WEBVTT
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Hello all! Welcome to EmacsConf 2021.
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I'm Tom Gillespie.
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Thank you to the organizers for
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all your hard work,
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and for inviting me to
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give this short talk on
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"Org as an executable format".
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The links to the talk page,
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the GitHub page for the project,
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and the package on MELPA
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are listed on the right.
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Let's start with one of the motivating
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use cases for executable Org files.
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Many users keep global configuration
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for Org in an init.el file,
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which works for many workflows.
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However, for reproducible research,
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this is a challenge
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because if an Org file is
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dissociated from the init.el file,
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then often it will no longer
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function as expected.
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One potential solution to this problem
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is to be able to include all of the
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global configuration for Emacs
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and the environment in the Org file itself,
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in which case when you
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go to reuse the Org file,
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it will work as expected.
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What does an executable Org file
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look like in action?
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Here's a demo of an executable Org file
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running in Bash, Dash, Zsh, and PowerShell.
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So, we are currently in Bash,
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and we can run our demo,
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and it will print some stuff,
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and wait for input.
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We can also run it in Dash,
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which is the default for Debian
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and derivatives.
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Same program works as expected.
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Zsh also. And lastly PowerShell,
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if we try to run demo.org itself,
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we see (that) we get an error
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because PowerShell cares
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about file extensions,
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so, if we symlink to ps1,
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then it works as expected,
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and there are ways to alias this,
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so that you can run it as a program
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without the ps1 extension.
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So, how does this work?
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There are three components
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to an executable Org file
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that all need to be present
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in order for this to work.
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Starting from the top of the file,
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we have a shebang block.
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Next we have an Org Babel block
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written in Emacs Lisp,
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which is what we actually saw executing,
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and then there are some
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eval local variables or Elvs
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that are involved in making this
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actually executable.
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Let's start with the shebang block.
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Org syntax does not have support
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for shebang lines.
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However, it supports the shebang block.
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This is because Org comments, blocks,
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keywords, etc. that start with the
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sharp sign have the same syntax as
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comments in POSIX and PowerShell.
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This block is in fact valid
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Bash, Dash, Zsh, PowerShell,
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and maybe some other shells as well.
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In essence what it does is,
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perform some setup
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to avoid polluting standard output,
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and then it runs Emacs
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to load the file itself.
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The Elisp that is passed on the command line
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is explicated over here on the right,
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and in essence what it does is,
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to keep the startup time minimal
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and as low as possible,
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it loads the absolute bare minimum
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needed for Babel,
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and then it calls hack-local-variables
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triggering the eval-local-variables.
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What do the eval-local-variables do,
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and how those work?
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The essence of the approach is to
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use org-confirm-babel-evaluate
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to allow Babel execution.
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We can't set it to nil because that is
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an arbitrary code execution vector,
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which we don't want if we're sharing files.
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Instead what we do is,
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we use the fact that it can be a function,
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and we normalize the block of code,
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we checksum it, and then we check
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that it matches this checksum up here
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at the top of the file,
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and then sort of inside there,
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inside of org-sbe,
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which is Org source block evaluate,
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we call the block.
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The actual implementation of this
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is somewhat more complicated.
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However, it's small enough to fit in
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the local variables at the end of the file.
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One thing to note is that
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if you are using PowerShell,
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PowerShell parses the whole file
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which means that
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for any normal Org content,
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you need to put it in
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a multi-line PowerShell comment,
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and close it.
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So, once we hit
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hack-local-variables at the end,
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we run the eval-local-variables block,
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then we enter this Elisp block,
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and you can write whatever you want.
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All the power of Org Babel is
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now at your fingertips
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in order to do what you need
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for this file.
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Finally, let's do a quick demo
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of how to use this to make
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your own Org files executable.
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Orgstrap is available on MELPA as mentioned,
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and it can be installed using package.el
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by calling package-install orgstrap.
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It will download, and it will install.
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Then you can open an existing file
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or a new file. In this case,
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let me open a file called example.org.
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And then orgstrap provides
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command called orgstrap-init.
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What orgstrap-init does is,
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it populates a file with the machinery
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needed to run an orgstrap block.
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We're just going to do a message
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"hello orgstrap!".
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If you look up at the top,
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you will see that the
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orgstrap-block-checksum will change
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when I save the file.
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This makes it much easier to author files
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with orgstrap blocks.
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And then we need one last piece
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of machinery,
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which is the shebang block.
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I am just going to steal
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the shebang block from
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this other file over here
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since it is available.
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You can also get it from shebang.org,
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and I have plans to add a command
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to insert this into the file directly,
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which may actually be done by the time
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this video is actually posted and visible.
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There's one last step,
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which is that we need to run dired
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in order to… There we go.
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So, we use Shift m, capital m,
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in order to make our
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example file executable,
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and then if we come back to here,
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we see that example.org is now executable,
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and we can run it.
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"hello orgstrap!", and we're done.
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So, that's the basic workflow
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for getting orgstrap files
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to be executable.
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I will be around to answer questions live,
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and I will be also available in
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the #emacsconf IRC channel all day.
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I hope you have found this useful,
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and thank you very much for watching.
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[captions by bhavin192 (Bhavin Gandhi)]
