In the shell I find a marvelous mess of constellations, nebulae, interstellar gaps, awesome gullies, that provokes in me an indescribable sense of vertigo, as if I am hanging from earth upside down on the brink of infinite space, with terrestrial gravity still holding me by the heels but about to release me any moment.

Nancy Mauro-Flude, 2008

The shell is a computer programme which launches other programmes. This efficient, textual method of interacting with a computer raises practical and ethical questions. On a practical level the question arises as to which shell to choose from. bash is the default login shell on linux distributions such as Debian and Rasbian. However, it is possible to choose a different shell. This choice leads to a discussion of the ethical issue of accessibility. A feature of this discussion involves unpacking the relationship between norms and defaults. In this wiki page I outline some implications of switching to a shell other than bash by way of several examples. I describe why I have chosen to use one shell, rather than another shell and argue in favour of fish as a default shell.

A Two-Part Syntax Highlighter

Below are two fish scripts, the second works in tandem with the first. The first function, highlight, utilises the sed command to edit HTML snippets generated by Emacs' Org Mode's HTML export backend. The second script works by calling the highlight function several times on the same file. Really this should be a single script, but I cannot figure out how to execute sed this many times in a row...

`higlight.fish`

#! /usr/bin/fish

function highlight -d "Highlight HTML code" -a file

   argparse --name='highlight' 'h/help' -- $argv;
   sed -i 's/<pre/<div/' $argv;
   sed -i 's/<\/pre>/<\/div>/' $argv;
   sed -i 's/style=/style=/' $argv;
   sed -i -E 's/"src src-[[:alpha:]]*"/"font-family: Monospace; background-color: #dbe6f0;"/' $argv;
   sed -i 's/"color:teal"/"color:teal"/' $argv;
   sed -i 's/"color:teal"/"color:teal"/' $argv;
   sed -i 's/"color:green"/"color:green"/' $argv;
   sed -i 's/"color:yellow"/"color:yellow"/' $argv;
   sed -i 's/"color:orange"/"color:orange"/' $argv;
   sed -i 's/"color:olive"/"color:olive"/' $argv;
   sed -i 's/"color:gray"/"color:gray"/' $argv;
   sed -i 's/"color:purple"/"color:purple"/' $argv;

end

The s command in sed language is a shorthand for substitute. s commands are of the form

's/find/replace/'

With the s command, sed queries a text file for the presence of a particular string, or regular expression, and replaces what is found with user defined text. In the above example, classes of HTML elements are restyled with colour to highlight different parts of the script.

`higlight_all.fish`

#! /usr/bin/fish

function highlight_all -d "Call the highlight command several times" -a file

   set -l options (fish_opt -s h -l help)
   argparse --name='highlight_all' 'h/help' -- $argv;
   for n in (seq 1 5);
       highlight $argv;
   end

end

This command calls highlight multiple times to ensure the script runs to completion. I could improve this such that only one script is required. I'm curious as to whether shell scripts can accept user input.