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Command line interface

A CLI, or command-line interface, is a console that helps users issue commands to a program.
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Command line interface

A CLI that runs HTTP requests defined in a simple plain text format

There are a lot of HTTP client tools out there. This one is neat because of its simple/repeatable plain text API that I’d imagine works great for writing integration tests.

# Get home:

HTTP/1.1 200
csrf_token: xpath "string(//meta[@name='_csrf_token']/@content)"

# Do login!
X-CSRF-TOKEN: {{csrf_token}}

HTTP/1.1 302


Datree is a CLI to ensure K8s manifests and Helm charts follow best practices

Datree is a CLI tool that supports Kubernetes admins in their roles, by preventing developers from making errors in Kubernetes configurations that can cause clusters to fail in production. Our CLI tool is open source, enabling it to be supported by the Kubernetes community.

It’s far more effective than manual processes, such as sending an email to a slew of developers, begging them to set various limits, which likely falls on deaf ears because developers are already overwhelmed.

In addition the CIL, Datree provides a web app interface which you can see in action right here.


A highly customizable and lightweight framework for crafting Go CLIs

Nice is a highly customizable and lightweight framework for crafting CLI apps.

Nice respects idiomatic Go code and focuses to be clear, efficient and easy to write and maintain.

You can use it as a full-featured non-opinionated framework or use any nice packages as stand-alone libraries.

I’m a big fan of the similar projects section in the README. Classy!

A highly customizable and lightweight framework for crafting Go CLIs


Getting to know JQ

This is a solid primer on the usefulness of jq (a lightweight, command-line JSON processor.)

In this article, I’m going to go over the basics building blocks of jq in enough depth that you will be able to understand how jq works. Of course, you still might occasionally need to head to google to find a function name or check your syntax, but at least you’ll have a firm grounding in the basics.

Command line interface

Bashly - Bash CLI Framework and Generator

This comment on HN does a great job summarizing Bashly.

…think of this as an argparse equivalent for Bash. You provide a YAML file listing commands, subcommands, arguments, and flags, and it automatically generates a Bash script that can parse and validate them, provide help messages, and run your code for each command.

It also lets you keep the actual code for each command and subcommand in separate files, which are merged together into one distributable Bash script at generation time. It’s basically a templating system to auto-generate argument parsing so you don’t have to solve that again or deal with things like optparse.

Brett Cannon

Introducing the Python launcher for Unix

Brett Cannon:

… over 3 years ago I set out to re-implement the Python Launcher for Unix in Rust. On July 24, 2021, I launched 1.0.0 of the Python Launcher for Unix… This gives you a py command on Unix which will always use the newest version of Python.

He goes on to describe some workflow niceties that a built in and also what this project is not about:

The Launcher is purely a convenience and not meant to be The Launcher For All Things; this should never end up in a Docker container.

Nick Janetakis

Using `envsubst` to merge environment variables into config files

Nick told us about this on our modern Unix tooling episode, but I thought I’d link up his excellent writeup/video on the subject for those who had a hard time following with audio only.

Let’s say you have an nginx or Kubernetes config file which doesn’t support templating out of the box and you want to dynamically create config files based on 1 or more environment variables. This is what envsubst lets you do.

Command line interface

Slice and dice logs on the command line with Angle Grinder

Angle-grinder allows you to parse, aggregate, sum, average, min/max, percentile, and sort your data. You can see it, live-updating, in your terminal. Angle grinder is designed for when, for whatever reason, you don’t have your data in graphite/honeycomb/kibana/sumologic/splunk/etc. but still want to be able to do sophisticated analytics.

Angle grinder can process well above 1M rows per second (simple pipelines as high as 5M), so it’s usable for fairly meaty aggregation. The results will live update in your terminal as data is processed. Angle grinder is a bare bones functional programming language coupled with a pretty terminal UI.

I’m not gonna lie, they had me with the name on this one.

Slice and dice logs on the command line with Angle Grinder

Liran Tal

The largest Node.js CLI Apps best practices list ✨

A bad CLI can easily discourage users from interacting with it. Building successful CLIs requires attention to detail and empathy for the user in order to create a good user experience. It is very easy to get wrong.

In this guide I have compiled a list of best practices across areas of focus which aim to optimize for an ideal user experience when interacting with a CLI application.

Command line interface

Command-line tools for speech and intent recognition on Linux

This isn’t merely a speech-to-text thing. It also provides intent recognition, which makes it great for doing voice commands. For example, when trained with this template, the following command:

$ voice2json transcribe-wav \
      < turn-on-the-light.wav | \
      voice2json recognize-intent | \
      jq .

Produces this JSON event:

    "text": "turn on the light",
    "intent": {
        "name": "LightState"
    "slots": {
        "state": "on"

And it can be retrained quickly enough to do it at runtime. Cool stuff!

Command line interface

rpg-cli —your filesystem as a dungeon!

rpg-cli is a bare-bones JRPG-inspired terminal game written in Rust. It can work as an alternative to cd where you randomly encounter enemies as you change directories.

You’ll want to practice a bit first, then once you get good at it go ahead and override the builtin cd by adding this function to your bash profile.

cd () {
   rpg-cli "$@"
   builtin cd "$(rpg-cli --pwd)"
rpg-cli —your filesystem as a dungeon!


google/zx – a tool for writing better scripts

Bash is great, but when it comes to writing scripts, people usually choose a more convenient programming language. JavaScript is a perfect choice, but standard Node.js library requires additional hassle before using. zx package provides useful wrappers around child_process, escapes arguments and gives sensible defaults.

I wouldn’t say JavaScript is a perfect choice for this kind of scripting, but it’s definitely a suitable one (especially if it’s the language you already know well). Here’s what scripting looks like with zx:

#!/usr/bin/env zx

await $`cat package.json | grep name`

let branch = await $`git branch --show-current`
await $`dep deploy --branch=${branch}`

await Promise.all([
  $`sleep 1; echo 1`,
  $`sleep 2; echo 2`,
  $`sleep 3; echo 3`,

let name = 'foo bar'
await $`mkdir /tmp/${name}`

Top-level await sure makes things nicer. (Deno supports this out of the box, btw.)

Julia Evans

A tool to spy on your DNS queries

You can think of Julia Evans’ new dnspeep tool as similar to tcpdump but specifically for watching your machine’s DNS queries.

One thing I like about this tool is that it gives me a sense for what programs on my computer are using the Internet! For example, I found out that something on my computer is making requests to from time to time for some reason, probably to check I’m connected to the internet.

A friend of mine actually discovered using this tool that he had some corporate monitoring software installed on his computer from an old job that he’d forgotten to uninstall, so you might even find something you want to remove.

It also probably comes in handy when debugging those pesky “could it be DNS?” issues, but this might be a limitation on that front:

One thing this program doesn’t do is tell you which process made the DNS query, there’s a tool called dnssnoop I found that does that. It uses eBPF and it looks cool but I haven’t tried it.

Command line interface

fselect – find files with SQL-like queries

This doesn’t aim to entirely replace find and ls, but if you already know SQL (like many of us do), why not be able to leverage that knowledge for your more advanced file-finding needs? Here’s a couple of examples so you get the idea:

Find temporary or config files (full path and size):

fselect size, path from /home/user where name = '*.cfg' or name = '*.tmp'

Use aggregate functions:

fselect "MIN(size), MAX(size), AVG(size), SUM(size), COUNT(*) from /home/user/Downloads"

Find by date and time intervals:

fselect path from /home/user where modified gte 2017-05-01

Command line interface

A tool for generating regular expressions from user-provided test cases

grex is a library as well as a command-line utility that is meant to simplify the often complicated and tedious task of creating regular expressions. It does so by automatically generating a single regular expression from user-provided test cases. The resulting expression is guaranteed to match the test cases which it was generated from.

Unfortunately, the tool’s authors still think you need learn how to write regexes, even when grex works flawlessly (and I tend to agree with them).

Command line interface

Crush – a command line shell that is also a modern programming language

Crush is an attempt to make a traditional command line shell that is also a modern programming language. It has the features one would expect from a modern programming language like a type system, closures and lexical scoping, but with a syntax geared toward both batch and interactive shell usage.

Check out the overview of features right here.

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