• Using bashly to create a CLI

    bashly is a command-line application that let’s you generate feature-rich command line tools. The idea is that you specify via a YAML file what subcommands, arguments, flags and environment variables you want for your executable, and bashly takes care of generating all the boilerplate on a bash script, so that you can focus on your code. Many languages support similar via libraries, like optparse in ruby.

    I recently used it to port a series of scripts for personal use that where all part of a series of commands I use to manage my personal note taking. I turned the all those separate scripts into a CLI with subcommands. Instead of zk_title and zk_today, I know have zk title and zk today, among others).

    Here are my observations:

    1. The documentation is well done. In particular the examples showed me how to do everything I needed.
    2. The ability to check for required environment variables was very useful. If only a particular command requires a certain environment variable, that can be configured too.
    3. Reading from stdin or from a file is a very common use case. It’s well supported.
    4. Commands can be aliased to shorter names.
    5. Flag handling is great. Short flags can be combined (i.e. zk title -ps instead of zk title -p -s)
    6. Each command lives in it’s own file. If needed, custom functions that are called from other commands are supported.
    7. Some of my previous commands were written in Ruby. bashly supports heredocs, which make it possible to continue using ruby for portions of your script, albeit this is a bit of a hack and makes the script less portable:
    /usr/bin/env ruby - ${arguments} <<-RUBY
    puts "hello #{ARGV}"

    Note that for heredocs to work, the following environment variable needs to be set BASHLY_TAB_INDENT=1.

    Overall, I was happy with the results. All the boilerplate code like creating global and command --help output, argument and environment variable checking, and flag handling was abstracted away.

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  • The REPL: Issue 101 - January 2023

    CTEs as lookup tables

    Short and sweet. The syntax is nicer to read, and in my mind it fits better with the SQL mental model of relations.

    Ransacking your password reset tokens

    The ransack gem is a popular ruby gem to add searching capabilities to a Rails application. This article describes, compellingly, how ransack by default is open to exploitation and can be used to reveal sensitive information in an application. This process reminds me about how Rails allowed (insecurely) mass-assignment of params, which later was changed to not allow any params, unless specifically permitted. That approach is possible with Ransack, too. For existing applications, it can lead to a lot of allow-listing.

    Anti-Pattern: Iteratively Building a Collection

    It resonates with me that iteratively building an array feels wrong. But why?

    The author states:

    What follows are some lengthy method definitions followed by rewrites that are not only more concise but also more clear in their intentions.

    So… is clarity the key?

    Brevity and clarity are great, but one of the things that motivates me to use functional approaches over iterations is to minimize mutation. Written in a functional style your code handles less mutation of data structures, which means that it handles less state. Handling state is were a lot of complexity hides, and the source of bugs. According to Joe Amstrong, creator of Erlang:

    Mutable state is the root of all evil.

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  • The REPL: Issue 100 - December 2022

    Just Use Postgres for Everything

    Complexity can be reduced by having less dependencies and systems. Postgres is a fantastic technology, and getting better with every release. I’ve been doing what this article advocates for years: Using Postgres by default (e.g. JSON storage, back a job queue, full-text search), and only moving away when needed.

    SQLite’s automatic indexes

    Preetam Jinka explains how SQLite handles join on un-indexed fields: It creates a temporary index! This saves postgres from having to implement hash joins.

    What I learned from pairing by default

    Eve Ragins talks about what he learned when pairing by default. I’ve done a fair amount of pairing, but my sweet spot is no more than 2 or 3 hours a day. After that it becomes to tiresome. There is some exploratory work that I also rather do by myself, to avoid having to talk through everything I am thinking.

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  • The REPL: Issue 99 - November 2022

    Postgres: Safely renaming a table with no downtime using updatable views

    Once again, Brandur posts a practical example of using Postgres effectively. The article covers how to rename a table safely using views. Other renames can be a bit more complicated, for example in that example, a table was renamed from chainweel to sprocket. In a typical app, there will also be foreign keys pointing to the table, named chainweel_id (or similar). Those would still need to be renamed to sprocket_id. Postgres includes support for generated columns:

    A generated column is a special column that is always computed from other columns. Thus, it is for columns what a view is for tables.

    but it doesn’t quite have all the functionality needed to be able to change a column name without down time.

    Vanilla Rails is plenty

    Jorge Manrubia, from 37 Signals, objects to criticism that Rails encourages poor separation of concerns. Among the things that I agree with, is that the use of plain Ruby objects (POROs) is probably underused in most application. I don’t like some of the prescriptions in the article, though.

    I don’t like concerns. While it’s nice that functionality is split into it’s own file, when included in models they end up making the API of then ActiveRecord model bigger. It’s already huge to start with. With large code bases, it can be very challenging knowing all the ways that ActiveRecord objects are being used. Adding more domain methods doesn’t make it better. Instead, I’ve had better luck using service objects. They make the APIs narrower. A win in my book.

    In the last few years, I’ve found that separating data from functionality is one of the patterns that gives great results and scales well. Value or data objects encapsulate the data. Other classes manipulate that data. Each has it’s own lifecycle. Mixing them together is the OOO way – which Rails leans heavily on – but it tends to create very broad interfaces (see ActiveRecord).

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  • Asdf, Direnv Together

    I previously wrote about how I use asdf and dirvenv together to setup per-project postgres versions. I recently learned about asdf-direnv, a direnv plugin for asdf.

    asdf works by creating shims of every executable. This adds some overhead. The plugin works by leveraging direnv to change the PATH to the actual executable, instead of the shim.


    I use asdf to install most versions that I want to control precisely for my projects. Usually, this means the ruby and postgres version. Let’s time the performance without using asdf-direnv:

    $ which ruby
    $ time ruby -e "puts 'hello'"
    ruby -e "puts 'hello'"  0.04s user 0.02s system 38% cpu 0.155 total
    $ which psql
    $ time psql -c 'select now()'
     2022-11-28 17:01:07.470615-08
    (1 row)
    Time: 0.142 ms
    psql -c 'select now()'  0.01s user 0.01s system 12% cpu 0.129 total

    Installing asdf-direnv is straight forward, as listed in the documentation. Once enabled in my .envrc file:

    $ cat .envrc
    use asdf
    watch_file ".ruby-version"

    We can see the performance gains:

    $ which ruby
    $ time ruby -e "puts 'hello'"
    ruby -e "puts 'hello'"  0.04s user 0.02s system 93% cpu 0.065 total
    $ which psql
    $ time psql -c 'select now()'
     2022-11-28 17:01:42.357192-08
    (1 row)
    Time: 0.195 ms
    psql -c 'select now()'  0.00s user 0.00s system 56% cpu 0.012 total
    Command With shim (s) Without shim (s)
    ruby 0.155 0.065
    psql 0.129 0.012

    In both cases, the savings are ~90 ms. It’s commonly said that anything below 200 ms is acceptable UX as “immediate”. To me, my terminal feels much snappier.

    I’ve been using this setup for a few weeks. The only issue I’ve encountered was that the plugin seems to fail to pickup the occasional changes in .ruby-toolbox even though the documentation states that watch_file in the documentation should fix that. I’ve been able to work around that by with touch .envrc, which forces the PATH to be re-calculated.

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