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4 ..
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5 .em XX
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6 .\".nr PI 0
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7 .\".if t .nr PD .5v
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8 .\".if n .nr PD 1v
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9 .nr lu 0
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10 .de CW
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11 .nr PQ \\n(.f
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12 .if t .ft CW
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13 .ie \\$1 .if n .ul 999
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14 .el .if n .ul 1
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15 .if t .if !\\$1 \&\\$1\f\\n(PQ\\$2
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17 .if n .if \\n(.$>1 \&\\$1\c
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18 .if n .if \\n(.$>1 \&\\$2
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19 ..
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20 .ds [. \ [
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21 .ds .] ]
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22 .\"----------------------------------------
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23 .TL
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24 Why the Unix Philosophy matters
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25 .AU
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26 markus schnalke <meillo@marmaro.de>
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27 .AB
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28 .ti \n(.iu
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29 This paper discusses the importance of the Unix Philosophy in software design.
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30 Today, few software designers are aware of these concepts,
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31 and thus most modern software is limited and does not make use of software leverage.
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32 Knowing and following the tenets of the Unix Philosophy makes software more valuable.
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33 .AE
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34
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35 .if t .2C
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36
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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
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46 .NH 1
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47 Introduction
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48 .LP
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49 Building a software is a process from an idea of the purpose of the software
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50 to its release.
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51 No matter \fIhow\fP the process is run, two things are common:
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52 the initial idea and the release.
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53 The process inbetween can be of any shape.
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54 The the maintainance work after the release is ignored for the moment.
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55 .PP
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56 The process of building splits mainly in two parts:
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57 the planning of what and how to build, and implementing the plan by writing code.
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58 This paper focuses on the planning part \(en the designing of the software.
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59 .PP
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60 Software design is the plan of how the internals and externals of the software should look like,
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61 based on the requirements.
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62 This paper discusses the recommendations of the Unix Philosphy about software design.
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63 .PP
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64 The here discussed ideas can get applied by any development process.
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65 The Unix Philosphy does recommend how the software development process should look like,
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66 but this shall not be of matter here.
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67 Similar, the question of how to write the code is out of focus.
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68 .PP
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69 The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet.
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70 The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed.
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71 It is no limited set of rules, but what people see to be common to typical Unix software.
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72 Several people stated their view on the Unix Philosophy.
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73 Best known are:
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74 .IP \(bu
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75 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
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76 .[
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77 %A M. D. McIlroy
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78 %A E. N. Pinson
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meillo@1
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79 %A B. A. Taque
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meillo@1
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80 %T UNIX Time-Sharing System Forward
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81 %J The Bell System Technical Journal
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82 %D 1978
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83 %V 57
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84 %N 6
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85 %P 1902
|
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86 .]
|
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87 .IP \(bu
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88 Mike Gancarz' book ``The UNIX Philosophy''.
|
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89 .[
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90 %A Mike Gancarz
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91 %T The UNIX Philosophy
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92 %D 1995
|
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93 %I Digital Press
|
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94 .]
|
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95 .IP \(bu
|
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96 Eric S. Raymond's book ``The Art of UNIX Programming''.
|
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|
97 .[
|
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98 %A Eric S. Raymond
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99 %T The Art of UNIX Programming
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100 %D 2003
|
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101 %I Addison-Wesley
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102 %O .CW \s-1http://www.faqs.org/docs/artu/
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103 .]
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104 .LP
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105 These different views on the Unix Philosophy have much in common.
|
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106 Especially, the main concepts are similar for all of them.
|
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107 But there are also points on which they differ.
|
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108 This only underlines what the Unix Philosophy is:
|
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109 A retrospective view on the main concepts of Unix software;
|
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110 especially those that were sucessful and unique to Unix.
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111 .PP
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112 Before we will have a look at concrete concepts,
|
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113 we discuss why software design is important
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114 and what problems bad design introduces.
|
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115
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116
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117 .NH 1
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118 Importance of software design
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119 .LP
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meillo@2
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120 Why should we design software at all?
|
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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.
|
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|
125 Software design is the shape of the built software.
|
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|
126 This means, that different designs of a software would be different target points to go to.
|
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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
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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''
|
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163
|
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164
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165
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166
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167 .NH 1
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168 The Unix Philosophy
|
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169 .LP
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170 The origins of the Unix Philosophy were already introduced.
|
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171 This chapter explains the philosophy and shows concrete examples of its application.
|
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172 .NH 2
|
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173 Examples
|
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174 .LP
|
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175 Following are some examples to demonstrate how applied Unix Philosophy feels like.
|
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176 Knowledge of using the Unix shell is assumed.
|
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177 .PP
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178 Counting the number of files in the current directory:
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179 .DS
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180 .CW
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181 ls | wc -l
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182 .DE
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183 The
|
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184 .CW ls
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185 command lists all files in the current directory, one per line,
|
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186 and
|
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187 .CW "wc -l
|
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188 counts how many lines they are.
|
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189 .PP
|
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190 Counting all files that do not contain ``foo'' in their name:
|
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191 .DS
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192 .CW
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193 ls | grep -v foo | wc -l
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194 .DE
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195 Here, the list of files is filtered by
|
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196 .CW grep
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197 to remove all that contain ``foo''.
|
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198 The rest is the same as in the previous example.
|
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199 .PP
|
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200 Finding the five largest entries in the current directory.
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201 .DS
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202 .CW
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203 du -s * | sort -nr | sed 5q
|
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204 .DE
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205 .CW "du -s *
|
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|
206 returns the recursively summed sizes of all files
|
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207 -- no matter if they are regular files or directories.
|
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208 .CW "sort -nr
|
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209 sorts the list numerically in reverse order.
|
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|
210 Finally,
|
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211 .CW "sed 5q
|
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212 quits after it has printed the fifth line.
|
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213 .PP
|
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214 The presented command lines are examples of what Unix people would use
|
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215 to get the desired output.
|
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216 There are also other ways to get the same output.
|
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217 It's a user's decision which way to go.
|
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218 .NH 2
|
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219 Pipes
|
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220 .LP
|
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221 The examples show that a lot of tasks on a Unix system
|
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|
222 are accomplished by combining several small programs.
|
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223 The connection between the single programs is denoted by the pipe operator `|'.
|
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224 .PP
|
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225 Pipes, and their extensive and easy use, are one of the great
|
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226 achievements of the Unix system.
|
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227 Pipes between programs have been possible in earlier operating systems,
|
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228 but it has never been a so central part of the concept.
|
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229 When, in the early seventies, Doug McIlroy introduced pipes for the
|
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230 Unix system,
|
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231 ``it was this concept and notation for linking several programs together
|
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232 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
|
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233 .[
|
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234 %T Unix: An Oral History
|
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235 %O http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
|
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236 .]
|
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237 .PP
|
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238 Being able to specify pipelines in an easy way is,
|
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|
239 however, not enough by itself.
|
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240 It is only one part.
|
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241 The other is the design of the programs that are used in the pipeline.
|
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242 They have to be of an external shape that allows them to be be used in a pipeline.
|
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243
|
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244
|
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245
|
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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.
|
meillo@2
|
250
|
meillo@2
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251 the topic here
|
meillo@2
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252
|
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|
253 .NH 2
|
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|
254 Interface architecture
|
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|
255 .LP
|
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256 standalone vs. tool chain
|
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|
257 .LP
|
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258 software leverage
|
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|
259 .LP
|
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|
260 possiblities
|
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261
|
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262 .NH 2
|
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|
263 Results
|
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|
264 .LP
|
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|
265 The unix phil is an answer to the sw design question
|
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|
266 .LP
|
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267 tool chains empower the uses of sw
|
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268
|
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269 .NH 1
|
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|
270 Case study: nmh
|
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|
271
|
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272 .NH 2
|
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|
273 History
|
meillo@0
|
274 .LP
|
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275 MH, nmh.
|
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276 They are old.
|
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|
277
|
meillo@0
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278 .NH 2
|
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|
279 Contrasts to similar sw
|
meillo@0
|
280 .LP
|
meillo@0
|
281 vs. Thunderbird, mutt, mailx, pine
|
meillo@0
|
282 .LP
|
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283 flexibility, no redundancy, use the shell
|
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284
|
meillo@0
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285 .NH 2
|
meillo@0
|
286 Gains of the design
|
meillo@0
|
287 .LP
|
meillo@0
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288
|
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289 .NH 2
|
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|
290 Problems
|
meillo@0
|
291 .LP
|
meillo@0
|
292
|
meillo@0
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293 .NH 1
|
meillo@0
|
294 Case study: uzbl
|
meillo@0
|
295
|
meillo@0
|
296 .NH 2
|
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|
297 History
|
meillo@0
|
298 .LP
|
meillo@0
|
299 uzbl is young
|
meillo@0
|
300
|
meillo@0
|
301 .NH 2
|
meillo@0
|
302 Contrasts to similar sw
|
meillo@0
|
303 .LP
|
meillo@0
|
304 like with nmh
|
meillo@0
|
305 .LP
|
meillo@0
|
306 addons, plugins, modules
|
meillo@0
|
307
|
meillo@0
|
308 .NH 2
|
meillo@0
|
309 Gains of the design
|
meillo@0
|
310 .LP
|
meillo@0
|
311
|
meillo@0
|
312 .NH 2
|
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|
313 Problems
|
meillo@0
|
314 .LP
|
meillo@0
|
315 broken web
|
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|
316
|
meillo@0
|
317 .NH 1
|
meillo@0
|
318 Final thoughts
|
meillo@0
|
319
|
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|
320 .NH 2
|
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|
321 Quick summary
|
meillo@0
|
322 .LP
|
meillo@0
|
323 good design
|
meillo@0
|
324 .LP
|
meillo@0
|
325 unix phil
|
meillo@0
|
326 .LP
|
meillo@0
|
327 case studies
|
meillo@0
|
328
|
meillo@0
|
329 .NH 2
|
meillo@0
|
330 Why people should choose
|
meillo@0
|
331 .LP
|
meillo@0
|
332 Make the right choice!
|
meillo@0
|
333
|
meillo@0
|
334 .nr PI .5i
|
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|
335 .rm ]<
|
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|
336 .de ]<
|
meillo@0
|
337 .LP
|
meillo@0
|
338 .de FP
|
meillo@0
|
339 .IP \\\\$1.
|
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|
340 \\..
|
meillo@0
|
341 .rm FS FE
|
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|
342 ..
|
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|
343 .SH
|
meillo@0
|
344 References
|
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|
345 .[
|
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|
346 $LIST$
|
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|
347 .]
|
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|
348 .wh -1p
|