meillo@36: .nr PS 11
meillo@36: .nr VS 13
meillo@0: .nr lu 0
meillo@0: .de CW
meillo@0: .nr PQ \\n(.f
meillo@0: .if t .ft CW
meillo@17: .ie ^\\$1^^ .if n .ul 999
meillo@0: .el .if n .ul 1
meillo@17: .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@39: This paper explains the importance of the Unix Philosophy for software design.
meillo@0: Today, few software designers are aware of these concepts,
meillo@39: and thus a lot of modern software is more limited than necessary
meillo@39: and makes less use of software leverage than possible.
meillo@38: Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
meillo@0: .AE
meillo@0: 
meillo@2: .FS
meillo@2: .ps -1
meillo@39: This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
meillo@39: Mentor was professor Schweiggert. 2010-04-05
meillo@2: .br
meillo@39: You may retrieve this document from
meillo@39: .CW \s-1http://marmaro.de/docs \ .
meillo@2: .FE
meillo@2: 
meillo@0: .NH 1
meillo@0: Introduction
meillo@0: .LP
meillo@40: The Unix Philosophy is the essence of how the Unix operating system,
meillo@40: especially its toolchest, was designed.
meillo@40: It is no limited set of fixed rules,
meillo@40: but a loose set of guidelines which tell how to write software that
meillo@40: suites well into Unix.
meillo@40: Actually, the Unix Philosophy describes what is common to typical Unix software.
meillo@40: The Wikipedia has an accurate definition:
meillo@40: .[
meillo@40: %A Wikipedia
meillo@40: %T Unix philosophy
meillo@40: %P Wikipedia, The Free Encyclopedia
meillo@40: %D 2010-03-21 17:20 UTC
meillo@40: %O .CW \s-1http://en.wikipedia.org/w/index.php?title=Unix_philosophy&oldid=351189719
meillo@40: .]
meillo@40: .QP
meillo@41: .ps -1
meillo@40: The \fIUnix philosophy\fP is a set of cultural norms and philosophical
meillo@40: approaches to developing software based on the experience of leading
meillo@40: developers of the Unix operating system.
meillo@1: .PP
meillo@40: As there is no single definition of the Unix Philosophy,
meillo@40: several people have stated their view on what it comprises.
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@40: Especially, the main concepts are similar in all of them.
meillo@40: McIlroy's definition can surely be called the core of the Unix Philosophy,
meillo@40: but the fundamental idea behind it all, is ``small is beautiful''.
meillo@40: 
meillo@40: .PP
meillo@40: The Unix Philosophy tells how to design and write good software for Unix.
meillo@40: Many concepts described here base on facilities of Unix.
meillo@40: Other operating systems may not offer such facilities,
meillo@41: hence it may not be possible to design software in the way of the
meillo@41: Unix Philosophy for them.
meillo@40: .PP
meillo@41: The Unix Philosophy has an idea of how the process of software development
meillo@41: should look like, but large parts of the philosophy are quite independent
meillo@41: from the development process used.
meillo@41: However, one will soon recognize that some development processes work well
meillo@41: with the ideas of the Unix Philosophy and support them, while others are
meillo@41: at cross-purposes.
meillo@41: Kent Beck's books about Extreme Programming are valuable supplimental
meillo@41: resources.
meillo@1: .PP
meillo@41: The question of how to actually write code and how the code should looks
meillo@41: like internally, are out of focus here.
meillo@41: ``The Practice of Programming'' by Kernighan and Pike,
meillo@41: .[
meillo@41: %A Brian W. Kernighan
meillo@41: %A Rob Pike
meillo@41: %T The Practice of Programming
meillo@41: %I Addison-Wesley
meillo@41: %D 1999
meillo@41: .]
meillo@41: is a good book that covers this topic.
meillo@41: Its point of view matches to the one of this paper.
meillo@0: 
meillo@0: .NH 1
meillo@6: Importance of software design in general
meillo@0: .LP
meillo@40: Software design is the planning of how the internal structure
meillo@40: and external interfaces of a software should look like.
meillo@39: It has nothing to do with visual appearance.
meillo@39: If we take a program as a car, then its color is of no matter.
meillo@39: Its design would be the car's size, its shape, the locations of doors,
meillo@39: the passenger/space ratio, the luggage capacity, and so forth.
meillo@39: .PP
meillo@39: Why should software get designed at all?
meillo@6: It is general knowledge, that even a bad plan is better than no plan.
meillo@39: Not designing software means programming without plan.
meillo@39: This will pretty sure lead to horrible results.
meillo@39: Horrible to use and horrible to maintain.
meillo@39: These two aspects are the visible ones.
meillo@39: Often invisible are the wasted possible gains.
meillo@39: Good software design can make these gains available.
meillo@2: .PP
meillo@39: A software's design deals with quality properties.
meillo@39: Good design leads to good quality, and quality is important.
meillo@39: Any car may be able to drive from A to B,
meillo@39: but it depends on the car's properties whether it is a good choice
meillo@39: for passenger transport or not.
meillo@39: It depends on its  properties if it is a good choice
meillo@39: for a rough mountain area.
meillo@39: And it depends on its properties if the ride will be fun.
meillo@39: 
meillo@2: .PP
meillo@39: Requirements for a software are twofold:
meillo@39: functional and non-functional.
meillo@39: .IP \(bu
meillo@39: Functional requirements define directly the software's functions.
meillo@39: They are the reason why software gets written.
meillo@39: Someone has a problem and needs a tool to solve it.
meillo@39: Being able to solve the problem is the main functional goal.
meillo@39: It is the driving force behind all programming effort.
meillo@39: Functional requirements are easier to define and to verify.
meillo@39: .IP \(bu
meillo@39: Non-functional requirements are also called \fIquality\fP requirements.
meillo@39: The quality of a software are the properties that are not directly related to
meillo@39: the software's basic functions.
meillo@39: Tools of bad quality often solve the problems they were written for,
meillo@39: but introduce problems and difficulties for usage and development, later on.
meillo@39: Quality aspects are often overlooked at first sight,
meillo@39: and they are often difficult to define clearly and to verify.
meillo@2: .PP
meillo@39: Quality is of few matter when the software gets built initially,
meillo@39: but it is of matter for usage and maintenance of the software.
meillo@6: A short-sighted might see in developing a software mainly building something up.
meillo@39: But experience shows, that building the software the first time is
meillo@39: only a small amount of the overall work.
meillo@39: Bug fixing, extending, rebuilding of parts
meillo@39: \(en maintenance work, for short \(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@39: Thus, quality must not be neglected.
meillo@39: The problem with quality is that you hardly ``stumble over''
meillo@39: 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@39: Software design is less the basic function of a software \(en
meillo@39: this requirement will get satisfied anyway.
meillo@39: Software design is more about quality aspects of the software.
meillo@39: Good design leads to good quality, bad design to bad quality.
meillo@6: The primary functions of the software will be affected modestly by bad quality,
meillo@39: but good quality can provide a lot of additional gain,
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@23: (analyzability, changeability, stability, testability)
meillo@6: .IP \(bu
meillo@6: .I Portability
meillo@6: (adaptability, installability, co-existence, replaceability)
meillo@6: .LP
meillo@39: Good design can improve these properties of a software,
meillo@39: bad designed software probably suffers from not having 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@39: Consistent internal structure and consistent interfaces to the outside
meillo@39: can be provided by good design.
meillo@7: .PP
meillo@39: Software should be well designed because good design avoids many
meillo@39: problems during the software's lifetime.
meillo@39: And software should be well designed because good design can offer
meillo@39: much additional gain.
meillo@39: Indeed, much effort should be spent into good design to make software more valuable.
meillo@39: The Unix Philosophy shows a way of 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@16: .NH 2
meillo@14: Pipes
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@41: .DS
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@41: .DS
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@41: .DS
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@14: .PP
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@16: .NH 2
meillo@14: Interface design
meillo@5: .LP
meillo@11: Unix is, first of all, simple \(en 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@11: then there is exactly one standardized data 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@11: Programs might also have a separate control interface,
meillo@11: besides their data interface.
meillo@11: The control interface is often called ``user interface'',
meillo@11: because it is usually designed to be used by humans.
meillo@11: The Unix Philosophy discourages to assume the user to be human.
meillo@11: Interactive use of software is slow use of software,
meillo@11: because the program waits for user input most of the time.
meillo@11: Interactive software requires the user to be in front of the computer
meillo@11: all the time.
meillo@11: Interactive software occupy the user's attention while they are running.
meillo@11: .PP
meillo@11: Now we come back to the idea of using several small programs, combined,
meillo@11: to have a more specific function.
meillo@11: If these single tools would all be interactive,
meillo@11: how would the user control them?
meillo@11: It is not only a problem to control several programs at once if they run at the same time,
meillo@11: it also very inefficient to have to control each of the single programs
meillo@11: that are intended to work as one large program.
meillo@11: Hence, the Unix Philosophy discourages programs to demand interactive use.
meillo@11: The behavior of programs should be defined at invocation.
meillo@11: This is done by specifying arguments (``command line switches'') to the program call.
meillo@11: Gancarz discusses this topic as ``avoid captive user interfaces''.
meillo@11: .[
meillo@11: %A Mike Gancarz
meillo@11: %T The UNIX Philosophy
meillo@11: %I Digital Press
meillo@11: %D 1995
meillo@11: %P 88 ff.
meillo@11: .]
meillo@11: .PP
meillo@11: Non-interactive use is, during development, also an advantage for testing.
meillo@11: Testing of interactive programs is much more complicated,
meillo@11: than testing of non-interactive programs.
meillo@5: 
meillo@16: .NH 2
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@11: The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
meillo@11: that are filters on byte streams.
meillo@11: They are, to a large extend, unrelated in their function.
meillo@11: Hence, the Unix toolchest provides a large set of functions
meillo@11: that can be accessed by combining the programs in the desired way.
meillo@11: .PP
meillo@11: There are also advantages for developing small toolchest programs.
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@13: But it is also possible, that he just can not imagine 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@41: .DS
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@41: .DS
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@16: .NH 2
meillo@8: A powerful shell
meillo@8: .LP
meillo@10: It was already said, that the Unix shell provides the possibility to
meillo@10: combine small programs into large ones easily.
meillo@10: A powerful shell is a great feature in other ways, too.
meillo@8: .PP
meillo@10: For instance by including a scripting language.
meillo@10: The control statements are build into the shell.
meillo@8: The functions, however, are the normal programs, everyone can use on the system.
meillo@10: Thus, the programs are known, so learning to program in the shell is easy.
meillo@8: Using normal programs as functions in the shell programming language
meillo@10: is only possible because they are small and 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@10: .PP
meillo@10: The shell also encourages rapid prototyping.
meillo@10: Many well known programs started as quickly hacked shell scripts,
meillo@10: and turned into ``real'' programs, written in C, later.
meillo@10: Building a prototype first is a way to avoid the biggest problems
meillo@10: in application development.
meillo@10: Fred Brooks writes in ``No Silver Bullet'':
meillo@10: .[
meillo@10: %A Frederick P. Brooks, Jr.
meillo@10: %T No Silver Bullet: Essence and Accidents of Software Engineering
meillo@10: %B Information Processing 1986, the Proceedings of the IFIP Tenth World Computing Conference
meillo@10: %E H.-J. Kugler
meillo@10: %D 1986
meillo@10: %P 1069\(en1076
meillo@10: %I Elsevier Science B.V.
meillo@10: %C Amsterdam, The Netherlands
meillo@10: .]
meillo@10: .QP
meillo@41: .ps -1
meillo@10: The hardest single part of building a software system is deciding precisely what to build.
meillo@10: No other part of the conceptual work is so difficult as establishing the detailed
meillo@10: technical requirements, [...].
meillo@10: No other part of the work so cripples the resulting system if done wrong.
meillo@10: No other part is more difficult to rectify later.
meillo@10: .PP
meillo@10: Writing a prototype is a great method to become familiar with the requirements
meillo@10: and to actually run into real problems.
meillo@10: Today, prototyping is often seen as a first step in building a software.
meillo@10: This is, of course, good.
meillo@10: However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
meillo@10: After having built the prototype, one might notice, that the prototype is already
meillo@10: \fIgood enough\fP.
meillo@10: Hence, no reimplementation, in a more sophisticated programming language, might be of need,
meillo@10: for the moment.
meillo@23: Maybe later, it might be necessary to rewrite the software, but not now.
meillo@10: .PP
meillo@10: By delaying further work, one keeps the flexibility to react easily on
meillo@10: changing requirements.
meillo@10: Software parts that are not written will not miss the requirements.
meillo@10: 
meillo@16: .NH 2
meillo@10: Worse is better
meillo@10: .LP
meillo@10: The Unix Philosophy aims for the 80% solution;
meillo@10: others call it the ``Worse is better'' approach.
meillo@10: .PP
meillo@10: First, practical experience shows, that it is almost never possible to define the
meillo@10: requirements completely and correctly the first time.
meillo@10: Hence one should not try to; it will fail anyway.
meillo@10: Second, practical experience shows, that requirements change during time.
meillo@10: Hence it is best to delay requirement-based design decisions as long as possible.
meillo@10: Also, the software should be small and flexible as long as possible
meillo@10: to react on changing requirements.
meillo@10: Shell scripts, for example, are more easily adjusted as C programs.
meillo@10: Third, practical experience shows, that maintenance is hard work.
meillo@10: Hence, one should keep the amount of software as small as possible;
meillo@10: it should just fulfill the \fIcurrent\fP requirements.
meillo@10: Software parts that will be written later, do not need maintenance now.
meillo@10: .PP
meillo@10: Starting with a prototype in a scripting language has several advantages:
meillo@10: .IP \(bu
meillo@10: As the initial effort is low, one will likely start right away.
meillo@10: .IP \(bu
meillo@10: As working parts are available soon, the real requirements can get identified soon.
meillo@10: .IP \(bu
meillo@10: When a software is usable, it gets used, and thus tested.
meillo@10: Hence problems will be found at early stages of the development.
meillo@10: .IP \(bu
meillo@10: The prototype might be enough for the moment,
meillo@10: thus further work on the software can be delayed to a time
meillo@10: when one knows better about the requirements and problems,
meillo@10: than now.
meillo@10: .IP \(bu
meillo@10: Implementing now only the parts that are actually needed now,
meillo@10: requires fewer maintenance work.
meillo@10: .IP \(bu
meillo@10: If the global situation changes so that the software is not needed anymore,
meillo@10: then less effort was spent into the project, than it would have be
meillo@10: when a different approach had been used.
meillo@10: 
meillo@16: .NH 2
meillo@11: Upgrowth and survival of software
meillo@11: .LP
meillo@12: So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
meillo@13: Although these are just verbs, they do imply a specific view on the work process
meillo@13: they describe.
meillo@12: The better verb, however, is to \fIgrow\fP.
meillo@12: .PP
meillo@12: Creating software in the sense of the Unix Philosophy is an incremental process.
meillo@12: It starts with a first prototype, which evolves as requirements change.
meillo@12: A quickly hacked shell script might become a large, sophisticated,
meillo@13: compiled program this way.
meillo@13: Its lifetime begins with the initial prototype and ends when the software is not used anymore.
meillo@13: While being alive it will get extended, rearranged, rebuilt (from scratch).
meillo@12: Growing software matches the view that ``software is never finished. It is only released.''
meillo@12: .[
meillo@13: %O FIXME
meillo@13: %A Mike Gancarz
meillo@13: %T The UNIX Philosophy
meillo@13: %P 26
meillo@12: .]
meillo@12: .PP
meillo@13: Software can be seen as being controlled by evolutionary processes.
meillo@13: Successful software is software that is used by many for a long time.
meillo@12: This implies that the software is needed, useful, and better than alternatives.
meillo@12: Darwin talks about: ``The survival of the fittest.''
meillo@12: .[
meillo@13: %O FIXME
meillo@13: %A Charles Darwin
meillo@12: .]
meillo@12: Transferred to software: The most successful software, is the fittest,
meillo@12: is the one that survives.
meillo@13: (This may be at the level of one creature, or at the level of one species.)
meillo@13: The fitness of software is affected mainly by four properties:
meillo@15: portability of code, portability of data, range of usability, and reusability of parts.
meillo@15: .\" .IP \(bu
meillo@15: .\" portability of code
meillo@15: .\" .IP \(bu
meillo@15: .\" portability of data
meillo@15: .\" .IP \(bu
meillo@15: .\" range of usability
meillo@15: .\" .IP \(bu
meillo@15: .\" reuseability of parts
meillo@13: .PP
meillo@15: (1)
meillo@15: .I "Portability of code
meillo@15: means, using high-level programming languages,
meillo@13: sticking to the standard,
meillo@13: and avoiding optimizations that introduce dependencies on specific hardware.
meillo@13: Hardware has a much lower lifetime than software.
meillo@13: By chaining software to a specific hardware,
meillo@13: the software's lifetime gets shortened to that of this hardware.
meillo@13: In contrast, software should be easy to port \(en
meillo@23: adaptation is the key to success.
meillo@13: .\" cf. practice of prog: ch08
meillo@13: .PP
meillo@15: (2)
meillo@15: .I "Portability of data
meillo@15: is best achieved by avoiding binary representations
meillo@13: to store data, because binary representations differ from machine to machine.
meillo@23: Textual representation is favored.
meillo@13: Historically, ASCII was the charset of choice.
meillo@13: In the future, UTF-8 might be the better choice, however.
meillo@13: Important is that it is a plain text representation in a
meillo@13: very common charset encoding.
meillo@13: Apart from being able to transfer data between machines,
meillo@13: readable data has the great advantage, that humans are able
meillo@13: to directly edit it with text editors and other tools from the Unix toolchest.
meillo@13: .\" gancarz tenet 5
meillo@13: .PP
meillo@15: (3)
meillo@15: A large
meillo@15: .I "range of usability
meillo@23: ensures good adaptation, and thus good survival.
meillo@13: It is a special distinction if a software becomes used in fields of action,
meillo@13: the original authors did never imagine.
meillo@13: Software that solves problems in a general way will likely be used
meillo@13: for all kinds of similar problems.
meillo@13: Being too specific limits the range of uses.
meillo@13: Requirements change through time, thus use cases change or even vanish.
meillo@13: A good example in this point is Allman's sendmail.
meillo@13: Allman identifies flexibility to be one major reason for sendmail's success:
meillo@13: .[
meillo@13: %O FIXME
meillo@13: %A Allman
meillo@13: %T sendmail
meillo@13: .]
meillo@13: .QP
meillo@41: .ps -1
meillo@13: Second, I limited myself to the routing function [...].
meillo@13: This was a departure from the dominant thought of the time, [...].
meillo@13: .QP
meillo@41: .ps -1
meillo@13: Third, the sendmail configuration file was flexible enough to adopt
meillo@13: to a rapidly changing world [...].
meillo@12: .LP
meillo@13: Successful software adopts itself to the changing world.
meillo@13: .PP
meillo@15: (4)
meillo@15: .I "Reuse of parts
meillo@15: is even one step further.
meillo@13: A software may completely lose its field of action,
meillo@13: but parts of which the software is build may be general and independent enough
meillo@13: to survive this death.
meillo@13: If software is build by combining small independent programs,
meillo@13: then there are parts readily available for reuse.
meillo@13: Who cares if the large program is a failure,
meillo@13: but parts of it become successful instead?
meillo@10: 
meillo@16: .NH 2
meillo@14: Summary
meillo@0: .LP
meillo@14: This chapter explained the central ideas of the Unix Philosophy.
meillo@14: For each of the ideas, it was exposed what advantages they introduce.
meillo@14: The Unix Philosophy are guidelines that help to write valuable software.
meillo@14: From the view point of a software developer or software designer,
meillo@14: the Unix Philosophy provides answers to many software design problem.
meillo@14: .PP
meillo@14: The various ideas of the Unix Philosophy are very interweaved
meillo@14: and can hardly be applied independently.
meillo@14: However, the probably most important messages are:
meillo@14: .I "``Do one thing well!''" ,
meillo@14: .I "``Keep it simple!''" ,
meillo@14: and
meillo@14: .I "``Use software leverage!''
meillo@0: 
meillo@8: 
meillo@8: 
meillo@0: .NH 1
meillo@19: Case study: \s-1MH\s0
meillo@18: .LP
meillo@30: The previous chapter introduced and explained the Unix Philosophy
meillo@18: from a general point of view.
meillo@30: The driving force were the guidelines; references to
meillo@18: existing software were given only sparsely.
meillo@18: In this and the next chapter, concrete software will be
meillo@18: the driving force in the discussion.
meillo@18: .PP
meillo@23: This first case study is about the mail user agents (\s-1MUA\s0)
meillo@23: \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
meillo@23: (``new mail handler'').
meillo@23: \s-1MUA\s0s provide functions to read, compose, and organize mail,
meillo@23: but (ideally) not to transfer.
meillo@19: In this document, the name \s-1MH\s0 will be used for both of them.
meillo@19: A distinction will only be made if differences between
meillo@19: them are described.
meillo@18: 
meillo@0: 
meillo@0: .NH 2
meillo@19: Historical background
meillo@0: .LP
meillo@19: Electronic mail was available in Unix very early.
meillo@30: The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
meillo@30: which was already present in the First Edition.
meillo@30: .[
meillo@30: %A Peter H. Salus
meillo@30: %T A Quarter Century of UNIX
meillo@30: %D 1994
meillo@30: %I Addison-Wesley
meillo@30: %P 41 f.
meillo@30: .]
meillo@30: It was a small program that either prints the user's mailbox file
meillo@19: or appends text to someone elses mailbox file,
meillo@19: depending on the command line arguments.
meillo@19: .[
meillo@19: %O http://cm.bell-labs.com/cm/cs/who/dmr/pdfs/man12.pdf
meillo@19: .]
meillo@19: It was a program that did one job well.
meillo@23: This job was emailing, which was very simple then.
meillo@19: .PP
meillo@23: Later, emailing became more powerful, and thus more complex.
meillo@19: The simple \f(CWmail\fP, which knew nothing of subjects,
meillo@19: independent handling of single messages,
meillo@19: and long-time storage of them, was not powerful enough anymore.
meillo@19: At Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
meillo@19: in 1978 to provide additional functions for emailing.
meillo@19: Mail was still one program, but now it was large and did
meillo@19: several jobs.
meillo@23: Its user interface is modeled after the one of \fIed\fP.
meillo@19: It is designed for humans, but is still scriptable.
meillo@23: \fImailx\fP is the adaptation of Berkeley Mail into System V.
meillo@19: .[
meillo@19: %A Gunnar Ritter
meillo@19: %O http://heirloom.sourceforge.net/mailx_history.html
meillo@19: .]
meillo@30: Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
meillo@19: followed Mail's direction.
meillo@19: They are large, monolithic programs which include all emailing functions.
meillo@19: .PP
meillo@23: A different way was taken by the people of \s-1RAND\s0 Corporation.
meillo@38: In the beginning, they also had used a monolithic mail system,
meillo@30: called \s-1MS\s0 (for ``mail system'').
meillo@19: But in 1977, Stockton Gaines and Norman Shapiro
meillo@19: came up with a proposal of a new email system concept \(en
meillo@19: one that honors the Unix Philosophy.
meillo@19: The concept was implemented by Bruce Borden in 1978 and 1979.
meillo@19: This was the birth of \s-1MH\s0 \(en the ``mail handler''.
meillo@18: .PP
meillo@18: Since then, \s-1RAND\s0, the University of California at Irvine and
meillo@19: at Berkeley, and several others have contributed to the software.
meillo@18: However, it's core concepts remained the same.
meillo@23: In the late 90s, when development of \s-1MH\s0 slowed down,
meillo@19: Richard Coleman started with \fInmh\fP, the new mail handler.
meillo@19: His goal was to improve \s-1MH\s0, especially in regard of 
meillo@23: the requirements of modern emailing.
meillo@19: Today, nmh is developed by various people on the Internet.
meillo@18: .[
meillo@18: %T RAND and the Information Evolution: A History in Essays and Vignettes
meillo@18: %A Willis H. Ware 
meillo@18: %D 2008
meillo@18: %I The RAND Corporation
meillo@18: %P 128\(en137
meillo@18: %O .CW \s-1http://www.rand.org/pubs/corporate_pubs/CP537/
meillo@18: .]
meillo@18: .[
meillo@18: %T MH & xmh: Email for Users & Programmers
meillo@18: %A Jerry Peek
meillo@18: %D 1991, 1992, 1995
meillo@18: %I O'Reilly & Associates, Inc.
meillo@18: %P Appendix B
meillo@18: %O Also available online: \f(CW\s-2http://rand-mh.sourceforge.net/book/\fP
meillo@18: .]
meillo@0: 
meillo@0: .NH 2
meillo@20: Contrasts to monolithic mail systems
meillo@0: .LP
meillo@19: All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
meillo@38: Although there might actually exist further, very little known,
meillo@30: toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
meillo@19: .PP
meillo@30: Monolithic \s-1MUA\s0s gather all their functions in one program.
meillo@30: In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
meillo@23: Following is a list of important programs of \s-1MH\s0's toolchest
meillo@30: and their function.
meillo@30: It gives a feeling of how the toolchest looks like.
meillo@19: .IP \(bu
meillo@19: .CW inc :
meillo@30: incorporate new mail (this is how mail enters the system)
meillo@19: .IP \(bu
meillo@19: .CW scan :
meillo@19: list messages in folder
meillo@19: .IP \(bu
meillo@19: .CW show :
meillo@19: show message
meillo@19: .IP \(bu
meillo@19: .CW next\fR/\fPprev :
meillo@19: show next/previous message
meillo@19: .IP \(bu
meillo@19: .CW folder :
meillo@19: change current folder
meillo@19: .IP \(bu
meillo@19: .CW refile :
meillo@19: refile message into folder
meillo@19: .IP \(bu
meillo@19: .CW rmm :
meillo@19: remove message
meillo@19: .IP \(bu
meillo@19: .CW comp : 
meillo@19: compose a new message
meillo@19: .IP \(bu
meillo@19: .CW repl :
meillo@19: reply to a message
meillo@19: .IP \(bu
meillo@19: .CW forw : 
meillo@19: forward a message
meillo@19: .IP \(bu
meillo@19: .CW send : 
meillo@30: send a prepared message (this is how mail leaves the system)
meillo@0: .LP
meillo@19: \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
meillo@19: The user does not leave the shell to run \s-1MH\s0,
meillo@30: but he uses the various \s-1MH\s0 programs within the shell.
meillo@23: Using a monolithic program with a captive user interface
meillo@23: means ``entering'' the program, using it, and ``exiting'' the program.
meillo@23: Using toolchests like \s-1MH\s0 means running programs,
meillo@38: alone or in combination with others, even from other toolchests,
meillo@23: without leaving the shell.
meillo@30: 
meillo@30: .NH 2
meillo@30: Data storage
meillo@30: .LP
meillo@34: \s-1MH\s0's mail storage is a directory tree under the user's
meillo@34: \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
meillo@34: where mail folders are directories and mail messages are text files
meillo@34: within them.
meillo@34: Each mail folder contains a file \f(CW.mh_sequences\fP which lists
meillo@34: the public message sequences of that folder, for instance new messages.
meillo@34: Mail messages are text files located in a mail folder.
meillo@34: The files contain the messages as they were received.
meillo@34: They are numbered in ascending order in each folder.
meillo@19: .PP
meillo@30: This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
meillo@30: Alternatives are \fImbox\fP and \fImaildir\fP.
meillo@30: In the mbox format all messages are stored within one file.
meillo@30: This was a good solution in the early days, when messages
meillo@30: were only a few lines of text and were deleted soon.
meillo@30: Today, when single messages often include several megabytes
meillo@30: of attachments, it is a bad solution.
meillo@30: Another disadvantage of the mbox format is that it is
meillo@30: more difficult to write tools that work on mail messages,
meillo@30: because it is always necessary to first find and extract
meillo@30: the relevant message in the mbox file.
meillo@30: With the \s-1MH\s0 mailbox format,
meillo@30: each message is a self-standing item, by definition.
meillo@30: Also, the problem of concurrent access to one mailbox is
meillo@30: reduced to the problem of concurrent access to one message.
meillo@30: Maildir is generally similar to \s-1MH\s0's format,
meillo@30: but modified towards guaranteed reliability.
meillo@30: This involves some complexity, unfortunately.
meillo@34: .PP
meillo@34: Working with \s-1MH\s0's toolchest on mailboxes is much like
meillo@34: working with Unix' toolchest on directory trees:
meillo@34: \f(CWscan\fP is like \f(CWls\fP,
meillo@34: \f(CWshow\fP is like \f(CWcat\fP,
meillo@34: \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
meillo@34: \f(CWrefile\fP is like \f(CWmv\fP,
meillo@34: and \f(CWrmm\fP is like \f(CWrm\fP.
meillo@34: .PP
meillo@34: The context of tools in Unix consists mainly the current working directory,
meillo@34: the user identification, and the environment variables.
meillo@34: \s-1MH\s0 extends this context by two more items:
meillo@34: .IP \(bu
meillo@34: The current mail folder, which is similar to the current working directory.
meillo@34: For mail folders, \f(CWfolder\fP provides the corresponding functionality
meillo@34: of \f(CWcd\fP and \f(CWpwd\fP for directories.
meillo@34: .IP \(bu
meillo@34: Sequences, which are named sets of messages in a mail folder.
meillo@34: The current message, relative to a mail folder, is a special sequence.
meillo@34: It enables commands like \f(CWnext\fP and \f(CWprev\fP.
meillo@34: .LP
meillo@34: In contrast to Unix' context, which is chained to the shell session,
meillo@34: \s-1MH\s0's context is independent.
meillo@34: Usually there is one context for each user, but a user can have many
meillo@34: contexts.
meillo@34: Public sequences are an exception, as they belong to the mail folder.
meillo@34: .[
meillo@34: %O mh-profile(5) and mh-sequence(5)
meillo@34: .]
meillo@20: 
meillo@0: .NH 2
meillo@20: Discussion of the design
meillo@0: .LP
meillo@20: The following paragraphs discuss \s-1MH\s0 in regard to the tenets
meillo@23: of the Unix Philosophy which Gancarz identified.
meillo@20: 
meillo@20: .PP
meillo@33: .B "Small is beautiful
meillo@20: and
meillo@33: .B "do one thing well
meillo@20: are two design goals that are directly visible in \s-1MH\s0.
meillo@20: Gancarz actually presents \s-1MH\s0 as example under the headline
meillo@20: ``Making UNIX Do One Thing Well'':
meillo@41: .[
meillo@41: %A Mike Gancarz
meillo@41: %T unix-phil
meillo@41: %P 125
meillo@41: .]
meillo@20: .QP
meillo@41: .ps -1
meillo@20: [\s-1MH\s0] consists of a series of programs which
meillo@20: when combined give the user an enormous ability
meillo@20: to manipulate electronic mail messages.
meillo@20: A complex application, it shows that not only is it
meillo@20: possible to build large applications from smaller
meillo@20: components, but also that such designs are actually preferable.
meillo@20: .LP
meillo@20: The various small programs of \s-1MH\s0 were relatively easy
meillo@23: to write, because each of them is small, limited to one function,
meillo@23: and has clear boundaries.
meillo@20: For the same reasons, they are also good to maintain.
meillo@20: Further more, the system can easily get extended.
meillo@20: One only needs to put a new program into the toolchest.
meillo@23: This was done, for instance, when \s-1MIME\s0 support was added
meillo@20: (e.g. \f(CWmhbuild\fP).
meillo@20: Also, different programs can exist to do the basically same job
meillo@20: in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
meillo@20: If someone needs a mail system with some additionally
meillo@23: functions that are available nowhere yet, he best takes a
meillo@20: toolchest system like \s-1MH\s0 where he can add the
meillo@20: functionality with little work.
meillo@20: 
meillo@20: .PP
meillo@34: .B "Store data in flat text files
meillo@34: is followed by \s-1MH\s0.
meillo@34: This is not surprising, because email messages are already plain text.
meillo@34: \s-1MH\s0 stores the messages as it receives them,
meillo@34: thus any other tool that works on RFC 2822 mail messages can operate
meillo@34: on the messages in an \s-1MH\s0 mailbox.
meillo@34: All other files \s-1MH\s0 uses are plain text too.
meillo@34: It is therefore possible and encouraged to use the text processing
meillo@34: tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
meillo@20: 
meillo@20: .PP
meillo@33: .B "Avoid captive user interfaces" .
meillo@19: \s-1MH\s0 is perfectly suited for non-interactive use.
meillo@19: It offers all functions directly and without captive user interfaces.
meillo@30: If, nonetheless, users want a graphical user interface,
meillo@20: they can have it with \fIxmh\fP or \fIexmh\fP, too.
meillo@19: These are graphical frontends for the \s-1MH\s0 toolchest.
meillo@19: This means, all email-related work is still done by \s-1MH\s0 tools,
meillo@20: but the frontend issues the appropriate calls when the user
meillo@30: clicks on buttons.
meillo@20: Providing easy-to-use user interfaces in form of frontends is a good
meillo@19: approach, because it does not limit the power of the backend itself.
meillo@20: The frontend will anyway only be able to make a subset of the
meillo@23: backend's power and flexibility available to the user.
meillo@20: But if it is a separate program,
meillo@20: then the missing parts can still be accessed at the backend directly.
meillo@19: If it is integrated, then this will hardly be possible.
meillo@30: Further more, it is possible to have different frontends to the same
meillo@30: backend.
meillo@19: 
meillo@19: .PP
meillo@33: .B "Choose portability over efficiency
meillo@20: and
meillo@33: .B "use shell scripts to increase leverage and portability" .
meillo@20: These two tenets are indirectly, but nicely, demonstrated by
meillo@30: Bolsky and Korn in their book about the Korn Shell.
meillo@20: .[
meillo@20: %T The KornShell: command and programming language
meillo@20: %A Morris I. Bolsky
meillo@20: %A David G. Korn
meillo@20: %I Prentice Hall
meillo@20: %D 1989
meillo@30: %P 254\(en290
meillo@20: %O \s-1ISBN\s0: 0-13-516972-0 
meillo@20: .]
meillo@30: They demonstrated, in chapter 18 of the book, a basic implementation
meillo@20: of a subset of \s-1MH\s0 in ksh scripts.
meillo@20: Of course, this was just a demonstration, but a brilliant one.
meillo@20: It shows how quickly one can implement such a prototype with shell scripts,
meillo@20: and how readable they are.
meillo@20: The implementation in the scripting language may not be very fast,
meillo@20: but it can be fast enough though, and this is all that matters.
meillo@20: By having the code in an interpreted language, like the shell,
meillo@20: portability becomes a minor issue, if we assume the interpreter
meillo@20: to be widespread.
meillo@20: This demonstration also shows how easy it is to create single programs
meillo@20: of a toolchest software.
meillo@30: There are eight tools (two of them have multiple names) and 16 functions
meillo@30: with supporting code.
meillo@30: Each tool comprises between 12 and 38 lines of ksh,
meillo@30: in total about 200 lines.
meillo@30: The functions comprise between 3 and 78 lines of ksh,
meillo@30: in total about 450 lines.
meillo@20: Such small software is easy to write, easy to understand,
meillo@20: and thus easy to maintain.
meillo@23: A toolchest improves the possibility to only write some parts
meillo@20: and though create a working result.
meillo@20: Expanding the toolchest without global changes will likely be
meillo@20: possible, too.
meillo@20: 
meillo@20: .PP
meillo@33: .B "Use software leverage to your advantage
meillo@20: and the lesser tenet
meillo@33: .B "allow the user to tailor the environment
meillo@20: are ideally followed in the design of \s-1MH\s0.
meillo@21: Tailoring the environment is heavily encouraged by the ability to
meillo@30: directly define default options to programs.
meillo@30: It is even possible to define different default options
meillo@21: depending on the name under which the program was called.
meillo@21: Software leverage is heavily encouraged by the ease it is to
meillo@21: create shell scripts that run a specific command line,
meillo@30: built of several \s-1MH\s0 programs.
meillo@21: There is few software that so much wants users to tailor their
meillo@21: environment and to leverage the use of the software, like \s-1MH\s0.
meillo@21: Just to make one example:
meillo@23: One might prefer a different listing format for the \f(CWscan\fP
meillo@21: program.
meillo@30: It is possible to take one of the distributed format files
meillo@21: or to write one yourself.
meillo@21: To use the format as default for \f(CWscan\fP, a single line,
meillo@21: reading
meillo@21: .DS
meillo@21: .CW
meillo@21: scan: -form FORMATFILE
meillo@21: .DE
meillo@21: must be added to \f(CW.mh_profile\fP.
meillo@21: If one wants this different format as an additional command,
meillo@23: instead of changing the default, he needs to create a link to
meillo@23: \f(CWscan\fP, for instance titled \f(CWscan2\fP.
meillo@21: The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
meillo@30: as the option should only be in effect when scan is called as
meillo@21: \f(CWscan2\fP.
meillo@20: 
meillo@20: .PP
meillo@33: .B "Make every program a filter
meillo@21: is hard to find in \s-1MH\s0.
meillo@21: The reason therefore is that most of \s-1MH\s0's tools provide
meillo@21: basic file system operations for the mailboxes.
meillo@30: The reason is the same because of which
meillo@21: \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP, and \f(CWrm\fP
meillo@21: aren't filters neither.
meillo@23: However, they build a basis on which filters can operate.
meillo@23: \s-1MH\s0 does not provide many filters itself, but it is a basis
meillo@23: to write filters for.
meillo@30: An example would be a mail message text highlighter,
meillo@30: that means a program that makes use of a color terminal to display
meillo@30: header lines, quotations, and signatures in distinct colors.
meillo@30: The author's version of this program, for instance,
meillo@30: is a 25 line awk script.
meillo@21: 
meillo@21: .PP
meillo@33: .B "Build a prototype as soon as possible
meillo@21: was again well followed by \s-1MH\s0.
meillo@21: This tenet, of course, focuses on early development, which is
meillo@21: long time ago for \s-1MH\s0.
meillo@21: But without following this guideline at the very beginning,
meillo@23: Bruce Borden may have not convinced the management of \s-1RAND\s0
meillo@23: to ever create \s-1MH\s0.
meillo@23: In Bruce' own words:
meillo@41: .[
meillo@41: %O FIXME
meillo@41: .]
meillo@21: .QP
meillo@41: .ps -1
meillo@30: [...] but they [Stockton Gaines and Norm Shapiro] were not able
meillo@23: to convince anyone that such a system would be fast enough to be usable.
meillo@21: I proposed a very short project to prove the basic concepts,
meillo@21: and my management agreed.
meillo@21: Looking back, I realize that I had been very lucky with my first design.
meillo@21: Without nearly enough design work,
meillo@21: I built a working environment and some header files
meillo@21: with key structures and wrote the first few \s-1MH\s0 commands:
meillo@21: inc, show/next/prev, and comp.
meillo@21: [...]
meillo@21: With these three, I was able to convince people that the structure was viable.
meillo@21: This took about three weeks.
meillo@0: 
meillo@0: .NH 2
meillo@0: Problems
meillo@0: .LP
meillo@22: \s-1MH\s0, for sure is not without problems.
meillo@30: There are two main problems: one is technical, the other is about human behavior.
meillo@22: .PP
meillo@22: \s-1MH\s0 is old and email today is very different to email in the time
meillo@22: when \s-1MH\s0 was designed.
meillo@22: \s-1MH\s0 adopted to the changes pretty well, but it is limited.
meillo@22: For example in development resources.
meillo@22: \s-1MIME\s0 support and support for different character encodings
meillo@22: is available, but only on a moderate level.
meillo@22: More active developers could quickly improve there.
meillo@22: It is also limited by design, which is the larger problem.
meillo@22: \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
meillo@22: These design conflicts are not easily solvable.
meillo@22: Possibly, they require a redesign.
meillo@30: Maybe \s-1IMAP\s0 is too different to the classic mail model which \s-1MH\s0 covers,
meillo@30: hence \s-1MH\s0 may never work well with \s-1IMAP\s0.
meillo@22: .PP
meillo@22: The other kind of problem is human habits.
meillo@22: When in this world almost all \s-1MUA\s0s are monolithic,
meillo@22: it is very difficult to convince people to use a toolbox style \s-1MUA\s0
meillo@22: like \s-1MH\s0.
meillo@22: The habits are so strong, that even people who understood the concept
meillo@30: and advantages of \s-1MH\s0 do not like to switch,
meillo@30: simply because \s-1MH\s0 is different.
meillo@30: Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
meillo@30: are quite outdated and thus not very appealing compared to the modern interfaces
meillo@30: which monolithic \s-1MUA\s0s offer.
meillo@20: 
meillo@20: .NH 2
meillo@20: Summary \s-1MH\s0
meillo@20: .LP
meillo@31: \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design
meillo@31: and implementation.
meillo@31: It consists of a toolchest of small tools, each of them does one job well.
meillo@31: The tools are orthogonal to each other, to a large extend.
meillo@31: However, for historical reasons, there also exist distinct tools
meillo@31: that cover the same task.
meillo@31: .PP
meillo@31: The toolchest approach offers great flexibility to the user.
meillo@31: He can use the complete power of the Unix shell with \s-1MH\s0.
meillo@31: This makes \s-1MH\s0 a very powerful mail system.
meillo@31: Extending and customizing \s-1MH\s0 is easy and encouraged, too.
meillo@31: .PP
meillo@31: Apart from the user's perspective, \s-1MH\s0 is development-friendly.
meillo@31: Its overall design follows clear rules.
meillo@31: The single tools do only one job, thus they are easy to understand,
meillo@31: easy to write, and good to maintain.
meillo@31: They are all independent and do not interfere with the others.
meillo@31: Automated testing of their function is a straight forward task.
meillo@31: .PP
meillo@31: It is sad, that \s-1MH\s0's differentness is its largest problem,
meillo@31: as its differentness is also its largest advantage.
meillo@31: Unfortunately, for most people their habits are stronger
meillo@31: than the attraction of the clear design and the power, \s-1MH\s0 offers.
meillo@0: 
meillo@8: 
meillo@8: 
meillo@0: .NH 1
meillo@0: Case study: uzbl
meillo@32: .LP
meillo@32: The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
meillo@32: this chapter is about uzbl, a web browser that adheres to the Unix Philosophy.
meillo@32: ``uzbl'' is the \fIlolcat\fP's word for the English adjective ``usable''.
meillo@32: It is pronounced the identical.
meillo@0: 
meillo@0: .NH 2
meillo@32: Historical background
meillo@0: .LP
meillo@32: Uzbl was started by Dieter Plaetinck in April 2009.
meillo@32: The idea was born in a thread in the Arch Linux forum.
meillo@32: .[
meillo@32: %O http://bbs.archlinux.org/viewtopic.php?id=67463
meillo@32: .]
meillo@32: After some discussion about failures of well known web browsers,
meillo@32: Plaetinck (alias Dieter@be) came up with a very sketchy proposal
meillo@32: of how a better web browser could look like.
meillo@32: To the question of another member, if Plaetinck would write that program,
meillo@32: because it would sound fantastic, Plaetinck replied:
meillo@32: ``Maybe, if I find the time ;-)''.
meillo@32: .PP
meillo@32: Fortunately, he found the time.
meillo@32: One day later, the first prototype was out.
meillo@32: One week later, uzbl had an own website.
meillo@32: One month after the first code showed up,
meillo@32: a mailing list was installed to coordinate and discuss further development.
meillo@32: A wiki was set up to store documentation and scripts that showed up on the
meillo@32: mailing list and elsewhere.
meillo@32: .PP
meillo@38: In the, now, one year of uzbl's existence, it was heavily developed in various branches.
meillo@32: Plaetinck's task became more and more to only merge the best code from the
meillo@32: different branches into his main branch, and to apply patches.
meillo@32: About once a month, Plaetinck released a new version.
meillo@32: In September 2009, he presented several forks of uzbl.
meillo@38: Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
meillo@32: .PP
meillo@32: In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
meillo@32: In September 2009, the uzbl web browser was on \fISlashdot\fP.
meillo@0: 
meillo@0: .NH 2
meillo@32: Contrasts to other web browsers
meillo@0: .LP
meillo@32: Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
meillo@32: most web browsers are monolithic, but uzbl is a frontend to a toolchest.
meillo@32: .PP
meillo@32: Today, uzbl is divided into uzbl-core and uzbl-browser.
meillo@32: Uzbl-core is, how its name already indicates, the core of uzbl.
meillo@32: It handles commands and events to interface other programs,
meillo@32: and also displays webpages by using webkit as render engine.
meillo@32: Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
meillo@32: an event manager, yanking, pasting, page searching, zooming, and more stuff,
meillo@32: to form a ``complete'' web browser.
meillo@32: In the following text, the term ``uzbl'' usually stands for uzbl-browser,
meillo@32: so uzbl-core is included.
meillo@32: .PP
meillo@32: Unlike most other web browsers, uzbl is mainly the mediator between the
meillo@32: various tools that cover single jobs of web browsing.
meillo@35: Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
meillo@35: and on stdin, and it writes events to a Unix socket and to stdout.
meillo@35: The graphical rendering of the webpage is done by webkit, a web content engine.
meillo@35: Uzbl-core is build around this library.
meillo@35: Loading a webpage in a running uzbl instance requires only:
meillo@32: .DS
meillo@32: .CW
meillo@32: echo 'uri http://example.org' >/path/to/uzbl-fifo
meillo@32: .DE
meillo@32: .PP
meillo@32: Downloads, browsing history, bookmarks, and thelike are not provided
meillo@32: by uzbl-core itself, as they are in other web browsers.
meillo@35: Uzbl-browser also only provides, so called, handler scripts that wrap
meillo@35: external applications which provide the actual functionality.
meillo@32: For instance, \fIwget\fP is used to download files and uzbl-browser
meillo@32: includes a script that calls wget with appropriate options in
meillo@32: a prepared environment.
meillo@32: .PP
meillo@32: Modern web browsers are proud to have addons, plugins, and modules, instead.
meillo@32: This is their effort to achieve similar goals.
meillo@35: But instead of using existing, external programs, modern web browsers
meillo@35: include these functions, although they might be loaded at runtime.
meillo@0: 
meillo@0: .NH 2
meillo@32: Discussion of the design
meillo@0: .LP
meillo@32: This section discusses uzbl in regard of the Unix Philosophy,
meillo@32: as identified by Gancarz.
meillo@32: 
meillo@32: .PP
meillo@35: .B "Make each program do one thing well" .
meillo@35: Uzbl tries to be a web browser and nothing else.
meillo@36: The common definition of a web browser is, of course, highly influenced by
meillo@36: existing implementations of web browsers, although they are degenerated.
meillo@35: Web browsers should be programs to browse the web, and nothing more.
meillo@35: This is the one thing they should do, as demanded by the Unix Philosophy.
meillo@36: .PP
meillo@36: Web browsers should, for instance, not manage downloads.
meillo@35: This is the job download managers exist for.
meillo@35: Download managers do primary care about being good in downloading files.
meillo@35: Modern web browsers provide download management only as a secondary feature.
meillo@35: How could they perform this job better, than programs that exist only for
meillo@35: this very job?
meillo@35: And how could anyone want less than the best download manager available?
meillo@32: .PP
meillo@35: A web browser's job is to let the user browse the web.
meillo@35: This means, navigating through websites by following links.
meillo@36: Rendering the \s-1HTML\s0 sources is a different job, too.
meillo@36: It is covered by the webkit render engine, in uzbl's case.
meillo@35: Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
meillo@36: are also not the job of a web browser.
meillo@36: They should be handled by external applications \(en
meillo@36: ones which's job is to handle such data.
meillo@35: Uzbl strives to do it this way.
meillo@36: .PP
meillo@36: Remember Doug McIlroy:
meillo@35: .I
meillo@35: ``Write programs that do one thing and do it well.
meillo@35: Write programs to work together.''
meillo@35: .R
meillo@35: .PP
meillo@35: The lesser tenet
meillo@35: .B "allow the user to tailor the environment
meillo@35: matches good here.
meillo@35: There was the question, how anyone could want anything less than the
meillo@35: best program for the job.
meillo@36: But as personal preferences matter much,
meillo@36: it is probably more important to ask:
meillo@35: How could anyone want something else than his preferred program for the job?
meillo@36: .PP
meillo@35: Usually users want one program for one job.
meillo@35: Hence, whenever the task is, for instance, downloading,
meillo@36: exactly one download manager should be used.
meillo@35: More advanced users might want to have this download manager in this
meillo@35: situation and that one in that situation.
meillo@35: They should be able to configure it this way.
meillo@35: With uzbl, one can use any download manager the user wants.
meillo@36: To switch to a different one, only one line in a small handler script
meillo@35: needs to be changed.
meillo@36: Alternatively it would be possible to query an entry in a global file
meillo@36: or an environment variable, which specifies the download manager to use,
meillo@35: in the handler script.
meillo@36: .PP
meillo@35: As uzbl does neither have its own download manager nor depends on a
meillo@35: specific one, thus uzbl's browsing abilities will not be lowered by having
meillo@35: a bad download manager.
meillo@36: Uzbl's download capabilities will just as good as the ones of the best
meillo@36: download manager available on the system.
meillo@38: Of course, this applies to all of the other supplementary tools, too.
meillo@32: 
meillo@32: .PP
meillo@36: .B "Use software leverage to your advantage" .
meillo@36: Shell scripts are a good choice to extend uzbl.
meillo@36: Uzbl is designed to be extended by external tools.
meillo@36: These external tools are usually wrapped by small handler shell scripts.
meillo@36: Shell scripts are the glue in this approach.
meillo@36: They make the various parts fit together.
meillo@36: .PP
meillo@36: As an example, the history mechanism of uzbl shall be presented.
meillo@36: Uzbl is configured to spawn a script to append an entry to the history
meillo@36: whenever the event of a fully loaded page occurs.
meillo@36: The script to append the entry to the history not much more than:
meillo@36: .DS
meillo@36: .CW
meillo@36: #!/bin/sh
meillo@36: file=/path/to/uzbl-history
meillo@36: echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
meillo@36: .DE
meillo@36: \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
meillo@36: For loading an entry, a key is bound to spawn a load from history script.
meillo@36: The script reverses the history to have newer entries first,
meillo@36: then displays \fIdmenu\fP to select an item,
meillo@36: and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
meillo@36: With error checking and corner cases removed, the script looks like this:
meillo@36: .DS
meillo@36: .CW
meillo@36: #!/bin/sh
meillo@36: file=/path/to/uzbl-history
meillo@36: goto=`tac $file | dmenu | cut -d' ' -f 3`
meillo@36: echo "uri $goto" > $4
meillo@36: .DE
meillo@36: \f(CW$4\fP expands to the path of the command input pipe of the current
meillo@36: uzbl instance.
meillo@32: 
meillo@32: .PP
meillo@33: .B "Avoid captive user interfaces" .
meillo@36: One could say, that uzbl, to a large extend, actually \fIis\fP
meillo@36: a captive user interface.
meillo@37: But the difference to most other web browsers is, that uzbl is only
meillo@37: the captive user interface frontend and the core of the backend.
meillo@38: Many parts of the backend are independent of uzbl.
meillo@37: Some are distributed with uzbl, for some external programs, handler scripts
meillo@37: are distributed, arbitrary additional functionality can be added if desired.
meillo@37: .PP
meillo@37: The frontend is captive \(en that is true.
meillo@37: This is okay for the task of browsing the web, as this task is only relevant
meillo@37: for humans.
meillo@37: Automated programs would \fIcrawl\fP the web.
meillo@37: That means, they read the source directly.
meillo@37: The source includes all the semantics.
meillo@37: The graphical representation is just for humans to transfer the semantics
meillo@37: more intuitively.
meillo@32: 
meillo@32: .PP
meillo@33: .B "Make every program a filter" .
meillo@37: Graphical web browsers are almost dead ends in the chain of information flow.
meillo@37: Thus it is difficult to see what graphical web browsers should filter.
meillo@37: Graphical web browsers exist almost only for interactive use by humans.
meillo@37: The only case when one might want to automate the rendering function is
meillo@37: to generate images of rendered webpages.
meillo@37: 
meillo@37: .PP
meillo@37: .B "Small is beautiful"
meillo@38: is not easy to apply to a web browser, primary because modern web technology
meillo@38: is very complex; hence the rendering task is very complex.
meillo@37: Modern web browsers will always consist of many thousand lines of code,
meillo@37: unfortunately.
meillo@37: Using the toolchest approach and wrappers can split the browser into
meillo@37: several small parts, tough.
meillo@37: .PP
meillo@37: Uzbl-core consists of about 3\,500 lines of C code.
meillo@37: The distribution includes another 3\,500 lines of Shell and Python code,
meillo@37: which are the handler scripts and plugins like a modal interface.
meillo@38: Further more, uzbl uses functionality of external tools like
meillo@38: \fIwget\fP and \fInetcat\fP.
meillo@37: Up to this point, uzbl looks pretty neat and small.
meillo@38: The ugly part of uzbl is the web content renderer, webkit.
meillo@37: Webkit consists of roughly 400\,000 (!) lines of code.
meillo@38: Unfortunately, small web render engines are not possible anymore
meillo@38: because of the modern web.
meillo@38: The problems section will explain this in more detail.
meillo@35: 
meillo@35: .PP
meillo@35: .B "Build a prototype as soon as possible" .
meillo@35: Plaetinck made his code public, right from the beginning.
meillo@38: Discussion and development was, and still is, open to everyone interested.
meillo@38: Development versions of uzbl can be obtained very simply from the code
meillo@38: repository.
meillo@38: Within the first year of uzbl's existence, a new version was released
meillo@35: more often than once a month.
meillo@38: Different forks and branches arose.
meillo@38: They introduced new features, which were tested for suitability.
meillo@35: The experiences of using prototypes influenced further development.
meillo@35: Actually, all development was community driven.
meillo@38: Plaetinck says, three months after uzbl's birth:
meillo@35: ``Right now I hardly code anything myself for Uzbl.
meillo@35: I just merge in other people's code, ponder a lot, and lead the discussions.''
meillo@35: .[
meillo@36: %A FIXME
meillo@35: %O http://lwn.net/Articles/341245/
meillo@35: .]
meillo@32: 
meillo@0: 
meillo@0: .NH 2
meillo@0: Problems
meillo@0: .LP
meillo@38: Similar to \s-1MH\s0, uzbl, too suffers from being different.
meillo@38: It is sad, but people use what they know.
meillo@38: Fortunately, uzbl's user interface can look and feel very much the
meillo@38: same as the one of the well known web browsers,
meillo@38: hiding the internal differences.
meillo@38: But uzbl has to provide this similar look and feel to be accepted
meillo@38: as a ``normal'' browser by ``normal'' users.
meillo@37: .PP
meillo@38: The more important problem is the modern web.
meillo@38: The modern web is simply broken.
meillo@38: It has state in a state-less protocol,
meillo@38: it misuses technologies,
meillo@38: and it is helplessly overloaded.
meillo@38: The result are web content render engines that must consist
meillo@38: of hundreds of thousands lines of code.
meillo@38: They also must combine and integrate many different technologies,
meillo@38: only to make our modern web usable.
meillo@38: Website to image converter are hardly possible to run without
meillo@38: human interaction because of state in sessions, impossible
meillo@38: deep-linking, and unautomatable technologies.
meillo@37: .PP
meillo@38: The web was misused to provide all kinds of imaginable wishes.
meillo@38: Now web browsers, and eventually the users, suffer from it.
meillo@37: 
meillo@8: 
meillo@32: .NH 2
meillo@32: Summary uzbl
meillo@32: .LP
meillo@38: ``Uzbl is a browser that adheres to the Unix Philosophy'',
meillo@38: that is how uzbl is seen by its authors.
meillo@38: Indeed, uzbl follows the Unix Philosophy in many ways.
meillo@38: It consists of independent parts that work together,
meillo@38: its core is mainly a mediator which glues the parts together.
meillo@38: .PP
meillo@38: Software leverage can excellently be seen in uzbl.
meillo@38: It makes use of external tools, separates independent tasks
meillo@38: in independent parts, and glues them together with small
meillo@38: handler scripts, around uzbl-core.
meillo@38: .PP
meillo@38: As uzbl, more or less, consists of a set of tools and a bit
meillo@38: of glue, anyone can put the parts together and expand it
meillo@38: in any desired way.
meillo@38: Uzbl is very flexible and customizable.
meillo@38: These properties make it valuable for advanced users,
meillo@38: but may keep novice users from using it.
meillo@38: .PP
meillo@38: Uzbl's main problem is the modern web, that makes it hard
meillo@38: to design a sane web browser.
meillo@38: Despite this bad situation, uzbl does a fairly good job.
meillo@32: 
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