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@ -79,12 +79,7 @@ not license it under more restrictive terms than that.</p> |
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<li><a href="#d-i-y-utilities">d.i.y. utilities</a></li> |
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</ul> |
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</li> |
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<li><a href="#general-purpose-programmering">5. general purpose programmering</a> |
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<ul> |
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<li><a href="#fear-and-loathing">fear and loathing</a></li> |
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</ul> |
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</li> |
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<li><a href="#general-purpose-programmering">5. general purpose programmering</a></li> |
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<li><a href="#diff-wdiff-git">6. diff, wdiff, git</a></li> |
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<li><a href="#further-reading">7. further reading</a></li> |
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<li><a href="#notes">notes</a></li> |
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@ -1787,7 +1782,7 @@ exit 0 |
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<!-- end --> |
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<p>These scripts aren’t much more complicated than their more specific |
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<p>These scripts aren’t much more complicated than their poem-specific |
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counterparts, but now they can be used to solve problems I haven’t even thought |
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of yet, and included in other scripts that need their functionality.</p> |
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@ -1795,19 +1790,89 @@ of yet, and included in other scripts that need their functionality.</p> |
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<h1><a name=general-purpose-programmering href=#general-purpose-programmering>#</a> 5. general purpose programmering</h1> |
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<h2><a name=fear-and-loathing href=#fear-and-loathing>#</a> fear and loathing</h2> |
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<p>I didn’t set out to write a book about programming, <em>as such</em>, but because |
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programming and the command line are so inextricably linked, this text |
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draws near the subject almost of its own accord.</p> |
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<p>If you’re not terribly interested in programming, this chapter can easily |
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enough be skipped.</p> |
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<p style="text-align:center;"> *</p> |
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<p>As I’ve said (and hopefully shown), the commands you write in your shell |
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are essentially little programs. Like other programs, they can be stored |
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for later use and recombined with other commands, creating new uses for |
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your ideas.</p> |
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<p>It would be hard to say that there’s any <em>one</em> reason command line environments |
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remain so vital after decades of evolution and hard-won refinement in computer |
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interfaces, but I’d suggest that this combinatory nature is somewhere near the |
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heart of it. The command line often lacks the polish of other interfaces we |
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depend on, but in exchange it offers a richness and freedom of expression |
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rarely seen elsewhere, and invites its users to build upon its basic |
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facilities.</p> |
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<p>What is it that makes last chapter’s <code>addprop</code> preferable to the more specific |
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<code>markpoem</code>? Let’s look at an alternative implementation of <code>markpoem</code>:</p> |
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<!-- exec --> |
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<pre><code>$ cat simple_markpoem |
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#!/bin/bash |
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addprop $1 meta-ok-poem |
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</code></pre> |
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<!-- end --> |
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<p>Is this script trivial? Absolutely. It’s so trivial that it barely seems to |
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exist, because I already wrote <code>addprop</code> to do all the heavy lifting and play |
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well with others, freeing us to imagine new uses for its central idea without |
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worrying about the implementation details.</p> |
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<p>Unlike <code>markpoem</code>, <code>addprop</code> doesn’t know anything about poetry. All it knows |
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about in fact, is putting a file (or three) in a particular place. And this is |
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in keeping with a basic insight of Unix: Pieces of software that do one very |
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simple thing generalize well. Good command line tools are like a hex wrench, |
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a hammer, a utility knife: They embody knowledge of turning, of striking, of |
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cutting – and with this kind of knowledge at hand, the user can change the |
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world even though no individual tool is made with complete knowledge of the |
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world as a whole. There’s a lot of power in the accumulation of small |
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competencies.</p> |
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<p>Of course, if your code is only good at one thing, to be of any use, it has to |
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talk to code that’s good at other things. There’s another basic insight in the |
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Unix tradition: Tools should be composable. All those little programs have to |
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share some assumptions, have to speak some kind of trade language, in order to |
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combine usefully. Which is a lot of how we’ve arrived at standard IO, |
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pipelines, filesystems, and text as as a lowest-common-denominator medium of |
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exchange. If you think about a lot of these things, they have some seriously |
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rough edges, but they give otherwise simple tools ways to communicate without |
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being super-complicated.</p> |
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<p style="text-align:center;"> *</p> |
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<p>What is the command line?</p> |
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<p>The command line is an environment of tool use.</p> |
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<p>So are kitchens, woodshops, libraries, and programming languages.</p> |
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<p style="text-align:center;"> *</p> |
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<p>Let me begin this chapter with a confession: I kind of hate shell scripts, and |
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I think it’s ok if you hate them too.</p> |
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<p>Here’s a confession: I don’t like writing shell scripts very much, and I |
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can’t blame anyone else for feeling the same way.</p> |
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<p>That doesn’t mean you shouldn’t <em>know</em> about them, or that you shouldn’t |
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<em>write</em> them. I write little tiny ones all the time, and the ability to puzzle |
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<em>write</em> them. I write little ones all the time, and the ability to puzzle |
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through other people’s scripts comes in handy. Oftentimes, the best, most |
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tasteful way to automate something is to build a script out of the commonly |
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available commands. The standard tools are already there on millions of |
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machines. Many of them have been pretty well understood for a generation, and |
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most will probably be around for a generation or three to come. They do neat |
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stuff. Scripts let you build on things you’ve already figured out, and give |
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stuff. Scripts let you build on ideas you’ve already worked out, and give |
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repeatable operations a memorable, user-friendly name. They encourage reuse of |
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existing programs, and help express your ideas to people who’ll come after you.</p> |
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@ -1824,13 +1889,15 @@ covered in 40 years of incidental cruft, long-form Bash scripts are even worse. |
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Bash is a useful glue language, particularly if you’re already comfortable |
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wiring commands together. Syntactic and conceptual innovations like pipes are |
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beautiful and necessary. What Bash is <em>not</em>, despite its power, is a very good |
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general purpose programming language.</p> |
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general purpose programming language. It’s just not especially good at things |
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like math, or complex data structures, or not looking like a punctuation-heavy |
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variety of alphabet soup.</p> |
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<p>It turns out that there’s a threshold of complexity beyond which life is easier |
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if you switch from shell scripting to a more robust language. Just where this |
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threshold is located varies a lot between users and problems, but I often start |
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thinking about switching languages before a shell script gets bigger than I can |
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view on my screen all at once. How long is last chapter’s <code>addprop</code>?</p> |
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thinking about switching languages before a script gets bigger than I can view |
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on my screen all at once. <code>addprop</code> is a good example:</p> |
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<!-- exec --> |
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@ -1842,8 +1909,9 @@ view on my screen all at once. How long is last chapter’s <code>addprop</ |
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<!-- end --> |
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<p>If I were going to add much in the way of features, I’d think pretty hard about |
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porting it to another language.</p> |
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<p>41 lines is a touch over what fits on one screen in the editor I usually use. |
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If I were going to add much in the way of features, I’d think pretty hard about |
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porting it to another language first.</p> |
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<hr /> |
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Brennen Bearnes
11 years ago