meillo@2: .\".if n .pl 1000i
meillo@0: .de XX
meillo@0: .pl 1v
meillo@0: ..
meillo@0: .em XX
meillo@1: .\".nr PI 0
meillo@1: .\".if t .nr PD .5v
meillo@1: .\".if n .nr PD 1v
meillo@0: .nr lu 0
meillo@0: .de CW
meillo@0: .nr PQ \\n(.f
meillo@0: .if t .ft CW
meillo@0: .ie \\$1 .if n .ul 999
meillo@0: .el .if n .ul 1
meillo@0: .if t .if !\\$1 \&\\$1\f\\n(PQ\\$2
meillo@0: .if n .if \\n(.$=1 \&\\$1
meillo@0: .if n .if \\n(.$>1 \&\\$1\c
meillo@0: .if n .if \\n(.$>1 \&\\$2
meillo@0: ..
meillo@0: .ds [. \ [
meillo@0: .ds .] ]
meillo@1: .\"----------------------------------------
meillo@0: .TL
meillo@6: Why the Unix Philosophy still 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@9: The process in between can be of any shape.
meillo@9: The the maintenance 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@9: This paper discusses the recommendations of the Unix Philosophy about software design.
meillo@3: .PP
meillo@3: The here discussed ideas can get applied by any development process.
meillo@9: The Unix Philosophy 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@9: especially those that were successful and unique to Unix.
meillo@6: .\" really?
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@6: Importance of software design in general
meillo@0: .LP
meillo@2: Why should we design software at all?
meillo@6: It is general knowledge, that even a bad plan is better than no plan.
meillo@6: Ignoring software design is programming without a plan.
meillo@6: This will lead pretty sure to horrible results.
meillo@2: .PP
meillo@6: The design of a software is its internal and external shape.
meillo@6: The design talked about here has nothing to do with visual appearance.
meillo@6: If we see a program as a car, then its color is of no matter.
meillo@6: Its design would be the car's size, its shape, the number and position of doors,
meillo@6: the ratio of passenger and cargo transport, and so forth.
meillo@2: .PP
meillo@6: A software's design is about quality properties.
meillo@6: Each of the cars may be able to drive from A to B,
meillo@6: but it depends on its properties whether it is a good car for passenger transport or not.
meillo@6: It also depends on its properties if it is a good choice for a rough mountain area.
meillo@2: .PP
meillo@6: Requirements to a software are twofold: functional and non-functional.
meillo@6: Functional requirements are easier to define and to verify.
meillo@6: They are directly the software's functions.
meillo@6: Functional requirements are the reason why software gets written.
meillo@6: Someone has a problem and needs a tool to solve it.
meillo@6: Being able to solve the problem is the main functional requirement.
meillo@6: It is the driving force behind all programming effort.
meillo@2: .PP
meillo@6: On the other hand, there are also non-functional requirements.
meillo@6: They are called \fIquality\fP requirements, too.
meillo@6: The quality of a software is about properties that are not directly related to
meillo@6: the software's basic functions.
meillo@6: Quality aspects are about the properties that are overlooked at first sight.
meillo@2: .PP
meillo@6: Quality is of few matter when the software gets initially built,
meillo@9: but it will be of matter in usage and maintenance of the software.
meillo@6: A short-sighted might see in developing a software mainly building something up.
meillo@6: Reality shows, that building the software the first time is only a small amount
meillo@6: of the overall work.
meillo@9: Bug fixing, extending, rebuilding of parts \(en short: maintenance work \(en
meillo@6: does soon take over the major part of the time spent on a software.
meillo@6: Not to forget the usage of the software.
meillo@6: These processes are highly influenced by the software's quality.
meillo@6: Thus, quality should never be neglected.
meillo@6: The problem is that you hardly ``stumble over'' bad quality during the first build,
meillo@6: but this is the time when you should care about good quality most.
meillo@6: .PP
meillo@6: Software design is not about the basic function of a software;
meillo@6: this requirement will get satisfied anyway, as it is the main driving force behind the development.
meillo@6: Software design is about quality aspects of the software.
meillo@6: Good design will lead to good quality, bad design to bad quality.
meillo@6: The primary functions of the software will be affected modestly by bad quality,
meillo@6: but good quality can provide a lot of additional gain from the software,
meillo@6: even at places where one never expected it.
meillo@6: .PP
meillo@6: The ISO/IEC 9126-1 standard, part 1,
meillo@6: .[
meillo@9: %I International Organization for Standardization
meillo@6: %T ISO Standard 9126: Software Engineering \(en Product Quality, part 1
meillo@6: %C Geneve
meillo@6: %D 2001
meillo@6: .]
meillo@6: defines the quality model as consisting out of:
meillo@6: .IP \(bu
meillo@6: .I Functionality
meillo@6: (suitability, accuracy, inter\%operability, security)
meillo@6: .IP \(bu
meillo@6: .I Reliability
meillo@6: (maturity, fault tolerance, recoverability)
meillo@6: .IP \(bu
meillo@6: .I Usability
meillo@6: (understandability, learnability, operability, attractiveness)
meillo@6: .IP \(bu
meillo@6: .I Efficiency
meillo@9: (time behavior, resource utilization)
meillo@6: .IP \(bu
meillo@6: .I Maintainability
meillo@6: (analysability, changeability, stability, testability)
meillo@6: .IP \(bu
meillo@6: .I Portability
meillo@6: (adaptability, installability, co-existence, replaceability)
meillo@6: .LP
meillo@6: These goals are parts of a software's design.
meillo@6: Good design can give these properties to a software,
meillo@6: bad designed software will miss them.
meillo@7: .PP
meillo@7: One further goal of software design is consistency.
meillo@7: Consistency eases understanding, working on, and using things.
meillo@7: Consistent internals and consistent interfaces to the outside can be provided by good design.
meillo@7: .PP
meillo@7: We should design software because good design avoids many problems during a software's lifetime.
meillo@7: And we should design software because good design can offer much gain,
meillo@7: that can be unrelated to the software main intend.
meillo@7: Indeed, we should spend much effort into good design to make the software more valuable.
meillo@7: The Unix Philosophy shows how to design software well.
meillo@7: It offers guidelines to achieve good quality and high gain for the effort spent.
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@8: This chapter explains the philosophy, oriented on Gancarz,
meillo@8: and shows concrete examples of its application.
meillo@5: 
meillo@5: .SH
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@9: .DS I 2n
meillo@4: .CW
meillo@9: .ps -1
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@8: counts the number of lines.
meillo@4: .PP
meillo@8: Counting the number of files that do not contain ``foo'' in their name:
meillo@9: .DS I 2n
meillo@4: .CW
meillo@9: .ps -1
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@9: .DS I 2n
meillo@4: .CW
meillo@9: .ps -1
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@8: \(en 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@5: 
meillo@5: .SH
meillo@4: Pipes
meillo@4: .LP
meillo@8: The examples show that many 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@5: %O .CW \s-1http://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@5: It is only one half.
meillo@4: The other is the design of the programs that are used in the pipeline.
meillo@8: They have to interfaces that allows them to be used in such a way.
meillo@5: 
meillo@5: .SH
meillo@5: Interface architecture
meillo@5: .LP
meillo@5: Unix is, first of all, simple: Everything is a file.
meillo@5: Files are sequences of bytes, without any special structure.
meillo@5: Programs should be filters, which read a stream of bytes from ``standard input'' (stdin)
meillo@5: and write a stream of bytes to ``standard output'' (stdout).
meillo@5: .PP
meillo@8: If the files \fIare\fP sequences of bytes,
meillo@8: and the programs \fIare\fP filters on byte streams,
meillo@5: then there is exactly one standardized interface.
meillo@5: Thus it is possible to combine them in any desired way.
meillo@5: .PP
meillo@5: Even a handful of small programs will yield a large set of combinations,
meillo@5: and thus a large set of different functions.
meillo@5: This is leverage!
meillo@5: If the programs are orthogonal to each other \(en the best case \(en
meillo@5: then the set of different functions is greatest.
meillo@5: .PP
meillo@8: The Unix toolchest \fIis\fP a set of small programs that
meillo@5: are filters on byte streams.
meillo@8: They are, to a large extend, unrelated in their function.
meillo@5: Hence, the Unix toolchest provides a large set of functions
meillo@5: that can be accessed by combining the programs in the desired way.
meillo@5: 
meillo@5: .SH
meillo@8: The toolchest approach
meillo@5: .LP
meillo@5: A toolchest is a set of tools.
meillo@5: Instead of having one big tool for all tasks, one has many small tools,
meillo@5: each for one task.
meillo@5: Difficult tasks are solved by combining several of the small, simple tools.
meillo@5: .PP
meillo@5: It is easier and less error-prone to write small programs.
meillo@5: It is also easier and less error-prone to write a large set of small programs,
meillo@5: than to write one large program with all the functionality included.
meillo@5: If the small programs are combinable, then they offer even a larger set
meillo@5: of functions than the single large program.
meillo@5: Hence, one gets two advantages out of writing small, combinable programs.
meillo@5: .PP
meillo@5: There are two drawbacks of the toolchest approach.
meillo@8: First, one simple, standardized, unidirectional interface has to be sufficient.
meillo@5: If one feels the need for more ``logic'' than a stream of bytes,
meillo@8: then a different approach might be of need.
meillo@9: But it is also possible, that he just can not imaging a design where
meillo@8: a stream of bytes is sufficient.
meillo@8: By becoming more familiar with the ``Unix style of thinking'',
meillo@8: developers will more often and easier find simple designs where
meillo@8: a stream of bytes is a sufficient interface.
meillo@8: .PP
meillo@8: The second drawback of a toolchest affects the users.
meillo@5: A toolchest is often more difficult to use for novices.
meillo@9: It is necessary to become familiar with each of the tools,
meillo@5: to be able to use the right one in a given situation.
meillo@9: Additionally, one needs to combine the tools in a senseful way on its own.
meillo@9: This is like a sharp knife \(en it is a powerful tool in the hand of a master,
meillo@5: but of no good value in the hand of an unskilled.
meillo@5: .PP
meillo@8: However, learning single, small tool of the toolchest is easier than
meillo@8: learning a complex tool.
meillo@8: The user will have a basic understanding of a yet unknown tool,
meillo@8: if the several tools of the toolchest have a common style.
meillo@8: He will be able to transfer knowledge over one tool to another.
meillo@8: .PP
meillo@8: Moreover, the second drawback can be removed easily by adding wrappers
meillo@8: around the single tools.
meillo@5: Novice users do not need to learn several tools if a professional wraps
meillo@8: the single commands into a more high-level script.
meillo@5: Note that the wrapper script still calls the small tools;
meillo@5: the wrapper script is just like a skin around.
meillo@8: No complexity is added this way,
meillo@8: but new programs can get created out of existing one with very low effort.
meillo@5: .PP
meillo@5: A wrapper script for finding the five largest entries in the current directory
meillo@5: could look like this:
meillo@9: .DS I 2n
meillo@5: .CW
meillo@9: .ps -1
meillo@5: #!/bin/sh
meillo@5: du -s * | sort -nr | sed 5q
meillo@5: .DE
meillo@5: The script itself is just a text file that calls the command line
meillo@5: a professional user would type in directly.
meillo@8: Making the program flexible on the number of entries it prints,
meillo@8: is easily possible:
meillo@9: .DS I 2n
meillo@8: .CW
meillo@9: .ps -1
meillo@8: #!/bin/sh
meillo@8: num=5
meillo@8: [ $# -eq 1 ] && num="$1"
meillo@8: du -sh * | sort -nr | sed "${num}q"
meillo@8: .DE
meillo@8: This script acts like the one before, when called without an argument.
meillo@8: But one can also specify a numerical argument to define the number of lines to print.
meillo@5: 
meillo@8: .SH
meillo@8: A powerful shell
meillo@8: .LP
meillo@8: The Unix shell provides the possibility to combine small programs into
meillo@8: large ones easily.
meillo@8: But the powerful shell is great feature in other ways, too.
meillo@8: .PP
meillo@8: It encourages rapid prototyping.
meillo@8: It includes a scripting language with built in control statements.
meillo@8: The functions, however, are the normal programs, everyone can use on the system.
meillo@8: Thus, the programs are known and learning to program in the shell is easy.
meillo@8: Using normal programs as functions in the shell programming language
meillo@8: is only possible because they are small, combinable tools in a toolchest style.
meillo@8: .PP
meillo@8: The Unix shell encourages to write small scripts out of other programs,
meillo@8: because it is so easy to do.
meillo@8: This is a great step towards automation.
meillo@8: It is wonderful if the effort to automate a task equals the effort
meillo@8: it takes to do it the second time by hand.
meillo@8: If it is so, then the user will be happy to automate everything he does more than once.
meillo@8: .PP
meillo@8: Small programs that do one job well, standardized interfaces between them,
meillo@8: a mechanism to combine parts to larger parts, and an easy way to automate tasks,
meillo@8: this will inevitably produce software leverage.
meillo@8: Getting multiple times the benefit of an investment is a great offer.
meillo@5: 
meillo@5: 
meillo@0: 
meillo@4: 
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@8: 
meillo@8: 
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@8: 
meillo@8: 
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@8: 
meillo@8: 
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