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meillo@1: .\"----------------------------------------
meillo@0: .TL
meillo@0: Why the Unix Philosophy matters
meillo@0: .AU
meillo@0: markus schnalke <meillo@marmaro.de>
meillo@0: .AB
meillo@1: .ti \n(.iu
meillo@2: This paper discusses the importance of the Unix Philosophy in software design.
meillo@0: Today, few software designers are aware of these concepts,
meillo@3: and thus most modern software is limited and does not make use of software leverage.
meillo@0: Knowing and following the tenets of the Unix Philosophy makes software more valuable.
meillo@0: .AE
meillo@0: 
meillo@2: .if t .2C
meillo@2: 
meillo@2: .FS
meillo@2: .ps -1
meillo@2: This paper was prepared for the seminar ``Software Analysis'' at University Ulm.
meillo@2: Mentor was professor Schweiggert. 2010-02-05
meillo@2: .br
meillo@2: You may get this document from my website
meillo@2: .CW \s-1http://marmaro.de/docs
meillo@2: .FE
meillo@2: 
meillo@0: .NH 1
meillo@0: Introduction
meillo@0: .LP
meillo@0: Building a software is a process from an idea of the purpose of the software
meillo@3: to its release.
meillo@0: No matter \fIhow\fP the process is run, two things are common:
meillo@0: the initial idea and the release.
meillo@3: The process inbetween can be of any shape.
meillo@3: The the maintainance work after the release is ignored for the moment.
meillo@1: .PP
meillo@0: The process of building splits mainly in two parts:
meillo@0: the planning of what and how to build, and implementing the plan by writing code.
meillo@3: This paper focuses on the planning part \(en the designing of the software.
meillo@3: .PP
meillo@3: Software design is the plan of how the internals and externals of the software should look like,
meillo@3: based on the requirements.
meillo@3: This paper discusses the recommendations of the Unix Philosphy about software design.
meillo@3: .PP
meillo@3: The here discussed ideas can get applied by any development process.
meillo@3: The Unix Philosphy does recommend how the software development process should look like,
meillo@3: but this shall not be of matter here.
meillo@0: Similar, the question of how to write the code is out of focus.
meillo@1: .PP
meillo@3: The name ``Unix Philosophy'' was already mentioned several times, but it was not explained yet.
meillo@1: The Unix Philosophy is the essence of how the Unix operating system and its toolchest was designed.
meillo@3: It is no limited set of rules, but what people see to be common to typical Unix software.
meillo@1: Several people stated their view on the Unix Philosophy.
meillo@1: Best known are:
meillo@1: .IP \(bu
meillo@1: Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
meillo@1: .[
meillo@1: %A M. D. McIlroy
meillo@1: %A E. N. Pinson
meillo@1: %A B. A. Taque
meillo@1: %T UNIX Time-Sharing System Forward
meillo@1: %J The Bell System Technical Journal
meillo@1: %D 1978
meillo@1: %V 57
meillo@1: %N 6
meillo@1: %P 1902
meillo@1: .]
meillo@1: .IP \(bu
meillo@1: Mike Gancarz' book ``The UNIX Philosophy''.
meillo@1: .[
meillo@1: %A Mike Gancarz
meillo@1: %T The UNIX Philosophy
meillo@1: %D 1995
meillo@1: %I Digital Press
meillo@1: .]
meillo@1: .IP \(bu
meillo@1: Eric S. Raymond's book ``The Art of UNIX Programming''.
meillo@1: .[
meillo@1: %A Eric S. Raymond
meillo@1: %T The Art of UNIX Programming
meillo@1: %D 2003
meillo@1: %I Addison-Wesley
meillo@2: %O .CW \s-1http://www.faqs.org/docs/artu/
meillo@1: .]
meillo@0: .LP
meillo@1: These different views on the Unix Philosophy have much in common.
meillo@3: Especially, the main concepts are similar for all of them.
meillo@1: But there are also points on which they differ.
meillo@1: This only underlines what the Unix Philosophy is:
meillo@1: A retrospective view on the main concepts of Unix software;
meillo@1: especially those that were sucessful and unique to Unix.
meillo@1: .PP
meillo@1: Before we will have a look at concrete concepts,
meillo@1: we discuss why software design is important
meillo@1: and what problems bad design introduces.
meillo@0: 
meillo@0: 
meillo@0: .NH 1
meillo@0: Importance of software design
meillo@0: .LP
meillo@2: Why should we design software at all?
meillo@3: It is general knowledge, that a bad plan is better than no plan.
meillo@2: As stated earlier in this document, the process of building a software
meillo@2: means going from an idea to a release.
meillo@2: The development process tells how to get from the idea to the release.
meillo@3: Software design is the shape of the built software.
meillo@3: This means, that different designs of a software would be different target points to go to.
meillo@3: Thus, the design of a software defines the global direction the development goes.
meillo@2: .PP
meillo@2: It is not enough that the released software offers all requested functionality.
meillo@2: It is a misbelief that only function matters.
meillo@2: Building a software the first time is only a small part of the overall work.
meillo@2: The larger part begins when the software is released for the first time
meillo@2: \(en maintainance and extending work..
meillo@2: This part soon covers more time than the time which was needed to build the software the first time.
meillo@2: .\" cf. brooks?
meillo@2: .PP
meillo@2: The extendability and maitainability of a software highly depends on its design.
meillo@2: Good design eases these tasks much.
meillo@2: Bad design, in contrast, requires much more effort for maintaining and
meillo@2: extending the software.
meillo@2: Developers should, for their own best, have maintainability and extendability in mind
meillo@2: when they design the software.
meillo@2: .PP
meillo@3: Users of the software, in contrast, do not care about maintainability and extendability,
meillo@2: at least not directly.
meillo@2: They care about usability and flexibility.
meillo@2: They want the software to directly solve their problems.
meillo@2: They want to be able to to use all its functions if they learned a few of them.
meillo@2: They want to use the software for similar tasks.
meillo@2: Software is successful if users enjoy using it.
meillo@2: Good software design can offer great flexibility and usability.
meillo@2: .PP
meillo@2: Good design matters for developers \fIand\fP for users.
meillo@2: Hence both groups should care about good software design.
meillo@2: Bad design limits the software in some way.
meillo@2: It may still provide all requested function, but it will have worse quality,
meillo@2: and thus require more work effort for developers or frustrate users.
meillo@2: .PP
meillo@2: Good software design is to the implementation like data structures are to algorithms
meillo@2: \(en if you get the former right, then you do not need to care about the latter,
meillo@2: it will simply go the right way.
meillo@2: .\" cf. ??? ``good data, bad algos''
meillo@0: 
meillo@0: 
meillo@0: 
meillo@0: 
meillo@0: .NH 1
meillo@0: The Unix Philosophy
meillo@4: .LP
meillo@4: The origins of the Unix Philosophy were already introduced.
meillo@4: This chapter explains the philosophy and shows concrete examples of its application.
meillo@4: .NH 2
meillo@4: Examples
meillo@4: .LP
meillo@4: Following are some examples to demonstrate how applied Unix Philosophy feels like.
meillo@4: Knowledge of using the Unix shell is assumed.
meillo@4: .PP
meillo@4: Counting the number of files in the current directory:
meillo@4: .DS
meillo@4: .CW
meillo@4: ls | wc -l
meillo@4: .DE
meillo@4: The
meillo@4: .CW ls
meillo@4: command lists all files in the current directory, one per line,
meillo@4: and
meillo@4: .CW "wc -l
meillo@4: counts how many lines they are.
meillo@4: .PP
meillo@4: Counting all files that do not contain ``foo'' in their name:
meillo@4: .DS
meillo@4: .CW
meillo@4: ls | grep -v foo | wc -l
meillo@4: .DE
meillo@4: Here, the list of files is filtered by
meillo@4: .CW grep
meillo@4: to remove all that contain ``foo''.
meillo@4: The rest is the same as in the previous example.
meillo@4: .PP
meillo@4: Finding the five largest entries in the current directory.
meillo@4: .DS
meillo@4: .CW
meillo@4: du -s * | sort -nr | sed 5q
meillo@4: .DE
meillo@4: .CW "du -s *
meillo@4: returns the recursively summed sizes of all files
meillo@4: -- no matter if they are regular files or directories.
meillo@4: .CW "sort -nr
meillo@4: sorts the list numerically in reverse order.
meillo@4: Finally,
meillo@4: .CW "sed 5q
meillo@4: quits after it has printed the fifth line.
meillo@4: .PP
meillo@4: The presented command lines are examples of what Unix people would use
meillo@4: to get the desired output.
meillo@4: There are also other ways to get the same output.
meillo@4: It's a user's decision which way to go.
meillo@4: .NH 2
meillo@4: Pipes
meillo@4: .LP
meillo@4: The examples show that a lot of tasks on a Unix system
meillo@4: are accomplished by combining several small programs.
meillo@4: The connection between the single programs is denoted by the pipe operator `|'.
meillo@4: .PP
meillo@4: Pipes, and their extensive and easy use, are one of the great
meillo@4: achievements of the Unix system.
meillo@4: Pipes between programs have been possible in earlier operating systems,
meillo@4: but it has never been a so central part of the concept.
meillo@4: When, in the early seventies, Doug McIlroy introduced pipes for the
meillo@4: Unix system,
meillo@4: ``it was this concept and notation for linking several programs together
meillo@4: that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
meillo@4: .[
meillo@4: %T Unix: An Oral History
meillo@4: %O http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
meillo@4: .] 
meillo@4: .PP
meillo@4: Being able to specify pipelines in an easy way is,
meillo@4: however, not enough by itself.
meillo@4: It is only one part.
meillo@4: The other is the design of the programs that are used in the pipeline.
meillo@4: They have to be of an external shape that allows them to be be used in a pipeline.
meillo@0: 
meillo@4: 
meillo@0: 
meillo@0: .NH 2
meillo@2: Architecture
meillo@2: .LP
meillo@2: the most important design decision.
meillo@2: 
meillo@2: the topic here
meillo@2: 
meillo@2: .NH 2
meillo@0: Interface architecture
meillo@0: .LP
meillo@0: standalone vs. tool chain
meillo@0: .LP
meillo@0: software leverage
meillo@0: .LP
meillo@0: possiblities
meillo@0: 
meillo@0: .NH 2
meillo@0: Results
meillo@0: .LP
meillo@0: The unix phil is an answer to the sw design question
meillo@0: .LP
meillo@0: tool chains empower the uses of sw
meillo@0: 
meillo@0: .NH 1
meillo@0: Case study: nmh
meillo@0: 
meillo@0: .NH 2
meillo@0: History
meillo@0: .LP
meillo@0: MH, nmh.
meillo@0: They are old.
meillo@0: 
meillo@0: .NH 2
meillo@0: Contrasts to similar sw
meillo@0: .LP
meillo@0: vs. Thunderbird, mutt, mailx, pine
meillo@0: .LP
meillo@0: flexibility, no redundancy, use the shell
meillo@0: 
meillo@0: .NH 2
meillo@0: Gains of the design
meillo@0: .LP
meillo@0: 
meillo@0: .NH 2
meillo@0: Problems
meillo@0: .LP
meillo@0: 
meillo@0: .NH 1
meillo@0: Case study: uzbl
meillo@0: 
meillo@0: .NH 2
meillo@0: History
meillo@0: .LP
meillo@0: uzbl is young
meillo@0: 
meillo@0: .NH 2
meillo@0: Contrasts to similar sw
meillo@0: .LP
meillo@0: like with nmh
meillo@0: .LP
meillo@0: addons, plugins, modules
meillo@0: 
meillo@0: .NH 2
meillo@0: Gains of the design
meillo@0: .LP
meillo@0: 
meillo@0: .NH 2
meillo@0: Problems
meillo@0: .LP
meillo@0: broken web
meillo@0: 
meillo@0: .NH 1
meillo@0: Final thoughts
meillo@0: 
meillo@0: .NH 2
meillo@0: Quick summary
meillo@0: .LP
meillo@0: good design
meillo@0: .LP
meillo@0: unix phil
meillo@0: .LP
meillo@0: case studies
meillo@0: 
meillo@0: .NH 2
meillo@0: Why people should choose
meillo@0: .LP
meillo@0: Make the right choice!
meillo@0: 
meillo@0: .nr PI .5i
meillo@0: .rm ]<
meillo@0: .de ]<
meillo@0: .LP
meillo@0: .de FP
meillo@0: .IP \\\\$1.
meillo@0: \\..
meillo@0: .rm FS FE
meillo@0: ..
meillo@0: .SH
meillo@0: References
meillo@0: .[
meillo@0: $LIST$
meillo@0: .]
meillo@0: .wh -1p