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---
title: "Keep Markdown Links in Order With mdrenum"
date: 2023-11-14T22:06:48-05:00
draft: false
references:
- title: "Tidying Markdown reference links - All this"
url: https://leancrew.com/all-this/2012/09/tidying-markdown-reference-links/
date: 2023-11-15T03:08:29Z
file: leancrew-com-7l5uqs.txt
---
I write all these posts in Markdown, and I tend to include a lot of links. I use numbered [reference-style links][1] and I like the numbers to be in sequential order. ([Here's the source of this post][2] to see what I mean.) I wrote a [Ruby script][3] to automate the process of renumbering links when I add a new one, and as mentioned in [last month's dispatch][4], I spent some time iterating on it to work with some new posts containing code blocks that I'd imported into my [Elsewhere][5] section.
[1]: https://www.markdownguide.org/basic-syntax/#reference-style-links
[2]: https://github.com/dce/davideisinger.com/blob/main/content/journal/keep-markdown-links-in-order-with-mdrenum/index.md?plain=1
[3]: https://github.com/dce/davideisinger.com/blob/a2da87fee76fed027b389fcdeb449ad7aa4b6c6d/bin/renumber
[4]: /journal/dispatch-9-november-2023/
[5]: /elsewhere
<!--more-->
As I was working on the script, it was pretty easy to think of cases in which it would fail -- it can handle fenced code blocks, for example, but not ones set off by spaces. I thought it'd be cool to build something in Go that uses a proper Markdown parser instead of regular expressions. This might strike you as an esoteric undertaking, but as [Dr. Drang put it][6] when he embarked on a similar journey:
> But there is an attraction to putting everything in apple pie order, even when no one but me will ever see it.
[6]: https://leancrew.com/all-this/2012/09/tidying-markdown-reference-links/
## First Attempts with Go
My very first attempt involved the [`gomarkdown`][7] package. It was super straightforward to turn a Markdown document into an <abbr title="abstract syntax tree">AST</abbr>, but after an hour or so of investigation, it was pretty clear that I wasn't going to be able to get the original text and position of the links. I switched over to [`goldmark`][8], which is what this website uses to turn Markdown into HTML. This seemed a lot more promising -- it has functions for retrieving the content of nodes, as well as `start` and `stop` attributes that indicate position in the original text. I thought I had it nailed, but as I started writing tests, I realized there were certain cases where I couldn't perfectly locate the links -- two links smashed right up against one another, as an example. I spent a long time trying to come up with something that covered all the weird edge cases, but eventually gave up in frustration.
[7]: https://pkg.go.dev/github.com/gomarkdown/markdown/ast
[8]: https://github.com/yuin/goldmark
Both of these libraries are built to take Markdown, parse it, and turn it into HTML. That's fine, that's what Markdown is for, but for my use case, they came up short. I briefly considered forking `goldmark` to add the functionality I needed, but instead decided to look elsewhere.
## A Promising JavaScript Library
I searched for generic Markdown/AST libraries just to see what else was out there, and a [helpful Stackoverflow comment][9] led me to [`mdast-util-from-markdown`][10], a JavaScript library for working with Markdown without a specific output format. I pulled it down and ran the example code, and it was immediately obvious that it would provide the data I needed.
[9]: https://stackoverflow.com/a/74062924
[10]: https://github.com/syntax-tree/mdast-util-from-markdown
But now I had a new problem: I like JavaScript (and especially TypeScript) just fine, but I find the ecosystem around it bewildering, and furthermore, most of it is tailored for delivering complex functionality to browsers, not distributing simple command-line programs. I even went so far as to investigate using AI to convert the JS code to Go; the [solution][11] I found has some pretty severe character limitations, but I wonder if seamlessly converting code written in one language to another will be a thing in five years.
[11]: https://www.codeconvert.ai/typescript-to-golang-converter
## New JS Runtimes to the Rescue
On a whim, I decided to check out [Deno][12], a newer alternative to Node.js for server-side JS. Turns out it has the ability to [compile JS into standalone executables][13]. I downloaded it and ran it against the example code, and it worked! I got a (rather large) executable with the same output as running my script with Node. A coworker recommended I check out [Bun][14], which has [a similar compilation feature][15] -- it worked just as well, and the resulting executable was about a third the size as Deno's, so I opted to go with that.
[12]: https://deno.com/
[13]: https://docs.deno.com/runtime/manual/tools/compiler
[14]: https://bun.sh/
[15]: https://bun.sh/docs/bundler/executables
Once I had a working proof-of-concept and a toolchain I was happy with, the rest was all fun; writing recursive functions that work with tree structures to do useful work is extremely my shit ([here's an old post I wrote about _The Little Schemer_][16] along these same lines). I added [Jest][17] and pulled in all my Go tests, as well as [Prettier][18] to stand in for `gofmt`. I wrapped things up earlier this week and published the result, which I've imaginatively called `mdrenum`, to [GitHub][19].
[16]: /elsewhere/the-little-schemer-will-expand-blow-your-mind/
[17]: https://jestjs.io/
[18]: https://prettier.io/
[19]: https://github.com/dce/mdrenum
Bun (compiler) + TypeScript (type checking) + Prettier (code formatting) is a pretty acceptable Go substitute. The resulting executable is big (~45MB, as compared with ~2MB for my Go solution), but, hey, disk space is cheap and this actually works.
## Integrating with Helix
I've been a [happy Helix user][20] for the last several months, and I thought it'd be cool to configure it to automatically renumber links every time I save a Markdown file. [The docs][21] do a pretty good job explaining how to add a language-specific formatter:
[20]: /journal/a-month-with-helix/
[21]: https://docs.helix-editor.com/languages.html#language-configuration
> The formatter for the language, it will take precedence over the lsp when defined. The formatter must be able to take the original file as input from stdin and write the formatted file to stdout
[This was pretty simple to add to the program][22], and then I added the following to `~/.config/helix/languages.toml`:
```toml
[[language]]
name = "markdown"
auto-format = true
formatter = { command = "mdrenum" , args = ["--stdin"] }
```
[22]: https://github.com/dce/mdrenum/blob/main/src/cli.ts#L7-L18
This totally works, and I'll say that it's uniquely satisfying to save a document and see the link numbers get instantly reordered properly.
---
Thanks for coming on this journey with me, and if this seems like a tool that might be useful to you, grab it from [GitHub][19] and open an issue if you have any questions.

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#[1]RSS Feed for ANIAT [2]JSON Feed for ANIAT
[snowman-200.jpg]
[3]And now it’s all this
I just said what I said and it was wrong
Or was taken wrong
[4]Next post [5]Previous post
[6]Tidying Markdown reference links
September 17, 2012 at 9:15 PM by Dr. Drang
Oscar Wilde—who would have been great on Twitter—[7]said “I couldn’t
help it. I can resist everything except temptation.” That’s my excuse
for this post.
Several days ago I got an email from a reader, asking if I knew of a
script that would tidy up [8]Markdown reference links in a document.
She wanted them reordered and renumbered at the end of the document to
match the order in which they appear in the body of the text. I didn’t
know of one^[9]1 and suggested she write it herself and let me know
when it’s done. I’ve been getting progress reports, but her script
isn’t finished yet.
There’s certainly no need to tidy the links up that way. Markdown
doesn’t care what order the reference links appear in or the labels
that are assigned to them. I’ve written dozens of posts in which the
order of the references at the end of the Markdown source were way off
from the order of the links in body. But…
But there is an attraction to putting everything in apple pie order,
even when no one but me will ever see it. Last night I succumbed and
wrote a script to tidy up the links. Sorry, Phaedra.
Here’s an example of a short Markdown document with out-of-order
reference links:
Species and their hybrids, How simply are these facts! How
strange that the pollen of each But we may thus have
[succeeded][2] in selecting so many exceptions to this rule.
but the species would not all the same species living on the
White Mountains, in the arctic regions of that large island.
The exceptions which are now large, and triumphant, and
which are known to every naturalist: scarcely a single
[character][4] in the descendants of the Glacial period,
would have been of use to the plants, have been accumulated
and if, in both regions.
Supposed to be extinct and unknown, form. We have seen that
it yields readily, when subjected as [under confinement][3],
to new and improved varieties will have been much
compressed, we may assume that the species, which are
already present in the ordinary spines serve as a prehensile
or snapping apparatus. Thus every gradation, from animals
with true lungs are descended from a marsupial form), "and
if so, there can be followed by which viscid matter, such as
that of making [slaves][1]. Let it be remembered that
selection may be extended--to the stigma of.
[1]: http://daringfireball.net/markdown/
[2]: http://www.google.com/
[3]: http://docs.python.org/library/index.html
[4]: http://www.kungfugrippe.com/
Note that the references are numbered 1, 2, 3, 4 at the bottom of the
document, but that they appear in the body in the order 2, 4, 3, 1. The
purpose of the script is to change the document to
Species and their hybrids, How simply are these facts! How
strange that the pollen of each But we may thus have
[succeeded][1] in selecting so many exceptions to this rule.
but the species would not all the same species living on the
White Mountains, in the arctic regions of that large island.
The exceptions which are now large, and triumphant, and
which are known to every naturalist: scarcely a single
[character][2] in the descendants of the Glacial period,
would have been of use to the plants, have been accumulated
and if, in both regions.
Supposed to be extinct and unknown, form. We have seen that
it yields readily, when subjected as [under confinement][3],
to new and improved varieties will have been much
compressed, we may assume that the species, which are
already present in the ordinary spines serve as a prehensile
or snapping apparatus. Thus every gradation, from animals
with true lungs are descended from a marsupial form), "and
if so, there can be followed by which viscid matter, such as
that of making [slaves][4]. Let it be remembered that
selection may be extended--to the stigma of.
[1]: http://www.google.com/
[2]: http://docs.python.org/library/index.html
[3]: http://www.kungfugrippe.com/
[4]: http://daringfireball.net/markdown/
Now the links are numbered 1, 2, 3, 4 in both the text and the end
references. The HTML produced when this document is run through a
Markdown processor will be the same as the previous one—the links will
still go to the right places—but the Markdown source looks better.
Here’s the script that does it:
python:
1: #!/usr/bin/python
2:
3: import sys
4: import re
5:
6: '''Read a Markdown file via standard input and tidy its
7: reference links. The reference links will be numbered in
8: the order they appear in the text and placed at the bottom
9: of the file.'''
10:
11: # The regex for finding reference links in the text. Don't find
12: # footnotes by mistake.
13: link = re.compile(r'\[([^\]]+)\]\[([^^\]]+)\]')
14:
15: # The regex for finding the label. Again, don't find footnotes
16: # by mistake.
17: label = re.compile(r'^\[([^^\]]+)\]:\s+(.+)$', re.MULTILINE)
18:
19: def refrepl(m):
20: 'Rewrite reference links with the reordered link numbers.'
21: return '[%s][%d]' % (m.group(1), order.index(m.group(2)) + 1)
22:
23: # Read in the file and find all the links and references.
24: text = sys.stdin.read()
25: links = link.findall(text)
26: labels = dict(label.findall(text))
27:
28: # Determine the order of the links in the text. If a link is used
29: # more than once, its order is its first position.
30: order = []
31: for i in links:
32: if order.count(i[1]) == 0:
33: order.append(i[1])
34:
35: # Make a list of the references in order of appearance.
36: newlabels = [ '[%d]: %s' % (i + 1, labels[j]) for (i, j) in enumerate(order
) ]
37:
38: # Remove the old references and put the new ones at the end of the text.
39: text = label.sub('', text).rstrip() + '\n'*3 + '\n'.join(newlabels)
40:
41: # Rewrite the links with the new reference numbers.
42: text = link.sub(refrepl, text)
43:
44: print text
The regular expressions in Lines 13 and 17 are fairly easy to
understand. The first one looks for the links in the body of the text
and the second looks for the labels.
The key to the script are the four data structures: links, labels,
order, and newlabels. For our example document, links is the list of
tuples
[('succeeded', '2'),
('single character', '4'),
('under confinement', '3'),
('slaves', '1')]
labels is the dictionary
{'1': 'http://daringfireball.net/markdown/',
'3': 'http://docs.python.org/library/index.html',
'2': 'http://www.google.com/',
'4': 'http://www.kungfugrippe.com/'}
order is the list
['2', '4', '3', '1']
and newlabels is the list of strings
['[1]: http://www.google.com/',
'[2]: http://docs.python.org/library/index.html',
'[3]: http://www.kungfugrippe.com/',
'[4]: http://daringfireball.net/markdown/']
links and labels are built via the regex findall method in Lines 25-26.
links is the direct output of the method and maintains the order in
which the links appear in the text. labels is that same output, but
converted to a dictionary. Its order, which we don’t care about, is
lost in the conversion, but it can be used to easily access the URL
from the link label.
order is the order in which the link labels first appear in the text.
The if statement in Line 32 ensures that repeated links don’t overwrite
each other.
newlabels is built from labels and order in Line 36. It’s the list of
labels after the renumbering. Line 39 deletes the original label lines
and puts the new ones at the end of the document.
Finally, Line 42 replaces all the link labels in the body of the text
with the new values. Rather than a replacement string, it uses a simple
replacement function defined in Lines 19-21 to do so.
Barring any bugs I haven’t found yet, this script (or filter) will work
on any Markdown document and can be used either directly from the
command line or through whatever system your text editor uses to call
external scripts. I have it stored in BBEdit’s Text Filters folder
under the name “Tidy Markdown Reference Links.py,” so I can call it
from the Text ‣ Apply Text Filter submenu.
I should mention that although this script is fairly compact and
simple, it didn’t spring from my head fully formed. There were starts
and stops as I figured out which data structures were needed and how
they could be built. Each little subsection of the script was tested as
I went along. The order list was originally a list of tuples; it wasn’t
until I had a working version of the entire script that I realized that
it could be simplified down to a list of link labels. That change
shortened the script by five lines or so and, more importantly,
clarified its logic.
Despite these improvements, the script is hardly foolproof. The
Markdown source of this very post confuses the hell out it. Not only
does it think there are links in the sample document (which you’d
probably guess), it also thinks the [%s][%d] in Line 21 of the script
is a link (and the one in this sentence, too). And why wouldn’t it? To
distinguish between real links and things that look like links in
embedded source code, the script would have to be able to parse
Markdown, not just match a couple of short regular expressions. This is
a variant on what Hamish Sanderson said in the comments on [10]an
earlier post.
At the moment, I’m not willing to sacrifice the simplicity of the Tidy
script to get it to handle weird posts like this one. But if I find
that it fails often with the kind of input I commonly give it, I’ll
have to revisit that decision.
As Wilde also said, “Experience is the name everyone gives to their
mistakes.”
__________________________________________________________________
1. I didn’t think [11]Seth Brown’s formd did that, but [12]this tweet
from Brett Terpsta says I was wrong about that. [13]↩
[14]Next post [15]Previous post
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References
1. https://leancrew.com/all-this/feed/
2. https://leancrew.com/all-this/feed.json
3. https://leancrew.com/all-this/
4. https://leancrew.com/all-this/2012/09/some-kind-of-druid-dudes-lifting-the-veil/
5. https://leancrew.com/all-this/2012/09/implementing-pubsubhubbub/
6. https://leancrew.com/all-this/2012/09/tidying-markdown-reference-links/
7. http://www.gutenberg.org/dirs/etext97/lwfan10h.htm
8. http://daringfireball.net/projects/markdown/syntax#link
9. file:///var/folders/q9/qlz2w5251kzdfgn0np7z2s4c0000gn/T/L97479-6275TMP.html#fn:formd
10. http://www.leancrew.com/all-this/2012/09/applescript-syntax-highlighting-finally/
11. http://www.drbunsen.org/formd-a-markdown-formatting-tool.html
12. https://twitter.com/ttscoff/status/247398632377184256
13. file:///var/folders/q9/qlz2w5251kzdfgn0np7z2s4c0000gn/T/L97479-6275TMP.html#fnref:formd
14. https://leancrew.com/all-this/2012/09/some-kind-of-druid-dudes-lifting-the-veil/
15. https://leancrew.com/all-this/2012/09/implementing-pubsubhubbub/
16. https://leancrew.com/all-this/archive/
17. https://leancrew.com/all-this/feed/
18. https://leancrew.com/all-this/feed.json
19. https://fosstodon.org/@drdrang
20. http://github.com/drdrang
21. http://www.mathjax.org/
22. http://creativecommons.org/licenses/by-sa/3.0/