Bash Completion For Pandoc Is Built In

This is more in the way of a note to myself. I was just starting to write a bash completion script for Pandoc when I came upon this  in the Pandoc documentation:

--bash-completion

Generate a bash completion script. To enable bash completion with pandoc, add this to your .bashrc:

 eval "$(pandoc --bash-completion)"

 

So no need for me to write one. Neat trick, generate your own bash completion script. John McFarlane really is a god. Oh, and the completion is top quality, it knows when you’ve typed an option that takes an input or output format and completes on those and other little tricks. I may end up using some of his tricks for my completions.

A Little Shell Will Fix It

Last night I went to Lights For The Wild at Taronga Zoo. As usual, I took a lot of photos with my DSLR camera, over 200, though a lot of that number are quite similar as I often take two or three to increase the chances of getting the right shot, sometimes I vary the speed so that one is better exposed.

The camera saves both a RAW file​ and a JPEG so I end up with over 400 images. Looking through them in QuickLook in the Finder can be painful as the RAW images take quite a while to load, then you get the problem that when you have decided which of the three shots you want to keep you also have to delete the matching JPEG or RAW file.

The easiest solution to both of these is to only go through the JPEG files and then delete the matching NEF file (which is what the Mac calls the RAW file).

So I open the folder and sort by ‘Kind’ which puts the JPEGs at the top. I then open the first in QuickLook by hitting space and using the up and down arrow keys to move through the list commanddelete deletes a file and displays the next. Easy.

Now I have 80 JPEG files from the original 240. How to get rid of the NEF files that match the JPEG files I have deleted? A little bash programming to the rescue.


for i in *.NEF ; do
  if [ ! -e `basename $i NEF`JPG ]; then 
    rm $i; 
  fi 
done

The secret to this is the basename utility. It’s a neat little tool. Pass it a full file path such as /Users/tonyw/Documents/UselessRamblings.txt and it will return just
the file name without the path, UselessRamblings.txt. It has a matching tool, dirname which returns just the path portion. As you can see from my code basename has another trick, it will happily strip the suffix from the filename if you tell it what to strip.

More Tools For Building Tools

I’m working on more bash completions. This time for some of the command line tools Apple provides for sysadmins.

I decided there had to be a way to get a list of the options from the man page for a tool. After all they are all in there.

So I built a command line piece by piece. As an example let’s get a list of the options (with some caveats) for the tool pkgbuild. We start with man pkgbuild | col -b , the col -b step takes out the special characters man uses to show bold on screen. Now find all lines containing -- with grep, I liked grep -e '--'. If you have a look at the output of that we are getting close.

Next I decided to use sed to do a find and replace for the option itself. After some playing around I ended up with sed -e 's#.*\(--[a-zA-Z-]*\).*$#\1#' An important note for young players, it did take some time and a few tries to get that substitution just right. Don’t be afraid and remember Google (and Stack Exchange) are your friends.

First, I should point out an old Unix hand’s trick. Most of the time you see sed substitution commands using / as the separator but sed can use anything but \ or newline – it uses the first character it sees after the ‘s’. I usually use # as it makes the \ used for special characters easier to spot and the string easier to read.

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Now We Have bash Completion For Munki

I’m on a roll. I’ve written the bash completions for Munki.

(tl;dr The completions are on Github )

It’s getting easier to write them. There was one little trick I used that I didn’t
mention in my last post that I thought I’d share. How to use find and replace with
regular expressions to generate some of your code.

For this I use Find... in BBEdit. I started with a list of the commands, one on each
line.

The first thing we need to do is generate a string with each command separated by
a space. This one is trivial. We just find \n and replace it with ` `. The second one is the
hardest. We want each of the switches in the case statement like this:

	repo-add) _autopkg_repo-add ;; 
	repo-delete) _autopkg_repo-delete ;; 
	repo-list) _autopkg_list_processors ;; 
	repo-update) _autopkg_repo-update ;;

when we start with:

repo-add
repo-delete
repo-list
repo-update

The “Find” is the easy part. We want to match everything on a line up to, but not
including, the newline at the end. This looks like (.*)\n – the parentheses define the
part we want to match. Now for the replace – we want a tab, then the name, then a
parenthesis and so on. You can see we need to insert the name into a template twice.
This ends up as \t\1) _autopkg_\1 ;;\n – the \1 means “the first match in the Find”.

So I just enter those into the dialog and hit “Replace All” and the list of commands is
changed into the required bash code. After pasting the result into my script I can
hit “Undo” and the list is back ready for me to use it again. I can even generate
boilerplate code using a different replace:

_autopkg_\1() {
  local cur="${COMP_WORDS[COMP_CWORD]}"
  case "$cur" in
    --*)
      __autopkgcomp "--help ****"
      return
      ;;
  esac
}

The advantage of doing things this way is not just less typing. By generating the code
I can be sure that the switches and the function names are correct and match
each other. (BTW – notice that I have a **** in the boilerplate. This marks where I
need to alter the function and also marks it as not finished.)

Many years ago I was tutored by two of Brain Kernighan’s books – ‘Software Tools’ and
‘The Unix Programming Environment’ and this is exactly the sort of thing he evangelised.
If you can use a tool to write your code, all the better.

bash completion for autopkg

Over the weekend I was feeling a little bored so I decided to try my hand at writing a shell script to add custom completion for autopkg to bash.

(tl;dr – the script is on GitHub.)

I found an example for the zsh shell which lacked a couple of features and I spent some time examining the script for brew so I wasn’t totally in the dark.

There are a number of tutorials available for writing them but none are particularly detailed so that wasn’t much help.

Writing Shell Scripts

The first thing I should say is that I find writing shell scripts totally different to writing for any other language. I probably write shell scripts incredibly old school, shell and C were the two languages I was paid to write way back in the 1980’s. It feels like coming home.

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Containers Rock! Why I’m A Docker Fan

Docker for the Macintosh has recently emerged from beta and I’m ecstatic.

Docker implements a way of walling off a piece of software from the underlying operating system using a tech they call “containers”.

This is an absolute godsend for deploying services. One of the problems in system administration is the cost and complexity of spinning up a new service and then removing it from a computer once it is no longer required.

Software when it is installed and run can spray pieces of itself all over the computer’s file system and getting it out again is difficult.

Previously we have used virtual machines to isolate this problem. That has it’s own costs, a virtual machine means you are running (at least) two complete operating systems on the hardware. It also has a cost in memory and hard disk space.

Containers lower the cost considerably. They have all the advantages of virtual machines but share the operating system kernel with each other and the underlying OS. This makes them smaller and consuming considerably less resources than virtual machines. This also makes them quicker to download and deploy.

Since Docker is open source it means that there is now a huge community around it. Docker containers are easily available for a huge range of applications, a quick visit to Dockerhub will show you how large.

Docker containers may well be the holy grail of app deployment. They certainly tick all the boxes system administrators require.

Using Docker

So how easy is it to use? Installing it is trivial, just download the install package and copy the Docker application to your Applications folder. You might also want to download
Kitematic which provides a GUI interface to Docker, it also just requires downloading and copying the app to your Applications folder. It is just as easily installed on a Linux box.

You can also install bash completion for docker with this

curl -XGET https://raw.githubusercontent.com/docker/docker/master/contrib/completion/bash/docker > brew --prefix/etc/bash_completion.d/docker

I wish I could tell you how easy it is to build a Docker container from scratch but every time I searched DockerHub for a container I wanted someone else had already built it, or built a large chunk of it.

As an example, I wanted a container running Python 3, Jupyter and the add-on for bash notebooks. Sure, I could have built it from scratch but Continuum, the Anaconda people, already have a Docker container with Python 3 and Jupyter (along with a bunch of other useful Python libraries) installed so :-

docker run -it continuumio/anaconda3 /bin/bash

which will download and run the Python 3 version of Anaconda in a container. Then when the container runs (the -it makes it an interactive container) :-

pip install bash_kernel
python -m bash_kernel.install

then exit the container and at the terminal prompt

docker ps -a
docker commit <container_name> tonyw/jupyter

The ps -a lists all the containers so I know which one to commit and the commit saves the changed container with (optionally) a new name. Now we can run the new container.

docker -d -p 8888:8888 -v /Users:/Users -rm tonyw/jupyter 
 jupyter notebook --ip='*' --port=8888 
 --notebook-dir /Users/tonyw/dev/Notebooks 
 --no-browser

This runs the Docker container in ‘daemon’ mode and when the container starts runs the command at the end, in this case Jupyter in notebook mode.

Of course if I just want to run Python 3.5 instead of Jupyter I can always replace the -d with -it and the jupyter command with bash and I get a shell in the container.

Docker Magic

Now all the Docker gurus out there are screaming at me that I should use a Dockerfile to build my custom container and define all sorts of magical stuff like the default command to run when the container starts and the working directory and all the rest so I didn’t need them all in my long command line. Frankly, while that would probably be a good idea I haven’t quite managed to learn how to do all that automated magic and it almost seems like too much work.

Perhaps for my next blog post.

Further Reading

Macadmins Dockerhub
Pepijn Bruienne’s talk on Docker from PSU MacAdmins 2015

BBEdit Really Doesn’t Suck

Recently, with version 11, BBEdit introduced a demo mode so I thought to take another look at the big brother of TextWrangler. I have to say BareBones Software’s tag line for BBEdit is true “BBEdit – It doesn’t suck!”.

There are two tasks that I use an editor for, writing Python and writing Markdown so those are the two that I looked at.

There are a number of things you can do to improve BBEdit as a Python IDE. The first is to install Dash. This is a brilliant tool for searching documentation sets and can be easily searched from BBEdit. Just select a library call and choose “Find In Reference…” under the Search menu and BBEdit will pass the search to Dash. Dash will search across all your documentation sets but it is easy to set the sort order so the Python entries are close to the top and in the Dash results window there is a little Python icon next to the Python results.

The other neat item under the Search menu is “Find Definition”, this will find where in your file a function is defined – useful if you have a long source file.

But how does that work if our project is in multiple source files? Well, Unix has long known of that problem and had a solution. It’s a tags file, first used in vi. This is a file that lists all the function definitions and variables used in all the files in a directory tree. Not only can BBEdit use a tags file but it can (using the open source utility cats) generate them. At the top of your project directory tree, on the command line bbedit --maketags will generate a tags file and now “Find Definition” will work across all the Python files in the tree.

BBEdit can also run a syntax check across your source. You will find “Check Syntax under the ”#!“ menu which also allows you to run your Python code. The final entry in this menu ”Show Module Documentation” displays a new text window with the output from running pydoc across your file. I love this, it encourages me to properly document my code as I write with pydoc strings for each function. The output is extremely useful as a memory aide for large programs and modules.

Next up is running a lint across our Python source. BBEdit comes with another command line tool, bbresults which turns formatted error output from Unix command-line tools into a BBEdit results windows. This is an exceptionally neat trick. At the command line flake8 example.py | bbresults will give you a window in BBEdit with each of the errors and warnings listed and a click on one will take you to the exact spot in your source. If you don’t have flake8 installed then you can install it with conda or pip.

By the way, this works because the bbedit and bbresults command line tools understand the +n argument syntax for going to line n in a file. Sublime Text and other editors on the Mac could learn this.

A final tip for programmers, BBEdit recommends setting the $EDITOR shell variable to bbedit -w where the -w flag has the bbedit command line tool wait till you close the window before exiting. If you add the --resume flag as well then when you close the window in BBEdit it will return the Terminal to the front. Exceptionally handy.

Markdown

One complaint I would make, and I make it about a number of editors, is that the Markdown syntax highlighting is on the stupid side. This is generally due to the flaws in using nothing but regular expressions to do the highlighting. The most obvious flaw is that underlines in such things as a URL will trigger highlighting for italics.

If you want you can “lint” your prose using proselint and bbresults. Personally I find proselint rarely throws up something I actually want to change but your mileage might vary, it’s a good tool for looking at prose text.

BBEdit has no special facilities for writing Markdown such as inserting the codes for text styles or formatting but it does have the ability to use “Clippings”, a short piece of text, and clippings can be kept in sets and a clipping can have a keyboard shortcut. I don’t use it, I have a few Keyboard Maestro macros for such things as web links and otherwise just type the few extra keystrokes.

BBEdit also has “Text Filters”, which allow you to run the current selection through a script. For Markdown I have one that turns tab separated text into a Markdown table, incredibly useful for tables copied from a spreadsheet. Not sure where I got it but I suspect it was from Brett Terpstra’s blog.

BBEdit is a good editor, well worth the $50 purchase price and has a number of advantages over it’s free little brother TextWrangler. As both a general purpose editor and an editor for programming I’d have to say that it is the best editor available on the Mac at the moment though Sublime Text comes close.