Elixir scripting (.exs, not escript)

Every year I help my friend with his taxes, he has an itinerary of places that he’s been to for work and I scrape the google maps API to get driving distances. This year I did it in elixir. The major challenge is figuring out how to load external libraries (CSV, JSON) into an .exs script (no framework). Mix isn’t like python-pip (and that’s a really good thing TM) but every once in a while you just want it to do what you want it to. I can’t say that what I did is necessary “best practice”, but after a lot of hemming and hawwing, I figured out a reasonable solution. I’m leaving it here to hopefully help/inspire other people that need to do something quick 'n dirty.:

#  fail early if no filename is provided.
[filename] = System.argv()
File.exists?(filename) || raise "bad filename."
file_root = Path.basename(filename, ".csv")

#  before running, install jason and csv.
#  mix archive.install hex jason 1.1.2
#  mix archive.install hex csv 2.3.1
#  mix archive.install hex parallel_stream 1.0.6

# load up all of the libraries.
~w(jason 1.1.2 csv 2.3.1 parallel_stream 1.0.6)
|> Enum.chunk_every(2)
|> Enum.map(fn [lib, ver] -> "~/.mix/archives/#{lib}-#{ver}/#{lib}-#{ver}/ebin" end)
|> Enum.map(&Path.expand/1)
|> Enum.map(&Code.prepend_path/1)

# make sure the libraries are there.

# marshall the address into a dict.
addresses = "addresses.csv"
|> File.stream!
|> CSV.decode!
|> Enum.map(&List.to_tuple/1)
|> Enum.into(%{})

# read the paths.
driving_lines = filename
|> File.stream!
|> CSV.decode!

# check that they are all kosher
|> Stream.with_index
|> Enum.each(fn
  {_, 0} -> :ok
  {[_, start_name, dest_name | _], line} ->
    :erlang.is_map_key(start_name, addresses) || raise "bad line #{line + 1}, #{start_name}"
    :erlang.is_map_key(dest_name, addresses)  || raise "bad line #{line + 1}, #{dest_name}"
  _ -> :ok

# this time I will remember to deactivate this API key
# generate the curl query  Mostly just using google's API.
curl_query = fn start_addr, dest_addr ->
  start_http = Regex.replace(~r/\s/, start_addr, "+")
  dest_http  = Regex.replace(~r/\s/, dest_addr, "+")

{rows, _} = driving_lines
|> Stream.reject(fn [_, a, b | _] -> a == "" || b == "" end)  # get rid of empty lines.
|> Stream.with_index
|> Enum.map_reduce(%{}, fn
  # ignore the first line, which is just for fun titles.
  {line, 0}, acc -> {line, acc}

  # if our start and destination are cached, then use that instead.
  {[r, start_name, dest_name | _], _}, acc when
      :erlang.is_map_key({start_name, dest_name}, acc) ->

    start_addr = addresses[start_name]
    dest_addr = addresses[dest_name]
    {[r, start_addr, dest_addr, acc[{start_name, dest_name}]], acc}

  {[r, start_name, dest_name | _], _}, acc ->
    # dereference the stard and destination addresses from our dictionary.
    start_addr = addresses[start_name]
    dest_addr  = addresses[dest_name]

    # run the curl command
    {res, _} = System.cmd("curl", ["--stderr", "/dev/null", curl_query.(start_addr, dest_addr)])

    # destructure google's insane JSON here.
    v = case Jason.decode!(res) do
      %{"rows" => [%{"elements" => [%{"distance" => %{"text" => distance}}]}]} ->
        # of course the string has "mi" attached to it.  Strip it out.
        {v, _} = Float.parse(distance); v
      _ -> "?"

    # put the line back together, this time with full addresses and distances for the IRS.
    # cache the result into our accumulator map.
    {[r, start_addr, dest_addr, v], Map.put(acc, {start_name, dest_name}, v)}

  # lines which don't conform to our dogma get released
  {line, _}, acc -> {line, acc}

# encode back into CSV.
|> CSV.encode
|> Stream.into(File.stream!(file_root <> "-finished.csv"))
|> Stream.run

You can put .exs files in a mix project and run them using mix run script.exs. That’ll start the script with all dependencies of the mix project present.


who’s got time to make a mix project =D


Is this a joke?

mix new your_project is all it takes.

Also you can put a shebang in the file, chmod a+rx <yourfile> and just run it standalone like a bash script (without the dependencies).

#!/usr/bin/env elixir

1 Like

Please do not do that! That can cause a lot of nasty to debug errors when you happen to develop an application that has direct or transient dependencies to one of this packages!

The proper way is to create a mix project, specify dependencies and compile it into an escript!

I prefer this way:

[jason: "1.1.2", csv: "2.3.1", parallel_stream: "1.0.6"]
|> Enum.map(fn {lib, vsn} -> "~/.mix/archives/#{lib}-#{vsn}/#{lib}-#{vsn}/ebin" end)
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Yeah escript is a better option.

1 Like