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1 .\".if n .pl 1000i
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2 .nr PS 11
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3 .nr VS 13
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4 .de XX
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5 .pl 1v
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6 ..
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7 .em XX
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8 .\".nr PI 0
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9 .\".if t .nr PD .5v
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10 .\".if n .nr PD 1v
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11 .nr lu 0
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12 .de CW
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13 .nr PQ \\n(.f
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14 .if t .ft CW
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15 .ie ^\\$1^^ .if n .ul 999
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16 .el .if n .ul 1
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meillo@17
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17 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2
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18 .if n .if \\n(.$=1 \&\\$1
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19 .if n .if \\n(.$>1 \&\\$1\c
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20 .if n .if \\n(.$>1 \&\\$2
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21 ..
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22 .ds [. \ [
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23 .ds .] ]
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meillo@1
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24 .\"----------------------------------------
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25 .TL
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26 Why the Unix Philosophy still matters
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27 .AU
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28 markus schnalke <meillo@marmaro.de>
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29 .AB
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30 .ti \n(.iu
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31 This paper explains the importance of the Unix Philosophy for software design.
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32 Today, few software designers are aware of these concepts,
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33 and thus a lot of modern software is more limited than necessary
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34 and makes less use of software leverage than possible.
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35 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
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36 .AE
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37
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38 .\".if t .2C
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39
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40 .FS
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41 .ps -1
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42 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
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43 Mentor was professor Schweiggert. 2010-04-05
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44 .br
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45 You may retrieve this document from
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46 .CW \s-1http://marmaro.de/docs \ .
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47 .FE
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48
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49 .NH 1
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50 Introduction
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51 .LP
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52 The Unix Philosophy is the essence of how the Unix operating system,
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53 especially its toolchest, was designed.
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54 It is no limited set of fixed rules,
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55 but a loose set of guidelines which tell how to write software that
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56 suites well into Unix.
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57 Actually, the Unix Philosophy describes what is common to typical Unix software.
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58 The Wikipedia has an accurate definition:
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59 .[
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meillo@40
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60 %A Wikipedia
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meillo@40
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61 %T Unix philosophy
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62 %P Wikipedia, The Free Encyclopedia
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63 %D 2010-03-21 17:20 UTC
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64 %O .CW \s-1http://en.wikipedia.org/w/index.php?title=Unix_philosophy&oldid=351189719
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65 .]
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66 .QP
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67 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
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68 approaches to developing software based on the experience of leading
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69 developers of the Unix operating system.
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70 .PP
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71 As there is no single definition of the Unix Philosophy,
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72 several people have stated their view on what it comprises.
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73 Best known are:
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74 .IP \(bu
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meillo@1
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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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meillo@1
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77 %A M. D. McIlroy
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78 %A E. N. Pinson
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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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meillo@1
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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''.
|
meillo@1
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89 .[
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meillo@1
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90 %A Mike Gancarz
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91 %T The UNIX Philosophy
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meillo@1
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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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meillo@1
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96 Eric S. Raymond's book ``The Art of UNIX Programming''.
|
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97 .[
|
meillo@1
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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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meillo@1
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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 in all of them.
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107 McIlroy's definition can surely be called the core of the Unix Philosophy,
|
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108 but the fundamental idea behind it all, is ``small is beautiful''.
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109
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110 .PP
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111 The Unix Philosophy tells how to design and write good software for Unix.
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112 Many concepts described here base on facilities of Unix.
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113 Other operating systems may not offer such facilities,
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114 hence it may not be possible to design software is the way of the Unix Philosophy.
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115
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116 FIXME
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117
|
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118 This paper discusses the recommendations of the Unix Philosophy about software design.
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119 .PP
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120 The here discussed ideas can get applied by any development process.
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121 The Unix Philosophy does recommend how the software development process should look like,
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122 but this shall not be of matter here.
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123 Similar, the question of how to write the code is out of focus.
|
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124 .PP
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125 Before we will have a look at concrete concepts,
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126 we discuss why software design is important
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127 and what problems bad design introduces.
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128
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129
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130 .NH 1
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131 Importance of software design in general
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132 .LP
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133 Software design is the planning of how the internal structure
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134 and external interfaces of a software should look like.
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135 It has nothing to do with visual appearance.
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136 If we take a program as a car, then its color is of no matter.
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137 Its design would be the car's size, its shape, the locations of doors,
|
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138 the passenger/space ratio, the luggage capacity, and so forth.
|
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139 .PP
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140 Why should software get designed at all?
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141 It is general knowledge, that even a bad plan is better than no plan.
|
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142 Not designing software means programming without plan.
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143 This will pretty sure lead to horrible results.
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144 Horrible to use and horrible to maintain.
|
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145 These two aspects are the visible ones.
|
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146 Often invisible are the wasted possible gains.
|
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147 Good software design can make these gains available.
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148 .PP
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149 A software's design deals with quality properties.
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150 Good design leads to good quality, and quality is important.
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151 Any car may be able to drive from A to B,
|
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152 but it depends on the car's properties whether it is a good choice
|
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153 for passenger transport or not.
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154 It depends on its properties if it is a good choice
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155 for a rough mountain area.
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156 And it depends on its properties if the ride will be fun.
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157
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158 .PP
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159 Requirements for a software are twofold:
|
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160 functional and non-functional.
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161 .IP \(bu
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162 Functional requirements define directly the software's functions.
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163 They are the reason why software gets written.
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164 Someone has a problem and needs a tool to solve it.
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165 Being able to solve the problem is the main functional goal.
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166 It is the driving force behind all programming effort.
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167 Functional requirements are easier to define and to verify.
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168 .IP \(bu
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169 Non-functional requirements are also called \fIquality\fP requirements.
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170 The quality of a software are the properties that are not directly related to
|
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171 the software's basic functions.
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172 Tools of bad quality often solve the problems they were written for,
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173 but introduce problems and difficulties for usage and development, later on.
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174 Quality aspects are often overlooked at first sight,
|
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175 and they are often difficult to define clearly and to verify.
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176 .PP
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177 Quality is of few matter when the software gets built initially,
|
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178 but it is of matter for usage and maintenance of the software.
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179 A short-sighted might see in developing a software mainly building something up.
|
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180 But experience shows, that building the software the first time is
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181 only a small amount of the overall work.
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182 Bug fixing, extending, rebuilding of parts
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183 \(en maintenance work, for short \(en
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184 does soon take over the major part of the time spent on a software.
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185 Not to forget the usage of the software.
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186 These processes are highly influenced by the software's quality.
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187 Thus, quality must not be neglected.
|
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188 The problem with quality is that you hardly ``stumble over''
|
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189 bad quality during the first build,
|
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190 but this is the time when you should care about good quality most.
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191 .PP
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192 Software design is less the basic function of a software \(en
|
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193 this requirement will get satisfied anyway.
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194 Software design is more about quality aspects of the software.
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195 Good design leads to good quality, bad design to bad quality.
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196 The primary functions of the software will be affected modestly by bad quality,
|
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197 but good quality can provide a lot of additional gain,
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198 even at places where one never expected it.
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199 .PP
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200 The ISO/IEC 9126-1 standard, part 1,
|
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201 .[
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202 %I International Organization for Standardization
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203 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1
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204 %C Geneve
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205 %D 2001
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206 .]
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207 defines the quality model as consisting out of:
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208 .IP \(bu
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209 .I Functionality
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210 (suitability, accuracy, inter\%operability, security)
|
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211 .IP \(bu
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212 .I Reliability
|
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213 (maturity, fault tolerance, recoverability)
|
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214 .IP \(bu
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215 .I Usability
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216 (understandability, learnability, operability, attractiveness)
|
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217 .IP \(bu
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218 .I Efficiency
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219 (time behavior, resource utilization)
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220 .IP \(bu
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221 .I Maintainability
|
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222 (analyzability, changeability, stability, testability)
|
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223 .IP \(bu
|
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224 .I Portability
|
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225 (adaptability, installability, co-existence, replaceability)
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226 .LP
|
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227 Good design can improve these properties of a software,
|
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228 bad designed software probably suffers from not having them.
|
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229 .PP
|
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230 One further goal of software design is consistency.
|
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231 Consistency eases understanding, working on, and using things.
|
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232 Consistent internal structure and consistent interfaces to the outside
|
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233 can be provided by good design.
|
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234 .PP
|
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235 Software should be well designed because good design avoids many
|
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236 problems during the software's lifetime.
|
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237 And software should be well designed because good design can offer
|
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238 much additional gain.
|
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239 Indeed, much effort should be spent into good design to make software more valuable.
|
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240 The Unix Philosophy shows a way of how to design software well.
|
meillo@7
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241 It offers guidelines to achieve good quality and high gain for the effort spent.
|
meillo@0
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242
|
meillo@0
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243
|
meillo@0
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244 .NH 1
|
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245 The Unix Philosophy
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246 .LP
|
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247 The origins of the Unix Philosophy were already introduced.
|
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248 This chapter explains the philosophy, oriented on Gancarz,
|
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249 and shows concrete examples of its application.
|
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250
|
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251 .NH 2
|
meillo@14
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252 Pipes
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253 .LP
|
meillo@4
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254 Following are some examples to demonstrate how applied Unix Philosophy feels like.
|
meillo@4
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255 Knowledge of using the Unix shell is assumed.
|
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256 .PP
|
meillo@4
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257 Counting the number of files in the current directory:
|
meillo@9
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258 .DS I 2n
|
meillo@4
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259 .CW
|
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260 .ps -1
|
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261 ls | wc -l
|
meillo@4
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262 .DE
|
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263 The
|
meillo@4
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264 .CW ls
|
meillo@4
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265 command lists all files in the current directory, one per line,
|
meillo@4
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266 and
|
meillo@4
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267 .CW "wc -l
|
meillo@8
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268 counts the number of lines.
|
meillo@4
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269 .PP
|
meillo@8
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270 Counting the number of files that do not contain ``foo'' in their name:
|
meillo@9
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271 .DS I 2n
|
meillo@4
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272 .CW
|
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273 .ps -1
|
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274 ls | grep -v foo | wc -l
|
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275 .DE
|
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276 Here, the list of files is filtered by
|
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277 .CW grep
|
meillo@4
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278 to remove all that contain ``foo''.
|
meillo@4
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279 The rest is the same as in the previous example.
|
meillo@4
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280 .PP
|
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281 Finding the five largest entries in the current directory.
|
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282 .DS I 2n
|
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283 .CW
|
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284 .ps -1
|
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285 du -s * | sort -nr | sed 5q
|
meillo@4
|
286 .DE
|
meillo@4
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287 .CW "du -s *
|
meillo@4
|
288 returns the recursively summed sizes of all files
|
meillo@8
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289 \(en no matter if they are regular files or directories.
|
meillo@4
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290 .CW "sort -nr
|
meillo@4
|
291 sorts the list numerically in reverse order.
|
meillo@4
|
292 Finally,
|
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293 .CW "sed 5q
|
meillo@4
|
294 quits after it has printed the fifth line.
|
meillo@4
|
295 .PP
|
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|
296 The presented command lines are examples of what Unix people would use
|
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|
297 to get the desired output.
|
meillo@4
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298 There are also other ways to get the same output.
|
meillo@4
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299 It's a user's decision which way to go.
|
meillo@14
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300 .PP
|
meillo@8
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301 The examples show that many tasks on a Unix system
|
meillo@4
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302 are accomplished by combining several small programs.
|
meillo@4
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303 The connection between the single programs is denoted by the pipe operator `|'.
|
meillo@4
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304 .PP
|
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305 Pipes, and their extensive and easy use, are one of the great
|
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306 achievements of the Unix system.
|
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307 Pipes between programs have been possible in earlier operating systems,
|
meillo@4
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308 but it has never been a so central part of the concept.
|
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309 When, in the early seventies, Doug McIlroy introduced pipes for the
|
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310 Unix system,
|
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311 ``it was this concept and notation for linking several programs together
|
meillo@4
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312 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
|
meillo@4
|
313 .[
|
meillo@4
|
314 %T Unix: An Oral History
|
meillo@5
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315 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
|
meillo@4
|
316 .]
|
meillo@4
|
317 .PP
|
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318 Being able to specify pipelines in an easy way is,
|
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319 however, not enough by itself.
|
meillo@5
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320 It is only one half.
|
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321 The other is the design of the programs that are used in the pipeline.
|
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322 They have to interfaces that allows them to be used in such a way.
|
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323
|
meillo@16
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324 .NH 2
|
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325 Interface design
|
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|
326 .LP
|
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327 Unix is, first of all, simple \(en Everything is a file.
|
meillo@5
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328 Files are sequences of bytes, without any special structure.
|
meillo@5
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329 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
|
meillo@5
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330 and write a stream of bytes to ``standard output'' (stdout).
|
meillo@5
|
331 .PP
|
meillo@8
|
332 If the files \fIare\fP sequences of bytes,
|
meillo@8
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333 and the programs \fIare\fP filters on byte streams,
|
meillo@11
|
334 then there is exactly one standardized data interface.
|
meillo@5
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335 Thus it is possible to combine them in any desired way.
|
meillo@5
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336 .PP
|
meillo@5
|
337 Even a handful of small programs will yield a large set of combinations,
|
meillo@5
|
338 and thus a large set of different functions.
|
meillo@5
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339 This is leverage!
|
meillo@5
|
340 If the programs are orthogonal to each other \(en the best case \(en
|
meillo@5
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341 then the set of different functions is greatest.
|
meillo@5
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342 .PP
|
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|
343 Programs might also have a separate control interface,
|
meillo@11
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344 besides their data interface.
|
meillo@11
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345 The control interface is often called ``user interface'',
|
meillo@11
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346 because it is usually designed to be used by humans.
|
meillo@11
|
347 The Unix Philosophy discourages to assume the user to be human.
|
meillo@11
|
348 Interactive use of software is slow use of software,
|
meillo@11
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349 because the program waits for user input most of the time.
|
meillo@11
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350 Interactive software requires the user to be in front of the computer
|
meillo@11
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351 all the time.
|
meillo@11
|
352 Interactive software occupy the user's attention while they are running.
|
meillo@11
|
353 .PP
|
meillo@11
|
354 Now we come back to the idea of using several small programs, combined,
|
meillo@11
|
355 to have a more specific function.
|
meillo@11
|
356 If these single tools would all be interactive,
|
meillo@11
|
357 how would the user control them?
|
meillo@11
|
358 It is not only a problem to control several programs at once if they run at the same time,
|
meillo@11
|
359 it also very inefficient to have to control each of the single programs
|
meillo@11
|
360 that are intended to work as one large program.
|
meillo@11
|
361 Hence, the Unix Philosophy discourages programs to demand interactive use.
|
meillo@11
|
362 The behavior of programs should be defined at invocation.
|
meillo@11
|
363 This is done by specifying arguments (``command line switches'') to the program call.
|
meillo@11
|
364 Gancarz discusses this topic as ``avoid captive user interfaces''.
|
meillo@11
|
365 .[
|
meillo@11
|
366 %A Mike Gancarz
|
meillo@11
|
367 %T The UNIX Philosophy
|
meillo@11
|
368 %I Digital Press
|
meillo@11
|
369 %D 1995
|
meillo@11
|
370 %P 88 ff.
|
meillo@11
|
371 .]
|
meillo@11
|
372 .PP
|
meillo@11
|
373 Non-interactive use is, during development, also an advantage for testing.
|
meillo@11
|
374 Testing of interactive programs is much more complicated,
|
meillo@11
|
375 than testing of non-interactive programs.
|
meillo@5
|
376
|
meillo@16
|
377 .NH 2
|
meillo@8
|
378 The toolchest approach
|
meillo@5
|
379 .LP
|
meillo@5
|
380 A toolchest is a set of tools.
|
meillo@5
|
381 Instead of having one big tool for all tasks, one has many small tools,
|
meillo@5
|
382 each for one task.
|
meillo@5
|
383 Difficult tasks are solved by combining several of the small, simple tools.
|
meillo@5
|
384 .PP
|
meillo@11
|
385 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
|
meillo@11
|
386 that are filters on byte streams.
|
meillo@11
|
387 They are, to a large extend, unrelated in their function.
|
meillo@11
|
388 Hence, the Unix toolchest provides a large set of functions
|
meillo@11
|
389 that can be accessed by combining the programs in the desired way.
|
meillo@11
|
390 .PP
|
meillo@11
|
391 There are also advantages for developing small toolchest programs.
|
meillo@5
|
392 It is easier and less error-prone to write small programs.
|
meillo@5
|
393 It is also easier and less error-prone to write a large set of small programs,
|
meillo@5
|
394 than to write one large program with all the functionality included.
|
meillo@5
|
395 If the small programs are combinable, then they offer even a larger set
|
meillo@5
|
396 of functions than the single large program.
|
meillo@5
|
397 Hence, one gets two advantages out of writing small, combinable programs.
|
meillo@5
|
398 .PP
|
meillo@5
|
399 There are two drawbacks of the toolchest approach.
|
meillo@8
|
400 First, one simple, standardized, unidirectional interface has to be sufficient.
|
meillo@5
|
401 If one feels the need for more ``logic'' than a stream of bytes,
|
meillo@8
|
402 then a different approach might be of need.
|
meillo@13
|
403 But it is also possible, that he just can not imagine a design where
|
meillo@8
|
404 a stream of bytes is sufficient.
|
meillo@8
|
405 By becoming more familiar with the ``Unix style of thinking'',
|
meillo@8
|
406 developers will more often and easier find simple designs where
|
meillo@8
|
407 a stream of bytes is a sufficient interface.
|
meillo@8
|
408 .PP
|
meillo@8
|
409 The second drawback of a toolchest affects the users.
|
meillo@5
|
410 A toolchest is often more difficult to use for novices.
|
meillo@9
|
411 It is necessary to become familiar with each of the tools,
|
meillo@5
|
412 to be able to use the right one in a given situation.
|
meillo@9
|
413 Additionally, one needs to combine the tools in a senseful way on its own.
|
meillo@9
|
414 This is like a sharp knife \(en it is a powerful tool in the hand of a master,
|
meillo@5
|
415 but of no good value in the hand of an unskilled.
|
meillo@5
|
416 .PP
|
meillo@8
|
417 However, learning single, small tool of the toolchest is easier than
|
meillo@8
|
418 learning a complex tool.
|
meillo@8
|
419 The user will have a basic understanding of a yet unknown tool,
|
meillo@8
|
420 if the several tools of the toolchest have a common style.
|
meillo@8
|
421 He will be able to transfer knowledge over one tool to another.
|
meillo@8
|
422 .PP
|
meillo@8
|
423 Moreover, the second drawback can be removed easily by adding wrappers
|
meillo@8
|
424 around the single tools.
|
meillo@5
|
425 Novice users do not need to learn several tools if a professional wraps
|
meillo@8
|
426 the single commands into a more high-level script.
|
meillo@5
|
427 Note that the wrapper script still calls the small tools;
|
meillo@5
|
428 the wrapper script is just like a skin around.
|
meillo@8
|
429 No complexity is added this way,
|
meillo@8
|
430 but new programs can get created out of existing one with very low effort.
|
meillo@5
|
431 .PP
|
meillo@5
|
432 A wrapper script for finding the five largest entries in the current directory
|
meillo@5
|
433 could look like this:
|
meillo@9
|
434 .DS I 2n
|
meillo@5
|
435 .CW
|
meillo@9
|
436 .ps -1
|
meillo@5
|
437 #!/bin/sh
|
meillo@5
|
438 du -s * | sort -nr | sed 5q
|
meillo@5
|
439 .DE
|
meillo@5
|
440 The script itself is just a text file that calls the command line
|
meillo@5
|
441 a professional user would type in directly.
|
meillo@8
|
442 Making the program flexible on the number of entries it prints,
|
meillo@8
|
443 is easily possible:
|
meillo@9
|
444 .DS I 2n
|
meillo@8
|
445 .CW
|
meillo@9
|
446 .ps -1
|
meillo@8
|
447 #!/bin/sh
|
meillo@8
|
448 num=5
|
meillo@8
|
449 [ $# -eq 1 ] && num="$1"
|
meillo@8
|
450 du -sh * | sort -nr | sed "${num}q"
|
meillo@8
|
451 .DE
|
meillo@8
|
452 This script acts like the one before, when called without an argument.
|
meillo@8
|
453 But one can also specify a numerical argument to define the number of lines to print.
|
meillo@5
|
454
|
meillo@16
|
455 .NH 2
|
meillo@8
|
456 A powerful shell
|
meillo@8
|
457 .LP
|
meillo@10
|
458 It was already said, that the Unix shell provides the possibility to
|
meillo@10
|
459 combine small programs into large ones easily.
|
meillo@10
|
460 A powerful shell is a great feature in other ways, too.
|
meillo@8
|
461 .PP
|
meillo@10
|
462 For instance by including a scripting language.
|
meillo@10
|
463 The control statements are build into the shell.
|
meillo@8
|
464 The functions, however, are the normal programs, everyone can use on the system.
|
meillo@10
|
465 Thus, the programs are known, so learning to program in the shell is easy.
|
meillo@8
|
466 Using normal programs as functions in the shell programming language
|
meillo@10
|
467 is only possible because they are small and combinable tools in a toolchest style.
|
meillo@8
|
468 .PP
|
meillo@8
|
469 The Unix shell encourages to write small scripts out of other programs,
|
meillo@8
|
470 because it is so easy to do.
|
meillo@8
|
471 This is a great step towards automation.
|
meillo@8
|
472 It is wonderful if the effort to automate a task equals the effort
|
meillo@8
|
473 it takes to do it the second time by hand.
|
meillo@8
|
474 If it is so, then the user will be happy to automate everything he does more than once.
|
meillo@8
|
475 .PP
|
meillo@8
|
476 Small programs that do one job well, standardized interfaces between them,
|
meillo@8
|
477 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
|
meillo@8
|
478 this will inevitably produce software leverage.
|
meillo@8
|
479 Getting multiple times the benefit of an investment is a great offer.
|
meillo@10
|
480 .PP
|
meillo@10
|
481 The shell also encourages rapid prototyping.
|
meillo@10
|
482 Many well known programs started as quickly hacked shell scripts,
|
meillo@10
|
483 and turned into ``real'' programs, written in C, later.
|
meillo@10
|
484 Building a prototype first is a way to avoid the biggest problems
|
meillo@10
|
485 in application development.
|
meillo@10
|
486 Fred Brooks writes in ``No Silver Bullet'':
|
meillo@10
|
487 .[
|
meillo@10
|
488 %A Frederick P. Brooks, Jr.
|
meillo@10
|
489 %T No Silver Bullet: Essence and Accidents of Software Engineering
|
meillo@10
|
490 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference
|
meillo@10
|
491 %E H.-J. Kugler
|
meillo@10
|
492 %D 1986
|
meillo@10
|
493 %P 1069\(en1076
|
meillo@10
|
494 %I Elsevier Science B.V.
|
meillo@10
|
495 %C Amsterdam, The Netherlands
|
meillo@10
|
496 .]
|
meillo@10
|
497 .QP
|
meillo@10
|
498 The hardest single part of building a software system is deciding precisely what to build.
|
meillo@10
|
499 No other part of the conceptual work is so difficult as establishing the detailed
|
meillo@10
|
500 technical requirements, [...].
|
meillo@10
|
501 No other part of the work so cripples the resulting system if done wrong.
|
meillo@10
|
502 No other part is more difficult to rectify later.
|
meillo@10
|
503 .PP
|
meillo@10
|
504 Writing a prototype is a great method to become familiar with the requirements
|
meillo@10
|
505 and to actually run into real problems.
|
meillo@10
|
506 Today, prototyping is often seen as a first step in building a software.
|
meillo@10
|
507 This is, of course, good.
|
meillo@10
|
508 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
|
meillo@10
|
509 After having built the prototype, one might notice, that the prototype is already
|
meillo@10
|
510 \fIgood enough\fP.
|
meillo@10
|
511 Hence, no reimplementation, in a more sophisticated programming language, might be of need,
|
meillo@10
|
512 for the moment.
|
meillo@23
|
513 Maybe later, it might be necessary to rewrite the software, but not now.
|
meillo@10
|
514 .PP
|
meillo@10
|
515 By delaying further work, one keeps the flexibility to react easily on
|
meillo@10
|
516 changing requirements.
|
meillo@10
|
517 Software parts that are not written will not miss the requirements.
|
meillo@10
|
518
|
meillo@16
|
519 .NH 2
|
meillo@10
|
520 Worse is better
|
meillo@10
|
521 .LP
|
meillo@10
|
522 The Unix Philosophy aims for the 80% solution;
|
meillo@10
|
523 others call it the ``Worse is better'' approach.
|
meillo@10
|
524 .PP
|
meillo@10
|
525 First, practical experience shows, that it is almost never possible to define the
|
meillo@10
|
526 requirements completely and correctly the first time.
|
meillo@10
|
527 Hence one should not try to; it will fail anyway.
|
meillo@10
|
528 Second, practical experience shows, that requirements change during time.
|
meillo@10
|
529 Hence it is best to delay requirement-based design decisions as long as possible.
|
meillo@10
|
530 Also, the software should be small and flexible as long as possible
|
meillo@10
|
531 to react on changing requirements.
|
meillo@10
|
532 Shell scripts, for example, are more easily adjusted as C programs.
|
meillo@10
|
533 Third, practical experience shows, that maintenance is hard work.
|
meillo@10
|
534 Hence, one should keep the amount of software as small as possible;
|
meillo@10
|
535 it should just fulfill the \fIcurrent\fP requirements.
|
meillo@10
|
536 Software parts that will be written later, do not need maintenance now.
|
meillo@10
|
537 .PP
|
meillo@10
|
538 Starting with a prototype in a scripting language has several advantages:
|
meillo@10
|
539 .IP \(bu
|
meillo@10
|
540 As the initial effort is low, one will likely start right away.
|
meillo@10
|
541 .IP \(bu
|
meillo@10
|
542 As working parts are available soon, the real requirements can get identified soon.
|
meillo@10
|
543 .IP \(bu
|
meillo@10
|
544 When a software is usable, it gets used, and thus tested.
|
meillo@10
|
545 Hence problems will be found at early stages of the development.
|
meillo@10
|
546 .IP \(bu
|
meillo@10
|
547 The prototype might be enough for the moment,
|
meillo@10
|
548 thus further work on the software can be delayed to a time
|
meillo@10
|
549 when one knows better about the requirements and problems,
|
meillo@10
|
550 than now.
|
meillo@10
|
551 .IP \(bu
|
meillo@10
|
552 Implementing now only the parts that are actually needed now,
|
meillo@10
|
553 requires fewer maintenance work.
|
meillo@10
|
554 .IP \(bu
|
meillo@10
|
555 If the global situation changes so that the software is not needed anymore,
|
meillo@10
|
556 then less effort was spent into the project, than it would have be
|
meillo@10
|
557 when a different approach had been used.
|
meillo@10
|
558
|
meillo@16
|
559 .NH 2
|
meillo@11
|
560 Upgrowth and survival of software
|
meillo@11
|
561 .LP
|
meillo@12
|
562 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
|
meillo@13
|
563 Although these are just verbs, they do imply a specific view on the work process
|
meillo@13
|
564 they describe.
|
meillo@12
|
565 The better verb, however, is to \fIgrow\fP.
|
meillo@12
|
566 .PP
|
meillo@12
|
567 Creating software in the sense of the Unix Philosophy is an incremental process.
|
meillo@12
|
568 It starts with a first prototype, which evolves as requirements change.
|
meillo@12
|
569 A quickly hacked shell script might become a large, sophisticated,
|
meillo@13
|
570 compiled program this way.
|
meillo@13
|
571 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
|
meillo@13
|
572 While being alive it will get extended, rearranged, rebuilt (from scratch).
|
meillo@12
|
573 Growing software matches the view that ``software is never finished. It is only released.''
|
meillo@12
|
574 .[
|
meillo@13
|
575 %O FIXME
|
meillo@13
|
576 %A Mike Gancarz
|
meillo@13
|
577 %T The UNIX Philosophy
|
meillo@13
|
578 %P 26
|
meillo@12
|
579 .]
|
meillo@12
|
580 .PP
|
meillo@13
|
581 Software can be seen as being controlled by evolutionary processes.
|
meillo@13
|
582 Successful software is software that is used by many for a long time.
|
meillo@12
|
583 This implies that the software is needed, useful, and better than alternatives.
|
meillo@12
|
584 Darwin talks about: ``The survival of the fittest.''
|
meillo@12
|
585 .[
|
meillo@13
|
586 %O FIXME
|
meillo@13
|
587 %A Charles Darwin
|
meillo@12
|
588 .]
|
meillo@12
|
589 Transferred to software: The most successful software, is the fittest,
|
meillo@12
|
590 is the one that survives.
|
meillo@13
|
591 (This may be at the level of one creature, or at the level of one species.)
|
meillo@13
|
592 The fitness of software is affected mainly by four properties:
|
meillo@15
|
593 portability of code, portability of data, range of usability, and reusability of parts.
|
meillo@15
|
594 .\" .IP \(bu
|
meillo@15
|
595 .\" portability of code
|
meillo@15
|
596 .\" .IP \(bu
|
meillo@15
|
597 .\" portability of data
|
meillo@15
|
598 .\" .IP \(bu
|
meillo@15
|
599 .\" range of usability
|
meillo@15
|
600 .\" .IP \(bu
|
meillo@15
|
601 .\" reuseability of parts
|
meillo@13
|
602 .PP
|
meillo@15
|
603 (1)
|
meillo@15
|
604 .I "Portability of code
|
meillo@15
|
605 means, using high-level programming languages,
|
meillo@13
|
606 sticking to the standard,
|
meillo@13
|
607 and avoiding optimizations that introduce dependencies on specific hardware.
|
meillo@13
|
608 Hardware has a much lower lifetime than software.
|
meillo@13
|
609 By chaining software to a specific hardware,
|
meillo@13
|
610 the software's lifetime gets shortened to that of this hardware.
|
meillo@13
|
611 In contrast, software should be easy to port \(en
|
meillo@23
|
612 adaptation is the key to success.
|
meillo@13
|
613 .\" cf. practice of prog: ch08
|
meillo@13
|
614 .PP
|
meillo@15
|
615 (2)
|
meillo@15
|
616 .I "Portability of data
|
meillo@15
|
617 is best achieved by avoiding binary representations
|
meillo@13
|
618 to store data, because binary representations differ from machine to machine.
|
meillo@23
|
619 Textual representation is favored.
|
meillo@13
|
620 Historically, ASCII was the charset of choice.
|
meillo@13
|
621 In the future, UTF-8 might be the better choice, however.
|
meillo@13
|
622 Important is that it is a plain text representation in a
|
meillo@13
|
623 very common charset encoding.
|
meillo@13
|
624 Apart from being able to transfer data between machines,
|
meillo@13
|
625 readable data has the great advantage, that humans are able
|
meillo@13
|
626 to directly edit it with text editors and other tools from the Unix toolchest.
|
meillo@13
|
627 .\" gancarz tenet 5
|
meillo@13
|
628 .PP
|
meillo@15
|
629 (3)
|
meillo@15
|
630 A large
|
meillo@15
|
631 .I "range of usability
|
meillo@23
|
632 ensures good adaptation, and thus good survival.
|
meillo@13
|
633 It is a special distinction if a software becomes used in fields of action,
|
meillo@13
|
634 the original authors did never imagine.
|
meillo@13
|
635 Software that solves problems in a general way will likely be used
|
meillo@13
|
636 for all kinds of similar problems.
|
meillo@13
|
637 Being too specific limits the range of uses.
|
meillo@13
|
638 Requirements change through time, thus use cases change or even vanish.
|
meillo@13
|
639 A good example in this point is Allman's sendmail.
|
meillo@13
|
640 Allman identifies flexibility to be one major reason for sendmail's success:
|
meillo@13
|
641 .[
|
meillo@13
|
642 %O FIXME
|
meillo@13
|
643 %A Allman
|
meillo@13
|
644 %T sendmail
|
meillo@13
|
645 .]
|
meillo@13
|
646 .QP
|
meillo@13
|
647 Second, I limited myself to the routing function [...].
|
meillo@13
|
648 This was a departure from the dominant thought of the time, [...].
|
meillo@13
|
649 .QP
|
meillo@13
|
650 Third, the sendmail configuration file was flexible enough to adopt
|
meillo@13
|
651 to a rapidly changing world [...].
|
meillo@12
|
652 .LP
|
meillo@13
|
653 Successful software adopts itself to the changing world.
|
meillo@13
|
654 .PP
|
meillo@15
|
655 (4)
|
meillo@15
|
656 .I "Reuse of parts
|
meillo@15
|
657 is even one step further.
|
meillo@13
|
658 A software may completely lose its field of action,
|
meillo@13
|
659 but parts of which the software is build may be general and independent enough
|
meillo@13
|
660 to survive this death.
|
meillo@13
|
661 If software is build by combining small independent programs,
|
meillo@13
|
662 then there are parts readily available for reuse.
|
meillo@13
|
663 Who cares if the large program is a failure,
|
meillo@13
|
664 but parts of it become successful instead?
|
meillo@10
|
665
|
meillo@16
|
666 .NH 2
|
meillo@14
|
667 Summary
|
meillo@0
|
668 .LP
|
meillo@14
|
669 This chapter explained the central ideas of the Unix Philosophy.
|
meillo@14
|
670 For each of the ideas, it was exposed what advantages they introduce.
|
meillo@14
|
671 The Unix Philosophy are guidelines that help to write valuable software.
|
meillo@14
|
672 From the view point of a software developer or software designer,
|
meillo@14
|
673 the Unix Philosophy provides answers to many software design problem.
|
meillo@14
|
674 .PP
|
meillo@14
|
675 The various ideas of the Unix Philosophy are very interweaved
|
meillo@14
|
676 and can hardly be applied independently.
|
meillo@14
|
677 However, the probably most important messages are:
|
meillo@14
|
678 .I "``Do one thing well!''" ,
|
meillo@14
|
679 .I "``Keep it simple!''" ,
|
meillo@14
|
680 and
|
meillo@14
|
681 .I "``Use software leverage!''
|
meillo@0
|
682
|
meillo@8
|
683
|
meillo@8
|
684
|
meillo@0
|
685 .NH 1
|
meillo@19
|
686 Case study: \s-1MH\s0
|
meillo@18
|
687 .LP
|
meillo@30
|
688 The previous chapter introduced and explained the Unix Philosophy
|
meillo@18
|
689 from a general point of view.
|
meillo@30
|
690 The driving force were the guidelines; references to
|
meillo@18
|
691 existing software were given only sparsely.
|
meillo@18
|
692 In this and the next chapter, concrete software will be
|
meillo@18
|
693 the driving force in the discussion.
|
meillo@18
|
694 .PP
|
meillo@23
|
695 This first case study is about the mail user agents (\s-1MUA\s0)
|
meillo@23
|
696 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
|
meillo@23
|
697 (``new mail handler'').
|
meillo@23
|
698 \s-1MUA\s0s provide functions to read, compose, and organize mail,
|
meillo@23
|
699 but (ideally) not to transfer.
|
meillo@19
|
700 In this document, the name \s-1MH\s0 will be used for both of them.
|
meillo@19
|
701 A distinction will only be made if differences between
|
meillo@19
|
702 them are described.
|
meillo@18
|
703
|
meillo@0
|
704
|
meillo@0
|
705 .NH 2
|
meillo@19
|
706 Historical background
|
meillo@0
|
707 .LP
|
meillo@19
|
708 Electronic mail was available in Unix very early.
|
meillo@30
|
709 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
|
meillo@30
|
710 which was already present in the First Edition.
|
meillo@30
|
711 .[
|
meillo@30
|
712 %A Peter H. Salus
|
meillo@30
|
713 %T A Quarter Century of UNIX
|
meillo@30
|
714 %D 1994
|
meillo@30
|
715 %I Addison-Wesley
|
meillo@30
|
716 %P 41 f.
|
meillo@30
|
717 .]
|
meillo@30
|
718 It was a small program that either prints the user's mailbox file
|
meillo@19
|
719 or appends text to someone elses mailbox file,
|
meillo@19
|
720 depending on the command line arguments.
|
meillo@19
|
721 .[
|
meillo@19
|
722 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf
|
meillo@19
|
723 .]
|
meillo@19
|
724 It was a program that did one job well.
|
meillo@23
|
725 This job was emailing, which was very simple then.
|
meillo@19
|
726 .PP
|
meillo@23
|
727 Later, emailing became more powerful, and thus more complex.
|
meillo@19
|
728 The simple \f(CWmail\fP, which knew nothing of subjects,
|
meillo@19
|
729 independent handling of single messages,
|
meillo@19
|
730 and long-time storage of them, was not powerful enough anymore.
|
meillo@19
|
731 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
|
meillo@19
|
732 in 1978 to provide additional functions for emailing.
|
meillo@19
|
733 Mail was still one program, but now it was large and did
|
meillo@19
|
734 several jobs.
|
meillo@23
|
735 Its user interface is modeled after the one of \fIed\fP.
|
meillo@19
|
736 It is designed for humans, but is still scriptable.
|
meillo@23
|
737 \fImailx\fP is the adaptation of Berkeley Mail into System V.
|
meillo@19
|
738 .[
|
meillo@19
|
739 %A Gunnar Ritter
|
meillo@19
|
740 %O http://heirloom.sourceforge.net/mailx_history.html
|
meillo@19
|
741 .]
|
meillo@30
|
742 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
|
meillo@19
|
743 followed Mail's direction.
|
meillo@19
|
744 They are large, monolithic programs which include all emailing functions.
|
meillo@19
|
745 .PP
|
meillo@23
|
746 A different way was taken by the people of \s-1RAND\s0 Corporation.
|
meillo@38
|
747 In the beginning, they also had used a monolithic mail system,
|
meillo@30
|
748 called \s-1MS\s0 (for ``mail system'').
|
meillo@19
|
749 But in 1977, Stockton Gaines and Norman Shapiro
|
meillo@19
|
750 came up with a proposal of a new email system concept \(en
|
meillo@19
|
751 one that honors the Unix Philosophy.
|
meillo@19
|
752 The concept was implemented by Bruce Borden in 1978 and 1979.
|
meillo@19
|
753 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
|
meillo@18
|
754 .PP
|
meillo@18
|
755 Since then, \s-1RAND\s0, the University of California at Irvine and
|
meillo@19
|
756 at Berkeley, and several others have contributed to the software.
|
meillo@18
|
757 However, it's core concepts remained the same.
|
meillo@23
|
758 In the late 90s, when development of \s-1MH\s0 slowed down,
|
meillo@19
|
759 Richard Coleman started with \fInmh\fP, the new mail handler.
|
meillo@19
|
760 His goal was to improve \s-1MH\s0, especially in regard of
|
meillo@23
|
761 the requirements of modern emailing.
|
meillo@19
|
762 Today, nmh is developed by various people on the Internet.
|
meillo@18
|
763 .[
|
meillo@18
|
764 %T RAND and the Information Evolution: A History in Essays and Vignettes
|
meillo@18
|
765 %A Willis H. Ware
|
meillo@18
|
766 %D 2008
|
meillo@18
|
767 %I The RAND Corporation
|
meillo@18
|
768 %P 128\(en137
|
meillo@18
|
769 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/
|
meillo@18
|
770 .]
|
meillo@18
|
771 .[
|
meillo@18
|
772 %T MH & xmh: Email for Users & Programmers
|
meillo@18
|
773 %A Jerry Peek
|
meillo@18
|
774 %D 1991, 1992, 1995
|
meillo@18
|
775 %I O'Reilly & Associates, Inc.
|
meillo@18
|
776 %P Appendix B
|
meillo@18
|
777 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP
|
meillo@18
|
778 .]
|
meillo@0
|
779
|
meillo@0
|
780 .NH 2
|
meillo@20
|
781 Contrasts to monolithic mail systems
|
meillo@0
|
782 .LP
|
meillo@19
|
783 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
|
meillo@38
|
784 Although there might actually exist further, very little known,
|
meillo@30
|
785 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
|
meillo@19
|
786 .PP
|
meillo@30
|
787 Monolithic \s-1MUA\s0s gather all their functions in one program.
|
meillo@30
|
788 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
|
meillo@23
|
789 Following is a list of important programs of \s-1MH\s0's toolchest
|
meillo@30
|
790 and their function.
|
meillo@30
|
791 It gives a feeling of how the toolchest looks like.
|
meillo@19
|
792 .IP \(bu
|
meillo@19
|
793 .CW inc :
|
meillo@30
|
794 incorporate new mail (this is how mail enters the system)
|
meillo@19
|
795 .IP \(bu
|
meillo@19
|
796 .CW scan :
|
meillo@19
|
797 list messages in folder
|
meillo@19
|
798 .IP \(bu
|
meillo@19
|
799 .CW show :
|
meillo@19
|
800 show message
|
meillo@19
|
801 .IP \(bu
|
meillo@19
|
802 .CW next\fR/\fPprev :
|
meillo@19
|
803 show next/previous message
|
meillo@19
|
804 .IP \(bu
|
meillo@19
|
805 .CW folder :
|
meillo@19
|
806 change current folder
|
meillo@19
|
807 .IP \(bu
|
meillo@19
|
808 .CW refile :
|
meillo@19
|
809 refile message into folder
|
meillo@19
|
810 .IP \(bu
|
meillo@19
|
811 .CW rmm :
|
meillo@19
|
812 remove message
|
meillo@19
|
813 .IP \(bu
|
meillo@19
|
814 .CW comp :
|
meillo@19
|
815 compose a new message
|
meillo@19
|
816 .IP \(bu
|
meillo@19
|
817 .CW repl :
|
meillo@19
|
818 reply to a message
|
meillo@19
|
819 .IP \(bu
|
meillo@19
|
820 .CW forw :
|
meillo@19
|
821 forward a message
|
meillo@19
|
822 .IP \(bu
|
meillo@19
|
823 .CW send :
|
meillo@30
|
824 send a prepared message (this is how mail leaves the system)
|
meillo@0
|
825 .LP
|
meillo@19
|
826 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
|
meillo@19
|
827 The user does not leave the shell to run \s-1MH\s0,
|
meillo@30
|
828 but he uses the various \s-1MH\s0 programs within the shell.
|
meillo@23
|
829 Using a monolithic program with a captive user interface
|
meillo@23
|
830 means ``entering'' the program, using it, and ``exiting'' the program.
|
meillo@23
|
831 Using toolchests like \s-1MH\s0 means running programs,
|
meillo@38
|
832 alone or in combination with others, even from other toolchests,
|
meillo@23
|
833 without leaving the shell.
|
meillo@30
|
834
|
meillo@30
|
835 .NH 2
|
meillo@30
|
836 Data storage
|
meillo@30
|
837 .LP
|
meillo@34
|
838 \s-1MH\s0's mail storage is a directory tree under the user's
|
meillo@34
|
839 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
|
meillo@34
|
840 where mail folders are directories and mail messages are text files
|
meillo@34
|
841 within them.
|
meillo@34
|
842 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
|
meillo@34
|
843 the public message sequences of that folder, for instance new messages.
|
meillo@34
|
844 Mail messages are text files located in a mail folder.
|
meillo@34
|
845 The files contain the messages as they were received.
|
meillo@34
|
846 They are numbered in ascending order in each folder.
|
meillo@19
|
847 .PP
|
meillo@30
|
848 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
|
meillo@30
|
849 Alternatives are \fImbox\fP and \fImaildir\fP.
|
meillo@30
|
850 In the mbox format all messages are stored within one file.
|
meillo@30
|
851 This was a good solution in the early days, when messages
|
meillo@30
|
852 were only a few lines of text and were deleted soon.
|
meillo@30
|
853 Today, when single messages often include several megabytes
|
meillo@30
|
854 of attachments, it is a bad solution.
|
meillo@30
|
855 Another disadvantage of the mbox format is that it is
|
meillo@30
|
856 more difficult to write tools that work on mail messages,
|
meillo@30
|
857 because it is always necessary to first find and extract
|
meillo@30
|
858 the relevant message in the mbox file.
|
meillo@30
|
859 With the \s-1MH\s0 mailbox format,
|
meillo@30
|
860 each message is a self-standing item, by definition.
|
meillo@30
|
861 Also, the problem of concurrent access to one mailbox is
|
meillo@30
|
862 reduced to the problem of concurrent access to one message.
|
meillo@30
|
863 Maildir is generally similar to \s-1MH\s0's format,
|
meillo@30
|
864 but modified towards guaranteed reliability.
|
meillo@30
|
865 This involves some complexity, unfortunately.
|
meillo@34
|
866 .PP
|
meillo@34
|
867 Working with \s-1MH\s0's toolchest on mailboxes is much like
|
meillo@34
|
868 working with Unix' toolchest on directory trees:
|
meillo@34
|
869 \f(CWscan\fP is like \f(CWls\fP,
|
meillo@34
|
870 \f(CWshow\fP is like \f(CWcat\fP,
|
meillo@34
|
871 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
|
meillo@34
|
872 \f(CWrefile\fP is like \f(CWmv\fP,
|
meillo@34
|
873 and \f(CWrmm\fP is like \f(CWrm\fP.
|
meillo@34
|
874 .PP
|
meillo@34
|
875 The context of tools in Unix consists mainly the current working directory,
|
meillo@34
|
876 the user identification, and the environment variables.
|
meillo@34
|
877 \s-1MH\s0 extends this context by two more items:
|
meillo@34
|
878 .IP \(bu
|
meillo@34
|
879 The current mail folder, which is similar to the current working directory.
|
meillo@34
|
880 For mail folders, \f(CWfolder\fP provides the corresponding functionality
|
meillo@34
|
881 of \f(CWcd\fP and \f(CWpwd\fP for directories.
|
meillo@34
|
882 .IP \(bu
|
meillo@34
|
883 Sequences, which are named sets of messages in a mail folder.
|
meillo@34
|
884 The current message, relative to a mail folder, is a special sequence.
|
meillo@34
|
885 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
|
meillo@34
|
886 .LP
|
meillo@34
|
887 In contrast to Unix' context, which is chained to the shell session,
|
meillo@34
|
888 \s-1MH\s0's context is independent.
|
meillo@34
|
889 Usually there is one context for each user, but a user can have many
|
meillo@34
|
890 contexts.
|
meillo@34
|
891 Public sequences are an exception, as they belong to the mail folder.
|
meillo@34
|
892 .[
|
meillo@34
|
893 %O mh-profile(5) and mh-sequence(5)
|
meillo@34
|
894 .]
|
meillo@20
|
895
|
meillo@0
|
896 .NH 2
|
meillo@20
|
897 Discussion of the design
|
meillo@0
|
898 .LP
|
meillo@20
|
899 The following paragraphs discuss \s-1MH\s0 in regard to the tenets
|
meillo@23
|
900 of the Unix Philosophy which Gancarz identified.
|
meillo@20
|
901
|
meillo@20
|
902 .PP
|
meillo@33
|
903 .B "Small is beautiful
|
meillo@20
|
904 and
|
meillo@33
|
905 .B "do one thing well
|
meillo@20
|
906 are two design goals that are directly visible in \s-1MH\s0.
|
meillo@20
|
907 Gancarz actually presents \s-1MH\s0 as example under the headline
|
meillo@20
|
908 ``Making UNIX Do One Thing Well'':
|
meillo@20
|
909 .QP
|
meillo@20
|
910 [\s-1MH\s0] consists of a series of programs which
|
meillo@20
|
911 when combined give the user an enormous ability
|
meillo@20
|
912 to manipulate electronic mail messages.
|
meillo@20
|
913 A complex application, it shows that not only is it
|
meillo@20
|
914 possible to build large applications from smaller
|
meillo@20
|
915 components, but also that such designs are actually preferable.
|
meillo@20
|
916 .[
|
meillo@20
|
917 %A Mike Gancarz
|
meillo@20
|
918 %T unix-phil
|
meillo@20
|
919 %P 125
|
meillo@20
|
920 .]
|
meillo@20
|
921 .LP
|
meillo@20
|
922 The various small programs of \s-1MH\s0 were relatively easy
|
meillo@23
|
923 to write, because each of them is small, limited to one function,
|
meillo@23
|
924 and has clear boundaries.
|
meillo@20
|
925 For the same reasons, they are also good to maintain.
|
meillo@20
|
926 Further more, the system can easily get extended.
|
meillo@20
|
927 One only needs to put a new program into the toolchest.
|
meillo@23
|
928 This was done, for instance, when \s-1MIME\s0 support was added
|
meillo@20
|
929 (e.g. \f(CWmhbuild\fP).
|
meillo@20
|
930 Also, different programs can exist to do the basically same job
|
meillo@20
|
931 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
|
meillo@20
|
932 If someone needs a mail system with some additionally
|
meillo@23
|
933 functions that are available nowhere yet, he best takes a
|
meillo@20
|
934 toolchest system like \s-1MH\s0 where he can add the
|
meillo@20
|
935 functionality with little work.
|
meillo@20
|
936
|
meillo@20
|
937 .PP
|
meillo@34
|
938 .B "Store data in flat text files
|
meillo@34
|
939 is followed by \s-1MH\s0.
|
meillo@34
|
940 This is not surprising, because email messages are already plain text.
|
meillo@34
|
941 \s-1MH\s0 stores the messages as it receives them,
|
meillo@34
|
942 thus any other tool that works on RFC 2822 mail messages can operate
|
meillo@34
|
943 on the messages in an \s-1MH\s0 mailbox.
|
meillo@34
|
944 All other files \s-1MH\s0 uses are plain text too.
|
meillo@34
|
945 It is therefore possible and encouraged to use the text processing
|
meillo@34
|
946 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
|
meillo@20
|
947
|
meillo@20
|
948 .PP
|
meillo@33
|
949 .B "Avoid captive user interfaces" .
|
meillo@19
|
950 \s-1MH\s0 is perfectly suited for non-interactive use.
|
meillo@19
|
951 It offers all functions directly and without captive user interfaces.
|
meillo@30
|
952 If, nonetheless, users want a graphical user interface,
|
meillo@20
|
953 they can have it with \fIxmh\fP or \fIexmh\fP, too.
|
meillo@19
|
954 These are graphical frontends for the \s-1MH\s0 toolchest.
|
meillo@19
|
955 This means, all email-related work is still done by \s-1MH\s0 tools,
|
meillo@20
|
956 but the frontend issues the appropriate calls when the user
|
meillo@30
|
957 clicks on buttons.
|
meillo@20
|
958 Providing easy-to-use user interfaces in form of frontends is a good
|
meillo@19
|
959 approach, because it does not limit the power of the backend itself.
|
meillo@20
|
960 The frontend will anyway only be able to make a subset of the
|
meillo@23
|
961 backend's power and flexibility available to the user.
|
meillo@20
|
962 But if it is a separate program,
|
meillo@20
|
963 then the missing parts can still be accessed at the backend directly.
|
meillo@19
|
964 If it is integrated, then this will hardly be possible.
|
meillo@30
|
965 Further more, it is possible to have different frontends to the same
|
meillo@30
|
966 backend.
|
meillo@19
|
967
|
meillo@19
|
968 .PP
|
meillo@33
|
969 .B "Choose portability over efficiency
|
meillo@20
|
970 and
|
meillo@33
|
971 .B "use shell scripts to increase leverage and portability" .
|
meillo@20
|
972 These two tenets are indirectly, but nicely, demonstrated by
|
meillo@30
|
973 Bolsky and Korn in their book about the Korn Shell.
|
meillo@20
|
974 .[
|
meillo@20
|
975 %T The KornShell: command and programming language
|
meillo@20
|
976 %A Morris I. Bolsky
|
meillo@20
|
977 %A David G. Korn
|
meillo@20
|
978 %I Prentice Hall
|
meillo@20
|
979 %D 1989
|
meillo@30
|
980 %P 254\(en290
|
meillo@20
|
981 %O \s-1ISBN\s0: 0-13-516972-0
|
meillo@20
|
982 .]
|
meillo@30
|
983 They demonstrated, in chapter 18 of the book, a basic implementation
|
meillo@20
|
984 of a subset of \s-1MH\s0 in ksh scripts.
|
meillo@20
|
985 Of course, this was just a demonstration, but a brilliant one.
|
meillo@20
|
986 It shows how quickly one can implement such a prototype with shell scripts,
|
meillo@20
|
987 and how readable they are.
|
meillo@20
|
988 The implementation in the scripting language may not be very fast,
|
meillo@20
|
989 but it can be fast enough though, and this is all that matters.
|
meillo@20
|
990 By having the code in an interpreted language, like the shell,
|
meillo@20
|
991 portability becomes a minor issue, if we assume the interpreter
|
meillo@20
|
992 to be widespread.
|
meillo@20
|
993 This demonstration also shows how easy it is to create single programs
|
meillo@20
|
994 of a toolchest software.
|
meillo@30
|
995 There are eight tools (two of them have multiple names) and 16 functions
|
meillo@30
|
996 with supporting code.
|
meillo@30
|
997 Each tool comprises between 12 and 38 lines of ksh,
|
meillo@30
|
998 in total about 200 lines.
|
meillo@30
|
999 The functions comprise between 3 and 78 lines of ksh,
|
meillo@30
|
1000 in total about 450 lines.
|
meillo@20
|
1001 Such small software is easy to write, easy to understand,
|
meillo@20
|
1002 and thus easy to maintain.
|
meillo@23
|
1003 A toolchest improves the possibility to only write some parts
|
meillo@20
|
1004 and though create a working result.
|
meillo@20
|
1005 Expanding the toolchest without global changes will likely be
|
meillo@20
|
1006 possible, too.
|
meillo@20
|
1007
|
meillo@20
|
1008 .PP
|
meillo@33
|
1009 .B "Use software leverage to your advantage
|
meillo@20
|
1010 and the lesser tenet
|
meillo@33
|
1011 .B "allow the user to tailor the environment
|
meillo@20
|
1012 are ideally followed in the design of \s-1MH\s0.
|
meillo@21
|
1013 Tailoring the environment is heavily encouraged by the ability to
|
meillo@30
|
1014 directly define default options to programs.
|
meillo@30
|
1015 It is even possible to define different default options
|
meillo@21
|
1016 depending on the name under which the program was called.
|
meillo@21
|
1017 Software leverage is heavily encouraged by the ease it is to
|
meillo@21
|
1018 create shell scripts that run a specific command line,
|
meillo@30
|
1019 built of several \s-1MH\s0 programs.
|
meillo@21
|
1020 There is few software that so much wants users to tailor their
|
meillo@21
|
1021 environment and to leverage the use of the software, like \s-1MH\s0.
|
meillo@21
|
1022 Just to make one example:
|
meillo@23
|
1023 One might prefer a different listing format for the \f(CWscan\fP
|
meillo@21
|
1024 program.
|
meillo@30
|
1025 It is possible to take one of the distributed format files
|
meillo@21
|
1026 or to write one yourself.
|
meillo@21
|
1027 To use the format as default for \f(CWscan\fP, a single line,
|
meillo@21
|
1028 reading
|
meillo@21
|
1029 .DS
|
meillo@21
|
1030 .CW
|
meillo@21
|
1031 scan: -form FORMATFILE
|
meillo@21
|
1032 .DE
|
meillo@21
|
1033 must be added to \f(CW.mh_profile\fP.
|
meillo@21
|
1034 If one wants this different format as an additional command,
|
meillo@23
|
1035 instead of changing the default, he needs to create a link to
|
meillo@23
|
1036 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
|
meillo@21
|
1037 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
|
meillo@30
|
1038 as the option should only be in effect when scan is called as
|
meillo@21
|
1039 \f(CWscan2\fP.
|
meillo@20
|
1040
|
meillo@20
|
1041 .PP
|
meillo@33
|
1042 .B "Make every program a filter
|
meillo@21
|
1043 is hard to find in \s-1MH\s0.
|
meillo@21
|
1044 The reason therefore is that most of \s-1MH\s0's tools provide
|
meillo@21
|
1045 basic file system operations for the mailboxes.
|
meillo@30
|
1046 The reason is the same because of which
|
meillo@21
|
1047 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP
|
meillo@21
|
1048 aren't filters neither.
|
meillo@23
|
1049 However, they build a basis on which filters can operate.
|
meillo@23
|
1050 \s-1MH\s0 does not provide many filters itself, but it is a basis
|
meillo@23
|
1051 to write filters for.
|
meillo@30
|
1052 An example would be a mail message text highlighter,
|
meillo@30
|
1053 that means a program that makes use of a color terminal to display
|
meillo@30
|
1054 header lines, quotations, and signatures in distinct colors.
|
meillo@30
|
1055 The author's version of this program, for instance,
|
meillo@30
|
1056 is a 25 line awk script.
|
meillo@21
|
1057
|
meillo@21
|
1058 .PP
|
meillo@33
|
1059 .B "Build a prototype as soon as possible
|
meillo@21
|
1060 was again well followed by \s-1MH\s0.
|
meillo@21
|
1061 This tenet, of course, focuses on early development, which is
|
meillo@21
|
1062 long time ago for \s-1MH\s0.
|
meillo@21
|
1063 But without following this guideline at the very beginning,
|
meillo@23
|
1064 Bruce Borden may have not convinced the management of \s-1RAND\s0
|
meillo@23
|
1065 to ever create \s-1MH\s0.
|
meillo@23
|
1066 In Bruce' own words:
|
meillo@21
|
1067 .QP
|
meillo@30
|
1068 [...] but they [Stockton Gaines and Norm Shapiro] were not able
|
meillo@23
|
1069 to convince anyone that such a system would be fast enough to be usable.
|
meillo@21
|
1070 I proposed a very short project to prove the basic concepts,
|
meillo@21
|
1071 and my management agreed.
|
meillo@21
|
1072 Looking back, I realize that I had been very lucky with my first design.
|
meillo@21
|
1073 Without nearly enough design work,
|
meillo@21
|
1074 I built a working environment and some header files
|
meillo@21
|
1075 with key structures and wrote the first few \s-1MH\s0 commands:
|
meillo@21
|
1076 inc, show/next/prev, and comp.
|
meillo@21
|
1077 [...]
|
meillo@21
|
1078 With these three, I was able to convince people that the structure was viable.
|
meillo@21
|
1079 This took about three weeks.
|
meillo@21
|
1080 .[
|
meillo@21
|
1081 %O FIXME
|
meillo@21
|
1082 .]
|
meillo@0
|
1083
|
meillo@0
|
1084 .NH 2
|
meillo@0
|
1085 Problems
|
meillo@0
|
1086 .LP
|
meillo@22
|
1087 \s-1MH\s0, for sure is not without problems.
|
meillo@30
|
1088 There are two main problems: one is technical, the other is about human behavior.
|
meillo@22
|
1089 .PP
|
meillo@22
|
1090 \s-1MH\s0 is old and email today is very different to email in the time
|
meillo@22
|
1091 when \s-1MH\s0 was designed.
|
meillo@22
|
1092 \s-1MH\s0 adopted to the changes pretty well, but it is limited.
|
meillo@22
|
1093 For example in development resources.
|
meillo@22
|
1094 \s-1MIME\s0 support and support for different character encodings
|
meillo@22
|
1095 is available, but only on a moderate level.
|
meillo@22
|
1096 More active developers could quickly improve there.
|
meillo@22
|
1097 It is also limited by design, which is the larger problem.
|
meillo@22
|
1098 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
|
meillo@22
|
1099 These design conflicts are not easily solvable.
|
meillo@22
|
1100 Possibly, they require a redesign.
|
meillo@30
|
1101 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers,
|
meillo@30
|
1102 hence \s-1MH\s0 may never work well with \s-1IMAP\s0.
|
meillo@22
|
1103 .PP
|
meillo@22
|
1104 The other kind of problem is human habits.
|
meillo@22
|
1105 When in this world almost all \s-1MUA\s0s are monolithic,
|
meillo@22
|
1106 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
|
meillo@22
|
1107 like \s-1MH\s0.
|
meillo@22
|
1108 The habits are so strong, that even people who understood the concept
|
meillo@30
|
1109 and advantages of \s-1MH\s0 do not like to switch,
|
meillo@30
|
1110 simply because \s-1MH\s0 is different.
|
meillo@30
|
1111 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
|
meillo@30
|
1112 are quite outdated and thus not very appealing compared to the modern interfaces
|
meillo@30
|
1113 which monolithic \s-1MUA\s0s offer.
|
meillo@20
|
1114
|
meillo@20
|
1115 .NH 2
|
meillo@20
|
1116 Summary \s-1MH\s0
|
meillo@20
|
1117 .LP
|
meillo@31
|
1118 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design
|
meillo@31
|
1119 and implementation.
|
meillo@31
|
1120 It consists of a toolchest of small tools, each of them does one job well.
|
meillo@31
|
1121 The tools are orthogonal to each other, to a large extend.
|
meillo@31
|
1122 However, for historical reasons, there also exist distinct tools
|
meillo@31
|
1123 that cover the same task.
|
meillo@31
|
1124 .PP
|
meillo@31
|
1125 The toolchest approach offers great flexibility to the user.
|
meillo@31
|
1126 He can use the complete power of the Unix shell with \s-1MH\s0.
|
meillo@31
|
1127 This makes \s-1MH\s0 a very powerful mail system.
|
meillo@31
|
1128 Extending and customizing \s-1MH\s0 is easy and encouraged, too.
|
meillo@31
|
1129 .PP
|
meillo@31
|
1130 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
|
meillo@31
|
1131 Its overall design follows clear rules.
|
meillo@31
|
1132 The single tools do only one job, thus they are easy to understand,
|
meillo@31
|
1133 easy to write, and good to maintain.
|
meillo@31
|
1134 They are all independent and do not interfere with the others.
|
meillo@31
|
1135 Automated testing of their function is a straight forward task.
|
meillo@31
|
1136 .PP
|
meillo@31
|
1137 It is sad, that \s-1MH\s0's differentness is its largest problem,
|
meillo@31
|
1138 as its differentness is also its largest advantage.
|
meillo@31
|
1139 Unfortunately, for most people their habits are stronger
|
meillo@31
|
1140 than the attraction of the clear design and the power, \s-1MH\s0 offers.
|
meillo@0
|
1141
|
meillo@8
|
1142
|
meillo@8
|
1143
|
meillo@0
|
1144 .NH 1
|
meillo@0
|
1145 Case study: uzbl
|
meillo@32
|
1146 .LP
|
meillo@32
|
1147 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
|
meillo@32
|
1148 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy.
|
meillo@32
|
1149 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''.
|
meillo@32
|
1150 It is pronounced the identical.
|
meillo@0
|
1151
|
meillo@0
|
1152 .NH 2
|
meillo@32
|
1153 Historical background
|
meillo@0
|
1154 .LP
|
meillo@32
|
1155 Uzbl was started by Dieter Plaetinck in April 2009.
|
meillo@32
|
1156 The idea was born in a thread in the Arch Linux forum.
|
meillo@32
|
1157 .[
|
meillo@32
|
1158 %O http://bbs.archlinux.org/viewtopic.php?id=67463
|
meillo@32
|
1159 .]
|
meillo@32
|
1160 After some discussion about failures of well known web browsers,
|
meillo@32
|
1161 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
|
meillo@32
|
1162 of how a better web browser could look like.
|
meillo@32
|
1163 To the question of another member, if Plaetinck would write that program,
|
meillo@32
|
1164 because it would sound fantastic, Plaetinck replied:
|
meillo@32
|
1165 ``Maybe, if I find the time ;-)''.
|
meillo@32
|
1166 .PP
|
meillo@32
|
1167 Fortunately, he found the time.
|
meillo@32
|
1168 One day later, the first prototype was out.
|
meillo@32
|
1169 One week later, uzbl had an own website.
|
meillo@32
|
1170 One month after the first code showed up,
|
meillo@32
|
1171 a mailing list was installed to coordinate and discuss further development.
|
meillo@32
|
1172 A wiki was set up to store documentation and scripts that showed up on the
|
meillo@32
|
1173 mailing list and elsewhere.
|
meillo@32
|
1174 .PP
|
meillo@38
|
1175 In the, now, one year of uzbl's existence, it was heavily developed in various branches.
|
meillo@32
|
1176 Plaetinck's task became more and more to only merge the best code from the
|
meillo@32
|
1177 different branches into his main branch, and to apply patches.
|
meillo@32
|
1178 About once a month, Plaetinck released a new version.
|
meillo@32
|
1179 In September 2009, he presented several forks of uzbl.
|
meillo@38
|
1180 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
|
meillo@32
|
1181 .PP
|
meillo@32
|
1182 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
|
meillo@32
|
1183 In September 2009, the uzbl web browser was on \fISlashdot\fP.
|
meillo@0
|
1184
|
meillo@0
|
1185 .NH 2
|
meillo@32
|
1186 Contrasts to other web browsers
|
meillo@0
|
1187 .LP
|
meillo@32
|
1188 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
|
meillo@32
|
1189 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
|
meillo@32
|
1190 .PP
|
meillo@32
|
1191 Today, uzbl is divided into uzbl-core and uzbl-browser.
|
meillo@32
|
1192 Uzbl-core is, how its name already indicates, the core of uzbl.
|
meillo@32
|
1193 It handles commands and events to interface other programs,
|
meillo@32
|
1194 and also displays webpages by using webkit as render engine.
|
meillo@32
|
1195 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
|
meillo@32
|
1196 an event manager, yanking, pasting, page searching, zooming, and more stuff,
|
meillo@32
|
1197 to form a ``complete'' web browser.
|
meillo@32
|
1198 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
|
meillo@32
|
1199 so uzbl-core is included.
|
meillo@32
|
1200 .PP
|
meillo@32
|
1201 Unlike most other web browsers, uzbl is mainly the mediator between the
|
meillo@32
|
1202 various tools that cover single jobs of web browsing.
|
meillo@35
|
1203 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
|
meillo@35
|
1204 and on stdin, and it writes events to a Unix socket and to stdout.
|
meillo@35
|
1205 The graphical rendering of the webpage is done by webkit, a web content engine.
|
meillo@35
|
1206 Uzbl-core is build around this library.
|
meillo@35
|
1207 Loading a webpage in a running uzbl instance requires only:
|
meillo@32
|
1208 .DS
|
meillo@32
|
1209 .CW
|
meillo@32
|
1210 echo 'uri http://example.org' >/path/to/uzbl-fifo
|
meillo@32
|
1211 .DE
|
meillo@32
|
1212 .PP
|
meillo@32
|
1213 Downloads, browsing history, bookmarks, and thelike are not provided
|
meillo@32
|
1214 by uzbl-core itself, as they are in other web browsers.
|
meillo@35
|
1215 Uzbl-browser also only provides, so called, handler scripts that wrap
|
meillo@35
|
1216 external applications which provide the actual functionality.
|
meillo@32
|
1217 For instance, \fIwget\fP is used to download files and uzbl-browser
|
meillo@32
|
1218 includes a script that calls wget with appropriate options in
|
meillo@32
|
1219 a prepared environment.
|
meillo@32
|
1220 .PP
|
meillo@32
|
1221 Modern web browsers are proud to have addons, plugins, and modules, instead.
|
meillo@32
|
1222 This is their effort to achieve similar goals.
|
meillo@35
|
1223 But instead of using existing, external programs, modern web browsers
|
meillo@35
|
1224 include these functions, although they might be loaded at runtime.
|
meillo@0
|
1225
|
meillo@0
|
1226 .NH 2
|
meillo@32
|
1227 Discussion of the design
|
meillo@0
|
1228 .LP
|
meillo@32
|
1229 This section discusses uzbl in regard of the Unix Philosophy,
|
meillo@32
|
1230 as identified by Gancarz.
|
meillo@32
|
1231
|
meillo@32
|
1232 .PP
|
meillo@35
|
1233 .B "Make each program do one thing well" .
|
meillo@35
|
1234 Uzbl tries to be a web browser and nothing else.
|
meillo@36
|
1235 The common definition of a web browser is, of course, highly influenced by
|
meillo@36
|
1236 existing implementations of web browsers, although they are degenerated.
|
meillo@35
|
1237 Web browsers should be programs to browse the web, and nothing more.
|
meillo@35
|
1238 This is the one thing they should do, as demanded by the Unix Philosophy.
|
meillo@36
|
1239 .PP
|
meillo@36
|
1240 Web browsers should, for instance, not manage downloads.
|
meillo@35
|
1241 This is the job download managers exist for.
|
meillo@35
|
1242 Download managers do primary care about being good in downloading files.
|
meillo@35
|
1243 Modern web browsers provide download management only as a secondary feature.
|
meillo@35
|
1244 How could they perform this job better, than programs that exist only for
|
meillo@35
|
1245 this very job?
|
meillo@35
|
1246 And how could anyone want less than the best download manager available?
|
meillo@32
|
1247 .PP
|
meillo@35
|
1248 A web browser's job is to let the user browse the web.
|
meillo@35
|
1249 This means, navigating through websites by following links.
|
meillo@36
|
1250 Rendering the \s-1HTML\s0 sources is a different job, too.
|
meillo@36
|
1251 It is covered by the webkit render engine, in uzbl's case.
|
meillo@35
|
1252 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
|
meillo@36
|
1253 are also not the job of a web browser.
|
meillo@36
|
1254 They should be handled by external applications \(en
|
meillo@36
|
1255 ones which's job is to handle such data.
|
meillo@35
|
1256 Uzbl strives to do it this way.
|
meillo@36
|
1257 .PP
|
meillo@36
|
1258 Remember Doug McIlroy:
|
meillo@35
|
1259 .I
|
meillo@35
|
1260 ``Write programs that do one thing and do it well.
|
meillo@35
|
1261 Write programs to work together.''
|
meillo@35
|
1262 .R
|
meillo@35
|
1263 .PP
|
meillo@35
|
1264 The lesser tenet
|
meillo@35
|
1265 .B "allow the user to tailor the environment
|
meillo@35
|
1266 matches good here.
|
meillo@35
|
1267 There was the question, how anyone could want anything less than the
|
meillo@35
|
1268 best program for the job.
|
meillo@36
|
1269 But as personal preferences matter much,
|
meillo@36
|
1270 it is probably more important to ask:
|
meillo@35
|
1271 How could anyone want something else than his preferred program for the job?
|
meillo@36
|
1272 .PP
|
meillo@35
|
1273 Usually users want one program for one job.
|
meillo@35
|
1274 Hence, whenever the task is, for instance, downloading,
|
meillo@36
|
1275 exactly one download manager should be used.
|
meillo@35
|
1276 More advanced users might want to have this download manager in this
|
meillo@35
|
1277 situation and that one in that situation.
|
meillo@35
|
1278 They should be able to configure it this way.
|
meillo@35
|
1279 With uzbl, one can use any download manager the user wants.
|
meillo@36
|
1280 To switch to a different one, only one line in a small handler script
|
meillo@35
|
1281 needs to be changed.
|
meillo@36
|
1282 Alternatively it would be possible to query an entry in a global file
|
meillo@36
|
1283 or an environment variable, which specifies the download manager to use,
|
meillo@35
|
1284 in the handler script.
|
meillo@36
|
1285 .PP
|
meillo@35
|
1286 As uzbl does neither have its own download manager nor depends on a
|
meillo@35
|
1287 specific one, thus uzbl's browsing abilities will not be lowered by having
|
meillo@35
|
1288 a bad download manager.
|
meillo@36
|
1289 Uzbl's download capabilities will just as good as the ones of the best
|
meillo@36
|
1290 download manager available on the system.
|
meillo@38
|
1291 Of course, this applies to all of the other supplementary tools, too.
|
meillo@32
|
1292
|
meillo@32
|
1293 .PP
|
meillo@36
|
1294 .B "Use software leverage to your advantage" .
|
meillo@36
|
1295 Shell scripts are a good choice to extend uzbl.
|
meillo@36
|
1296 Uzbl is designed to be extended by external tools.
|
meillo@36
|
1297 These external tools are usually wrapped by small handler shell scripts.
|
meillo@36
|
1298 Shell scripts are the glue in this approach.
|
meillo@36
|
1299 They make the various parts fit together.
|
meillo@36
|
1300 .PP
|
meillo@36
|
1301 As an example, the history mechanism of uzbl shall be presented.
|
meillo@36
|
1302 Uzbl is configured to spawn a script to append an entry to the history
|
meillo@36
|
1303 whenever the event of a fully loaded page occurs.
|
meillo@36
|
1304 The script to append the entry to the history not much more than:
|
meillo@36
|
1305 .DS
|
meillo@36
|
1306 .CW
|
meillo@36
|
1307 #!/bin/sh
|
meillo@36
|
1308 file=/path/to/uzbl-history
|
meillo@36
|
1309 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
|
meillo@36
|
1310 .DE
|
meillo@36
|
1311 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
|
meillo@36
|
1312 For loading an entry, a key is bound to spawn a load from history script.
|
meillo@36
|
1313 The script reverses the history to have newer entries first,
|
meillo@36
|
1314 then displays \fIdmenu\fP to select an item,
|
meillo@36
|
1315 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
|
meillo@36
|
1316 With error checking and corner cases removed, the script looks like this:
|
meillo@36
|
1317 .DS
|
meillo@36
|
1318 .CW
|
meillo@36
|
1319 #!/bin/sh
|
meillo@36
|
1320 file=/path/to/uzbl-history
|
meillo@36
|
1321 goto=`tac $file | dmenu | cut -d' ' -f 3`
|
meillo@36
|
1322 echo "uri $goto" > $4
|
meillo@36
|
1323 .DE
|
meillo@36
|
1324 \f(CW$4\fP expands to the path of the command input pipe of the current
|
meillo@36
|
1325 uzbl instance.
|
meillo@32
|
1326
|
meillo@32
|
1327 .PP
|
meillo@33
|
1328 .B "Avoid captive user interfaces" .
|
meillo@36
|
1329 One could say, that uzbl, to a large extend, actually \fIis\fP
|
meillo@36
|
1330 a captive user interface.
|
meillo@37
|
1331 But the difference to most other web browsers is, that uzbl is only
|
meillo@37
|
1332 the captive user interface frontend and the core of the backend.
|
meillo@38
|
1333 Many parts of the backend are independent of uzbl.
|
meillo@37
|
1334 Some are distributed with uzbl, for some external programs, handler scripts
|
meillo@37
|
1335 are distributed, arbitrary additional functionality can be added if desired.
|
meillo@37
|
1336 .PP
|
meillo@37
|
1337 The frontend is captive \(en that is true.
|
meillo@37
|
1338 This is okay for the task of browsing the web, as this task is only relevant
|
meillo@37
|
1339 for humans.
|
meillo@37
|
1340 Automated programs would \fIcrawl\fP the web.
|
meillo@37
|
1341 That means, they read the source directly.
|
meillo@37
|
1342 The source includes all the semantics.
|
meillo@37
|
1343 The graphical representation is just for humans to transfer the semantics
|
meillo@37
|
1344 more intuitively.
|
meillo@32
|
1345
|
meillo@32
|
1346 .PP
|
meillo@33
|
1347 .B "Make every program a filter" .
|
meillo@37
|
1348 Graphical web browsers are almost dead ends in the chain of information flow.
|
meillo@37
|
1349 Thus it is difficult to see what graphical web browsers should filter.
|
meillo@37
|
1350 Graphical web browsers exist almost only for interactive use by humans.
|
meillo@37
|
1351 The only case when one might want to automate the rendering function is
|
meillo@37
|
1352 to generate images of rendered webpages.
|
meillo@37
|
1353
|
meillo@37
|
1354 .PP
|
meillo@37
|
1355 .B "Small is beautiful"
|
meillo@38
|
1356 is not easy to apply to a web browser, primary because modern web technology
|
meillo@38
|
1357 is very complex; hence the rendering task is very complex.
|
meillo@37
|
1358 Modern web browsers will always consist of many thousand lines of code,
|
meillo@37
|
1359 unfortunately.
|
meillo@37
|
1360 Using the toolchest approach and wrappers can split the browser into
|
meillo@37
|
1361 several small parts, tough.
|
meillo@37
|
1362 .PP
|
meillo@37
|
1363 Uzbl-core consists of about 3\,500 lines of C code.
|
meillo@37
|
1364 The distribution includes another 3\,500 lines of Shell and Python code,
|
meillo@37
|
1365 which are the handler scripts and plugins like a modal interface.
|
meillo@38
|
1366 Further more, uzbl uses functionality of external tools like
|
meillo@38
|
1367 \fIwget\fP and \fInetcat\fP.
|
meillo@37
|
1368 Up to this point, uzbl looks pretty neat and small.
|
meillo@38
|
1369 The ugly part of uzbl is the web content renderer, webkit.
|
meillo@37
|
1370 Webkit consists of roughly 400\,000 (!) lines of code.
|
meillo@38
|
1371 Unfortunately, small web render engines are not possible anymore
|
meillo@38
|
1372 because of the modern web.
|
meillo@38
|
1373 The problems section will explain this in more detail.
|
meillo@35
|
1374
|
meillo@35
|
1375 .PP
|
meillo@35
|
1376 .B "Build a prototype as soon as possible" .
|
meillo@35
|
1377 Plaetinck made his code public, right from the beginning.
|
meillo@38
|
1378 Discussion and development was, and still is, open to everyone interested.
|
meillo@38
|
1379 Development versions of uzbl can be obtained very simply from the code
|
meillo@38
|
1380 repository.
|
meillo@38
|
1381 Within the first year of uzbl's existence, a new version was released
|
meillo@35
|
1382 more often than once a month.
|
meillo@38
|
1383 Different forks and branches arose.
|
meillo@38
|
1384 They introduced new features, which were tested for suitability.
|
meillo@35
|
1385 The experiences of using prototypes influenced further development.
|
meillo@35
|
1386 Actually, all development was community driven.
|
meillo@38
|
1387 Plaetinck says, three months after uzbl's birth:
|
meillo@35
|
1388 ``Right now I hardly code anything myself for Uzbl.
|
meillo@35
|
1389 I just merge in other people's code, ponder a lot, and lead the discussions.''
|
meillo@35
|
1390 .[
|
meillo@36
|
1391 %A FIXME
|
meillo@35
|
1392 %O http://lwn.net/Articles/341245/
|
meillo@35
|
1393 .]
|
meillo@32
|
1394
|
meillo@0
|
1395
|
meillo@0
|
1396 .NH 2
|
meillo@0
|
1397 Problems
|
meillo@0
|
1398 .LP
|
meillo@38
|
1399 Similar to \s-1MH\s0, uzbl, too suffers from being different.
|
meillo@38
|
1400 It is sad, but people use what they know.
|
meillo@38
|
1401 Fortunately, uzbl's user interface can look and feel very much the
|
meillo@38
|
1402 same as the one of the well known web browsers,
|
meillo@38
|
1403 hiding the internal differences.
|
meillo@38
|
1404 But uzbl has to provide this similar look and feel to be accepted
|
meillo@38
|
1405 as a ``normal'' browser by ``normal'' users.
|
meillo@37
|
1406 .PP
|
meillo@38
|
1407 The more important problem is the modern web.
|
meillo@38
|
1408 The modern web is simply broken.
|
meillo@38
|
1409 It has state in a state-less protocol,
|
meillo@38
|
1410 it misuses technologies,
|
meillo@38
|
1411 and it is helplessly overloaded.
|
meillo@38
|
1412 The result are web content render engines that must consist
|
meillo@38
|
1413 of hundreds of thousands lines of code.
|
meillo@38
|
1414 They also must combine and integrate many different technologies,
|
meillo@38
|
1415 only to make our modern web usable.
|
meillo@38
|
1416 Website to image converter are hardly possible to run without
|
meillo@38
|
1417 human interaction because of state in sessions, impossible
|
meillo@38
|
1418 deep-linking, and unautomatable technologies.
|
meillo@37
|
1419 .PP
|
meillo@38
|
1420 The web was misused to provide all kinds of imaginable wishes.
|
meillo@38
|
1421 Now web browsers, and eventually the users, suffer from it.
|
meillo@37
|
1422
|
meillo@8
|
1423
|
meillo@32
|
1424 .NH 2
|
meillo@32
|
1425 Summary uzbl
|
meillo@32
|
1426 .LP
|
meillo@38
|
1427 ``Uzbl is a browser that adheres to the Unix Philosophy'',
|
meillo@38
|
1428 that is how uzbl is seen by its authors.
|
meillo@38
|
1429 Indeed, uzbl follows the Unix Philosophy in many ways.
|
meillo@38
|
1430 It consists of independent parts that work together,
|
meillo@38
|
1431 its core is mainly a mediator which glues the parts together.
|
meillo@38
|
1432 .PP
|
meillo@38
|
1433 Software leverage can excellently be seen in uzbl.
|
meillo@38
|
1434 It makes use of external tools, separates independent tasks
|
meillo@38
|
1435 in independent parts, and glues them together with small
|
meillo@38
|
1436 handler scripts, around uzbl-core.
|
meillo@38
|
1437 .PP
|
meillo@38
|
1438 As uzbl, more or less, consists of a set of tools and a bit
|
meillo@38
|
1439 of glue, anyone can put the parts together and expand it
|
meillo@38
|
1440 in any desired way.
|
meillo@38
|
1441 Uzbl is very flexible and customizable.
|
meillo@38
|
1442 These properties make it valuable for advanced users,
|
meillo@38
|
1443 but may keep novice users from using it.
|
meillo@38
|
1444 .PP
|
meillo@38
|
1445 Uzbl's main problem is the modern web, that makes it hard
|
meillo@38
|
1446 to design a sane web browser.
|
meillo@38
|
1447 Despite this bad situation, uzbl does a fairly good job.
|
meillo@32
|
1448
|
meillo@8
|
1449
|
meillo@0
|
1450 .NH 1
|
meillo@0
|
1451 Final thoughts
|
meillo@0
|
1452
|
meillo@0
|
1453 .NH 2
|
meillo@0
|
1454 Quick summary
|
meillo@0
|
1455 .LP
|
meillo@0
|
1456 good design
|
meillo@0
|
1457 .LP
|
meillo@0
|
1458 unix phil
|
meillo@0
|
1459 .LP
|
meillo@0
|
1460 case studies
|
meillo@0
|
1461
|
meillo@0
|
1462 .NH 2
|
meillo@0
|
1463 Why people should choose
|
meillo@0
|
1464 .LP
|
meillo@0
|
1465 Make the right choice!
|
meillo@0
|
1466
|
meillo@0
|
1467 .nr PI .5i
|
meillo@0
|
1468 .rm ]<
|
meillo@0
|
1469 .de ]<
|
meillo@0
|
1470 .LP
|
meillo@0
|
1471 .de FP
|
meillo@0
|
1472 .IP \\\\$1.
|
meillo@0
|
1473 \\..
|
meillo@0
|
1474 .rm FS FE
|
meillo@0
|
1475 ..
|
meillo@0
|
1476 .SH
|
meillo@0
|
1477 References
|
meillo@0
|
1478 .[
|
meillo@0
|
1479 $LIST$
|
meillo@0
|
1480 .]
|
meillo@0
|
1481 .wh -1p
|