \fIare\fP sequences of bytes, |
| 304 and the programs \fIare\fP filters on byte streams, | |
| 11 | 305 then there is exactly one standardized data interface. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
306 Thus it is possible to combine them in any desired way. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
307 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
308 Even a handful of small programs will yield a large set of combinations, |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
309 and thus a large set of different functions. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
310 This is leverage! |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
311 If the programs are orthogonal to each other \(en the best case \(en |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
312 then the set of different functions is greatest. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
313 .PP |
| 11 | 314 Programs might also have a separate control interface, |
| 315 besides their data interface. | |
| 316 The control interface is often called ``user interface'', | |
| 317 because it is usually designed to be used by humans. | |
| 318 The Unix Philosophy discourages to assume the user to be human. | |
| 319 Interactive use of software is slow use of software, | |
| 320 because the program waits for user input most of the time. | |
| 321 Interactive software requires the user to be in front of the computer | |
| 322 all the time. | |
| 323 Interactive software occupy the user's attention while they are running. | |
| 324 .PP | |
| 325 Now we come back to the idea of using several small programs, combined, | |
| 326 to have a more specific function. | |
| 327 If these single tools would all be interactive, | |
| 328 how would the user control them? | |
| 329 It is not only a problem to control several programs at once if they run at the same time, | |
| 330 it also very inefficient to have to control each of the single programs | |
| 331 that are intended to work as one large program. | |
| 332 Hence, the Unix Philosophy discourages programs to demand interactive use. | |
| 333 The behavior of programs should be defined at invocation. | |
| 334 This is done by specifying arguments (``command line switches'') to the program call. | |
| 335 Gancarz discusses this topic as ``avoid captive user interfaces''. | |
| 336 .[ | |
| 337 %A Mike Gancarz | |
| 338 %T The UNIX Philosophy | |
| 339 %I Digital Press | |
| 340 %D 1995 | |
| 341 %P 88 ff. | |
| 342 .] | |
| 343 .PP | |
| 344 Non-interactive use is, during development, also an advantage for testing. | |
| 345 Testing of interactive programs is much more complicated, | |
| 346 than testing of non-interactive programs. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
347 |
| 16 | 348 .NH 2 |
| 8 | 349 The toolchest approach |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
350 .LP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
351 A toolchest is a set of tools. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
352 Instead of having one big tool for all tasks, one has many small tools, |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
353 each for one task. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
354 Difficult tasks are solved by combining several of the small, simple tools. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
355 .PP |
| 11 | 356 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 357 that are filters on byte streams. | |
| 358 They are, to a large extend, unrelated in their function. | |
| 359 Hence, the Unix toolchest provides a large set of functions | |
| 360 that can be accessed by combining the programs in the desired way. | |
| 361 .PP | |
| 362 There are also advantages for developing small toolchest programs. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
363 It is easier and less error-prone to write small programs. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
364 It is also easier and less error-prone to write a large set of small programs, |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
365 than to write one large program with all the functionality included. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
366 If the small programs are combinable, then they offer even a larger set |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
367 of functions than the single large program. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
368 Hence, one gets two advantages out of writing small, combinable programs. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
369 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
370 There are two drawbacks of the toolchest approach. |
| 8 | 371 First, one simple, standardized, unidirectional interface has to be sufficient. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
372 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 373 then a different approach might be of need. |
| 13 | 374 But it is also possible, that he just can not imagine a design where |
| 8 | 375 a stream of bytes is sufficient. |
| 376 By becoming more familiar with the ``Unix style of thinking'', | |
| 377 developers will more often and easier find simple designs where | |
| 378 a stream of bytes is a sufficient interface. | |
| 379 .PP | |
| 380 The second drawback of a toolchest affects the users. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
381 A toolchest is often more difficult to use for novices. |
| 9 | 382 It is necessary to become familiar with each of the tools, |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
383 to be able to use the right one in a given situation. |
| 9 | 384 Additionally, one needs to combine the tools in a senseful way on its own. |
| 385 This is like a sharp knife \(en it is a powerful tool in the hand of a master, | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
386 but of no good value in the hand of an unskilled. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
387 .PP |
| 8 | 388 However, learning single, small tool of the toolchest is easier than |
| 389 learning a complex tool. | |
| 390 The user will have a basic understanding of a yet unknown tool, | |
| 391 if the several tools of the toolchest have a common style. | |
| 392 He will be able to transfer knowledge over one tool to another. | |
| 393 .PP | |
| 394 Moreover, the second drawback can be removed easily by adding wrappers | |
| 395 around the single tools. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
396 Novice users do not need to learn several tools if a professional wraps |
| 8 | 397 the single commands into a more high-level script. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
398 Note that the wrapper script still calls the small tools; |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
399 the wrapper script is just like a skin around. |
| 8 | 400 No complexity is added this way, |
| 401 but new programs can get created out of existing one with very low effort. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
402 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
403 A wrapper script for finding the five largest entries in the current directory |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
404 could look like this: |
| 9 | 405 .DS I 2n |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
406 .CW |
| 9 | 407 .ps -1 |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
408 #!/bin/sh |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
409 du -s * | sort -nr | sed 5q |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
410 .DE |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
411 The script itself is just a text file that calls the command line |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
412 a professional user would type in directly. |
| 8 | 413 Making the program flexible on the number of entries it prints, |
| 414 is easily possible: | |
| 9 | 415 .DS I 2n |
| 8 | 416 .CW |
| 9 | 417 .ps -1 |
| 8 | 418 #!/bin/sh |
| 419 num=5 | |
| 420 [ $# -eq 1 ] && num="$1" | |
| 421 du -sh * | sort -nr | sed "${num}q" | |
| 422 .DE | |
| 423 This script acts like the one before, when called without an argument. | |
| 424 But one can also specify a numerical argument to define the number of lines to print. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
425 |
| 16 | 426 .NH 2 |
| 8 | 427 A powerful shell |
| 428 .LP | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
429 It was already said, that the Unix shell provides the possibility to |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
430 combine small programs into large ones easily. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
431 A powerful shell is a great feature in other ways, too. |
| 8 | 432 .PP |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
433 For instance by including a scripting language. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
434 The control statements are build into the shell. |
| 8 | 435 The functions, however, are the normal programs, everyone can use on the system. |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
436 Thus, the programs are known, so learning to program in the shell is easy. |
| 8 | 437 Using normal programs as functions in the shell programming language |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
438 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 439 .PP |
| 440 The Unix shell encourages to write small scripts out of other programs, | |
| 441 because it is so easy to do. | |
| 442 This is a great step towards automation. | |
| 443 It is wonderful if the effort to automate a task equals the effort | |
| 444 it takes to do it the second time by hand. | |
| 445 If it is so, then the user will be happy to automate everything he does more than once. | |
| 446 .PP | |
| 447 Small programs that do one job well, standardized interfaces between them, | |
| 448 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 449 this will inevitably produce software leverage. | |
| 450 Getting multiple times the benefit of an investment is a great offer. | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
451 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
452 The shell also encourages rapid prototyping. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
453 Many well known programs started as quickly hacked shell scripts, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
454 and turned into ``real'' programs, written in C, later. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
455 Building a prototype first is a way to avoid the biggest problems |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
456 in application development. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
457 Fred Brooks writes in ``No Silver Bullet'': |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
458 .[ |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
459 %A Frederick P. Brooks, Jr. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
460 %T No Silver Bullet: Essence and Accidents of Software Engineering |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
461 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
462 %E H.-J. Kugler |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
463 %D 1986 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
464 %P 1069\(en1076 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
465 %I Elsevier Science B.V. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
466 %C Amsterdam, The Netherlands |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
467 .] |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
468 .QP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
469 The hardest single part of building a software system is deciding precisely what to build. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
470 No other part of the conceptual work is so difficult as establishing the detailed |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
471 technical requirements, [...]. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
472 No other part of the work so cripples the resulting system if done wrong. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
473 No other part is more difficult to rectify later. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
474 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
475 Writing a prototype is a great method to become familiar with the requirements |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
476 and to actually run into real problems. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
477 Today, prototyping is often seen as a first step in building a software. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
478 This is, of course, good. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
479 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping: |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
480 After having built the prototype, one might notice, that the prototype is already |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
481 \fIgood enough\fP. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
482 Hence, no reimplementation, in a more sophisticated programming language, might be of need, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
483 for the moment. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
484 Maybe later, it might be neccessary to rewrite the software, but not now. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
485 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
486 By delaying further work, one keeps the flexibility to react easily on |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
487 changing requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
488 Software parts that are not written will not miss the requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
489 |
| 16 | 490 .NH 2 |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
491 Worse is better |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
492 .LP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
493 The Unix Philosophy aims for the 80% solution; |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
494 others call it the ``Worse is better'' approach. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
495 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
496 First, practical experience shows, that it is almost never possible to define the |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
497 requirements completely and correctly the first time. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
498 Hence one should not try to; it will fail anyway. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
499 Second, practical experience shows, that requirements change during time. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
500 Hence it is best to delay requirement-based design decisions as long as possible. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
501 Also, the software should be small and flexible as long as possible |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
502 to react on changing requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
503 Shell scripts, for example, are more easily adjusted as C programs. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
504 Third, practical experience shows, that maintenance is hard work. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
505 Hence, one should keep the amount of software as small as possible; |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
506 it should just fulfill the \fIcurrent\fP requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
507 Software parts that will be written later, do not need maintenance now. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
508 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
509 Starting with a prototype in a scripting language has several advantages: |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
510 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
511 As the initial effort is low, one will likely start right away. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
512 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
513 As working parts are available soon, the real requirements can get identified soon. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
514 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
515 When a software is usable, it gets used, and thus tested. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
516 Hence problems will be found at early stages of the development. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
517 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
518 The prototype might be enough for the moment, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
519 thus further work on the software can be delayed to a time |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
520 when one knows better about the requirements and problems, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
521 than now. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
522 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
523 Implementing now only the parts that are actually needed now, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
524 requires fewer maintenance work. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
525 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
526 If the global situation changes so that the software is not needed anymore, |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
527 then less effort was spent into the project, than it would have be |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
528 when a different approach had been used. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
529 |
| 16 | 530 .NH 2 |
| 11 | 531 Upgrowth and survival of software |
| 532 .LP | |
| 12 | 533 So far it was talked about \fIwriting\fP or \fIbuilding\fP software. |
| 13 | 534 Although these are just verbs, they do imply a specific view on the work process |
| 535 they describe. | |
| 12 | 536 The better verb, however, is to \fIgrow\fP. |
| 537 .PP | |
| 538 Creating software in the sense of the Unix Philosophy is an incremental process. | |
| 539 It starts with a first prototype, which evolves as requirements change. | |
| 540 A quickly hacked shell script might become a large, sophisticated, | |
| 13 | 541 compiled program this way. |
| 542 Its lifetime begins with the initial prototype and ends when the software is not used anymore. | |
| 543 While being alive it will get extended, rearranged, rebuilt (from scratch). | |
| 12 | 544 Growing software matches the view that ``software is never finished. It is only released.'' |
| 545 .[ | |
| 13 | 546 %O FIXME |
| 547 %A Mike Gancarz | |
| 548 %T The UNIX Philosophy | |
| 549 %P 26 | |
| 12 | 550 .] |
| 551 .PP | |
| 13 | 552 Software can be seen as being controlled by evolutionary processes. |
| 553 Successful software is software that is used by many for a long time. | |
| 12 | 554 This implies that the software is needed, useful, and better than alternatives. |
| 555 Darwin talks about: ``The survival of the fittest.'' | |
| 556 .[ | |
| 13 | 557 %O FIXME |
| 558 %A Charles Darwin | |
| 12 | 559 .] |
| 560 Transferred to software: The most successful software, is the fittest, | |
| 561 is the one that survives. | |
| 13 | 562 (This may be at the level of one creature, or at the level of one species.) |
| 563 The fitness of software is affected mainly by four properties: | |
| 15 | 564 portability of code, portability of data, range of usability, and reusability of parts. |
| 565 .\" .IP \(bu | |
| 566 .\" portability of code | |
| 567 .\" .IP \(bu | |
| 568 .\" portability of data | |
| 569 .\" .IP \(bu | |
| 570 .\" range of usability | |
| 571 .\" .IP \(bu | |
| 572 .\" reuseability of parts | |
| 13 | 573 .PP |
| 15 | 574 (1) |
| 575 .I "Portability of code | |
| 576 means, using high-level programming languages, | |
| 13 | 577 sticking to the standard, |
| 578 and avoiding optimizations that introduce dependencies on specific hardware. | |
| 579 Hardware has a much lower lifetime than software. | |
| 580 By chaining software to a specific hardware, | |
| 581 the software's lifetime gets shortened to that of this hardware. | |
| 582 In contrast, software should be easy to port \(en | |
| 583 adaption is the key to success. | |
| 584 .\" cf. practice of prog: ch08 | |
| 585 .PP | |
| 15 | 586 (2) |
| 587 .I "Portability of data | |
| 588 is best achieved by avoiding binary representations | |
| 13 | 589 to store data, because binary representations differ from machine to machine. |
| 590 Textual represenation is favored. | |
| 591 Historically, ASCII was the charset of choice. | |
| 592 In the future, UTF-8 might be the better choice, however. | |
| 593 Important is that it is a plain text representation in a | |
| 594 very common charset encoding. | |
| 595 Apart from being able to transfer data between machines, | |
| 596 readable data has the great advantage, that humans are able | |
| 597 to directly edit it with text editors and other tools from the Unix toolchest. | |
| 598 .\" gancarz tenet 5 | |
| 12 | 599 .PP |
| 15 | 600 (3) |
| 601 A large | |
| 602 .I "range of usability | |
| 603 ensures good adaption, and thus good survival. | |
| 13 | 604 It is a special distinction if a software becomes used in fields of action, |
| 605 the original authors did never imagine. | |
| 606 Software that solves problems in a general way will likely be used | |
| 607 for all kinds of similar problems. | |
| 608 Being too specific limits the range of uses. | |
| 609 Requirements change through time, thus use cases change or even vanish. | |
| 610 A good example in this point is Allman's sendmail. | |
| 611 Allman identifies flexibility to be one major reason for sendmail's success: | |
| 612 .[ | |
| 613 %O FIXME | |
| 614 %A Allman | |
| 615 %T sendmail | |
| 616 .] | |
| 617 .QP | |
| 618 Second, I limited myself to the routing function [...]. | |
| 619 This was a departure from the dominant thought of the time, [...]. | |
| 620 .QP | |
| 621 Third, the sendmail configuration file was flexible enough to adopt | |
| 622 to a rapidly changing world [...]. | |
| 623 .LP | |
| 624 Successful software adopts itself to the changing world. | |
| 12 | 625 .PP |
| 15 | 626 (4) |
| 627 .I "Reuse of parts | |
| 628 is even one step further. | |
| 13 | 629 A software may completely lose its field of action, |
| 630 but parts of which the software is build may be general and independent enough | |
| 631 to survive this death. | |
| 632 If software is build by combining small independent programs, | |
| 633 then there are parts readily available for reuse. | |
| 634 Who cares if the large program is a failure, | |
| 635 but parts of it become successful instead? | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
636 |
| 16 | 637 .NH 2 |
|
14
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
638 Summary |
| 0 | 639 .LP |
|
14
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
640 This chapter explained the central ideas of the Unix Philosophy. |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
641 For each of the ideas, it was exposed what advantages they introduce. |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
642 The Unix Philosophy are guidelines that help to write valuable software. |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
643 From the view point of a software developer or software designer, |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
644 the Unix Philosophy provides answers to many software design problem. |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
645 .PP |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
646 The various ideas of the Unix Philosophy are very interweaved |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
647 and can hardly be applied independently. |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
648 However, the probably most important messages are: |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
649 .I "``Do one thing well!''" , |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
650 .I "``Keep it simple!''" , |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
651 and |
|
59305c854751
rearrangements of headlines; summary (ch03)
meillo@marmaro.de
parents:
13
diff
changeset
|
652 .I "``Use software leverage!'' |
| 0 | 653 |
| 8 | 654 |
| 655 | |
| 0 | 656 .NH 1 |
| 19 | 657 Case study: \s-1MH\s0 |
| 18 | 658 .LP |
| 659 The last chapter introduced and explained the Unix Philosophy | |
| 660 from a general point of view. | |
| 661 The driving force were the guidelines and references to | |
| 662 existing software were given only sparsely. | |
| 663 In this and the next chapter, concrete software will be | |
| 664 the driving force in the discussion. | |
| 665 .PP | |
| 666 This first case study is about the mail user agents \s-1MH\s0 | |
| 667 (``mail handler'') and its descendent \fInmh\fP (``new mail handler''). | |
| 19 | 668 In this document, the name \s-1MH\s0 will be used for both of them. |
| 669 A distinction will only be made if differences between | |
| 670 them are described. | |
| 18 | 671 |
| 0 | 672 |
| 673 .NH 2 | |
| 19 | 674 Historical background |
| 0 | 675 .LP |
| 19 | 676 Electronic mail was available in Unix very early. |
| 677 It is out of matter that in the beginning mail was only | |
| 678 transferred within one machine. | |
| 679 This chapter is about a mail user agent (\s-1MUA\s0), | |
| 680 which provides functions to read, compose, and organize mail, | |
| 681 but (ideally) not to transfer. | |
| 682 .PP | |
| 683 The first \s-1MUA\s0 on Unix was \f(CWmail\fP. | |
| 684 It was a small program that either prints the own mailbox file | |
| 685 or appends text to someone elses mailbox file, | |
| 686 depending on the command line arguments. | |
| 687 .[ | |
| 688 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf | |
| 689 .] | |
| 690 It was a program that did one job well. | |
| 691 This job was emailing, which then was very simple. | |
| 692 .PP | |
| 693 Later, emailing became more powerfull, and thus more complex. | |
| 694 The simple \f(CWmail\fP, which knew nothing of subjects, | |
| 695 independent handling of single messages, | |
| 696 and long-time storage of them, was not powerful enough anymore. | |
| 697 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M') | |
| 698 in 1978 to provide additional functions for emailing. | |
| 699 Mail was still one program, but now it was large and did | |
| 700 several jobs. | |
| 701 Its user interface is modeled after the one of ed. | |
| 702 It is designed for humans, but is still scriptable. | |
| 703 \fImailx\fP is the adaption of Berkeley Mail into System V. | |
| 704 .[ | |
| 705 %A Gunnar Ritter | |
| 706 %O http://heirloom.sourceforge.net/mailx_history.html | |
| 707 .] | |
| 708 Elm, pine, mutt, and today a whole bunch of graphical \s-1MUA\s0s | |
| 709 followed Mail's direction. | |
| 710 They are large, monolithic programs which include all emailing functions. | |
| 711 .PP | |
| 712 A different way took the people of \s-1RAND\s0 Corporation. | |
| 713 In the beginning, they also had used a monolitic mail system, | |
| 714 simply called \s-1MS\s0 for ``mail system''. | |
| 715 But in 1977, Stockton Gaines and Norman Shapiro | |
| 716 came up with a proposal of a new email system concept \(en | |
| 717 one that honors the Unix Philosophy. | |
| 718 The concept was implemented by Bruce Borden in 1978 and 1979. | |
| 719 This was the birth of \s-1MH\s0 \(en the ``mail handler''. | |
| 18 | 720 .PP |
| 721 Since then, \s-1RAND\s0, the University of California at Irvine and | |
| 19 | 722 at Berkeley, and several others have contributed to the software. |
| 18 | 723 However, it's core concepts remained the same. |
| 19 | 724 In the 90s, when development of \s-1MH\s0 slowed down, |
| 725 Richard Coleman started with \fInmh\fP, the new mail handler. | |
| 726 This was in 1997. | |
| 727 His goal was to improve \s-1MH\s0, especially in regard of | |
| 728 the requirements of modern email. | |
| 729 Today, nmh is developed by various people on the Internet. | |
| 18 | 730 .[ |
| 731 %T RAND and the Information Evolution: A History in Essays and Vignettes | |
| 732 %A Willis H. Ware | |
| 733 %D 2008 | |
| 734 %I The RAND Corporation | |
| 735 %P 128\(en137 | |
| 736 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/ | |
| 737 .] | |
| 738 .[ | |
| 739 %T MH & xmh: Email for Users & Programmers | |
| 740 %A Jerry Peek | |
| 741 %D 1991, 1992, 1995 | |
| 742 %I O'Reilly & Associates, Inc. | |
| 743 %P Appendix B | |
| 744 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP | |
| 745 .] | |
| 0 | 746 |
| 747 .NH 2 | |
| 20 | 748 Contrasts to monolithic mail systems |
| 0 | 749 .LP |
| 19 | 750 All \s-1MUA\s0s are monolithic, except \s-1MH\s0. |
| 20 | 751 This might not be true, |
| 752 but it reflects the situation pretty well. | |
| 19 | 753 .PP |
| 754 While monolithic \s-1MUA\s0s gather all function in one program, | |
| 755 \s-1MH\s0 is a toolchest of many small tools \(en one for each job. | |
| 756 Following is a list of important programs of \s-1MH\s0's toolchest: | |
| 757 .IP \(bu | |
| 758 .CW inc : | |
| 759 incorporate new mail | |
| 760 .IP \(bu | |
| 761 .CW scan : | |
| 762 list messages in folder | |
| 763 .IP \(bu | |
| 764 .CW show : | |
| 765 show message | |
| 766 .IP \(bu | |
| 767 .CW next\fR/\fPprev : | |
| 768 show next/previous message | |
| 769 .IP \(bu | |
| 770 .CW folder : | |
| 771 change current folder | |
| 772 .IP \(bu | |
| 773 .CW refile : | |
| 774 refile message into folder | |
| 775 .IP \(bu | |
| 776 .CW rmm : | |
| 777 remove message | |
| 778 .IP \(bu | |
| 779 .CW comp : | |
| 780 compose a new message | |
| 781 .IP \(bu | |
| 782 .CW repl : | |
| 783 reply to a message | |
| 784 .IP \(bu | |
| 785 .CW forw : | |
| 786 forward a message | |
| 787 .IP \(bu | |
| 788 .CW send : | |
| 789 send a prepared message | |
| 0 | 790 .LP |
| 19 | 791 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have. |
| 792 The user does not leave the shell to run \s-1MH\s0, | |
| 793 but he uses \s-1MH\s0 within the shell. | |
| 794 \s-1MH\s0's mail storage is (only little more than) a directory tree | |
| 795 where directories are mail folders and files are mail messages. | |
| 796 Working with \s-1MH\s0's toolchest is much like working | |
| 797 with Unix' toolchest: | |
| 798 \f(CWscan\fP is like \f(CWls\fP, | |
| 799 \f(CWshow\fP is like \f(CWcat\fP, | |
| 800 \f(CWfolder\fP is like \f(CWcd\fP, | |
| 801 \f(CWrefile\fP is like \f(CWmv\fP, | |
| 802 and \f(CWrmm\fP is like \f(CWrm\fP. | |
| 803 .PP | |
| 804 The context of the Unix tools is mainly the current working directory, | |
| 805 the user identification, and the environment variables. | |
| 806 \s-1MH\s0 extends this context by two more items: | |
| 20 | 807 The current mail folder, similar to the current working directory, |
| 808 for which \f(CWfolder\fP provides the functionality of | |
| 809 \f(CWpwd\fP and \f(CWcd\fP. | |
| 810 And the current message, relative to the current mail folder, | |
| 811 which enables commands like \f(CWnext\fP and \f(CWprev\fP. | |
| 19 | 812 In contrast to Unix' context, which is chained to the shell session, |
| 813 \s-1MH\s0's context is meant to be chained to a mail account. | |
| 20 | 814 But actually, the current message is a property of the mail folder, |
| 815 which is mainly a legacy. | |
| 816 This will cause problems when multiple users work | |
| 817 in one mail folder simultaneously. | |
| 19 | 818 .PP |
| 819 Using a monolithic program with a captive user interface | |
| 20 | 820 means ``entering'' the program, using it, and ``exiting'' the program. |
| 821 Using toolchests like \s-1MH\s0 means running programs, | |
| 19 | 822 alone or in combinition with others, even from other toolchests, |
| 823 without leaving the shell. | |
| 0 | 824 |
| 20 | 825 |
| 0 | 826 .NH 2 |
| 20 | 827 Discussion of the design |
| 828 .LP | |
| 829 The following paragraphs discuss \s-1MH\s0 in regard to the tenets | |
| 830 of the Unix Philosophy Gancarz identified. | |
| 831 | |
| 832 .PP | |
| 833 .I "``Small is beautiful'' | |
| 834 and | |
| 835 .I "``do one thing well'' | |
| 836 are two design goals that are directly visible in \s-1MH\s0. | |
| 837 Gancarz actually presents \s-1MH\s0 as example under the headline | |
| 838 ``Making UNIX Do One Thing Well'': | |
| 839 .QP | |
| 840 [\s-1MH\s0] consists of a series of programs which | |
| 841 when combined give the user an enormous ability | |
| 842 to manipulate electronic mail messages. | |
| 843 A complex application, it shows that not only is it | |
| 844 possible to build large applications from smaller | |
| 845 components, but also that such designs are actually preferable. | |
| 846 .[ | |
| 847 %A Mike Gancarz | |
| 848 %T unix-phil | |
| 849 %P 125 | |
| 850 .] | |
| 0 | 851 .LP |
| 20 | 852 The various small programs of \s-1MH\s0 were relatively easy |
| 853 to write as each of them is small, limited to one function, | |
| 854 and has clear bounderies. | |
| 855 For the same reasons, they are also good to maintain. | |
| 856 Further more, the system can easily get extended. | |
| 857 One only needs to put a new program into the toolchest. | |
| 858 This was done when \s-1MIME\s0 support was added | |
| 859 (e.g. \f(CWmhbuild\fP). | |
| 860 Also, different programs can exist to do the basically same job | |
| 861 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP). | |
| 862 If someone needs a mail system with some additionally | |
| 863 functions that are nowhere available yet, he best takes a | |
| 864 toolchest system like \s-1MH\s0 where he can add the | |
| 865 functionality with little work. | |
| 866 | |
| 867 .PP | |
| 868 .I "Data storage. | |
| 869 How \s-1MH\s0 stores data was already mentioned. | |
| 870 Mail folders are directories (which contain a file | |
| 871 \&\f(CW.mh_sequences\fP) under the user's \s-1MH\s0 directory | |
| 872 (usually \f(CW$HOME/Mail\fP). | |
| 873 Mail messages are text files located in a mail folder. | |
| 874 The files contain the messages as they were received. | |
| 875 The messages are numbered in ascending order in each folder. | |
| 876 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0. | |
| 877 Alternatives are \fImbox\fP and \fImaildir\fP. | |
| 878 In the mbox format all messages are stored within one file. | |
| 879 This was a good solution in the early days, when messages | |
| 880 were only a few lines of text and were deleted soon. | |
| 881 Today, when single messages often include several megabytes | |
| 882 of attachments, it is a bad solution. | |
| 883 Another disadvantage of the mbox format is that it is | |
| 884 more difficult to write tools that work on mail messages, | |
| 885 because it is always neccessary to first find and extract | |
| 886 the relevant message in the mbox file. | |
| 887 With \s-1MH\s0 mailboxes, each message is a self-standing item, | |
| 888 by definition. | |
| 889 Also, the problem of concurrent access to one mailbox is | |
| 890 reduced to the problem of concurrent access to one message. | |
| 891 However, the issue of the shared parts of the context, | |
| 892 as mentioned above, remains. | |
| 893 Maildir is generally similar to \s-1MH\s0's format, | |
| 894 but modified towards guaranteed reliability. | |
| 895 This involves some complexity, unfortunately. | |
| 896 | |
| 897 .PP | |
| 898 .I "``Avoid captive user interfaces.'' | |
| 19 | 899 \s-1MH\s0 is perfectly suited for non-interactive use. |
| 900 It offers all functions directly and without captive user interfaces. | |
| 901 If users want a graphical user interface, anyhow, | |
| 20 | 902 they can have it with \fIxmh\fP or \fIexmh\fP, too. |
| 19 | 903 These are graphical frontends for the \s-1MH\s0 toolchest. |
| 904 This means, all email-related work is still done by \s-1MH\s0 tools, | |
| 20 | 905 but the frontend issues the appropriate calls when the user |
| 906 clicks on a button. | |
| 907 Providing easy-to-use user interfaces in form of frontends is a good | |
| 19 | 908 approach, because it does not limit the power of the backend itself. |
| 20 | 909 The frontend will anyway only be able to make a subset of the |
| 19 | 910 backend's power and flexibility available. |
| 20 | 911 But if it is a separate program, |
| 912 then the missing parts can still be accessed at the backend directly. | |
| 19 | 913 If it is integrated, then this will hardly be possible. |
| 914 | |
| 915 .PP | |
| 20 | 916 .I "``Choose portability over efficiency'' |
| 917 and | |
| 918 .I "``use shell scripts to increase leverage and portability'' . | |
| 919 These two tenets are indirectly, but nicely, demonstrated by | |
| 920 Bolsky and Korn in their book about the korn shell. | |
| 921 .[ | |
| 922 %T The KornShell: command and programming language | |
| 923 %A Morris I. Bolsky | |
| 924 %A David G. Korn | |
| 925 %I Prentice Hall | |
| 926 %D 1989 | |
| 927 %O \s-1ISBN\s0: 0-13-516972-0 | |
| 928 .] | |
| 929 They demonstrated, in one chapter of the book, a basic implementation | |
| 930 of a subset of \s-1MH\s0 in ksh scripts. | |
| 931 Of course, this was just a demonstration, but a brilliant one. | |
| 932 It shows how quickly one can implement such a prototype with shell scripts, | |
| 933 and how readable they are. | |
| 934 The implementation in the scripting language may not be very fast, | |
| 935 but it can be fast enough though, and this is all that matters. | |
| 936 By having the code in an interpreted language, like the shell, | |
| 937 portability becomes a minor issue, if we assume the interpreter | |
| 938 to be widespread. | |
| 939 This demonstration also shows how easy it is to create single programs | |
| 940 of a toolchest software. | |
| 941 Most of the single programs comprise less than a hundred lines of | |
| 942 shell code. | |
| 943 Such small software is easy to write, easy to understand, | |
| 944 and thus easy to maintain. | |
| 945 Being a toolchest improved the possibility to only write some parts | |
| 946 and though create a working result. | |
| 947 Expanding the toolchest without global changes will likely be | |
| 948 possible, too. | |
| 949 | |
| 950 .PP | |
| 951 .I "``Use software leverage to your advantage'' | |
| 952 and the lesser tenet | |
| 953 .I "``allow the user to tailor the environment'' | |
| 954 are ideally followed in the design of \s-1MH\s0. | |
| 955 | |
| 956 .PP | |
| 957 filters: many tools provide basic FS operations (like mv, rm, ...) | |
| 958 prototypes: affect dev, but MH is very matured | |
| 0 | 959 |
| 960 .NH 2 | |
| 961 Problems | |
| 962 .LP | |
| 20 | 963 modern emailing |
| 964 MIME | |
| 965 encodings | |
| 966 largest problem: different feeling | |
| 967 | |
| 968 .NH 2 | |
| 969 Summary \s-1MH\s0 | |
| 970 .LP | |
| 971 flexibility, no redundancy, use the shell | |
| 0 | 972 |
| 8 | 973 |
| 974 | |
| 0 | 975 .NH 1 |
| 976 Case study: uzbl | |
| 977 | |
| 978 .NH 2 | |
| 979 History | |
| 980 .LP | |
| 981 uzbl is young | |
| 982 | |
| 983 .NH 2 | |
| 984 Contrasts to similar sw | |
| 985 .LP | |
| 986 like with nmh | |
| 987 .LP | |
| 988 addons, plugins, modules | |
| 989 | |
| 990 .NH 2 | |
| 991 Gains of the design | |
| 992 .LP | |
| 993 | |
| 994 .NH 2 | |
| 995 Problems | |
| 996 .LP | |
| 997 broken web | |
| 998 | |
| 8 | 999 |
| 1000 | |
| 0 | 1001 .NH 1 |
| 1002 Final thoughts | |
| 1003 | |
| 1004 .NH 2 | |
| 1005 Quick summary | |
| 1006 .LP | |
| 1007 good design | |
| 1008 .LP | |
| 1009 unix phil | |
| 1010 .LP | |
| 1011 case studies | |
| 1012 | |
| 1013 .NH 2 | |
| 1014 Why people should choose | |
| 1015 .LP | |
| 1016 Make the right choice! | |
| 1017 | |
| 1018 .nr PI .5i | |
| 1019 .rm ]< | |
| 1020 .de ]< | |
| 1021 .LP | |
| 1022 .de FP | |
| 1023 .IP \\\\$1. | |
| 1024 \\.. | |
| 1025 .rm FS FE | |
| 1026 .. | |
| 1027 .SH | |
| 1028 References | |
| 1029 .[ | |
| 1030 $LIST$ | |
| 1031 .] | |
| 1032 .wh -1p |