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annotate unix-phil.ms @ 4:c707b0c5c849
new text about pipes
| author | meillo@marmaro.de |
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| date | Fri, 12 Feb 2010 19:30:13 +0100 |
| parents | aebbe3e76f5e |
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| 19 .. | |
| 20 .ds [. \ [ | |
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| 1 | 22 .\"---------------------------------------- |
| 0 | 23 .TL |
| 24 Why the Unix Philosophy matters | |
| 25 .AU | |
| 26 markus schnalke <meillo@marmaro.de> | |
| 27 .AB | |
| 1 | 28 .ti \n(.iu |
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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 | |
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35 .if t .2C |
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37 .FS |
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38 .ps -1 |
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39 This paper was prepared for the seminar ``Software Analysis'' at University Ulm. |
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40 Mentor was professor Schweiggert. 2010-02-05 |
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41 .br |
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42 You may get this document from my website |
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43 .CW \s-1http://marmaro.de/docs |
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44 .FE |
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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. | |
| 3 | 53 The process inbetween can be of any shape. |
| 54 The the maintainance 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. | |
| 62 This paper discusses the recommendations of the Unix Philosphy about software design. | |
| 63 .PP | |
| 64 The here discussed ideas can get applied by any development process. | |
| 65 The Unix Philosphy does recommend how the software development process should look like, | |
| 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 | |
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102 %O .CW \s-1http://www.faqs.org/docs/artu/ |
| 1 | 103 .] |
| 0 | 104 .LP |
| 1 | 105 These different views on the Unix Philosophy have much in common. |
| 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; | |
| 110 especially those that were sucessful and unique to Unix. | |
| 111 .PP | |
| 112 Before we will have a look at concrete concepts, | |
| 113 we discuss why software design is important | |
| 114 and what problems bad design introduces. | |
| 0 | 115 |
| 116 | |
| 117 .NH 1 | |
| 118 Importance of software design | |
| 119 .LP | |
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120 Why should we design software at all? |
| 3 | 121 It is general knowledge, that a bad plan is better than no plan. |
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122 As stated earlier in this document, the process of building a software |
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123 means going from an idea to a release. |
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124 The development process tells how to get from the idea to the release. |
| 3 | 125 Software design is the shape of the built software. |
| 126 This means, that different designs of a software would be different target points to go to. | |
| 127 Thus, the design of a software defines the global direction the development goes. | |
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128 .PP |
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129 It is not enough that the released software offers all requested functionality. |
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130 It is a misbelief that only function matters. |
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131 Building a software the first time is only a small part of the overall work. |
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132 The larger part begins when the software is released for the first time |
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133 \(en maintainance and extending work.. |
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134 This part soon covers more time than the time which was needed to build the software the first time. |
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135 .\" cf. brooks? |
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136 .PP |
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137 The extendability and maitainability of a software highly depends on its design. |
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138 Good design eases these tasks much. |
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139 Bad design, in contrast, requires much more effort for maintaining and |
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140 extending the software. |
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141 Developers should, for their own best, have maintainability and extendability in mind |
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142 when they design the software. |
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143 .PP |
| 3 | 144 Users of the software, in contrast, do not care about maintainability and extendability, |
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145 at least not directly. |
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146 They care about usability and flexibility. |
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147 They want the software to directly solve their problems. |
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148 They want to be able to to use all its functions if they learned a few of them. |
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149 They want to use the software for similar tasks. |
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150 Software is successful if users enjoy using it. |
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151 Good software design can offer great flexibility and usability. |
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152 .PP |
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153 Good design matters for developers \fIand\fP for users. |
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154 Hence both groups should care about good software design. |
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155 Bad design limits the software in some way. |
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156 It may still provide all requested function, but it will have worse quality, |
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157 and thus require more work effort for developers or frustrate users. |
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158 .PP |
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159 Good software design is to the implementation like data structures are to algorithms |
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160 \(en if you get the former right, then you do not need to care about the latter, |
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161 it will simply go the right way. |
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162 .\" cf. ??? ``good data, bad algos'' |
| 0 | 163 |
| 164 | |
| 165 | |
| 166 | |
| 167 .NH 1 | |
| 168 The Unix Philosophy | |
| 4 | 169 .LP |
| 170 The origins of the Unix Philosophy were already introduced. | |
| 171 This chapter explains the philosophy and shows concrete examples of its application. | |
| 0 | 172 .NH 2 |
| 4 | 173 Examples |
| 0 | 174 .LP |
| 4 | 175 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 176 Knowledge of using the Unix shell is assumed. | |
| 177 .PP | |
| 178 Counting the number of files in the current directory: | |
| 179 .DS | |
| 180 .CW | |
| 181 ls | wc -l | |
| 182 .DE | |
| 183 The | |
| 184 .CW ls | |
| 185 command lists all files in the current directory, one per line, | |
| 186 and | |
| 187 .CW "wc -l | |
| 188 counts how many lines they are. | |
| 189 .PP | |
| 190 Counting all files that do not contain ``foo'' in their name: | |
| 191 .DS | |
| 192 .CW | |
| 193 ls | grep -v foo | wc -l | |
| 194 .DE | |
| 195 Here, the list of files is filtered by | |
| 196 .CW grep | |
| 197 to remove all that contain ``foo''. | |
| 198 The rest is the same as in the previous example. | |
| 199 .PP | |
| 200 Finding the five largest entries in the current directory. | |
| 201 .DS | |
| 202 .CW | |
| 203 du -s * | sort -nr | sed 5q | |
| 204 .DE | |
| 205 .CW "du -s * | |
| 206 returns the recursively summed sizes of all files | |
| 207 -- no matter if they are regular files or directories. | |
| 208 .CW "sort -nr | |
| 209 sorts the list numerically in reverse order. | |
| 210 Finally, | |
| 211 .CW "sed 5q | |
| 212 quits after it has printed the fifth line. | |
| 213 .PP | |
| 214 The presented command lines are examples of what Unix people would use | |
| 215 to get the desired output. | |
| 216 There are also other ways to get the same output. | |
| 217 It's a user's decision which way to go. | |
| 218 .NH 2 | |
| 219 Pipes | |
| 0 | 220 .LP |
| 4 | 221 The examples show that a lot of tasks on a Unix system |
| 222 are accomplished by combining several small programs. | |
| 223 The connection between the single programs is denoted by the pipe operator `|'. | |
| 224 .PP | |
| 225 Pipes, and their extensive and easy use, are one of the great | |
| 226 achievements of the Unix system. | |
| 227 Pipes between programs have been possible in earlier operating systems, | |
| 228 but it has never been a so central part of the concept. | |
| 229 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 230 Unix system, | |
| 231 ``it was this concept and notation for linking several programs together | |
| 232 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 233 .[ | |
| 234 %T Unix: An Oral History | |
| 235 %O http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm | |
| 236 .] | |
| 237 .PP | |
| 238 Being able to specify pipelines in an easy way is, | |
| 239 however, not enough by itself. | |
| 240 It is only one part. | |
| 241 The other is the design of the programs that are used in the pipeline. | |
| 242 They have to be of an external shape that allows them to be be used in a pipeline. | |
| 243 | |
| 244 | |
| 0 | 245 |
| 246 .NH 2 | |
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247 Architecture |
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248 .LP |
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249 the most important design decision. |
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250 |
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251 the topic here |
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252 |
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253 .NH 2 |
| 0 | 254 Interface architecture |
| 255 .LP | |
| 256 standalone vs. tool chain | |
| 257 .LP | |
| 258 software leverage | |
| 259 .LP | |
| 260 possiblities | |
| 261 | |
| 262 .NH 2 | |
| 263 Results | |
| 264 .LP | |
| 265 The unix phil is an answer to the sw design question | |
| 266 .LP | |
| 267 tool chains empower the uses of sw | |
| 268 | |
| 269 .NH 1 | |
| 270 Case study: nmh | |
| 271 | |
| 272 .NH 2 | |
| 273 History | |
| 274 .LP | |
| 275 MH, nmh. | |
| 276 They are old. | |
| 277 | |
| 278 .NH 2 | |
| 279 Contrasts to similar sw | |
| 280 .LP | |
| 281 vs. Thunderbird, mutt, mailx, pine | |
| 282 .LP | |
| 283 flexibility, no redundancy, use the shell | |
| 284 | |
| 285 .NH 2 | |
| 286 Gains of the design | |
| 287 .LP | |
| 288 | |
| 289 .NH 2 | |
| 290 Problems | |
| 291 .LP | |
| 292 | |
| 293 .NH 1 | |
| 294 Case study: uzbl | |
| 295 | |
| 296 .NH 2 | |
| 297 History | |
| 298 .LP | |
| 299 uzbl is young | |
| 300 | |
| 301 .NH 2 | |
| 302 Contrasts to similar sw | |
| 303 .LP | |
| 304 like with nmh | |
| 305 .LP | |
| 306 addons, plugins, modules | |
| 307 | |
| 308 .NH 2 | |
| 309 Gains of the design | |
| 310 .LP | |
| 311 | |
| 312 .NH 2 | |
| 313 Problems | |
| 314 .LP | |
| 315 broken web | |
| 316 | |
| 317 .NH 1 | |
| 318 Final thoughts | |
| 319 | |
| 320 .NH 2 | |
| 321 Quick summary | |
| 322 .LP | |
| 323 good design | |
| 324 .LP | |
| 325 unix phil | |
| 326 .LP | |
| 327 case studies | |
| 328 | |
| 329 .NH 2 | |
| 330 Why people should choose | |
| 331 .LP | |
| 332 Make the right choice! | |
| 333 | |
| 334 .nr PI .5i | |
| 335 .rm ]< | |
| 336 .de ]< | |
| 337 .LP | |
| 338 .de FP | |
| 339 .IP \\\\$1. | |
| 340 \\.. | |
| 341 .rm FS FE | |
| 342 .. | |
| 343 .SH | |
| 344 References | |
| 345 .[ | |
| 346 $LIST$ | |
| 347 .] | |
| 348 .wh -1p |