Literate Lists

I’ve written before about literate programming, and how one of its most attractive features is that you can write code with the primary goal of conveying information to a person, and only secondarily of telling a computer what to do. So there’s a bit in my .bashrc that adds directories to $PATH that isn’t as reader-friendly as I’d like:

for dir in \
    /usr/sbin \
    /opt/sbin \
    /usr/local/sbin \
    /some/very/specific/directory \
    ; do

I’d like to be add a comment to each directory entry, explaining why I want it in $PATH, but sh syntax won’t let me: there’s just no way to interleave strings and comments this way. So far, I’ve documented these directories in a comment above the for loop, but that’s not exactly what I’d like to do. In fact, I’d like to do something like:

$PATH components

  • /usr/sbin
  • /usr/local/bin
for dir in \
    {{path-components}} \
    ; do

Or even:

$PATH components

/usr/sbinsbin directories contain sysadminny stuff, and should go before bin directories.
/usr/local/binLocally-installed utilities take precedence over vendor-installed ones.
for dir in \
    {{path-components}} \
    ; do

Spoiler alert: both are possible with org-mode.


The key is to use Library of Babel code blocks: these allow you to execute org-mode code blocks and use the results elsewhere. Let’s start by writing the code that we want to be able to write:

#+name: path-list
- /usr/bin
- /opt/bin
- /usr/local/bin
- /sbin
- /opt/sbin
- /usr/local/sbin

#+begin_src bash :noweb no-export :tangle
  for l in \
      <<org-list-to-sh(l=path-list)>> \
      ; do

Note the :noweb argument to the bash code block, and the <<org-list-to-sh()>> call in noweb brackets. This is a function we need to write. It’ll (somehow) take an org list as input and convert it into a string that can be inserted in this fragment of bash code.

This function is a Babel code block that we will evaluate, and which will return a string. We can write it in any supported language we like, such as R or Python, but for the sake of simplicity and portability, let’s stick with Emacs lisp.

Next, we’ll want a test rig to actually write the org-list-to-sh function. Let’s start with:

#+name: org-list-to-sh
#+begin_src emacs-lisp :var l='nil

#+name: test-list
- First
- Second
- Third

#+CALL: org-list-to-sh(l=test-list) :results value raw

The begin_src block at the top defines our function. For now, it simply takes one parameter, l, which defaults to nil, and returns l. Then there’s a list, to provide test data, and finally a #+CALL: line, which contains a call to org-list-to-sh and some header arguments, which we’ll get to in a moment.

If you press C-c C-c on the #+CALL line, Emacs will evaluate the call and write the result to a #+RESULTS block underneath. Go ahead and experiment with the Lisp code and any parameters you might be curious about.

The possible values for the :results header are listed under “Results of Evaluation” in the Org-Mode manual. There are a lot of them, but the one we care the most about is value: we’re going to execute code and take its return value, not its printed output. But this is the default, so it can be omitted.

If you tangle this file with C-c C-v C-t, you’ll see the following in

for l in \
    ((/usr/bin) (/opt/bin) (/usr/local/bin) (/sbin) (/opt/sbin) (/usr/local/sbin)) \
    ; do

    It looks as though our org-mode list got turned into a Lisp list. As it turns out, yes, but not really. Let’s change the source of the org-list-to-sh() function to illustrate what’s going on:

    #+name: org-list-to-sh
    #+begin_src emacs-lisp :var l='nil :results raw
      (format "aaa %s zzz" l)

    Now, when we tangle, it contains

        aaa ((/usr/bin) (/opt/bin) (/usr/local/bin) (/sbin) (/opt/sbin) (/usr/local/sbin)) zzz \

    So the return value from org-list-to-sh was turned into a string, and that string was inserted into the tangled file. This is because we chose :results raw in the definition of org-list-to-sh. If you play around with other values, you’ll see why they don’t work: vector wraps the result in extraneous parentheses, scalar adds extraneous quotation marks, and so on.

    Really, what we want is a plain string, generated from Lisp code and inserted in our sh code as-is. So we’ll need to change the org-list-to-sh code to return a string, and use :results raw to insert that string unchanged in the tangled file.

    We saw above that org-list-to-sh sees its parameter as a list of lists of strings, so let’s concatenate those strings, with space between them:

    #+name: org-list-to-sh
    #+begin_src emacs-lisp :var l='nil :results raw
      (mapconcat 'identity
    	      (lambda (elt)
    		(car elt)
    	     " ")

    This yields, in

    for l in \
        /usr/bin /opt/bin /usr/local/bin /sbin /opt/sbin /usr/local/sbin \
        ; do

    which looks pretty nice. It would be nice to break that list of strings across multiple lines, and also quote them (in case there are directories with spaces in them), but I’ll leave that as an exercise for the reader.


    That takes care of converting an org-mode list to a sh string. But earlier I said it would be even better to define the $PATH components in an org-mode table, with directories in the first column and comments in the second. This is easy, with what we’ve already done with strings. Let’s add a test table to our org-mode code, and some code to just return its input:

    #+name: echo-input
    #+begin_src emacs-lisp :var l='nil :results raw
    #+name: test-table
    | *Name*   | *Comment*        |
    | /bin     | First directory  |
    | /sbin    | Second directory |
    | /opt/bin | Third directory  |
    #+CALL: echo-input(l=test-table) :results value code

    Press C-c C-c on the #+CALL line to evaluate it, and you’ll see the results:

    #+begin_src emacs-lisp
    (("/bin" "First directory")
     ("/sbin" "Second directory")
     ("/opt/bin" "Third directory"))

    First of all, note that, just as with lists, the table is converted to a list of lists of strings, where the first string in each list is the name of the directory. So we can just reuse our existing org-list-to-sh code. Secondly, org has helpfully stripped the header line and the horizontal rule underneath it, giving us a clean set of data to work with (this seems a bit fragile, however, so in your own code, be sure to sanitize your inputs). Just convert the list of directories to a table of directories, and you’re done.


    We’ve seen how to convert org-mode lists and tables to code that can be inserted into a sh (or other language) source file when it’s tangled. This means that when our code includes data best represented by a list or table, we can, in the spirit of literate programming, use org-mode formatting to present that data to the user as a good-looking list or table, rather than just list it as code.

    One final homework assignment: in the list or table that describes the path elements, it would be nice to use org-mode formatting for the directory name itself: =/bin= rather than /bin. Update org-list-to-sh to strip the formatting before converting to sh code.

    Renewing an Overdue Docker Cert in QNAP

    Writing this down before I forget, somewhere where I won’t think to look for it the next time I need it.

    So you’re running Container Station (i.e., Docker) on a QNAP NAS, and naturally you’ve created a cert for it, because why wouldn’t you?, except that it expired a few days ago and you forgot to renew it, because apparently you didn’t have calendar technology when you originally created the cert, and now Container Station won’t renew the cert because it’s expired, and it won’t tell you that: it just passively-aggressively lets you click the Renew Certificate button, but nothing changes and the Docker port continues using the old, expired cert. What to do?

    1. Stop Container Station
    2. Log in to the NAS and delete /etc/docker/tls (or just rename it).
    3. Restart Container Station. Open it, and note the dialog box saying that the cert needs to be renewed.
    4. Under Preferences → Docker Certificate, download the new certificate.
    5. Restart Container Station to make it pick up the new cert.
    6. Unzip the cert in your local Docker certificate directory: either ~/.docker or whatever you’ve set $DOCKER_CERT_PATH to.
    7. Check that you have the right cert: the cert.pem that you just unzipped should be from the same keypair that’s being served by the Docker server:
      openssl x509 -noout -modulus -in cert.pem | openssl md5
      openssl s_client -connect $DOCKER_HOST:$DOCKER_PORT | openssl x509 -noout -modulus | openssl md5
      should return the same string.
    8. Check the expiration date on the new cert. Subtract 7 days, open a calendar at that date and write down “Renew Docker certificate” this time.
    A Few More Thoughts on Literate Programming

    A while back, I became intrigued by Donald Knuth’s idea of Literate Programming, and decided to give it a shot. That first attempt was basically just me writing down what I knew as quickly as I learned it, and trying to pass it off as a knowledgeable tutorial. More recently, I tried a second project, a web-app that solves Wordle, and thought I’d write it in the Literate style as well.

    The first time around, I learned the mechanics. The second time, I was able to learn one or two things about the coding itself.

    (For those who don’t remember, in literate programming, you write code intertwined with prose that explains the code, and a post-processor turns the result into a pretty document for humans to read, and ugly code for computers to process.

    1) The thing I liked the most, the part where literate programming really shines, is having the code be grouped not by function or by class, but by topic. I could introduce a <div class="message-box"></div> in the main HTML file, and in the next paragraph introduce the CSS that styles it, and the JavaScript code that manipulates it.

    2) In the same vein, several times I rearranged the source to make the explanations flow better, not discuss variables or functions until I had explained why they’re there and what they do, without it altering the underlying HTML or JavaScript source. In fact, this led to a stylistic quandary:

    3) I defined a few customization variables. You know, the kind that normally go at the top for easy customization:

    var MIN_FOO = 30;
    var MAX_FOO = 1500;
    var LOG_FILE = "/var/log/mylogfile.log";

    Of course, the natural tendency was to put them next to the code that they affect, somewhere in the middle of the source file. Should I have put them at the top of my source instead?

    4) Even smaller: how do you pass command-line option definitions to getopt()? If you have options -a, -b, and -c, each will normally be defined in its own section. So in principle, the literate thing to do would be to write


    and have a section that defines option-a as “a“. As you can see, though, defining single-letter strings isn’t terribly readable, and literate programming is all about readability.

    5) Speaking of readability, one thing that can come in really handy is the ability to generate a pretty document for human consumption. Knuth’s original tools generated TeX, of course, and it doesn’t get prettier than that.

    I used org-mode, which accepts TeX style math notation, but also allows you to embed images and graphviz graphs. In my case, I needed to calculate the entropy of a variable, so being able to use proper equations, with nicely-formatted sigmas and italicized variables, was very nice. I’ve worked in the past on a number of projects where it would have been useful to embed a diagram with circles and arrows, rather than using words or ASCII art.

    6) I was surprised to find that I had practically no comments in the base code (in the JavaScript, HTML, and CSS that were generated from my org-mode source file). I normally comment a lot. It’s not that I was less verbose. In fact, I was more verbose than usual. It’s just that I was putting all of the explanations about what I was trying to do, and why things were the way they are, in the human-docs part of the source, not the parts destined for computer consumption. Which, I guess, was the point.

    7) Related to this, I think I had fewer bugs than I would normally have gotten in a project of this size. I don’t know why, but I suspect that it was due to some combination of thinking “out loud” (or at least in prose) before pounding out a chunk of code, and of having related bits of code next to each other, and not scattered across multiple files.

    8) I don’t know whether I could tackle a large project in this way. You might say, “Why not? Donald Knuth wrote both TeX and Metafont as literate code, and even published the source in two fat books!” Well, yeah, but he’s Donald Knuth. Also, he was writing before IDEs, or even color-coded code, were available.

    I found org-mode to be the most comfortable tool for me to use for this project. But of course that effectively prevents people who don’t use Emacs (even though they obviously should) from contributing.

    One drawback of org-mode as a literate programming development environment is that you’re pretty much limited to one source file, which obviously doesn’t scale. There are other tools out there, like noweb, but I found those harder to set up, or they forced me to use (La)TeX when I didn’t want to, or the like.

    9) One serious drawback of org-mode is that it makes it nearly impossible to add cross-reference links. If you have a section like

    function myFunc() {
    var thing;
    {{calculate thing}}
    return thing;

    it would be very useful to have {{calculate thing}} be a link that you can click on to go to the definition of that chunk. But this is much harder to do in org-mode than it should be. So is labeling chunks, so that people can chase cross-references even without convenient links. It has a lot of work to be done in that regard.

    Readable Code: Variable Overload

    It’s well known that reading code is a lot harder than writing it. But I recently got some insight as to why that is.

    I was debugging someone else’s sh script. This one seemed harder to read than most. There was a section that involved figuring out a bunch of dates associated with a particular object. The author was careful to show their work, and not just have a bunch of opaque calculations in the code. I won’t quote their code, but imagine something like:

    NOW=$(date +%s)
    THING_CREATION_EPOCH=$(<get $THING creation time, in Unix time format>)
    THING_AGE_DAYS=$(( $THING_AGE_EPOCH / 86400 ))

    Now imagine this for three or four aspects of $THING, like last modification time, which other elements use $THING, things like that. The precise details don’t matter.

    Each variable makes sense. But there are four of them, just for the thing’s age since creation. And if you’re not as intimately familiar with it as someone who just wrote this code, that means you have to keep track of four variables in your head, and that gets very difficult very quickly.

    Part of the problem is that it’s unclear which variables will be needed further down (or even above, in functions that use global variables), so you have to hold on to these variables; you can’t mentally let them fall. Compare this to something like

    <Initialize some stuff>
    for i in $LIST_OF_THINGS; do
        ProcessStuff $i
    <Finalize some stuff>

    Here, you can be reasonably sure that $i won’t be used outside the loop. Once you get past done, you can let it go. Yes, it still exists, and it’s not illegal to use $i in the finalization code, but a well-meaning author won’t do that.

    Which leads to a lesson to be learned from this: limit the number of variables that are used in any given chunk of code. You don’t want to have to remember some variable five pages away. To do this, try to break your code down into independent modules. These can be functions, classes, even just paragraph-sized chunks in some function. Ideally, you want your reader to be able to close the chapter, forget most of the details, and move on to the next bit.

    In the same vein, this illustrates one reason global variables are frowned upon: they can potentially be accessed from anywhere in the code, which means that they never really disappear and can’t be completely ignored.

    Why Can’t I Subscribe to an Address Card?

    The other day, I was talking to an old friend and doing that annoying ritual where I told her all of the phone numbers and email addresses I had for her, and she told me which ones were out of date and which ones I was missing. And I wondered why there’s not a better way of doing this. Especially when it’s so simple.

    For those who don’t know: when you make an appointment to take your car to the garage and the web site allows you to add it to your calendar, or when your doctor emails you a reminder for your upcoming exam that you can click and add to your calendar, you’re downloading an iCalendar file. This is a file format for describing calendar events. All major calendar tools support it. It’s a well-known, widely-supported standard file type.

    You can also subscribe to a calendar: your school or community center can publish a calendar of events simply by publishing an iCalendar file on their web site. Then your desktop calendar program can check the calendar’s URL once an hour or whatever, and show you the events.

    Now, there’s another file type for contacts, called vCard or VCF. Where iCalendar is for appointments, vCard is for contacts: you can store a person’s name, addresses, job title, phone numbers, web site, and so on and so forth. Tools like Google Contacts allow you to export some or all of your contacts in vCard format because it’s so widely-supported.

    Which brings up the obvious question I asked above: why can’t I subscribe to an address card the same way I subscribe to a calendar? My friend could simply have put her iCalendar file on a web site somewhere, and my address book utility could check the URL once a day or so to see whether she changed her phone number or postal address, or added a Discord account or something.

    So… why?

    The Triumph of Looks over Function

    Back when the Macintosh first came out, in the 1980s, it was presented as a more user-friendly alternatives to PCs running MS-DOS: it had a mouse that you could point with, and a graphical interface. Instead of memorizing commands and reading cryptic error messages, you could click on icons, or explore menus to see what was available.

    Secondarily, Apple products have always been sleek. The iPod may have just been a microprocessor glued to a hard drive, it certainly looked attractive. Especially lately, any Apple product, be it server, desktop, wearable, or software, is sleek and uncluttered.

    But lately, Apple seems to have gone all in on sleek design at the expense of usability. They used to be a leader in usability and now, a lot of their design choices are just… bad.

    The latest example I ran across is in the Activity Monitor. The top of the window looks like:
    OSX Activity Monitor window

    The “x” in an octagon is a button to stop the currently-selected process. That’s pretty useful. Now, what if you don’t see the process you want to kill, but you know what it’s called? There’s a handy search tool. Let’s click on that:
    OSX Activity Monitor window with search button selected

    Now I can search for a process, but where did the buttons and tabs go? It’s not as though there isn’t space for any of them: when you open the search tool, there’s now a huge blank space next to the search field, that the buttons, at least, can easily fit into.

    But okay, you search for, and find, the process you want to kill, and highlight it:
    Activity Monitor with selected process and menu

    Aha. It turns out that that chevron was actually a menu button. And there’s our “Stop”. Except that originally, we saw an octagonal icon, and now we see a word. There’s nothing on the screen to indicate that the icon and the menu entry are the same thing, and that’s just poor design.

    I keep noticing this sort of thing more and more with Apple products, and it annoys me. This just happened to be a particularly egregious example.

    I’m still annoyed at the time I thought my annotations to an MP3 file had been deleted by iTunes. It turned out that the information was there, but beneath the bottom of the window, and iTunes couldn’t be bothered to show me a scroll bar or give any indication that there was more than one windowful of information.

    Staying on Top of the Wave

    I used to work for a computer researcher who didn’t actually use computers. Academics can sometimes be quirky, you know? He just had ~/.forward set up to print every message (on paper) as it came in. One problem with this setup was that people would send him résumés as PostScript (and later PDF) attachments. The printing system would print these out as plain text and use up all of the paper in the printer if someone didn’t catch it.

    This raised a question for someone:

    and I realized that the nightmare that printing under Unix is rather less nightmarish these days. The ubiquity of PDF means that I don’t really have to worry about converting files to the proper device-dependent format. Line printers are gone, so I don’t have to worry about the difference between printing text and printing graphics. Unicode means I don’t have to worry about whether a document is in English, French, or Russian.

    Of course, all of this convenience comes at a cost. For instance, Unicode is a complex soup of characters, codepoints, encodings, and normal forms. When I was learning C, way back when, in between mammoth hunts and rubbing sticks together to make fire, everything was US English, in ASCII, and a letter was a character was a byte was an octet.

    This may have been limited, but at least it made things easy to learn. Which made me wonder about people wading into the field these days: how do they learn, when even a simple “Hello world” program has all this complexity behind it?

    There are two answers to that: in some cases, say Unity or Electron, tutorials will typically give you a bunch of standard scaffolding — headers, includes, starter classes — and say “Don’t worry about all that for now; we’ll cover it later.” In other cases, say, Python, a lot of the complexity is optional enough that it doesn’t need to be shown to the beginner.

    XKCD cartoon of a jumble of blocks, representing software packages, piled precariously upon each other, as in a dependency diagram. A caption at the top describes the delicate edifice as "All modern digital infrastructure". An arrow points to a lone package that nearly everything depends on, off in a corner; the label says, "A project some random person in Nebraska has been thanklessly maintaining since 2003".

    New people are coming in at the top of this graph. I came in a bit further down, but my entry point was already on top of a bunch of existing work by other people. After all, I got to use (complicated) operating systems instead of running code on bare metal, text editors rather than toggling my code in on the front panel, and much besides. People starting out today are wading in in the middle, just like I did, just at a different point.

    And this is what we humans do. When Isaac Newton talked about standing on the shoulders of giants, this is what he was talking about. We build tools using existing tools, and then use those new tools to build newer tools, changing the world as we go.

    Of course, new technology can also disrupt and undermine the old way of doing things, and there’s a persistent fear of AI taking away jobs that used to be done by humans, just as automation has. Just as dockworkers now use forklifts to load cargo rather than carry it themselves, companies now use chatbots to handle the front line of customer support. Machines have largely supplanted travel agents, and have even started writing press releases. What’s a poor meat puppet to do?

    I keep thinking of how longshoremen became forklift operators: when new technology comes along, we still need to control it, steer it, decide what it ought to do. I used to install Unix on individual computers from CD, one at a time. These days, I use tools like Terraform and Puppet to orchestrate dozens or hundreds of machines. And I think that’s where the challenge is going to be in the future: staying on top of new technology and deciding what to do with it.

    What the Hell Is Up With MacOS Periodic Jobs?

    Yesterday, Feb. 25 at 13:19, my Mac ran periodic monthly. I thought it odd that this would run on the 25th rather than the 1st of the month, and in the afternoon rather than late at night, so I dug a little deeper.

    It looks as though Apple now deprecates cron in favor of launchd agents. Okay, fine. Yeah, I see that there are three periodic jobs:

    > launchctl list | grep periodic-
    -	-9
    13804	0
    -	-9

    launchctl print system/ shows details about the monthly job:

    event triggers = {
   => {
                    keepalive = 0
                    service =
                    descriptor = {
                            "Repeating" => true
                            "GracePeriod" => 14400
                            "Interval" => 2629746

    Nowhere does it say to run this job at a particular time on a particular day. Rather, as far as I can tell, it wants to run every 2629746 seconds. What’s that?

    launchctl print system/ shows

    "Interval" => 86400

    which makes perfect sense, since 86400 is 60 × 60 × 24, the number of seconds in a day. And runs every 60 × 60 × 24 × 7 = 604800 seconds.

    But 2629746, the monthly interval, is 43829.1 minutes = 730.485 hours = 30.4368 days. What the hell is that?

    I note that the average month length in a year is 365/12 = 30.4166 days, which is close. And what with leap years, the average year is really 365.25 days long; 365.25/12 = 30.4375, which is close to the periodic-monthly interval. So maybe Apple took the length of the average century, when all leap days, century non-leap days, and millennial non-non-leap days are taken into account, and divided by the number of months in a century? Or something else? Who knows?

    Maybe Apple has decided that it doesn’t matter when accounting and log-rotation jobs run, and that it’s okay for them to drift. Fine. Except that the simplest and easiest documented way of adding your own periodic jobs is to add a file to /etc/periodic/daily, /etc/periodic/weekly, or /etc/periodic/monthly. And people might want resource-intensive cleanup jobs to run in the middle of the night, and for reports to run on the first of the month. So what the hell, Apple?

    Ansible: Roles, Role Dependencies, and Variables

    I just spent some time banging my head against Ansible, and thought I’d share in case anyone else runs across it:

    I have a Firefox role that allows you to define a Firefox profile with various plugins, config settings, and the like. And I have a work-from-home (WFH) role that, among other things, sets up a couple of work profiles in Firefox, with certain proxy settings and plugins. I did this the way the documentation says to:

      - name: Profile Work 1
        role: firefox
          - profile: work1
              - ublock-origin
              - privacy-badger17
              - solarize-fox
            prefs: >-
              network.proxy.http: '""'
              network.proxy.http_port: 1234
      - name: Profile Work 2
        role: firefox
          - profile: work2
              - ublock-origin
              - privacy-badger17
              - solarized-light
            prefs: >-
              network.proxy.http: '""'
              network.proxy.http_port: 1234

    The WFH stuff worked fine at first, but then I added a new profile.

    - name: Roles
      hosts: my-host
        - role: wfh
        - role: firefox
          profile: third
            - bitwarden-password-manager
            - some fancy-theme

    This one didn’t have any prefs, but Ansible was applying the prefs from the WFH role.

    Eventually, I found that the problem lay in the two vars blocks in the wfh role’s dependencies: apparently those get set as variables for the entire task or play, not just for that invocation of the firefox role. The solution turned out to be undocumented: drop the vars blocks and pull the role parameters up a level:

      - name: Profile Work 1
        role: firefox
        profile: work1
          - ublock-origin
          - privacy-badger17
          - solarize-fox
        prefs: >-
          network.proxy.http: '""'
          network.proxy.http_port: 1234
      - name: Profile Work 2
        role: firefox
        profile: work2
          - ublock-origin
          - privacy-badger17
          - solarized-light
        prefs: >-
          network.proxy.http: '""'
          network.proxy.http_port: 1234

    I do like Ansible, but it’s full of fiddly stupid crap like this.

    Recursive grepping

    Sometimes you just need to grep recursively in a directory. If you’re using find $somedir -type f -exec grep $somestring {} \;, don’t:

    Use xargs to avoid creating a bazillion grep processes:
    find $somedir -type f -print | xargs grep $somestring

    But spaces in the output of find (i.e., spaces in filenames) will confuse xargs, so use -print0 and xargs -0 instead:
    find $somedir -type f -print0 | xargs -0 grep $somestring

    Except that you can achieve the same effect with find, with \+:
    find $somedir -type f -exec grep $somestring {} \+

    Or you can just use recursive grep:
    grep -r $somestring $somedir
    except that find allows you to filter by file type, name, age, etc.