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new content about interfaces and toolchests

author	meillo@marmaro.de
date	Sat, 13 Feb 2010 11:37:50 +0100
parents	c707b0c5c849
children	a6b837d822b7

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 .NH 1
 The Unix Philosophy
 .LP
 The origins of the Unix Philosophy were already introduced.
 This chapter explains the philosophy and shows concrete examples of its application.
-.NH 2
+.SH
 Examples
 .LP
 Following are some examples to demonstrate how applied Unix Philosophy feels like.
 Knowledge of using the Unix shell is assumed.
 .PP
 .PP
 The presented command lines are examples of what Unix people would use
 to get the desired output.
 There are also other ways to get the same output.
 It's a user's decision which way to go.
-.NH 2
+.SH
 Pipes
 .LP
 The examples show that a lot of tasks on a Unix system
 are accomplished by combining several small programs.
 The connection between the single programs is denoted by the pipe operator `|'.
 Unix system,
 ``it was this concept and notation for linking several programs together
 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
 .[
 %T Unix: An Oral History
-%O http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
+%O .CW \s-1http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
 .]
 .PP
 Being able to specify pipelines in an easy way is,
 however, not enough by itself.
-It is only one part.
+It is only one half.
 The other is the design of the programs that are used in the pipeline.
-They have to be of an external shape that allows them to be be used in a pipeline.
+They have to be of an external shape that allows them to be be used in such a way.
+.SH
-.NH 2
-Architecture
-.LP
-the most important design decision.
-the topic here
-.NH 2
 Interface architecture
+.LP
+Unix is, first of all, simple: Everything is a file.
+Files are sequences of bytes, without any special structure.
+Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
+and write a stream of bytes to ``standard output'' (stdout).
+.PP
+If our files \fIare\fP sequences of bytes,
+and our programs \fIare\fP filters on byte streams,
+then there is exactly one standardized interface.
+Thus it is possible to combine them in any desired way.
+.PP
+Even a handful of small programs will yield a large set of combinations,
+and thus a large set of different functions.
+This is leverage!
+.PP
+If the programs are orthogonal to each other \(en the best case \(en
+then the set of different functions is greatest.
+.PP
+Now, the Unix toolchest is a set of small programs that
+are filters on byte streams.
+They are to a large extend unrelated in their function.
+Hence, the Unix toolchest provides a large set of functions
+that can be accessed by combining the programs in the desired way.
+.SH
+Advantages of toolchests
+.LP
+A toolchest is a set of tools.
+Instead of having one big tool for all tasks, one has many small tools,
+each for one task.
+Difficult tasks are solved by combining several of the small, simple tools.
+.PP
+It is easier and less error-prone to write small programs.
+It is also easier and less error-prone to write a large set of small programs,
+than to write one large program with all the functionality included.
+If the small programs are combinable, then they offer even a larger set
+of functions than the single large program.
+Hence, one gets two advantages out of writing small, combinable programs.
+.PP
+There are two drawbacks of the toolchest approach.
+First, one simple, standardized, unidirectional Interface has to be sufficient.
+If one feels the need for more ``logic'' than a stream of bytes,
+then a different approach might be of need, or, more likely,
+he just did not came to a design where a stream of bytes is sufficient.
+The other drawback of a toolchest affects the users.
+A toolchest is often more difficult to use for novices.
+It is neccessary to become familiar with each of the tools,
+to be able to use the right one in a given situation.
+Additinally, one needs to combine the tools in a senseful way on its own.
+This is like a sharp knive \(en it is a powerful tool in the hand of a master,
+but of no good value in the hand of an unskilled.
+.PP
+Luckily, the second drawback can be solved easily by adding wrappers around the single tools.
+Novice users do not need to learn several tools if a professional wraps
+the single commands into a single script.
+Note that the wrapper script still calls the small tools;
+the wrapper script is just like a skin around.
+No complexity is added this way.
+.PP
+A wrapper script for finding the five largest entries in the current directory
+could look like this:
+.DS
+.CW
+#!/bin/sh
+du -s * | sort -nr | sed 5q
+.DE
+The script itself is just a text file that calls the command line
+a professional user would type in directly.
+.NH 2
+foo
 .LP
 standalone vs. tool chain
 .LP
 software leverage
 .LP

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