Mercurial > docs > unix-phil
annotate unix-phil.ms @ 5:48f1f3465550
new content about interfaces and toolchests
| author | meillo@marmaro.de |
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| date | Sat, 13 Feb 2010 11:37:50 +0100 |
| parents | c707b0c5c849 |
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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. | |
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173 .SH |
| 4 | 174 Examples |
| 0 | 175 .LP |
| 4 | 176 Following are some examples to demonstrate how applied Unix Philosophy feels like. |
| 177 Knowledge of using the Unix shell is assumed. | |
| 178 .PP | |
| 179 Counting the number of files in the current directory: | |
| 180 .DS | |
| 181 .CW | |
| 182 ls | wc -l | |
| 183 .DE | |
| 184 The | |
| 185 .CW ls | |
| 186 command lists all files in the current directory, one per line, | |
| 187 and | |
| 188 .CW "wc -l | |
| 189 counts how many lines they are. | |
| 190 .PP | |
| 191 Counting all files that do not contain ``foo'' in their name: | |
| 192 .DS | |
| 193 .CW | |
| 194 ls | grep -v foo | wc -l | |
| 195 .DE | |
| 196 Here, the list of files is filtered by | |
| 197 .CW grep | |
| 198 to remove all that contain ``foo''. | |
| 199 The rest is the same as in the previous example. | |
| 200 .PP | |
| 201 Finding the five largest entries in the current directory. | |
| 202 .DS | |
| 203 .CW | |
| 204 du -s * | sort -nr | sed 5q | |
| 205 .DE | |
| 206 .CW "du -s * | |
| 207 returns the recursively summed sizes of all files | |
| 208 -- no matter if they are regular files or directories. | |
| 209 .CW "sort -nr | |
| 210 sorts the list numerically in reverse order. | |
| 211 Finally, | |
| 212 .CW "sed 5q | |
| 213 quits after it has printed the fifth line. | |
| 214 .PP | |
| 215 The presented command lines are examples of what Unix people would use | |
| 216 to get the desired output. | |
| 217 There are also other ways to get the same output. | |
| 218 It's a user's decision which way to go. | |
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219 |
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220 .SH |
| 4 | 221 Pipes |
| 0 | 222 .LP |
| 4 | 223 The examples show that a lot of tasks on a Unix system |
| 224 are accomplished by combining several small programs. | |
| 225 The connection between the single programs is denoted by the pipe operator `|'. | |
| 226 .PP | |
| 227 Pipes, and their extensive and easy use, are one of the great | |
| 228 achievements of the Unix system. | |
| 229 Pipes between programs have been possible in earlier operating systems, | |
| 230 but it has never been a so central part of the concept. | |
| 231 When, in the early seventies, Doug McIlroy introduced pipes for the | |
| 232 Unix system, | |
| 233 ``it was this concept and notation for linking several programs together | |
| 234 that transformed Unix from a basic file-sharing system to an entirely new way of computing.'' | |
| 235 .[ | |
| 236 %T Unix: An Oral History | |
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237 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm |
| 4 | 238 .] |
| 239 .PP | |
| 240 Being able to specify pipelines in an easy way is, | |
| 241 however, not enough by itself. | |
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242 It is only one half. |
| 4 | 243 The other is the design of the programs that are used in the pipeline. |
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244 They have to be of an external shape that allows them to be be used in such a way. |
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245 |
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246 .SH |
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247 Interface architecture |
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248 .LP |
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249 Unix is, first of all, simple: Everything is a file. |
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250 Files are sequences of bytes, without any special structure. |
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251 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin) |
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252 and write a stream of bytes to ``standard output'' (stdout). |
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253 .PP |
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254 If our files \fIare\fP sequences of bytes, |
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255 and our programs \fIare\fP filters on byte streams, |
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256 then there is exactly one standardized interface. |
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257 Thus it is possible to combine them in any desired way. |
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258 .PP |
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259 Even a handful of small programs will yield a large set of combinations, |
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260 and thus a large set of different functions. |
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261 This is leverage! |
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262 .PP |
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263 If the programs are orthogonal to each other \(en the best case \(en |
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264 then the set of different functions is greatest. |
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265 .PP |
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266 Now, the Unix toolchest is a set of small programs that |
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267 are filters on byte streams. |
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268 They are to a large extend unrelated in their function. |
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269 Hence, the Unix toolchest provides a large set of functions |
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270 that can be accessed by combining the programs in the desired way. |
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271 |
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272 .SH |
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273 Advantages of toolchests |
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274 .LP |
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275 A toolchest is a set of tools. |
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276 Instead of having one big tool for all tasks, one has many small tools, |
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277 each for one task. |
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278 Difficult tasks are solved by combining several of the small, simple tools. |
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279 .PP |
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280 It is easier and less error-prone to write small programs. |
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281 It is also easier and less error-prone to write a large set of small programs, |
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282 than to write one large program with all the functionality included. |
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283 If the small programs are combinable, then they offer even a larger set |
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284 of functions than the single large program. |
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285 Hence, one gets two advantages out of writing small, combinable programs. |
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286 .PP |
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287 There are two drawbacks of the toolchest approach. |
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288 First, one simple, standardized, unidirectional Interface has to be sufficient. |
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289 If one feels the need for more ``logic'' than a stream of bytes, |
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290 then a different approach might be of need, or, more likely, |
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291 he just did not came to a design where a stream of bytes is sufficient. |
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292 The other drawback of a toolchest affects the users. |
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293 A toolchest is often more difficult to use for novices. |
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294 It is neccessary to become familiar with each of the tools, |
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295 to be able to use the right one in a given situation. |
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296 Additinally, one needs to combine the tools in a senseful way on its own. |
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297 This is like a sharp knive \(en it is a powerful tool in the hand of a master, |
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298 but of no good value in the hand of an unskilled. |
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299 .PP |
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300 Luckily, the second drawback can be solved easily by adding wrappers around the single tools. |
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301 Novice users do not need to learn several tools if a professional wraps |
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302 the single commands into a single script. |
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303 Note that the wrapper script still calls the small tools; |
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304 the wrapper script is just like a skin around. |
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305 No complexity is added this way. |
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306 .PP |
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307 A wrapper script for finding the five largest entries in the current directory |
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308 could look like this: |
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309 .DS |
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310 .CW |
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311 #!/bin/sh |
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312 du -s * | sort -nr | sed 5q |
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313 .DE |
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314 The script itself is just a text file that calls the command line |
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315 a professional user would type in directly. |
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316 |
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317 |
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318 |
| 4 | 319 |
| 320 | |
| 0 | 321 |
| 322 .NH 2 | |
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323 foo |
| 0 | 324 .LP |
| 325 standalone vs. tool chain | |
| 326 .LP | |
| 327 software leverage | |
| 328 .LP | |
| 329 possiblities | |
| 330 | |
| 331 .NH 2 | |
| 332 Results | |
| 333 .LP | |
| 334 The unix phil is an answer to the sw design question | |
| 335 .LP | |
| 336 tool chains empower the uses of sw | |
| 337 | |
| 338 .NH 1 | |
| 339 Case study: nmh | |
| 340 | |
| 341 .NH 2 | |
| 342 History | |
| 343 .LP | |
| 344 MH, nmh. | |
| 345 They are old. | |
| 346 | |
| 347 .NH 2 | |
| 348 Contrasts to similar sw | |
| 349 .LP | |
| 350 vs. Thunderbird, mutt, mailx, pine | |
| 351 .LP | |
| 352 flexibility, no redundancy, use the shell | |
| 353 | |
| 354 .NH 2 | |
| 355 Gains of the design | |
| 356 .LP | |
| 357 | |
| 358 .NH 2 | |
| 359 Problems | |
| 360 .LP | |
| 361 | |
| 362 .NH 1 | |
| 363 Case study: uzbl | |
| 364 | |
| 365 .NH 2 | |
| 366 History | |
| 367 .LP | |
| 368 uzbl is young | |
| 369 | |
| 370 .NH 2 | |
| 371 Contrasts to similar sw | |
| 372 .LP | |
| 373 like with nmh | |
| 374 .LP | |
| 375 addons, plugins, modules | |
| 376 | |
| 377 .NH 2 | |
| 378 Gains of the design | |
| 379 .LP | |
| 380 | |
| 381 .NH 2 | |
| 382 Problems | |
| 383 .LP | |
| 384 broken web | |
| 385 | |
| 386 .NH 1 | |
| 387 Final thoughts | |
| 388 | |
| 389 .NH 2 | |
| 390 Quick summary | |
| 391 .LP | |
| 392 good design | |
| 393 .LP | |
| 394 unix phil | |
| 395 .LP | |
| 396 case studies | |
| 397 | |
| 398 .NH 2 | |
| 399 Why people should choose | |
| 400 .LP | |
| 401 Make the right choice! | |
| 402 | |
| 403 .nr PI .5i | |
| 404 .rm ]< | |
| 405 .de ]< | |
| 406 .LP | |
| 407 .de FP | |
| 408 .IP \\\\$1. | |
| 409 \\.. | |
| 410 .rm FS FE | |
| 411 .. | |
| 412 .SH | |
| 413 References | |
| 414 .[ | |
| 415 $LIST$ | |
| 416 .] | |
| 417 .wh -1p |