Mercurial > docs > unix-phil
annotate unix-phil.ms @ 11:b32a43a62cae
some rework about interface arch (ch03)
| author | meillo@marmaro.de |
|---|---|
| date | Sat, 20 Feb 2010 15:24:40 +0100 |
| parents | 355ed69a34a8 |
| children | 018d5f9a2993 |
| 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 | |
| 13 .ie \\$1 .if n .ul 999 | |
| 14 .el .if n .ul 1 | |
| 15 .if t .if !\\$1 \&\\$1\f\\n(PQ\\$2 | |
| 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 |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
222 .SH |
| 4 | 223 Examples |
| 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. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
271 |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
272 .SH |
| 4 | 273 Pipes |
| 0 | 274 .LP |
| 8 | 275 The examples show that many tasks on a Unix system |
| 4 | 276 are accomplished by combining several small programs. |
| 277 The connection between the single programs is denoted by the pipe operator `|'. | |
| 278 .PP | |
| 279 Pipes, and their extensive and easy use, are one of the great | |
| 280 achievements of the Unix system. | |
| 281 Pipes between programs have been possible in earlier operating systems, | |
| 282 but it has never been a so central part of the concept. | |
| 283 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 284 Unix system, | |
| 285 ``it was this concept and notation for linking several programs together | |
| 286 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 287 .[ | |
| 288 %T Unix: An Oral History | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
289 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
| 4 | 290 .] |
| 291 .PP | |
| 292 Being able to specify pipelines in an easy way is, | |
| 293 however, not enough by itself. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
294 It is only one half. |
| 4 | 295 The other is the design of the programs that are used in the pipeline. |
| 8 | 296 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
|
297 |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
298 .SH |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
299 Interface architecture |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
300 .LP |
| 11 | 301 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
|
302 Files are sequences of bytes, without any special structure. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
303 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
|
304 and write a stream of bytes to ``standard output'' (stdout). |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
305 .PP |
| 8 | 306 If the files \fIare\fP sequences of bytes, |
| 307 and the programs \fIare\fP filters on byte streams, | |
| 11 | 308 then there is exactly one standardized data interface. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
309 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
|
310 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
311 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
|
312 and thus a large set of different functions. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
313 This is leverage! |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
314 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
|
315 then the set of different functions is greatest. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
316 .PP |
| 11 | 317 Programs might also have a separate control interface, |
| 318 besides their data interface. | |
| 319 The control interface is often called ``user interface'', | |
| 320 because it is usually designed to be used by humans. | |
| 321 The Unix Philosophy discourages to assume the user to be human. | |
| 322 Interactive use of software is slow use of software, | |
| 323 because the program waits for user input most of the time. | |
| 324 Interactive software requires the user to be in front of the computer | |
| 325 all the time. | |
| 326 Interactive software occupy the user's attention while they are running. | |
| 327 .PP | |
| 328 Now we come back to the idea of using several small programs, combined, | |
| 329 to have a more specific function. | |
| 330 If these single tools would all be interactive, | |
| 331 how would the user control them? | |
| 332 It is not only a problem to control several programs at once if they run at the same time, | |
| 333 it also very inefficient to have to control each of the single programs | |
| 334 that are intended to work as one large program. | |
| 335 Hence, the Unix Philosophy discourages programs to demand interactive use. | |
| 336 The behavior of programs should be defined at invocation. | |
| 337 This is done by specifying arguments (``command line switches'') to the program call. | |
| 338 Gancarz discusses this topic as ``avoid captive user interfaces''. | |
| 339 .[ | |
| 340 %A Mike Gancarz | |
| 341 %T The UNIX Philosophy | |
| 342 %I Digital Press | |
| 343 %D 1995 | |
| 344 %P 88 ff. | |
| 345 .] | |
| 346 .PP | |
| 347 Non-interactive use is, during development, also an advantage for testing. | |
| 348 Testing of interactive programs is much more complicated, | |
| 349 than testing of non-interactive programs. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
350 |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
351 .SH |
| 8 | 352 The toolchest approach |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
353 .LP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
354 A toolchest is a set of tools. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
355 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
|
356 each for one task. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
357 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
|
358 .PP |
| 11 | 359 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs |
| 360 that are filters on byte streams. | |
| 361 They are, to a large extend, unrelated in their function. | |
| 362 Hence, the Unix toolchest provides a large set of functions | |
| 363 that can be accessed by combining the programs in the desired way. | |
| 364 .PP | |
| 365 There are also advantages for developing small toolchest programs. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
366 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
|
367 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
|
368 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
|
369 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
|
370 of functions than the single large program. |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
371 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
|
372 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
373 There are two drawbacks of the toolchest approach. |
| 8 | 374 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
|
375 If one feels the need for more ``logic'' than a stream of bytes, |
| 8 | 376 then a different approach might be of need. |
| 9 | 377 But it is also possible, that he just can not imaging a design where |
| 8 | 378 a stream of bytes is sufficient. |
| 379 By becoming more familiar with the ``Unix style of thinking'', | |
| 380 developers will more often and easier find simple designs where | |
| 381 a stream of bytes is a sufficient interface. | |
| 382 .PP | |
| 383 The second drawback of a toolchest affects the users. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
384 A toolchest is often more difficult to use for novices. |
| 9 | 385 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
|
386 to be able to use the right one in a given situation. |
| 9 | 387 Additionally, one needs to combine the tools in a senseful way on its own. |
| 388 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
|
389 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
|
390 .PP |
| 8 | 391 However, learning single, small tool of the toolchest is easier than |
| 392 learning a complex tool. | |
| 393 The user will have a basic understanding of a yet unknown tool, | |
| 394 if the several tools of the toolchest have a common style. | |
| 395 He will be able to transfer knowledge over one tool to another. | |
| 396 .PP | |
| 397 Moreover, the second drawback can be removed easily by adding wrappers | |
| 398 around the single tools. | |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
399 Novice users do not need to learn several tools if a professional wraps |
| 8 | 400 the single commands into a more high-level script. |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
401 Note that the wrapper script still calls the small tools; |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
402 the wrapper script is just like a skin around. |
| 8 | 403 No complexity is added this way, |
| 404 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
|
405 .PP |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
406 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
|
407 could look like this: |
| 9 | 408 .DS I 2n |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
409 .CW |
| 9 | 410 .ps -1 |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
411 #!/bin/sh |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
412 du -s * | sort -nr | sed 5q |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
413 .DE |
|
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
414 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
|
415 a professional user would type in directly. |
| 8 | 416 Making the program flexible on the number of entries it prints, |
| 417 is easily possible: | |
| 9 | 418 .DS I 2n |
| 8 | 419 .CW |
| 9 | 420 .ps -1 |
| 8 | 421 #!/bin/sh |
| 422 num=5 | |
| 423 [ $# -eq 1 ] && num="$1" | |
| 424 du -sh * | sort -nr | sed "${num}q" | |
| 425 .DE | |
| 426 This script acts like the one before, when called without an argument. | |
| 427 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
|
428 |
| 8 | 429 .SH |
| 430 A powerful shell | |
| 431 .LP | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
432 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
|
433 combine small programs into large ones easily. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
434 A powerful shell is a great feature in other ways, too. |
| 8 | 435 .PP |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
436 For instance by including a scripting language. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
437 The control statements are build into the shell. |
| 8 | 438 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
|
439 Thus, the programs are known, so learning to program in the shell is easy. |
| 8 | 440 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
|
441 is only possible because they are small and combinable tools in a toolchest style. |
| 8 | 442 .PP |
| 443 The Unix shell encourages to write small scripts out of other programs, | |
| 444 because it is so easy to do. | |
| 445 This is a great step towards automation. | |
| 446 It is wonderful if the effort to automate a task equals the effort | |
| 447 it takes to do it the second time by hand. | |
| 448 If it is so, then the user will be happy to automate everything he does more than once. | |
| 449 .PP | |
| 450 Small programs that do one job well, standardized interfaces between them, | |
| 451 a mechanism to combine parts to larger parts, and an easy way to automate tasks, | |
| 452 this will inevitably produce software leverage. | |
| 453 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
|
454 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
455 The shell also encourages rapid prototyping. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
456 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
|
457 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
|
458 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
|
459 in application development. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
460 Fred Brooks writes in ``No Silver Bullet'': |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
461 .[ |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
462 %A Frederick P. Brooks, Jr. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
463 %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
|
464 %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
|
465 %E H.-J. Kugler |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
466 %D 1986 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
467 %P 1069\(en1076 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
468 %I Elsevier Science B.V. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
469 %C Amsterdam, The Netherlands |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
470 .] |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
471 .QP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
472 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
|
473 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
|
474 technical requirements, [...]. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
475 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
|
476 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
|
477 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
478 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
|
479 and to actually run into real problems. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
480 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
|
481 This is, of course, good. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
482 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
|
483 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
|
484 \fIgood enough\fP. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
485 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
|
486 for the moment. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
487 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
|
488 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
489 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
|
490 changing requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
491 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
|
492 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
493 .SH |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
494 Worse is better |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
495 .LP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
496 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
|
497 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
|
498 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
499 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
|
500 requirements completely and correctly the first time. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
501 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
|
502 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
|
503 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
|
504 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
|
505 to react on changing requirements. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
506 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
|
507 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
|
508 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
|
509 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
|
510 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
|
511 .PP |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
512 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
|
513 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
514 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
|
515 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
516 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
|
517 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
518 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
|
519 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
|
520 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
521 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
|
522 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
|
523 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
|
524 than now. |
|
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 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
|
527 requires fewer maintenance work. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
528 .IP \(bu |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
529 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
|
530 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
|
531 when a different approach had been used. |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
532 |
| 11 | 533 .SH |
| 534 Upgrowth and survival of software | |
| 535 .LP | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
536 |
| 11 | 537 portability |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
538 |
| 11 | 539 text files |
| 540 | |
| 541 reuse of independent parts | |
|
10
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
542 |
|
355ed69a34a8
more about the shell and worse is better (ch03)
meillo@marmaro.de
parents:
9
diff
changeset
|
543 |
|
5
48f1f3465550
new content about interfaces and toolchests
meillo@marmaro.de
parents:
4
diff
changeset
|
544 |
| 4 | 545 |
| 546 | |
| 0 | 547 |
| 548 | |
| 549 .NH 2 | |
| 550 Results | |
| 551 .LP | |
| 552 The unix phil is an answer to the sw design question | |
| 553 .LP | |
| 554 tool chains empower the uses of sw | |
| 555 | |
| 8 | 556 |
| 557 | |
| 0 | 558 .NH 1 |
| 559 Case study: nmh | |
| 560 | |
| 561 .NH 2 | |
| 562 History | |
| 563 .LP | |
| 564 MH, nmh. | |
| 565 They are old. | |
| 566 | |
| 567 .NH 2 | |
| 568 Contrasts to similar sw | |
| 569 .LP | |
| 570 vs. Thunderbird, mutt, mailx, pine | |
| 571 .LP | |
| 572 flexibility, no redundancy, use the shell | |
| 573 | |
| 574 .NH 2 | |
| 575 Gains of the design | |
| 576 .LP | |
| 577 | |
| 578 .NH 2 | |
| 579 Problems | |
| 580 .LP | |
| 581 | |
| 8 | 582 |
| 583 | |
| 0 | 584 .NH 1 |
| 585 Case study: uzbl | |
| 586 | |
| 587 .NH 2 | |
| 588 History | |
| 589 .LP | |
| 590 uzbl is young | |
| 591 | |
| 592 .NH 2 | |
| 593 Contrasts to similar sw | |
| 594 .LP | |
| 595 like with nmh | |
| 596 .LP | |
| 597 addons, plugins, modules | |
| 598 | |
| 599 .NH 2 | |
| 600 Gains of the design | |
| 601 .LP | |
| 602 | |
| 603 .NH 2 | |
| 604 Problems | |
| 605 .LP | |
| 606 broken web | |
| 607 | |
| 8 | 608 |
| 609 | |
| 0 | 610 .NH 1 |
| 611 Final thoughts | |
| 612 | |
| 613 .NH 2 | |
| 614 Quick summary | |
| 615 .LP | |
| 616 good design | |
| 617 .LP | |
| 618 unix phil | |
| 619 .LP | |
| 620 case studies | |
| 621 | |
| 622 .NH 2 | |
| 623 Why people should choose | |
| 624 .LP | |
| 625 Make the right choice! | |
| 626 | |
| 627 .nr PI .5i | |
| 628 .rm ]< | |
| 629 .de ]< | |
| 630 .LP | |
| 631 .de FP | |
| 632 .IP \\\\$1. | |
| 633 \\.. | |
| 634 .rm FS FE | |
| 635 .. | |
| 636 .SH | |
| 637 References | |
| 638 .[ | |
| 639 $LIST$ | |
| 640 .] | |
| 641 .wh -1p |