I spent a frustrating couple of days earlier this week while preparing a presentation for my local .Net user group NE Bytes on Azure Machine Learning.

I was using a technique I've used before to avoid PowerPoint or Keynote and just create slides with simple html using reveal.js. Basically, I use the functionality provided by Github Pages to generate a little static website that then serves up the slides. All that's needed is to set up a github repository, create a "gh-pages" branch and check in individual slides as discrete .html files, ordered by an imaginary date that jekyll understands.

The data prefix is meant to be used to identify blog post dates but works well for ordering slides as well. For example, the first slide in the deck is given the prefix 2016-01-01-first.html and the end slide could be 2016-12-31-last.html, so you could create slides at will and reorder them just by changing the date prefixes relative to each other.

My frustration came in when creating the slides on a Windows machine with a local jekyll install I could proceed through all the slides end to end with no problem. When I checked out the repo on my mac I could only get about 25 slides! The slide generation code was no different but jekyll on the mac (and on the live github pages on github.com) seemed to stop after a certain number.

I know jekyll can be a little bit flaky with file content and unusual characters so I spent a good deal of time checking the slide content for rogue values and trying to move slides around but to no avail. After a little consideration, it actually became obvious once I looked at the date prefixes again. All the working slides were before the current date and any that weren't included were dated in the "future"; jekyll won't process "future" files!

At this point I had something like 50 files/slides so I didn't fancy renumbering them by hand and with the deadline of the talk looming. Luckily, I remembered my old friend PowerShell and the implementation took a minute or two and saved me a lot of stress.

Get-ChildItem -Path .\_posts\*.html | Rename-Item -NewName { $_.name -Replace "2016-", "2015-" }

Jekyll is quite happy for all the dates to be in the past so changing all the dates from 2016 to 2015 took the problem away and I could concentrate on the content I wanted to present.

I got the talk completed and it was well received on the night, lots of good questions, thoughtful comments and good discussion of some of the underlying issues.