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1 .nr PS 11
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2 .nr VS 13
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3 .nr lu 0
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4 .de CW
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5 .nr PQ \\n(.f
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6 .if t .ft CW
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7 .ie ^\\$1^^ .if n .ul 999
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8 .el .if n .ul 1
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9 .if t .if !^\\$1^^ \&\\$1\f\\n(PQ\\$2
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10 .if n .if \\n(.$=1 \&\\$1
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11 .if n .if \\n(.$>1 \&\\$1\c
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12 .if n .if \\n(.$>1 \&\\$2
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13 ..
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14 .ds [. \ [
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15 .ds .] ]
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16
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17 .rn NH _N
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18 .de NH
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19 .if '\\$1'1' .sp 2v
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20 .if '\\$1'1' .nr PS +2
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21 ._N \\$1
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22 .if '\\$1'1' .nr PS -2
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23 ..
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24
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25 .\"----------------------------------------
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26
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27 .TL
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28 .ps +4
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meillo@6
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29 Why the Unix Philosophy still matters
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30 .AU
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meillo@0
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31 markus schnalke <meillo@marmaro.de>
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32 .AB
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33 .ti \n(.iu
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34 This paper explains the importance of the Unix Philosophy for software design.
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35 Today, few software designers are aware of these concepts,
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36 and thus a lot of modern software is more limited than necessary
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37 and makes less use of software leverage than possible.
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38 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
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39 .AE
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40
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41 .FS
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42 .ps -1
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43 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
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44 Mentor was professor Schweiggert. 2010-04-05
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45 .br
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46 You may retrieve this document from
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47 .CW \s-1http://marmaro.de/docs \ .
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48 .FE
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49
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50 .NH 1
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51 Introduction
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52 .XS
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53 \*(SN Introduction
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54 .XE
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55 .LP
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56 The Unix Philosophy is the essence of how the Unix operating system,
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57 especially its toolchest, was designed.
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58 It is no limited set of fixed rules,
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59 but a loose set of guidelines which tell how to write software that
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60 suites well into Unix.
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61 Actually, the Unix Philosophy describes what is common to typical Unix software.
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62 The Wikipedia has an accurate definition:
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63 .[
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meillo@40
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64 %A Wikipedia
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meillo@40
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65 %T Unix philosophy
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66 %P Wikipedia, The Free Encyclopedia
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67 %D 2010-03-21 17:20 UTC
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68 %O .CW \s-1http://en.wikipedia.org/w/index.php?title=Unix_philosophy&oldid=351189719
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69 .]
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70 .QP
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71 .ps -1
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72 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
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73 approaches to developing software based on the experience of leading
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74 developers of the Unix operating system.
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75 .PP
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76 As there is no single definition of the Unix Philosophy,
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77 several people have stated their view on what it comprises.
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78 Best known are:
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79 .IP \(bu
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meillo@1
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80 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
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81 .[
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meillo@1
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82 %A M. D. McIlroy
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83 %A E. N. Pinson
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meillo@1
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84 %A B. A. Taque
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meillo@1
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85 %T UNIX Time-Sharing System Forward
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meillo@1
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86 %J The Bell System Technical Journal
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87 %D 1978
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88 %V 57
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89 %N 6
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90 %P 1902
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91 .]
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92 .IP \(bu
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meillo@1
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93 Mike Gancarz' book ``The UNIX Philosophy''.
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meillo@1
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94 .[
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meillo@1
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95 %A Mike Gancarz
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meillo@1
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96 %T The UNIX Philosophy
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meillo@1
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97 %D 1995
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meillo@1
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98 %I Digital Press
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meillo@1
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99 .]
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100 .IP \(bu
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101 Eric S. Raymond's book ``The Art of UNIX Programming''.
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102 .[
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meillo@1
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103 %A Eric S. Raymond
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meillo@1
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104 %T The Art of UNIX Programming
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meillo@1
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105 %D 2003
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meillo@1
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106 %I Addison-Wesley
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meillo@2
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107 %O .CW \s-1http://www.faqs.org/docs/artu/
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108 .]
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meillo@0
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109 .LP
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110 These different views on the Unix Philosophy have much in common.
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111 Especially, the main concepts are similar in all of them.
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meillo@40
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112 McIlroy's definition can surely be called the core of the Unix Philosophy,
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113 but the fundamental idea behind it all, is ``small is beautiful''.
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114
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115 .PP
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116 The Unix Philosophy tells how to design and write good software for Unix.
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117 Many concepts described here base on facilities of Unix.
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118 Other operating systems may not offer such facilities,
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119 hence it may not be possible to design software in the way of the
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120 Unix Philosophy for them.
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121 .PP
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122 The Unix Philosophy has an idea of how the process of software development
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123 should look like, but large parts of the philosophy are quite independent
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124 from the development process used.
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125 However, one will soon recognize that some development processes work well
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126 with the ideas of the Unix Philosophy and support them, while others are
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127 at cross-purposes.
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128 Kent Beck's books about Extreme Programming are valuable supplimental
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129 resources.
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130 .PP
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131 The question of how to actually write code and how the code should looks
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132 like internally, are out of focus here.
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133 ``The Practice of Programming'' by Kernighan and Pike,
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134 .[
|
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meillo@41
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135 %A Brian W. Kernighan
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136 %A Rob Pike
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137 %T The Practice of Programming
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138 %I Addison-Wesley
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139 %D 1999
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140 .]
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meillo@41
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141 is a good book that covers this topic.
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meillo@41
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142 Its point of view matches to the one of this paper.
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143
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144 .NH 1
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145 Importance of software design in general
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146 .XS
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147 .sp .5v
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148 \*(SN Importance of software design in general
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149 .XE
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150 .LP
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151 Software design is the planning of how the internal structure
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152 and external interfaces of a software should look like.
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153 It has nothing to do with visual appearance.
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meillo@39
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154 If we take a program as a car, then its color is of no matter.
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meillo@39
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155 Its design would be the car's size, its shape, the locations of doors,
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156 the passenger/space ratio, the luggage capacity, and so forth.
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157 .PP
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158 Why should software get designed at all?
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meillo@6
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159 It is general knowledge, that even a bad plan is better than no plan.
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160 Not designing software means programming without plan.
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161 This will pretty sure lead to horrible results.
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162 Horrible to use and horrible to maintain.
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163 These two aspects are the visible ones.
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164 Often invisible are the wasted possible gains.
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165 Good software design can make these gains available.
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166 .PP
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167 A software's design deals with quality properties.
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168 Good design leads to good quality, and quality is important.
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169 Any car may be able to drive from A to B,
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170 but it depends on the car's properties whether it is a good choice
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171 for passenger transport or not.
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172 It depends on its properties if it is a good choice
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173 for a rough mountain area.
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174 And it depends on its properties if the ride will be fun.
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175
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176 .PP
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177 Requirements for a software are twofold:
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178 functional and non-functional.
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179 .IP \(bu
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180 Functional requirements define directly the software's functions.
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181 They are the reason why software gets written.
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182 Someone has a problem and needs a tool to solve it.
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183 Being able to solve the problem is the main functional goal.
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184 It is the driving force behind all programming effort.
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185 Functional requirements are easier to define and to verify.
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186 .IP \(bu
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187 Non-functional requirements are also called \fIquality\fP requirements.
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188 The quality of a software are the properties that are not directly related to
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189 the software's basic functions.
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190 Tools of bad quality often solve the problems they were written for,
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191 but introduce problems and difficulties for usage and development, later on.
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192 Quality aspects are often overlooked at first sight,
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193 and they are often difficult to define clearly and to verify.
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194 .PP
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195 Quality is of few matter when the software gets built initially,
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196 but it is of matter for usage and maintenance of the software.
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197 A short-sighted might see in developing a software mainly building something up.
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198 But experience shows, that building the software the first time is
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199 only a small amount of the overall work.
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200 Bug fixing, extending, rebuilding of parts
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201 \(en maintenance work, for short \(en
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202 does soon take over the major part of the time spent on a software.
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203 Not to forget the usage of the software.
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204 These processes are highly influenced by the software's quality.
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205 Thus, quality must not be neglected.
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206 The problem with quality is that you hardly ``stumble over''
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207 bad quality during the first build,
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208 but this is the time when you should care about good quality most.
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209 .PP
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210 Software design is less the basic function of a software \(en
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211 this requirement will get satisfied anyway.
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212 Software design is more about quality aspects of the software.
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213 Good design leads to good quality, bad design to bad quality.
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214 The primary functions of the software will be affected modestly by bad quality,
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215 but good quality can provide a lot of additional gain,
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216 even at places where one never expected it.
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217 .PP
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218 The ISO/IEC 9126-1 standard, part 1,
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219 .[
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220 %I International Organization for Standardization
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221 %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1
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222 %C Geneve
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223 %D 2001
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224 .]
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225 defines the quality model as consisting out of:
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226 .IP \(bu
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227 .I Functionality
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228 (suitability, accuracy, inter\%operability, security)
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229 .IP \(bu
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230 .I Reliability
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231 (maturity, fault tolerance, recoverability)
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232 .IP \(bu
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233 .I Usability
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234 (understandability, learnability, operability, attractiveness)
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235 .IP \(bu
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236 .I Efficiency
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237 (time behavior, resource utilization)
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238 .IP \(bu
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239 .I Maintainability
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240 (analyzability, changeability, stability, testability)
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241 .IP \(bu
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242 .I Portability
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meillo@6
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243 (adaptability, installability, co-existence, replaceability)
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244 .LP
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245 Good design can improve these properties of a software,
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246 bad designed software probably suffers from not having them.
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meillo@7
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247 .PP
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248 One further goal of software design is consistency.
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249 Consistency eases understanding, working on, and using things.
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250 Consistent internal structure and consistent interfaces to the outside
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251 can be provided by good design.
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252 .PP
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253 Software should be well designed because good design avoids many
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254 problems during the software's lifetime.
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255 And software should be well designed because good design can offer
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256 much additional gain.
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257 Indeed, much effort should be spent into good design to make software more valuable.
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258 The Unix Philosophy shows a way of how to design software well.
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259 It offers guidelines to achieve good quality and high gain for the effort spent.
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260
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261
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262 .NH 1
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263 The Unix Philosophy
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264 .XS
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265 .sp .5v
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266 \*(SN The Unix Philosophy
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267 .XE
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268 .LP
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269 The origins of the Unix Philosophy were already introduced.
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270 This chapter explains the philosophy, oriented on Gancarz,
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271 and shows concrete examples of its application.
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272
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273 .NH 2
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274 Pipes
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275 .XS
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276 \*(SN Pipes
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277 .XE
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278 .LP
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meillo@4
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279 Following are some examples to demonstrate how applied Unix Philosophy feels like.
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280 Knowledge of using the Unix shell is assumed.
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281 .PP
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meillo@4
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282 Counting the number of files in the current directory:
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283 .DS
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284 .CW
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285 .ps -1
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286 ls | wc -l
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287 .DE
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288 The
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289 .CW ls
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290 command lists all files in the current directory, one per line,
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291 and
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292 .CW "wc -l
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meillo@8
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293 counts the number of lines.
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294 .PP
|
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meillo@8
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295 Counting the number of files that do not contain ``foo'' in their name:
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296 .DS
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meillo@4
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297 .CW
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298 .ps -1
|
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299 ls | grep -v foo | wc -l
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300 .DE
|
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meillo@4
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301 Here, the list of files is filtered by
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meillo@4
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302 .CW grep
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303 to remove all that contain ``foo''.
|
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meillo@4
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304 The rest is the same as in the previous example.
|
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meillo@4
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305 .PP
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306 Finding the five largest entries in the current directory.
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307 .DS
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308 .CW
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309 .ps -1
|
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meillo@4
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310 du -s * | sort -nr | sed 5q
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311 .DE
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meillo@4
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312 .CW "du -s *
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meillo@4
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313 returns the recursively summed sizes of all files
|
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meillo@8
|
314 \(en no matter if they are regular files or directories.
|
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meillo@4
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315 .CW "sort -nr
|
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meillo@4
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316 sorts the list numerically in reverse order.
|
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meillo@4
|
317 Finally,
|
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318 .CW "sed 5q
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meillo@4
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319 quits after it has printed the fifth line.
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meillo@4
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320 .PP
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321 The presented command lines are examples of what Unix people would use
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meillo@4
|
322 to get the desired output.
|
|
meillo@4
|
323 There are also other ways to get the same output.
|
|
meillo@4
|
324 It's a user's decision which way to go.
|
|
meillo@14
|
325 .PP
|
|
meillo@8
|
326 The examples show that many tasks on a Unix system
|
|
meillo@4
|
327 are accomplished by combining several small programs.
|
|
meillo@4
|
328 The connection between the single programs is denoted by the pipe operator `|'.
|
|
meillo@4
|
329 .PP
|
|
meillo@4
|
330 Pipes, and their extensive and easy use, are one of the great
|
|
meillo@4
|
331 achievements of the Unix system.
|
|
meillo@4
|
332 Pipes between programs have been possible in earlier operating systems,
|
|
meillo@4
|
333 but it has never been a so central part of the concept.
|
|
meillo@4
|
334 When, in the early seventies, Doug McIlroy introduced pipes for the
|
|
meillo@4
|
335 Unix system,
|
|
meillo@4
|
336 ``it was this concept and notation for linking several programs together
|
|
meillo@4
|
337 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
|
|
meillo@4
|
338 .[
|
|
meillo@4
|
339 %T Unix: An Oral History
|
|
meillo@5
|
340 %O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
|
|
meillo@4
|
341 .]
|
|
meillo@4
|
342 .PP
|
|
meillo@4
|
343 Being able to specify pipelines in an easy way is,
|
|
meillo@4
|
344 however, not enough by itself.
|
|
meillo@5
|
345 It is only one half.
|
|
meillo@4
|
346 The other is the design of the programs that are used in the pipeline.
|
|
meillo@8
|
347 They have to interfaces that allows them to be used in such a way.
|
|
meillo@5
|
348
|
|
meillo@16
|
349 .NH 2
|
|
meillo@14
|
350 Interface design
|
|
meillo@42
|
351 .XS
|
|
meillo@42
|
352 \*(SN Interface design
|
|
meillo@42
|
353 .XE
|
|
meillo@5
|
354 .LP
|
|
meillo@11
|
355 Unix is, first of all, simple \(en Everything is a file.
|
|
meillo@5
|
356 Files are sequences of bytes, without any special structure.
|
|
meillo@5
|
357 Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
|
|
meillo@5
|
358 and write a stream of bytes to ``standard output'' (stdout).
|
|
meillo@5
|
359 .PP
|
|
meillo@8
|
360 If the files \fIare\fP sequences of bytes,
|
|
meillo@8
|
361 and the programs \fIare\fP filters on byte streams,
|
|
meillo@11
|
362 then there is exactly one standardized data interface.
|
|
meillo@5
|
363 Thus it is possible to combine them in any desired way.
|
|
meillo@5
|
364 .PP
|
|
meillo@5
|
365 Even a handful of small programs will yield a large set of combinations,
|
|
meillo@5
|
366 and thus a large set of different functions.
|
|
meillo@5
|
367 This is leverage!
|
|
meillo@5
|
368 If the programs are orthogonal to each other \(en the best case \(en
|
|
meillo@5
|
369 then the set of different functions is greatest.
|
|
meillo@5
|
370 .PP
|
|
meillo@11
|
371 Programs might also have a separate control interface,
|
|
meillo@11
|
372 besides their data interface.
|
|
meillo@11
|
373 The control interface is often called ``user interface'',
|
|
meillo@11
|
374 because it is usually designed to be used by humans.
|
|
meillo@11
|
375 The Unix Philosophy discourages to assume the user to be human.
|
|
meillo@11
|
376 Interactive use of software is slow use of software,
|
|
meillo@11
|
377 because the program waits for user input most of the time.
|
|
meillo@11
|
378 Interactive software requires the user to be in front of the computer
|
|
meillo@11
|
379 all the time.
|
|
meillo@11
|
380 Interactive software occupy the user's attention while they are running.
|
|
meillo@11
|
381 .PP
|
|
meillo@11
|
382 Now we come back to the idea of using several small programs, combined,
|
|
meillo@11
|
383 to have a more specific function.
|
|
meillo@11
|
384 If these single tools would all be interactive,
|
|
meillo@11
|
385 how would the user control them?
|
|
meillo@11
|
386 It is not only a problem to control several programs at once if they run at the same time,
|
|
meillo@11
|
387 it also very inefficient to have to control each of the single programs
|
|
meillo@11
|
388 that are intended to work as one large program.
|
|
meillo@11
|
389 Hence, the Unix Philosophy discourages programs to demand interactive use.
|
|
meillo@11
|
390 The behavior of programs should be defined at invocation.
|
|
meillo@11
|
391 This is done by specifying arguments (``command line switches'') to the program call.
|
|
meillo@11
|
392 Gancarz discusses this topic as ``avoid captive user interfaces''.
|
|
meillo@11
|
393 .[
|
|
meillo@11
|
394 %A Mike Gancarz
|
|
meillo@11
|
395 %T The UNIX Philosophy
|
|
meillo@11
|
396 %I Digital Press
|
|
meillo@11
|
397 %D 1995
|
|
meillo@11
|
398 %P 88 ff.
|
|
meillo@11
|
399 .]
|
|
meillo@11
|
400 .PP
|
|
meillo@11
|
401 Non-interactive use is, during development, also an advantage for testing.
|
|
meillo@11
|
402 Testing of interactive programs is much more complicated,
|
|
meillo@11
|
403 than testing of non-interactive programs.
|
|
meillo@5
|
404
|
|
meillo@16
|
405 .NH 2
|
|
meillo@8
|
406 The toolchest approach
|
|
meillo@42
|
407 .XS
|
|
meillo@42
|
408 \*(SN The toolchest approach
|
|
meillo@42
|
409 .XE
|
|
meillo@5
|
410 .LP
|
|
meillo@5
|
411 A toolchest is a set of tools.
|
|
meillo@5
|
412 Instead of having one big tool for all tasks, one has many small tools,
|
|
meillo@5
|
413 each for one task.
|
|
meillo@5
|
414 Difficult tasks are solved by combining several of the small, simple tools.
|
|
meillo@5
|
415 .PP
|
|
meillo@11
|
416 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
|
|
meillo@11
|
417 that are filters on byte streams.
|
|
meillo@11
|
418 They are, to a large extend, unrelated in their function.
|
|
meillo@11
|
419 Hence, the Unix toolchest provides a large set of functions
|
|
meillo@11
|
420 that can be accessed by combining the programs in the desired way.
|
|
meillo@11
|
421 .PP
|
|
meillo@11
|
422 There are also advantages for developing small toolchest programs.
|
|
meillo@5
|
423 It is easier and less error-prone to write small programs.
|
|
meillo@5
|
424 It is also easier and less error-prone to write a large set of small programs,
|
|
meillo@5
|
425 than to write one large program with all the functionality included.
|
|
meillo@5
|
426 If the small programs are combinable, then they offer even a larger set
|
|
meillo@5
|
427 of functions than the single large program.
|
|
meillo@5
|
428 Hence, one gets two advantages out of writing small, combinable programs.
|
|
meillo@5
|
429 .PP
|
|
meillo@5
|
430 There are two drawbacks of the toolchest approach.
|
|
meillo@8
|
431 First, one simple, standardized, unidirectional interface has to be sufficient.
|
|
meillo@5
|
432 If one feels the need for more ``logic'' than a stream of bytes,
|
|
meillo@8
|
433 then a different approach might be of need.
|
|
meillo@13
|
434 But it is also possible, that he just can not imagine a design where
|
|
meillo@8
|
435 a stream of bytes is sufficient.
|
|
meillo@8
|
436 By becoming more familiar with the ``Unix style of thinking'',
|
|
meillo@8
|
437 developers will more often and easier find simple designs where
|
|
meillo@8
|
438 a stream of bytes is a sufficient interface.
|
|
meillo@8
|
439 .PP
|
|
meillo@8
|
440 The second drawback of a toolchest affects the users.
|
|
meillo@5
|
441 A toolchest is often more difficult to use for novices.
|
|
meillo@9
|
442 It is necessary to become familiar with each of the tools,
|
|
meillo@5
|
443 to be able to use the right one in a given situation.
|
|
meillo@9
|
444 Additionally, one needs to combine the tools in a senseful way on its own.
|
|
meillo@9
|
445 This is like a sharp knife \(en it is a powerful tool in the hand of a master,
|
|
meillo@5
|
446 but of no good value in the hand of an unskilled.
|
|
meillo@5
|
447 .PP
|
|
meillo@8
|
448 However, learning single, small tool of the toolchest is easier than
|
|
meillo@8
|
449 learning a complex tool.
|
|
meillo@8
|
450 The user will have a basic understanding of a yet unknown tool,
|
|
meillo@8
|
451 if the several tools of the toolchest have a common style.
|
|
meillo@8
|
452 He will be able to transfer knowledge over one tool to another.
|
|
meillo@8
|
453 .PP
|
|
meillo@8
|
454 Moreover, the second drawback can be removed easily by adding wrappers
|
|
meillo@8
|
455 around the single tools.
|
|
meillo@5
|
456 Novice users do not need to learn several tools if a professional wraps
|
|
meillo@8
|
457 the single commands into a more high-level script.
|
|
meillo@5
|
458 Note that the wrapper script still calls the small tools;
|
|
meillo@5
|
459 the wrapper script is just like a skin around.
|
|
meillo@8
|
460 No complexity is added this way,
|
|
meillo@8
|
461 but new programs can get created out of existing one with very low effort.
|
|
meillo@5
|
462 .PP
|
|
meillo@5
|
463 A wrapper script for finding the five largest entries in the current directory
|
|
meillo@5
|
464 could look like this:
|
|
meillo@41
|
465 .DS
|
|
meillo@5
|
466 .CW
|
|
meillo@9
|
467 .ps -1
|
|
meillo@5
|
468 #!/bin/sh
|
|
meillo@5
|
469 du -s * | sort -nr | sed 5q
|
|
meillo@5
|
470 .DE
|
|
meillo@5
|
471 The script itself is just a text file that calls the command line
|
|
meillo@5
|
472 a professional user would type in directly.
|
|
meillo@8
|
473 Making the program flexible on the number of entries it prints,
|
|
meillo@8
|
474 is easily possible:
|
|
meillo@41
|
475 .DS
|
|
meillo@8
|
476 .CW
|
|
meillo@9
|
477 .ps -1
|
|
meillo@8
|
478 #!/bin/sh
|
|
meillo@8
|
479 num=5
|
|
meillo@8
|
480 [ $# -eq 1 ] && num="$1"
|
|
meillo@8
|
481 du -sh * | sort -nr | sed "${num}q"
|
|
meillo@8
|
482 .DE
|
|
meillo@8
|
483 This script acts like the one before, when called without an argument.
|
|
meillo@8
|
484 But one can also specify a numerical argument to define the number of lines to print.
|
|
meillo@5
|
485
|
|
meillo@16
|
486 .NH 2
|
|
meillo@8
|
487 A powerful shell
|
|
meillo@42
|
488 .XS
|
|
meillo@42
|
489 \*(SN A powerful shell
|
|
meillo@42
|
490 .XE
|
|
meillo@8
|
491 .LP
|
|
meillo@10
|
492 It was already said, that the Unix shell provides the possibility to
|
|
meillo@10
|
493 combine small programs into large ones easily.
|
|
meillo@10
|
494 A powerful shell is a great feature in other ways, too.
|
|
meillo@8
|
495 .PP
|
|
meillo@10
|
496 For instance by including a scripting language.
|
|
meillo@10
|
497 The control statements are build into the shell.
|
|
meillo@8
|
498 The functions, however, are the normal programs, everyone can use on the system.
|
|
meillo@10
|
499 Thus, the programs are known, so learning to program in the shell is easy.
|
|
meillo@8
|
500 Using normal programs as functions in the shell programming language
|
|
meillo@10
|
501 is only possible because they are small and combinable tools in a toolchest style.
|
|
meillo@8
|
502 .PP
|
|
meillo@8
|
503 The Unix shell encourages to write small scripts out of other programs,
|
|
meillo@8
|
504 because it is so easy to do.
|
|
meillo@8
|
505 This is a great step towards automation.
|
|
meillo@8
|
506 It is wonderful if the effort to automate a task equals the effort
|
|
meillo@8
|
507 it takes to do it the second time by hand.
|
|
meillo@8
|
508 If it is so, then the user will be happy to automate everything he does more than once.
|
|
meillo@8
|
509 .PP
|
|
meillo@8
|
510 Small programs that do one job well, standardized interfaces between them,
|
|
meillo@8
|
511 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
|
|
meillo@8
|
512 this will inevitably produce software leverage.
|
|
meillo@8
|
513 Getting multiple times the benefit of an investment is a great offer.
|
|
meillo@10
|
514 .PP
|
|
meillo@10
|
515 The shell also encourages rapid prototyping.
|
|
meillo@10
|
516 Many well known programs started as quickly hacked shell scripts,
|
|
meillo@10
|
517 and turned into ``real'' programs, written in C, later.
|
|
meillo@10
|
518 Building a prototype first is a way to avoid the biggest problems
|
|
meillo@10
|
519 in application development.
|
|
meillo@10
|
520 Fred Brooks writes in ``No Silver Bullet'':
|
|
meillo@10
|
521 .[
|
|
meillo@10
|
522 %A Frederick P. Brooks, Jr.
|
|
meillo@10
|
523 %T No Silver Bullet: Essence and Accidents of Software Engineering
|
|
meillo@10
|
524 %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference
|
|
meillo@10
|
525 %E H.-J. Kugler
|
|
meillo@10
|
526 %D 1986
|
|
meillo@10
|
527 %P 1069\(en1076
|
|
meillo@10
|
528 %I Elsevier Science B.V.
|
|
meillo@10
|
529 %C Amsterdam, The Netherlands
|
|
meillo@10
|
530 .]
|
|
meillo@10
|
531 .QP
|
|
meillo@41
|
532 .ps -1
|
|
meillo@10
|
533 The hardest single part of building a software system is deciding precisely what to build.
|
|
meillo@10
|
534 No other part of the conceptual work is so difficult as establishing the detailed
|
|
meillo@10
|
535 technical requirements, [...].
|
|
meillo@10
|
536 No other part of the work so cripples the resulting system if done wrong.
|
|
meillo@10
|
537 No other part is more difficult to rectify later.
|
|
meillo@10
|
538 .PP
|
|
meillo@10
|
539 Writing a prototype is a great method to become familiar with the requirements
|
|
meillo@10
|
540 and to actually run into real problems.
|
|
meillo@10
|
541 Today, prototyping is often seen as a first step in building a software.
|
|
meillo@10
|
542 This is, of course, good.
|
|
meillo@10
|
543 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
|
|
meillo@10
|
544 After having built the prototype, one might notice, that the prototype is already
|
|
meillo@10
|
545 \fIgood enough\fP.
|
|
meillo@10
|
546 Hence, no reimplementation, in a more sophisticated programming language, might be of need,
|
|
meillo@10
|
547 for the moment.
|
|
meillo@23
|
548 Maybe later, it might be necessary to rewrite the software, but not now.
|
|
meillo@10
|
549 .PP
|
|
meillo@10
|
550 By delaying further work, one keeps the flexibility to react easily on
|
|
meillo@10
|
551 changing requirements.
|
|
meillo@10
|
552 Software parts that are not written will not miss the requirements.
|
|
meillo@10
|
553
|
|
meillo@16
|
554 .NH 2
|
|
meillo@10
|
555 Worse is better
|
|
meillo@42
|
556 .XS
|
|
meillo@42
|
557 \*(SN Worse is better
|
|
meillo@42
|
558 .XE
|
|
meillo@10
|
559 .LP
|
|
meillo@10
|
560 The Unix Philosophy aims for the 80% solution;
|
|
meillo@10
|
561 others call it the ``Worse is better'' approach.
|
|
meillo@10
|
562 .PP
|
|
meillo@10
|
563 First, practical experience shows, that it is almost never possible to define the
|
|
meillo@10
|
564 requirements completely and correctly the first time.
|
|
meillo@10
|
565 Hence one should not try to; it will fail anyway.
|
|
meillo@10
|
566 Second, practical experience shows, that requirements change during time.
|
|
meillo@10
|
567 Hence it is best to delay requirement-based design decisions as long as possible.
|
|
meillo@10
|
568 Also, the software should be small and flexible as long as possible
|
|
meillo@10
|
569 to react on changing requirements.
|
|
meillo@10
|
570 Shell scripts, for example, are more easily adjusted as C programs.
|
|
meillo@10
|
571 Third, practical experience shows, that maintenance is hard work.
|
|
meillo@10
|
572 Hence, one should keep the amount of software as small as possible;
|
|
meillo@10
|
573 it should just fulfill the \fIcurrent\fP requirements.
|
|
meillo@10
|
574 Software parts that will be written later, do not need maintenance now.
|
|
meillo@10
|
575 .PP
|
|
meillo@10
|
576 Starting with a prototype in a scripting language has several advantages:
|
|
meillo@10
|
577 .IP \(bu
|
|
meillo@10
|
578 As the initial effort is low, one will likely start right away.
|
|
meillo@10
|
579 .IP \(bu
|
|
meillo@10
|
580 As working parts are available soon, the real requirements can get identified soon.
|
|
meillo@10
|
581 .IP \(bu
|
|
meillo@10
|
582 When a software is usable, it gets used, and thus tested.
|
|
meillo@10
|
583 Hence problems will be found at early stages of the development.
|
|
meillo@10
|
584 .IP \(bu
|
|
meillo@10
|
585 The prototype might be enough for the moment,
|
|
meillo@10
|
586 thus further work on the software can be delayed to a time
|
|
meillo@10
|
587 when one knows better about the requirements and problems,
|
|
meillo@10
|
588 than now.
|
|
meillo@10
|
589 .IP \(bu
|
|
meillo@10
|
590 Implementing now only the parts that are actually needed now,
|
|
meillo@10
|
591 requires fewer maintenance work.
|
|
meillo@10
|
592 .IP \(bu
|
|
meillo@10
|
593 If the global situation changes so that the software is not needed anymore,
|
|
meillo@10
|
594 then less effort was spent into the project, than it would have be
|
|
meillo@10
|
595 when a different approach had been used.
|
|
meillo@10
|
596
|
|
meillo@16
|
597 .NH 2
|
|
meillo@11
|
598 Upgrowth and survival of software
|
|
meillo@42
|
599 .XS
|
|
meillo@42
|
600 \*(SN Upgrowth and survival of software
|
|
meillo@42
|
601 .XE
|
|
meillo@11
|
602 .LP
|
|
meillo@12
|
603 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
|
|
meillo@13
|
604 Although these are just verbs, they do imply a specific view on the work process
|
|
meillo@13
|
605 they describe.
|
|
meillo@12
|
606 The better verb, however, is to \fIgrow\fP.
|
|
meillo@12
|
607 .PP
|
|
meillo@12
|
608 Creating software in the sense of the Unix Philosophy is an incremental process.
|
|
meillo@12
|
609 It starts with a first prototype, which evolves as requirements change.
|
|
meillo@12
|
610 A quickly hacked shell script might become a large, sophisticated,
|
|
meillo@13
|
611 compiled program this way.
|
|
meillo@13
|
612 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
|
|
meillo@13
|
613 While being alive it will get extended, rearranged, rebuilt (from scratch).
|
|
meillo@12
|
614 Growing software matches the view that ``software is never finished. It is only released.''
|
|
meillo@12
|
615 .[
|
|
meillo@13
|
616 %O FIXME
|
|
meillo@13
|
617 %A Mike Gancarz
|
|
meillo@13
|
618 %T The UNIX Philosophy
|
|
meillo@13
|
619 %P 26
|
|
meillo@12
|
620 .]
|
|
meillo@12
|
621 .PP
|
|
meillo@13
|
622 Software can be seen as being controlled by evolutionary processes.
|
|
meillo@13
|
623 Successful software is software that is used by many for a long time.
|
|
meillo@12
|
624 This implies that the software is needed, useful, and better than alternatives.
|
|
meillo@12
|
625 Darwin talks about: ``The survival of the fittest.''
|
|
meillo@12
|
626 .[
|
|
meillo@13
|
627 %O FIXME
|
|
meillo@13
|
628 %A Charles Darwin
|
|
meillo@12
|
629 .]
|
|
meillo@12
|
630 Transferred to software: The most successful software, is the fittest,
|
|
meillo@12
|
631 is the one that survives.
|
|
meillo@13
|
632 (This may be at the level of one creature, or at the level of one species.)
|
|
meillo@13
|
633 The fitness of software is affected mainly by four properties:
|
|
meillo@15
|
634 portability of code, portability of data, range of usability, and reusability of parts.
|
|
meillo@15
|
635 .\" .IP \(bu
|
|
meillo@15
|
636 .\" portability of code
|
|
meillo@15
|
637 .\" .IP \(bu
|
|
meillo@15
|
638 .\" portability of data
|
|
meillo@15
|
639 .\" .IP \(bu
|
|
meillo@15
|
640 .\" range of usability
|
|
meillo@15
|
641 .\" .IP \(bu
|
|
meillo@15
|
642 .\" reuseability of parts
|
|
meillo@13
|
643 .PP
|
|
meillo@15
|
644 (1)
|
|
meillo@15
|
645 .I "Portability of code
|
|
meillo@15
|
646 means, using high-level programming languages,
|
|
meillo@13
|
647 sticking to the standard,
|
|
meillo@13
|
648 and avoiding optimizations that introduce dependencies on specific hardware.
|
|
meillo@13
|
649 Hardware has a much lower lifetime than software.
|
|
meillo@13
|
650 By chaining software to a specific hardware,
|
|
meillo@13
|
651 the software's lifetime gets shortened to that of this hardware.
|
|
meillo@13
|
652 In contrast, software should be easy to port \(en
|
|
meillo@23
|
653 adaptation is the key to success.
|
|
meillo@13
|
654 .\" cf. practice of prog: ch08
|
|
meillo@13
|
655 .PP
|
|
meillo@15
|
656 (2)
|
|
meillo@15
|
657 .I "Portability of data
|
|
meillo@15
|
658 is best achieved by avoiding binary representations
|
|
meillo@13
|
659 to store data, because binary representations differ from machine to machine.
|
|
meillo@23
|
660 Textual representation is favored.
|
|
meillo@13
|
661 Historically, ASCII was the charset of choice.
|
|
meillo@13
|
662 In the future, UTF-8 might be the better choice, however.
|
|
meillo@13
|
663 Important is that it is a plain text representation in a
|
|
meillo@13
|
664 very common charset encoding.
|
|
meillo@13
|
665 Apart from being able to transfer data between machines,
|
|
meillo@13
|
666 readable data has the great advantage, that humans are able
|
|
meillo@13
|
667 to directly edit it with text editors and other tools from the Unix toolchest.
|
|
meillo@13
|
668 .\" gancarz tenet 5
|
|
meillo@13
|
669 .PP
|
|
meillo@15
|
670 (3)
|
|
meillo@15
|
671 A large
|
|
meillo@15
|
672 .I "range of usability
|
|
meillo@23
|
673 ensures good adaptation, and thus good survival.
|
|
meillo@13
|
674 It is a special distinction if a software becomes used in fields of action,
|
|
meillo@13
|
675 the original authors did never imagine.
|
|
meillo@13
|
676 Software that solves problems in a general way will likely be used
|
|
meillo@13
|
677 for all kinds of similar problems.
|
|
meillo@13
|
678 Being too specific limits the range of uses.
|
|
meillo@13
|
679 Requirements change through time, thus use cases change or even vanish.
|
|
meillo@13
|
680 A good example in this point is Allman's sendmail.
|
|
meillo@13
|
681 Allman identifies flexibility to be one major reason for sendmail's success:
|
|
meillo@13
|
682 .[
|
|
meillo@13
|
683 %O FIXME
|
|
meillo@13
|
684 %A Allman
|
|
meillo@13
|
685 %T sendmail
|
|
meillo@13
|
686 .]
|
|
meillo@13
|
687 .QP
|
|
meillo@41
|
688 .ps -1
|
|
meillo@13
|
689 Second, I limited myself to the routing function [...].
|
|
meillo@13
|
690 This was a departure from the dominant thought of the time, [...].
|
|
meillo@13
|
691 .QP
|
|
meillo@41
|
692 .ps -1
|
|
meillo@13
|
693 Third, the sendmail configuration file was flexible enough to adopt
|
|
meillo@13
|
694 to a rapidly changing world [...].
|
|
meillo@12
|
695 .LP
|
|
meillo@13
|
696 Successful software adopts itself to the changing world.
|
|
meillo@13
|
697 .PP
|
|
meillo@15
|
698 (4)
|
|
meillo@15
|
699 .I "Reuse of parts
|
|
meillo@15
|
700 is even one step further.
|
|
meillo@13
|
701 A software may completely lose its field of action,
|
|
meillo@13
|
702 but parts of which the software is build may be general and independent enough
|
|
meillo@13
|
703 to survive this death.
|
|
meillo@13
|
704 If software is build by combining small independent programs,
|
|
meillo@13
|
705 then there are parts readily available for reuse.
|
|
meillo@13
|
706 Who cares if the large program is a failure,
|
|
meillo@13
|
707 but parts of it become successful instead?
|
|
meillo@10
|
708
|
|
meillo@16
|
709 .NH 2
|
|
meillo@14
|
710 Summary
|
|
meillo@42
|
711 .XS
|
|
meillo@42
|
712 \*(SN Summary
|
|
meillo@42
|
713 .XE
|
|
meillo@0
|
714 .LP
|
|
meillo@14
|
715 This chapter explained the central ideas of the Unix Philosophy.
|
|
meillo@14
|
716 For each of the ideas, it was exposed what advantages they introduce.
|
|
meillo@14
|
717 The Unix Philosophy are guidelines that help to write valuable software.
|
|
meillo@14
|
718 From the view point of a software developer or software designer,
|
|
meillo@14
|
719 the Unix Philosophy provides answers to many software design problem.
|
|
meillo@14
|
720 .PP
|
|
meillo@14
|
721 The various ideas of the Unix Philosophy are very interweaved
|
|
meillo@14
|
722 and can hardly be applied independently.
|
|
meillo@14
|
723 However, the probably most important messages are:
|
|
meillo@14
|
724 .I "``Do one thing well!''" ,
|
|
meillo@14
|
725 .I "``Keep it simple!''" ,
|
|
meillo@14
|
726 and
|
|
meillo@14
|
727 .I "``Use software leverage!''
|
|
meillo@0
|
728
|
|
meillo@8
|
729
|
|
meillo@8
|
730
|
|
meillo@0
|
731 .NH 1
|
|
meillo@19
|
732 Case study: \s-1MH\s0
|
|
meillo@42
|
733 .XS
|
|
meillo@42
|
734 .sp .5v
|
|
meillo@42
|
735 \*(SN Case study: \s-1MH\s0
|
|
meillo@42
|
736 .XE
|
|
meillo@18
|
737 .LP
|
|
meillo@30
|
738 The previous chapter introduced and explained the Unix Philosophy
|
|
meillo@18
|
739 from a general point of view.
|
|
meillo@30
|
740 The driving force were the guidelines; references to
|
|
meillo@18
|
741 existing software were given only sparsely.
|
|
meillo@18
|
742 In this and the next chapter, concrete software will be
|
|
meillo@18
|
743 the driving force in the discussion.
|
|
meillo@18
|
744 .PP
|
|
meillo@23
|
745 This first case study is about the mail user agents (\s-1MUA\s0)
|
|
meillo@23
|
746 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
|
|
meillo@23
|
747 (``new mail handler'').
|
|
meillo@23
|
748 \s-1MUA\s0s provide functions to read, compose, and organize mail,
|
|
meillo@23
|
749 but (ideally) not to transfer.
|
|
meillo@19
|
750 In this document, the name \s-1MH\s0 will be used for both of them.
|
|
meillo@19
|
751 A distinction will only be made if differences between
|
|
meillo@19
|
752 them are described.
|
|
meillo@18
|
753
|
|
meillo@0
|
754
|
|
meillo@0
|
755 .NH 2
|
|
meillo@19
|
756 Historical background
|
|
meillo@42
|
757 .XS
|
|
meillo@42
|
758 \*(SN Historical background
|
|
meillo@42
|
759 .XE
|
|
meillo@0
|
760 .LP
|
|
meillo@19
|
761 Electronic mail was available in Unix very early.
|
|
meillo@30
|
762 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
|
|
meillo@30
|
763 which was already present in the First Edition.
|
|
meillo@30
|
764 .[
|
|
meillo@30
|
765 %A Peter H. Salus
|
|
meillo@30
|
766 %T A Quarter Century of UNIX
|
|
meillo@30
|
767 %D 1994
|
|
meillo@30
|
768 %I Addison-Wesley
|
|
meillo@30
|
769 %P 41 f.
|
|
meillo@30
|
770 .]
|
|
meillo@30
|
771 It was a small program that either prints the user's mailbox file
|
|
meillo@19
|
772 or appends text to someone elses mailbox file,
|
|
meillo@19
|
773 depending on the command line arguments.
|
|
meillo@19
|
774 .[
|
|
meillo@19
|
775 %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf
|
|
meillo@19
|
776 .]
|
|
meillo@19
|
777 It was a program that did one job well.
|
|
meillo@23
|
778 This job was emailing, which was very simple then.
|
|
meillo@19
|
779 .PP
|
|
meillo@23
|
780 Later, emailing became more powerful, and thus more complex.
|
|
meillo@19
|
781 The simple \f(CWmail\fP, which knew nothing of subjects,
|
|
meillo@19
|
782 independent handling of single messages,
|
|
meillo@19
|
783 and long-time storage of them, was not powerful enough anymore.
|
|
meillo@19
|
784 At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
|
|
meillo@19
|
785 in 1978 to provide additional functions for emailing.
|
|
meillo@19
|
786 Mail was still one program, but now it was large and did
|
|
meillo@19
|
787 several jobs.
|
|
meillo@23
|
788 Its user interface is modeled after the one of \fIed\fP.
|
|
meillo@19
|
789 It is designed for humans, but is still scriptable.
|
|
meillo@23
|
790 \fImailx\fP is the adaptation of Berkeley Mail into System V.
|
|
meillo@19
|
791 .[
|
|
meillo@19
|
792 %A Gunnar Ritter
|
|
meillo@19
|
793 %O http://heirloom.sourceforge.net/mailx_history.html
|
|
meillo@19
|
794 .]
|
|
meillo@30
|
795 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
|
|
meillo@19
|
796 followed Mail's direction.
|
|
meillo@19
|
797 They are large, monolithic programs which include all emailing functions.
|
|
meillo@19
|
798 .PP
|
|
meillo@23
|
799 A different way was taken by the people of \s-1RAND\s0 Corporation.
|
|
meillo@38
|
800 In the beginning, they also had used a monolithic mail system,
|
|
meillo@30
|
801 called \s-1MS\s0 (for ``mail system'').
|
|
meillo@19
|
802 But in 1977, Stockton Gaines and Norman Shapiro
|
|
meillo@19
|
803 came up with a proposal of a new email system concept \(en
|
|
meillo@19
|
804 one that honors the Unix Philosophy.
|
|
meillo@19
|
805 The concept was implemented by Bruce Borden in 1978 and 1979.
|
|
meillo@19
|
806 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
|
|
meillo@18
|
807 .PP
|
|
meillo@18
|
808 Since then, \s-1RAND\s0, the University of California at Irvine and
|
|
meillo@19
|
809 at Berkeley, and several others have contributed to the software.
|
|
meillo@18
|
810 However, it's core concepts remained the same.
|
|
meillo@23
|
811 In the late 90s, when development of \s-1MH\s0 slowed down,
|
|
meillo@19
|
812 Richard Coleman started with \fInmh\fP, the new mail handler.
|
|
meillo@19
|
813 His goal was to improve \s-1MH\s0, especially in regard of
|
|
meillo@23
|
814 the requirements of modern emailing.
|
|
meillo@19
|
815 Today, nmh is developed by various people on the Internet.
|
|
meillo@18
|
816 .[
|
|
meillo@18
|
817 %T RAND and the Information Evolution: A History in Essays and Vignettes
|
|
meillo@18
|
818 %A Willis H. Ware
|
|
meillo@18
|
819 %D 2008
|
|
meillo@18
|
820 %I The RAND Corporation
|
|
meillo@18
|
821 %P 128\(en137
|
|
meillo@18
|
822 %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/
|
|
meillo@18
|
823 .]
|
|
meillo@18
|
824 .[
|
|
meillo@18
|
825 %T MH & xmh: Email for Users & Programmers
|
|
meillo@18
|
826 %A Jerry Peek
|
|
meillo@18
|
827 %D 1991, 1992, 1995
|
|
meillo@18
|
828 %I O'Reilly & Associates, Inc.
|
|
meillo@18
|
829 %P Appendix B
|
|
meillo@18
|
830 %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP
|
|
meillo@18
|
831 .]
|
|
meillo@0
|
832
|
|
meillo@0
|
833 .NH 2
|
|
meillo@20
|
834 Contrasts to monolithic mail systems
|
|
meillo@42
|
835 .XS
|
|
meillo@42
|
836 \*(SN Contrasts to monolithic mail systems
|
|
meillo@42
|
837 .XE
|
|
meillo@0
|
838 .LP
|
|
meillo@19
|
839 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
|
|
meillo@38
|
840 Although there might actually exist further, very little known,
|
|
meillo@30
|
841 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
|
|
meillo@19
|
842 .PP
|
|
meillo@30
|
843 Monolithic \s-1MUA\s0s gather all their functions in one program.
|
|
meillo@30
|
844 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
|
|
meillo@23
|
845 Following is a list of important programs of \s-1MH\s0's toolchest
|
|
meillo@30
|
846 and their function.
|
|
meillo@30
|
847 It gives a feeling of how the toolchest looks like.
|
|
meillo@19
|
848 .IP \(bu
|
|
meillo@19
|
849 .CW inc :
|
|
meillo@30
|
850 incorporate new mail (this is how mail enters the system)
|
|
meillo@19
|
851 .IP \(bu
|
|
meillo@19
|
852 .CW scan :
|
|
meillo@19
|
853 list messages in folder
|
|
meillo@19
|
854 .IP \(bu
|
|
meillo@19
|
855 .CW show :
|
|
meillo@19
|
856 show message
|
|
meillo@19
|
857 .IP \(bu
|
|
meillo@19
|
858 .CW next\fR/\fPprev :
|
|
meillo@19
|
859 show next/previous message
|
|
meillo@19
|
860 .IP \(bu
|
|
meillo@19
|
861 .CW folder :
|
|
meillo@19
|
862 change current folder
|
|
meillo@19
|
863 .IP \(bu
|
|
meillo@19
|
864 .CW refile :
|
|
meillo@19
|
865 refile message into folder
|
|
meillo@19
|
866 .IP \(bu
|
|
meillo@19
|
867 .CW rmm :
|
|
meillo@19
|
868 remove message
|
|
meillo@19
|
869 .IP \(bu
|
|
meillo@19
|
870 .CW comp :
|
|
meillo@19
|
871 compose a new message
|
|
meillo@19
|
872 .IP \(bu
|
|
meillo@19
|
873 .CW repl :
|
|
meillo@19
|
874 reply to a message
|
|
meillo@19
|
875 .IP \(bu
|
|
meillo@19
|
876 .CW forw :
|
|
meillo@19
|
877 forward a message
|
|
meillo@19
|
878 .IP \(bu
|
|
meillo@19
|
879 .CW send :
|
|
meillo@30
|
880 send a prepared message (this is how mail leaves the system)
|
|
meillo@0
|
881 .LP
|
|
meillo@19
|
882 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
|
|
meillo@19
|
883 The user does not leave the shell to run \s-1MH\s0,
|
|
meillo@30
|
884 but he uses the various \s-1MH\s0 programs within the shell.
|
|
meillo@23
|
885 Using a monolithic program with a captive user interface
|
|
meillo@23
|
886 means ``entering'' the program, using it, and ``exiting'' the program.
|
|
meillo@23
|
887 Using toolchests like \s-1MH\s0 means running programs,
|
|
meillo@38
|
888 alone or in combination with others, even from other toolchests,
|
|
meillo@23
|
889 without leaving the shell.
|
|
meillo@30
|
890
|
|
meillo@30
|
891 .NH 2
|
|
meillo@30
|
892 Data storage
|
|
meillo@42
|
893 .XS
|
|
meillo@42
|
894 \*(SN Data storage
|
|
meillo@42
|
895 .XE
|
|
meillo@30
|
896 .LP
|
|
meillo@34
|
897 \s-1MH\s0's mail storage is a directory tree under the user's
|
|
meillo@34
|
898 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
|
|
meillo@34
|
899 where mail folders are directories and mail messages are text files
|
|
meillo@34
|
900 within them.
|
|
meillo@34
|
901 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
|
|
meillo@34
|
902 the public message sequences of that folder, for instance new messages.
|
|
meillo@34
|
903 Mail messages are text files located in a mail folder.
|
|
meillo@34
|
904 The files contain the messages as they were received.
|
|
meillo@34
|
905 They are numbered in ascending order in each folder.
|
|
meillo@19
|
906 .PP
|
|
meillo@30
|
907 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
|
|
meillo@30
|
908 Alternatives are \fImbox\fP and \fImaildir\fP.
|
|
meillo@30
|
909 In the mbox format all messages are stored within one file.
|
|
meillo@30
|
910 This was a good solution in the early days, when messages
|
|
meillo@30
|
911 were only a few lines of text and were deleted soon.
|
|
meillo@30
|
912 Today, when single messages often include several megabytes
|
|
meillo@30
|
913 of attachments, it is a bad solution.
|
|
meillo@30
|
914 Another disadvantage of the mbox format is that it is
|
|
meillo@30
|
915 more difficult to write tools that work on mail messages,
|
|
meillo@30
|
916 because it is always necessary to first find and extract
|
|
meillo@30
|
917 the relevant message in the mbox file.
|
|
meillo@30
|
918 With the \s-1MH\s0 mailbox format,
|
|
meillo@30
|
919 each message is a self-standing item, by definition.
|
|
meillo@30
|
920 Also, the problem of concurrent access to one mailbox is
|
|
meillo@30
|
921 reduced to the problem of concurrent access to one message.
|
|
meillo@30
|
922 Maildir is generally similar to \s-1MH\s0's format,
|
|
meillo@30
|
923 but modified towards guaranteed reliability.
|
|
meillo@30
|
924 This involves some complexity, unfortunately.
|
|
meillo@34
|
925 .PP
|
|
meillo@34
|
926 Working with \s-1MH\s0's toolchest on mailboxes is much like
|
|
meillo@34
|
927 working with Unix' toolchest on directory trees:
|
|
meillo@34
|
928 \f(CWscan\fP is like \f(CWls\fP,
|
|
meillo@34
|
929 \f(CWshow\fP is like \f(CWcat\fP,
|
|
meillo@34
|
930 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
|
|
meillo@34
|
931 \f(CWrefile\fP is like \f(CWmv\fP,
|
|
meillo@34
|
932 and \f(CWrmm\fP is like \f(CWrm\fP.
|
|
meillo@34
|
933 .PP
|
|
meillo@34
|
934 The context of tools in Unix consists mainly the current working directory,
|
|
meillo@34
|
935 the user identification, and the environment variables.
|
|
meillo@34
|
936 \s-1MH\s0 extends this context by two more items:
|
|
meillo@34
|
937 .IP \(bu
|
|
meillo@34
|
938 The current mail folder, which is similar to the current working directory.
|
|
meillo@34
|
939 For mail folders, \f(CWfolder\fP provides the corresponding functionality
|
|
meillo@34
|
940 of \f(CWcd\fP and \f(CWpwd\fP for directories.
|
|
meillo@34
|
941 .IP \(bu
|
|
meillo@34
|
942 Sequences, which are named sets of messages in a mail folder.
|
|
meillo@34
|
943 The current message, relative to a mail folder, is a special sequence.
|
|
meillo@34
|
944 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
|
|
meillo@34
|
945 .LP
|
|
meillo@34
|
946 In contrast to Unix' context, which is chained to the shell session,
|
|
meillo@34
|
947 \s-1MH\s0's context is independent.
|
|
meillo@34
|
948 Usually there is one context for each user, but a user can have many
|
|
meillo@34
|
949 contexts.
|
|
meillo@34
|
950 Public sequences are an exception, as they belong to the mail folder.
|
|
meillo@34
|
951 .[
|
|
meillo@34
|
952 %O mh-profile(5) and mh-sequence(5)
|
|
meillo@34
|
953 .]
|
|
meillo@20
|
954
|
|
meillo@0
|
955 .NH 2
|
|
meillo@20
|
956 Discussion of the design
|
|
meillo@42
|
957 .XS
|
|
meillo@42
|
958 \*(SN Discussion of the design
|
|
meillo@42
|
959 .XE
|
|
meillo@0
|
960 .LP
|
|
meillo@20
|
961 The following paragraphs discuss \s-1MH\s0 in regard to the tenets
|
|
meillo@23
|
962 of the Unix Philosophy which Gancarz identified.
|
|
meillo@20
|
963
|
|
meillo@20
|
964 .PP
|
|
meillo@33
|
965 .B "Small is beautiful
|
|
meillo@20
|
966 and
|
|
meillo@33
|
967 .B "do one thing well
|
|
meillo@20
|
968 are two design goals that are directly visible in \s-1MH\s0.
|
|
meillo@20
|
969 Gancarz actually presents \s-1MH\s0 as example under the headline
|
|
meillo@20
|
970 ``Making UNIX Do One Thing Well'':
|
|
meillo@41
|
971 .[
|
|
meillo@41
|
972 %A Mike Gancarz
|
|
meillo@41
|
973 %T unix-phil
|
|
meillo@41
|
974 %P 125
|
|
meillo@41
|
975 .]
|
|
meillo@20
|
976 .QP
|
|
meillo@41
|
977 .ps -1
|
|
meillo@20
|
978 [\s-1MH\s0] consists of a series of programs which
|
|
meillo@20
|
979 when combined give the user an enormous ability
|
|
meillo@20
|
980 to manipulate electronic mail messages.
|
|
meillo@20
|
981 A complex application, it shows that not only is it
|
|
meillo@20
|
982 possible to build large applications from smaller
|
|
meillo@20
|
983 components, but also that such designs are actually preferable.
|
|
meillo@20
|
984 .LP
|
|
meillo@20
|
985 The various small programs of \s-1MH\s0 were relatively easy
|
|
meillo@23
|
986 to write, because each of them is small, limited to one function,
|
|
meillo@23
|
987 and has clear boundaries.
|
|
meillo@20
|
988 For the same reasons, they are also good to maintain.
|
|
meillo@20
|
989 Further more, the system can easily get extended.
|
|
meillo@20
|
990 One only needs to put a new program into the toolchest.
|
|
meillo@23
|
991 This was done, for instance, when \s-1MIME\s0 support was added
|
|
meillo@20
|
992 (e.g. \f(CWmhbuild\fP).
|
|
meillo@20
|
993 Also, different programs can exist to do the basically same job
|
|
meillo@20
|
994 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
|
|
meillo@20
|
995 If someone needs a mail system with some additionally
|
|
meillo@23
|
996 functions that are available nowhere yet, he best takes a
|
|
meillo@20
|
997 toolchest system like \s-1MH\s0 where he can add the
|
|
meillo@20
|
998 functionality with little work.
|
|
meillo@20
|
999
|
|
meillo@20
|
1000 .PP
|
|
meillo@34
|
1001 .B "Store data in flat text files
|
|
meillo@34
|
1002 is followed by \s-1MH\s0.
|
|
meillo@34
|
1003 This is not surprising, because email messages are already plain text.
|
|
meillo@34
|
1004 \s-1MH\s0 stores the messages as it receives them,
|
|
meillo@34
|
1005 thus any other tool that works on RFC 2822 mail messages can operate
|
|
meillo@34
|
1006 on the messages in an \s-1MH\s0 mailbox.
|
|
meillo@34
|
1007 All other files \s-1MH\s0 uses are plain text too.
|
|
meillo@34
|
1008 It is therefore possible and encouraged to use the text processing
|
|
meillo@34
|
1009 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
|
|
meillo@20
|
1010
|
|
meillo@20
|
1011 .PP
|
|
meillo@33
|
1012 .B "Avoid captive user interfaces" .
|
|
meillo@19
|
1013 \s-1MH\s0 is perfectly suited for non-interactive use.
|
|
meillo@19
|
1014 It offers all functions directly and without captive user interfaces.
|
|
meillo@30
|
1015 If, nonetheless, users want a graphical user interface,
|
|
meillo@20
|
1016 they can have it with \fIxmh\fP or \fIexmh\fP, too.
|
|
meillo@19
|
1017 These are graphical frontends for the \s-1MH\s0 toolchest.
|
|
meillo@19
|
1018 This means, all email-related work is still done by \s-1MH\s0 tools,
|
|
meillo@20
|
1019 but the frontend issues the appropriate calls when the user
|
|
meillo@30
|
1020 clicks on buttons.
|
|
meillo@20
|
1021 Providing easy-to-use user interfaces in form of frontends is a good
|
|
meillo@19
|
1022 approach, because it does not limit the power of the backend itself.
|
|
meillo@20
|
1023 The frontend will anyway only be able to make a subset of the
|
|
meillo@23
|
1024 backend's power and flexibility available to the user.
|
|
meillo@20
|
1025 But if it is a separate program,
|
|
meillo@20
|
1026 then the missing parts can still be accessed at the backend directly.
|
|
meillo@19
|
1027 If it is integrated, then this will hardly be possible.
|
|
meillo@30
|
1028 Further more, it is possible to have different frontends to the same
|
|
meillo@30
|
1029 backend.
|
|
meillo@19
|
1030
|
|
meillo@19
|
1031 .PP
|
|
meillo@33
|
1032 .B "Choose portability over efficiency
|
|
meillo@20
|
1033 and
|
|
meillo@33
|
1034 .B "use shell scripts to increase leverage and portability" .
|
|
meillo@20
|
1035 These two tenets are indirectly, but nicely, demonstrated by
|
|
meillo@30
|
1036 Bolsky and Korn in their book about the Korn Shell.
|
|
meillo@20
|
1037 .[
|
|
meillo@20
|
1038 %T The KornShell: command and programming language
|
|
meillo@20
|
1039 %A Morris I. Bolsky
|
|
meillo@20
|
1040 %A David G. Korn
|
|
meillo@20
|
1041 %I Prentice Hall
|
|
meillo@20
|
1042 %D 1989
|
|
meillo@30
|
1043 %P 254\(en290
|
|
meillo@20
|
1044 %O \s-1ISBN\s0: 0-13-516972-0
|
|
meillo@20
|
1045 .]
|
|
meillo@30
|
1046 They demonstrated, in chapter 18 of the book, a basic implementation
|
|
meillo@20
|
1047 of a subset of \s-1MH\s0 in ksh scripts.
|
|
meillo@20
|
1048 Of course, this was just a demonstration, but a brilliant one.
|
|
meillo@20
|
1049 It shows how quickly one can implement such a prototype with shell scripts,
|
|
meillo@20
|
1050 and how readable they are.
|
|
meillo@20
|
1051 The implementation in the scripting language may not be very fast,
|
|
meillo@20
|
1052 but it can be fast enough though, and this is all that matters.
|
|
meillo@20
|
1053 By having the code in an interpreted language, like the shell,
|
|
meillo@20
|
1054 portability becomes a minor issue, if we assume the interpreter
|
|
meillo@20
|
1055 to be widespread.
|
|
meillo@20
|
1056 This demonstration also shows how easy it is to create single programs
|
|
meillo@20
|
1057 of a toolchest software.
|
|
meillo@30
|
1058 There are eight tools (two of them have multiple names) and 16 functions
|
|
meillo@30
|
1059 with supporting code.
|
|
meillo@30
|
1060 Each tool comprises between 12 and 38 lines of ksh,
|
|
meillo@30
|
1061 in total about 200 lines.
|
|
meillo@30
|
1062 The functions comprise between 3 and 78 lines of ksh,
|
|
meillo@30
|
1063 in total about 450 lines.
|
|
meillo@20
|
1064 Such small software is easy to write, easy to understand,
|
|
meillo@20
|
1065 and thus easy to maintain.
|
|
meillo@23
|
1066 A toolchest improves the possibility to only write some parts
|
|
meillo@20
|
1067 and though create a working result.
|
|
meillo@20
|
1068 Expanding the toolchest without global changes will likely be
|
|
meillo@20
|
1069 possible, too.
|
|
meillo@20
|
1070
|
|
meillo@20
|
1071 .PP
|
|
meillo@33
|
1072 .B "Use software leverage to your advantage
|
|
meillo@20
|
1073 and the lesser tenet
|
|
meillo@33
|
1074 .B "allow the user to tailor the environment
|
|
meillo@20
|
1075 are ideally followed in the design of \s-1MH\s0.
|
|
meillo@21
|
1076 Tailoring the environment is heavily encouraged by the ability to
|
|
meillo@30
|
1077 directly define default options to programs.
|
|
meillo@30
|
1078 It is even possible to define different default options
|
|
meillo@21
|
1079 depending on the name under which the program was called.
|
|
meillo@21
|
1080 Software leverage is heavily encouraged by the ease it is to
|
|
meillo@21
|
1081 create shell scripts that run a specific command line,
|
|
meillo@30
|
1082 built of several \s-1MH\s0 programs.
|
|
meillo@21
|
1083 There is few software that so much wants users to tailor their
|
|
meillo@21
|
1084 environment and to leverage the use of the software, like \s-1MH\s0.
|
|
meillo@21
|
1085 Just to make one example:
|
|
meillo@23
|
1086 One might prefer a different listing format for the \f(CWscan\fP
|
|
meillo@21
|
1087 program.
|
|
meillo@30
|
1088 It is possible to take one of the distributed format files
|
|
meillo@21
|
1089 or to write one yourself.
|
|
meillo@21
|
1090 To use the format as default for \f(CWscan\fP, a single line,
|
|
meillo@21
|
1091 reading
|
|
meillo@21
|
1092 .DS
|
|
meillo@21
|
1093 .CW
|
|
meillo@21
|
1094 scan: -form FORMATFILE
|
|
meillo@21
|
1095 .DE
|
|
meillo@21
|
1096 must be added to \f(CW.mh_profile\fP.
|
|
meillo@21
|
1097 If one wants this different format as an additional command,
|
|
meillo@23
|
1098 instead of changing the default, he needs to create a link to
|
|
meillo@23
|
1099 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
|
|
meillo@21
|
1100 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
|
|
meillo@30
|
1101 as the option should only be in effect when scan is called as
|
|
meillo@21
|
1102 \f(CWscan2\fP.
|
|
meillo@20
|
1103
|
|
meillo@20
|
1104 .PP
|
|
meillo@33
|
1105 .B "Make every program a filter
|
|
meillo@21
|
1106 is hard to find in \s-1MH\s0.
|
|
meillo@21
|
1107 The reason therefore is that most of \s-1MH\s0's tools provide
|
|
meillo@21
|
1108 basic file system operations for the mailboxes.
|
|
meillo@30
|
1109 The reason is the same because of which
|
|
meillo@21
|
1110 \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP
|
|
meillo@21
|
1111 aren't filters neither.
|
|
meillo@23
|
1112 However, they build a basis on which filters can operate.
|
|
meillo@23
|
1113 \s-1MH\s0 does not provide many filters itself, but it is a basis
|
|
meillo@23
|
1114 to write filters for.
|
|
meillo@30
|
1115 An example would be a mail message text highlighter,
|
|
meillo@30
|
1116 that means a program that makes use of a color terminal to display
|
|
meillo@30
|
1117 header lines, quotations, and signatures in distinct colors.
|
|
meillo@30
|
1118 The author's version of this program, for instance,
|
|
meillo@30
|
1119 is a 25 line awk script.
|
|
meillo@21
|
1120
|
|
meillo@21
|
1121 .PP
|
|
meillo@33
|
1122 .B "Build a prototype as soon as possible
|
|
meillo@21
|
1123 was again well followed by \s-1MH\s0.
|
|
meillo@21
|
1124 This tenet, of course, focuses on early development, which is
|
|
meillo@21
|
1125 long time ago for \s-1MH\s0.
|
|
meillo@21
|
1126 But without following this guideline at the very beginning,
|
|
meillo@23
|
1127 Bruce Borden may have not convinced the management of \s-1RAND\s0
|
|
meillo@23
|
1128 to ever create \s-1MH\s0.
|
|
meillo@23
|
1129 In Bruce' own words:
|
|
meillo@41
|
1130 .[
|
|
meillo@41
|
1131 %O FIXME
|
|
meillo@41
|
1132 .]
|
|
meillo@21
|
1133 .QP
|
|
meillo@41
|
1134 .ps -1
|
|
meillo@30
|
1135 [...] but they [Stockton Gaines and Norm Shapiro] were not able
|
|
meillo@23
|
1136 to convince anyone that such a system would be fast enough to be usable.
|
|
meillo@21
|
1137 I proposed a very short project to prove the basic concepts,
|
|
meillo@21
|
1138 and my management agreed.
|
|
meillo@21
|
1139 Looking back, I realize that I had been very lucky with my first design.
|
|
meillo@21
|
1140 Without nearly enough design work,
|
|
meillo@21
|
1141 I built a working environment and some header files
|
|
meillo@21
|
1142 with key structures and wrote the first few \s-1MH\s0 commands:
|
|
meillo@21
|
1143 inc, show/next/prev, and comp.
|
|
meillo@21
|
1144 [...]
|
|
meillo@21
|
1145 With these three, I was able to convince people that the structure was viable.
|
|
meillo@21
|
1146 This took about three weeks.
|
|
meillo@0
|
1147
|
|
meillo@0
|
1148 .NH 2
|
|
meillo@0
|
1149 Problems
|
|
meillo@42
|
1150 .XS
|
|
meillo@42
|
1151 \*(SN Problems
|
|
meillo@42
|
1152 .XE
|
|
meillo@0
|
1153 .LP
|
|
meillo@22
|
1154 \s-1MH\s0, for sure is not without problems.
|
|
meillo@30
|
1155 There are two main problems: one is technical, the other is about human behavior.
|
|
meillo@22
|
1156 .PP
|
|
meillo@22
|
1157 \s-1MH\s0 is old and email today is very different to email in the time
|
|
meillo@22
|
1158 when \s-1MH\s0 was designed.
|
|
meillo@22
|
1159 \s-1MH\s0 adopted to the changes pretty well, but it is limited.
|
|
meillo@22
|
1160 For example in development resources.
|
|
meillo@22
|
1161 \s-1MIME\s0 support and support for different character encodings
|
|
meillo@22
|
1162 is available, but only on a moderate level.
|
|
meillo@22
|
1163 More active developers could quickly improve there.
|
|
meillo@22
|
1164 It is also limited by design, which is the larger problem.
|
|
meillo@22
|
1165 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
|
|
meillo@22
|
1166 These design conflicts are not easily solvable.
|
|
meillo@22
|
1167 Possibly, they require a redesign.
|
|
meillo@30
|
1168 Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers,
|
|
meillo@30
|
1169 hence \s-1MH\s0 may never work well with \s-1IMAP\s0.
|
|
meillo@22
|
1170 .PP
|
|
meillo@22
|
1171 The other kind of problem is human habits.
|
|
meillo@22
|
1172 When in this world almost all \s-1MUA\s0s are monolithic,
|
|
meillo@22
|
1173 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
|
|
meillo@22
|
1174 like \s-1MH\s0.
|
|
meillo@22
|
1175 The habits are so strong, that even people who understood the concept
|
|
meillo@30
|
1176 and advantages of \s-1MH\s0 do not like to switch,
|
|
meillo@30
|
1177 simply because \s-1MH\s0 is different.
|
|
meillo@30
|
1178 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
|
|
meillo@30
|
1179 are quite outdated and thus not very appealing compared to the modern interfaces
|
|
meillo@30
|
1180 which monolithic \s-1MUA\s0s offer.
|
|
meillo@20
|
1181
|
|
meillo@20
|
1182 .NH 2
|
|
meillo@20
|
1183 Summary \s-1MH\s0
|
|
meillo@42
|
1184 .XS
|
|
meillo@42
|
1185 \*(SN Summary \s-1MH\s0
|
|
meillo@42
|
1186 .XE
|
|
meillo@20
|
1187 .LP
|
|
meillo@31
|
1188 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design
|
|
meillo@31
|
1189 and implementation.
|
|
meillo@31
|
1190 It consists of a toolchest of small tools, each of them does one job well.
|
|
meillo@31
|
1191 The tools are orthogonal to each other, to a large extend.
|
|
meillo@31
|
1192 However, for historical reasons, there also exist distinct tools
|
|
meillo@31
|
1193 that cover the same task.
|
|
meillo@31
|
1194 .PP
|
|
meillo@31
|
1195 The toolchest approach offers great flexibility to the user.
|
|
meillo@31
|
1196 He can use the complete power of the Unix shell with \s-1MH\s0.
|
|
meillo@31
|
1197 This makes \s-1MH\s0 a very powerful mail system.
|
|
meillo@31
|
1198 Extending and customizing \s-1MH\s0 is easy and encouraged, too.
|
|
meillo@31
|
1199 .PP
|
|
meillo@31
|
1200 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
|
|
meillo@31
|
1201 Its overall design follows clear rules.
|
|
meillo@31
|
1202 The single tools do only one job, thus they are easy to understand,
|
|
meillo@31
|
1203 easy to write, and good to maintain.
|
|
meillo@31
|
1204 They are all independent and do not interfere with the others.
|
|
meillo@31
|
1205 Automated testing of their function is a straight forward task.
|
|
meillo@31
|
1206 .PP
|
|
meillo@31
|
1207 It is sad, that \s-1MH\s0's differentness is its largest problem,
|
|
meillo@31
|
1208 as its differentness is also its largest advantage.
|
|
meillo@31
|
1209 Unfortunately, for most people their habits are stronger
|
|
meillo@31
|
1210 than the attraction of the clear design and the power, \s-1MH\s0 offers.
|
|
meillo@0
|
1211
|
|
meillo@8
|
1212
|
|
meillo@8
|
1213
|
|
meillo@0
|
1214 .NH 1
|
|
meillo@0
|
1215 Case study: uzbl
|
|
meillo@42
|
1216 .XS
|
|
meillo@42
|
1217 .sp .5v
|
|
meillo@42
|
1218 \*(SN Case study: uzbl
|
|
meillo@42
|
1219 .XE
|
|
meillo@32
|
1220 .LP
|
|
meillo@32
|
1221 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
|
|
meillo@32
|
1222 this chapter is about uzbl, a web browser that adheres to the Unix Philosophy.
|
|
meillo@32
|
1223 ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''.
|
|
meillo@32
|
1224 It is pronounced the identical.
|
|
meillo@0
|
1225
|
|
meillo@0
|
1226 .NH 2
|
|
meillo@32
|
1227 Historical background
|
|
meillo@42
|
1228 .XS
|
|
meillo@42
|
1229 \*(SN Historical background
|
|
meillo@42
|
1230 .XE
|
|
meillo@0
|
1231 .LP
|
|
meillo@32
|
1232 Uzbl was started by Dieter Plaetinck in April 2009.
|
|
meillo@32
|
1233 The idea was born in a thread in the Arch Linux forum.
|
|
meillo@32
|
1234 .[
|
|
meillo@32
|
1235 %O http://bbs.archlinux.org/viewtopic.php?id=67463
|
|
meillo@32
|
1236 .]
|
|
meillo@32
|
1237 After some discussion about failures of well known web browsers,
|
|
meillo@32
|
1238 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
|
|
meillo@32
|
1239 of how a better web browser could look like.
|
|
meillo@32
|
1240 To the question of another member, if Plaetinck would write that program,
|
|
meillo@32
|
1241 because it would sound fantastic, Plaetinck replied:
|
|
meillo@32
|
1242 ``Maybe, if I find the time ;-)''.
|
|
meillo@32
|
1243 .PP
|
|
meillo@32
|
1244 Fortunately, he found the time.
|
|
meillo@32
|
1245 One day later, the first prototype was out.
|
|
meillo@32
|
1246 One week later, uzbl had an own website.
|
|
meillo@32
|
1247 One month after the first code showed up,
|
|
meillo@32
|
1248 a mailing list was installed to coordinate and discuss further development.
|
|
meillo@32
|
1249 A wiki was set up to store documentation and scripts that showed up on the
|
|
meillo@32
|
1250 mailing list and elsewhere.
|
|
meillo@32
|
1251 .PP
|
|
meillo@38
|
1252 In the, now, one year of uzbl's existence, it was heavily developed in various branches.
|
|
meillo@32
|
1253 Plaetinck's task became more and more to only merge the best code from the
|
|
meillo@32
|
1254 different branches into his main branch, and to apply patches.
|
|
meillo@32
|
1255 About once a month, Plaetinck released a new version.
|
|
meillo@32
|
1256 In September 2009, he presented several forks of uzbl.
|
|
meillo@38
|
1257 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
|
|
meillo@32
|
1258 .PP
|
|
meillo@32
|
1259 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
|
|
meillo@32
|
1260 In September 2009, the uzbl web browser was on \fISlashdot\fP.
|
|
meillo@0
|
1261
|
|
meillo@0
|
1262 .NH 2
|
|
meillo@32
|
1263 Contrasts to other web browsers
|
|
meillo@42
|
1264 .XS
|
|
meillo@42
|
1265 \*(SN Contrasts to other web browsers
|
|
meillo@42
|
1266 .XE
|
|
meillo@0
|
1267 .LP
|
|
meillo@32
|
1268 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
|
|
meillo@32
|
1269 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
|
|
meillo@32
|
1270 .PP
|
|
meillo@32
|
1271 Today, uzbl is divided into uzbl-core and uzbl-browser.
|
|
meillo@32
|
1272 Uzbl-core is, how its name already indicates, the core of uzbl.
|
|
meillo@32
|
1273 It handles commands and events to interface other programs,
|
|
meillo@32
|
1274 and also displays webpages by using webkit as render engine.
|
|
meillo@32
|
1275 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
|
|
meillo@32
|
1276 an event manager, yanking, pasting, page searching, zooming, and more stuff,
|
|
meillo@32
|
1277 to form a ``complete'' web browser.
|
|
meillo@32
|
1278 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
|
|
meillo@32
|
1279 so uzbl-core is included.
|
|
meillo@32
|
1280 .PP
|
|
meillo@32
|
1281 Unlike most other web browsers, uzbl is mainly the mediator between the
|
|
meillo@32
|
1282 various tools that cover single jobs of web browsing.
|
|
meillo@35
|
1283 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
|
|
meillo@35
|
1284 and on stdin, and it writes events to a Unix socket and to stdout.
|
|
meillo@35
|
1285 The graphical rendering of the webpage is done by webkit, a web content engine.
|
|
meillo@35
|
1286 Uzbl-core is build around this library.
|
|
meillo@35
|
1287 Loading a webpage in a running uzbl instance requires only:
|
|
meillo@32
|
1288 .DS
|
|
meillo@32
|
1289 .CW
|
|
meillo@32
|
1290 echo 'uri http://example.org' >/path/to/uzbl-fifo
|
|
meillo@32
|
1291 .DE
|
|
meillo@32
|
1292 .PP
|
|
meillo@32
|
1293 Downloads, browsing history, bookmarks, and thelike are not provided
|
|
meillo@32
|
1294 by uzbl-core itself, as they are in other web browsers.
|
|
meillo@35
|
1295 Uzbl-browser also only provides, so called, handler scripts that wrap
|
|
meillo@35
|
1296 external applications which provide the actual functionality.
|
|
meillo@32
|
1297 For instance, \fIwget\fP is used to download files and uzbl-browser
|
|
meillo@32
|
1298 includes a script that calls wget with appropriate options in
|
|
meillo@32
|
1299 a prepared environment.
|
|
meillo@32
|
1300 .PP
|
|
meillo@32
|
1301 Modern web browsers are proud to have addons, plugins, and modules, instead.
|
|
meillo@32
|
1302 This is their effort to achieve similar goals.
|
|
meillo@35
|
1303 But instead of using existing, external programs, modern web browsers
|
|
meillo@35
|
1304 include these functions, although they might be loaded at runtime.
|
|
meillo@0
|
1305
|
|
meillo@0
|
1306 .NH 2
|
|
meillo@32
|
1307 Discussion of the design
|
|
meillo@42
|
1308 .XS
|
|
meillo@42
|
1309 \*(SN Discussion of the design
|
|
meillo@42
|
1310 .XE
|
|
meillo@0
|
1311 .LP
|
|
meillo@32
|
1312 This section discusses uzbl in regard of the Unix Philosophy,
|
|
meillo@32
|
1313 as identified by Gancarz.
|
|
meillo@32
|
1314
|
|
meillo@32
|
1315 .PP
|
|
meillo@35
|
1316 .B "Make each program do one thing well" .
|
|
meillo@35
|
1317 Uzbl tries to be a web browser and nothing else.
|
|
meillo@36
|
1318 The common definition of a web browser is, of course, highly influenced by
|
|
meillo@36
|
1319 existing implementations of web browsers, although they are degenerated.
|
|
meillo@35
|
1320 Web browsers should be programs to browse the web, and nothing more.
|
|
meillo@35
|
1321 This is the one thing they should do, as demanded by the Unix Philosophy.
|
|
meillo@36
|
1322 .PP
|
|
meillo@36
|
1323 Web browsers should, for instance, not manage downloads.
|
|
meillo@35
|
1324 This is the job download managers exist for.
|
|
meillo@35
|
1325 Download managers do primary care about being good in downloading files.
|
|
meillo@35
|
1326 Modern web browsers provide download management only as a secondary feature.
|
|
meillo@35
|
1327 How could they perform this job better, than programs that exist only for
|
|
meillo@35
|
1328 this very job?
|
|
meillo@35
|
1329 And how could anyone want less than the best download manager available?
|
|
meillo@32
|
1330 .PP
|
|
meillo@35
|
1331 A web browser's job is to let the user browse the web.
|
|
meillo@35
|
1332 This means, navigating through websites by following links.
|
|
meillo@36
|
1333 Rendering the \s-1HTML\s0 sources is a different job, too.
|
|
meillo@36
|
1334 It is covered by the webkit render engine, in uzbl's case.
|
|
meillo@35
|
1335 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
|
|
meillo@36
|
1336 are also not the job of a web browser.
|
|
meillo@36
|
1337 They should be handled by external applications \(en
|
|
meillo@36
|
1338 ones which's job is to handle such data.
|
|
meillo@35
|
1339 Uzbl strives to do it this way.
|
|
meillo@36
|
1340 .PP
|
|
meillo@36
|
1341 Remember Doug McIlroy:
|
|
meillo@35
|
1342 .I
|
|
meillo@35
|
1343 ``Write programs that do one thing and do it well.
|
|
meillo@35
|
1344 Write programs to work together.''
|
|
meillo@35
|
1345 .R
|
|
meillo@35
|
1346 .PP
|
|
meillo@35
|
1347 The lesser tenet
|
|
meillo@35
|
1348 .B "allow the user to tailor the environment
|
|
meillo@35
|
1349 matches good here.
|
|
meillo@35
|
1350 There was the question, how anyone could want anything less than the
|
|
meillo@35
|
1351 best program for the job.
|
|
meillo@36
|
1352 But as personal preferences matter much,
|
|
meillo@36
|
1353 it is probably more important to ask:
|
|
meillo@35
|
1354 How could anyone want something else than his preferred program for the job?
|
|
meillo@36
|
1355 .PP
|
|
meillo@35
|
1356 Usually users want one program for one job.
|
|
meillo@35
|
1357 Hence, whenever the task is, for instance, downloading,
|
|
meillo@36
|
1358 exactly one download manager should be used.
|
|
meillo@35
|
1359 More advanced users might want to have this download manager in this
|
|
meillo@35
|
1360 situation and that one in that situation.
|
|
meillo@35
|
1361 They should be able to configure it this way.
|
|
meillo@35
|
1362 With uzbl, one can use any download manager the user wants.
|
|
meillo@36
|
1363 To switch to a different one, only one line in a small handler script
|
|
meillo@35
|
1364 needs to be changed.
|
|
meillo@36
|
1365 Alternatively it would be possible to query an entry in a global file
|
|
meillo@36
|
1366 or an environment variable, which specifies the download manager to use,
|
|
meillo@35
|
1367 in the handler script.
|
|
meillo@36
|
1368 .PP
|
|
meillo@35
|
1369 As uzbl does neither have its own download manager nor depends on a
|
|
meillo@35
|
1370 specific one, thus uzbl's browsing abilities will not be lowered by having
|
|
meillo@35
|
1371 a bad download manager.
|
|
meillo@36
|
1372 Uzbl's download capabilities will just as good as the ones of the best
|
|
meillo@36
|
1373 download manager available on the system.
|
|
meillo@38
|
1374 Of course, this applies to all of the other supplementary tools, too.
|
|
meillo@32
|
1375
|
|
meillo@32
|
1376 .PP
|
|
meillo@36
|
1377 .B "Use software leverage to your advantage" .
|
|
meillo@36
|
1378 Shell scripts are a good choice to extend uzbl.
|
|
meillo@36
|
1379 Uzbl is designed to be extended by external tools.
|
|
meillo@36
|
1380 These external tools are usually wrapped by small handler shell scripts.
|
|
meillo@36
|
1381 Shell scripts are the glue in this approach.
|
|
meillo@36
|
1382 They make the various parts fit together.
|
|
meillo@36
|
1383 .PP
|
|
meillo@36
|
1384 As an example, the history mechanism of uzbl shall be presented.
|
|
meillo@36
|
1385 Uzbl is configured to spawn a script to append an entry to the history
|
|
meillo@36
|
1386 whenever the event of a fully loaded page occurs.
|
|
meillo@36
|
1387 The script to append the entry to the history not much more than:
|
|
meillo@36
|
1388 .DS
|
|
meillo@36
|
1389 .CW
|
|
meillo@36
|
1390 #!/bin/sh
|
|
meillo@36
|
1391 file=/path/to/uzbl-history
|
|
meillo@36
|
1392 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
|
|
meillo@36
|
1393 .DE
|
|
meillo@36
|
1394 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
|
|
meillo@36
|
1395 For loading an entry, a key is bound to spawn a load from history script.
|
|
meillo@36
|
1396 The script reverses the history to have newer entries first,
|
|
meillo@36
|
1397 then displays \fIdmenu\fP to select an item,
|
|
meillo@36
|
1398 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
|
|
meillo@36
|
1399 With error checking and corner cases removed, the script looks like this:
|
|
meillo@36
|
1400 .DS
|
|
meillo@36
|
1401 .CW
|
|
meillo@36
|
1402 #!/bin/sh
|
|
meillo@36
|
1403 file=/path/to/uzbl-history
|
|
meillo@36
|
1404 goto=`tac $file | dmenu | cut -d' ' -f 3`
|
|
meillo@36
|
1405 echo "uri $goto" > $4
|
|
meillo@36
|
1406 .DE
|
|
meillo@36
|
1407 \f(CW$4\fP expands to the path of the command input pipe of the current
|
|
meillo@36
|
1408 uzbl instance.
|
|
meillo@32
|
1409
|
|
meillo@32
|
1410 .PP
|
|
meillo@33
|
1411 .B "Avoid captive user interfaces" .
|
|
meillo@36
|
1412 One could say, that uzbl, to a large extend, actually \fIis\fP
|
|
meillo@36
|
1413 a captive user interface.
|
|
meillo@37
|
1414 But the difference to most other web browsers is, that uzbl is only
|
|
meillo@37
|
1415 the captive user interface frontend and the core of the backend.
|
|
meillo@38
|
1416 Many parts of the backend are independent of uzbl.
|
|
meillo@37
|
1417 Some are distributed with uzbl, for some external programs, handler scripts
|
|
meillo@37
|
1418 are distributed, arbitrary additional functionality can be added if desired.
|
|
meillo@37
|
1419 .PP
|
|
meillo@37
|
1420 The frontend is captive \(en that is true.
|
|
meillo@37
|
1421 This is okay for the task of browsing the web, as this task is only relevant
|
|
meillo@37
|
1422 for humans.
|
|
meillo@37
|
1423 Automated programs would \fIcrawl\fP the web.
|
|
meillo@37
|
1424 That means, they read the source directly.
|
|
meillo@37
|
1425 The source includes all the semantics.
|
|
meillo@37
|
1426 The graphical representation is just for humans to transfer the semantics
|
|
meillo@37
|
1427 more intuitively.
|
|
meillo@32
|
1428
|
|
meillo@32
|
1429 .PP
|
|
meillo@33
|
1430 .B "Make every program a filter" .
|
|
meillo@37
|
1431 Graphical web browsers are almost dead ends in the chain of information flow.
|
|
meillo@37
|
1432 Thus it is difficult to see what graphical web browsers should filter.
|
|
meillo@37
|
1433 Graphical web browsers exist almost only for interactive use by humans.
|
|
meillo@37
|
1434 The only case when one might want to automate the rendering function is
|
|
meillo@37
|
1435 to generate images of rendered webpages.
|
|
meillo@37
|
1436
|
|
meillo@37
|
1437 .PP
|
|
meillo@37
|
1438 .B "Small is beautiful"
|
|
meillo@38
|
1439 is not easy to apply to a web browser, primary because modern web technology
|
|
meillo@38
|
1440 is very complex; hence the rendering task is very complex.
|
|
meillo@37
|
1441 Modern web browsers will always consist of many thousand lines of code,
|
|
meillo@37
|
1442 unfortunately.
|
|
meillo@37
|
1443 Using the toolchest approach and wrappers can split the browser into
|
|
meillo@37
|
1444 several small parts, tough.
|
|
meillo@37
|
1445 .PP
|
|
meillo@37
|
1446 Uzbl-core consists of about 3\,500 lines of C code.
|
|
meillo@37
|
1447 The distribution includes another 3\,500 lines of Shell and Python code,
|
|
meillo@37
|
1448 which are the handler scripts and plugins like a modal interface.
|
|
meillo@38
|
1449 Further more, uzbl uses functionality of external tools like
|
|
meillo@38
|
1450 \fIwget\fP and \fInetcat\fP.
|
|
meillo@37
|
1451 Up to this point, uzbl looks pretty neat and small.
|
|
meillo@38
|
1452 The ugly part of uzbl is the web content renderer, webkit.
|
|
meillo@37
|
1453 Webkit consists of roughly 400\,000 (!) lines of code.
|
|
meillo@38
|
1454 Unfortunately, small web render engines are not possible anymore
|
|
meillo@38
|
1455 because of the modern web.
|
|
meillo@38
|
1456 The problems section will explain this in more detail.
|
|
meillo@35
|
1457
|
|
meillo@35
|
1458 .PP
|
|
meillo@35
|
1459 .B "Build a prototype as soon as possible" .
|
|
meillo@35
|
1460 Plaetinck made his code public, right from the beginning.
|
|
meillo@38
|
1461 Discussion and development was, and still is, open to everyone interested.
|
|
meillo@38
|
1462 Development versions of uzbl can be obtained very simply from the code
|
|
meillo@38
|
1463 repository.
|
|
meillo@38
|
1464 Within the first year of uzbl's existence, a new version was released
|
|
meillo@35
|
1465 more often than once a month.
|
|
meillo@38
|
1466 Different forks and branches arose.
|
|
meillo@38
|
1467 They introduced new features, which were tested for suitability.
|
|
meillo@35
|
1468 The experiences of using prototypes influenced further development.
|
|
meillo@35
|
1469 Actually, all development was community driven.
|
|
meillo@38
|
1470 Plaetinck says, three months after uzbl's birth:
|
|
meillo@35
|
1471 ``Right now I hardly code anything myself for Uzbl.
|
|
meillo@35
|
1472 I just merge in other people's code, ponder a lot, and lead the discussions.''
|
|
meillo@35
|
1473 .[
|
|
meillo@36
|
1474 %A FIXME
|
|
meillo@35
|
1475 %O http://lwn.net/Articles/341245/
|
|
meillo@35
|
1476 .]
|
|
meillo@32
|
1477
|
|
meillo@0
|
1478
|
|
meillo@0
|
1479 .NH 2
|
|
meillo@0
|
1480 Problems
|
|
meillo@42
|
1481 .XS
|
|
meillo@42
|
1482 \*(SN Problems
|
|
meillo@42
|
1483 .XE
|
|
meillo@0
|
1484 .LP
|
|
meillo@38
|
1485 Similar to \s-1MH\s0, uzbl, too suffers from being different.
|
|
meillo@38
|
1486 It is sad, but people use what they know.
|
|
meillo@38
|
1487 Fortunately, uzbl's user interface can look and feel very much the
|
|
meillo@38
|
1488 same as the one of the well known web browsers,
|
|
meillo@38
|
1489 hiding the internal differences.
|
|
meillo@38
|
1490 But uzbl has to provide this similar look and feel to be accepted
|
|
meillo@38
|
1491 as a ``normal'' browser by ``normal'' users.
|
|
meillo@37
|
1492 .PP
|
|
meillo@38
|
1493 The more important problem is the modern web.
|
|
meillo@38
|
1494 The modern web is simply broken.
|
|
meillo@38
|
1495 It has state in a state-less protocol,
|
|
meillo@38
|
1496 it misuses technologies,
|
|
meillo@38
|
1497 and it is helplessly overloaded.
|
|
meillo@38
|
1498 The result are web content render engines that must consist
|
|
meillo@38
|
1499 of hundreds of thousands lines of code.
|
|
meillo@38
|
1500 They also must combine and integrate many different technologies,
|
|
meillo@38
|
1501 only to make our modern web usable.
|
|
meillo@38
|
1502 Website to image converter are hardly possible to run without
|
|
meillo@38
|
1503 human interaction because of state in sessions, impossible
|
|
meillo@38
|
1504 deep-linking, and unautomatable technologies.
|
|
meillo@37
|
1505 .PP
|
|
meillo@38
|
1506 The web was misused to provide all kinds of imaginable wishes.
|
|
meillo@38
|
1507 Now web browsers, and eventually the users, suffer from it.
|
|
meillo@37
|
1508
|
|
meillo@8
|
1509
|
|
meillo@32
|
1510 .NH 2
|
|
meillo@32
|
1511 Summary uzbl
|
|
meillo@42
|
1512 .XS
|
|
meillo@42
|
1513 \*(SN Summary uzbl
|
|
meillo@42
|
1514 .XE
|
|
meillo@32
|
1515 .LP
|
|
meillo@38
|
1516 ``Uzbl is a browser that adheres to the Unix Philosophy'',
|
|
meillo@38
|
1517 that is how uzbl is seen by its authors.
|
|
meillo@38
|
1518 Indeed, uzbl follows the Unix Philosophy in many ways.
|
|
meillo@38
|
1519 It consists of independent parts that work together,
|
|
meillo@38
|
1520 its core is mainly a mediator which glues the parts together.
|
|
meillo@38
|
1521 .PP
|
|
meillo@38
|
1522 Software leverage can excellently be seen in uzbl.
|
|
meillo@38
|
1523 It makes use of external tools, separates independent tasks
|
|
meillo@38
|
1524 in independent parts, and glues them together with small
|
|
meillo@38
|
1525 handler scripts, around uzbl-core.
|
|
meillo@38
|
1526 .PP
|
|
meillo@38
|
1527 As uzbl, more or less, consists of a set of tools and a bit
|
|
meillo@38
|
1528 of glue, anyone can put the parts together and expand it
|
|
meillo@38
|
1529 in any desired way.
|
|
meillo@38
|
1530 Uzbl is very flexible and customizable.
|
|
meillo@38
|
1531 These properties make it valuable for advanced users,
|
|
meillo@38
|
1532 but may keep novice users from using it.
|
|
meillo@38
|
1533 .PP
|
|
meillo@38
|
1534 Uzbl's main problem is the modern web, that makes it hard
|
|
meillo@38
|
1535 to design a sane web browser.
|
|
meillo@38
|
1536 Despite this bad situation, uzbl does a fairly good job.
|
|
meillo@32
|
1537
|
|
meillo@8
|
1538
|
|
meillo@0
|
1539 .NH 1
|
|
meillo@0
|
1540 Final thoughts
|
|
meillo@42
|
1541 .XS
|
|
meillo@42
|
1542 .sp .5v
|
|
meillo@42
|
1543 \*(SN Final thoughts
|
|
meillo@42
|
1544 .XE
|
|
meillo@0
|
1545
|
|
meillo@0
|
1546 .NH 2
|
|
meillo@0
|
1547 Quick summary
|
|
meillo@42
|
1548 .XS
|
|
meillo@42
|
1549 \*(SN Quick summary
|
|
meillo@42
|
1550 .XE
|
|
meillo@0
|
1551 .LP
|
|
meillo@0
|
1552 good design
|
|
meillo@0
|
1553 .LP
|
|
meillo@0
|
1554 unix phil
|
|
meillo@0
|
1555 .LP
|
|
meillo@0
|
1556 case studies
|
|
meillo@0
|
1557
|
|
meillo@0
|
1558 .NH 2
|
|
meillo@0
|
1559 Why people should choose
|
|
meillo@42
|
1560 .XS
|
|
meillo@42
|
1561 \*(SN Why people should choose
|
|
meillo@42
|
1562 .XE
|
|
meillo@0
|
1563 .LP
|
|
meillo@0
|
1564 Make the right choice!
|
|
meillo@0
|
1565
|
|
meillo@42
|
1566 .nr PI .3i
|
|
meillo@0
|
1567 .rm ]<
|
|
meillo@0
|
1568 .de ]<
|
|
meillo@0
|
1569 .LP
|
|
meillo@0
|
1570 .de FP
|
|
meillo@0
|
1571 .IP \\\\$1.
|
|
meillo@0
|
1572 \\..
|
|
meillo@0
|
1573 .rm FS FE
|
|
meillo@0
|
1574 ..
|
|
meillo@42
|
1575 .ds CH "
|
|
meillo@42
|
1576 .bp
|
|
meillo@42
|
1577 .rs
|
|
meillo@42
|
1578 .sp .3i
|
|
meillo@42
|
1579 .TL
|
|
meillo@0
|
1580 References
|
|
meillo@42
|
1581 .LP
|
|
meillo@42
|
1582 .XS
|
|
meillo@42
|
1583 .sp .5v
|
|
meillo@42
|
1584 References
|
|
meillo@42
|
1585 .XE
|
|
meillo@42
|
1586 .sp 2v
|
|
meillo@42
|
1587 .nr PS -1
|
|
meillo@42
|
1588 .nr VS -1
|
|
meillo@0
|
1589 .[
|
|
meillo@0
|
1590 $LIST$
|
|
meillo@0
|
1591 .]
|
|
meillo@42
|
1592 .\".wh -1p
|
|
meillo@42
|
1593 .bp
|
|
meillo@42
|
1594 .PX
|
