Clojure

Creating Linux Command-Line Tools in Clojure

Mihalis Tsoukalos — Fri, 29 Mar 2019 12:00:00 +0000

Learn how the leiningen utility can help you manage your Clojure projects.

This article is a gentle introduction to the Clojure Functional Programming language that is based on LISP, uses the Java JVM and has a handy REPL. And, as Clojure is based on LISP, be prepared to see lots of parentheses!

Installing Clojure

You can install Clojure on a Debian Linux machine by executing the following command as root or using sudo:


# apt-get install clojure

Finding the version of Clojure you are using is as simple as executing one of the following commands inside the Clojure REPL, which you can enter by running clojure:


# clojure
Clojure 1.8.0
user=> *clojure-version*
{:major 1, :minor 8, :incremental 0, :qualifier nil}
user=> (clojure-version)
"1.8.0"
user=> (println *clojure-version*)
{:major 1, :minor 8, :incremental 0, :qualifier nil}
nil

The first command gets you into the Clojure REPL, which displays the user=> prompt and waits for user input. The remaining three commands that should be executed within the Clojure REPL will generate the same output, which, in this example, shows that Clojure version 1.8.0 is being used. So, if you're following along, congratulations! You have just run your first Clojure code!

The leiningen Utility

The first thing you should do after getting Clojure is to install a very handy utility named leiningen, which is the easiest way to use and manage Clojure projects on your Linux machine. Follow the instructions at leiningen.org or use your favourite package manager to install leiningen on your Linux machine. Additionally, if you are using Clojure all the time and working with large Clojure projects, tools like Jenkins and Semaphore will automate your build and test phases and save you lots of time.

After installing leiningen, use the lein command (which is the name of the executable file for the leiningen package) to create a new project named hw:


$ lein new hw
Generating a project called hw based on the 'default' template.
The default template is intended for library projects,
not applications. To see other templates (app, plugin, etc),
try `lein help new`.

The preceding command will create a new directory named hw that will contain files and other directories. You'll need to make some changes to some of the project files in order to execute the project. First, you'll need to edit the project.clj that can be found inside the hw directory and make it as follows:

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Linux Journal October 2018: Programming

Carlie Fairchild — Mon, 01 Oct 2018 14:59:55 +0000

by Carlie Fairchild

Welcome to the Programming issue, October 2018, of Linux Journal. This month we highlight programming languages new and old including Go, Rust, Clojure and Bash. Take a look at this month's complete line-up:

Featured articles in this issue include:

Understanding Bash: Elements of Programming** This article is available online now as a sneak peak in to our October issue.
Getting Started with Rust: Working with Files and Doing File I/O
Introductory Go Programming Tutorial
Creating Linux Command-Line Tools in Clojure

Additional articles:

Shall We Study Amazon's Pricing Together?
Review: System76 Oryx Pro Laptop
3D-Printed Firearms Are Blowing Up
FOSS Project Spotlight: Tutanota, the First Encrypted Email Service with an App on F-Droid
Introducing Genius, the Advanced Scientific Calculator for Linux

Columns:

Kyle Rankin's Hack and /: Papa's Got a Brand New NAS: the Software
Shawn Powers' The Open-Source Classroom: Have a Plan for Netplan
Reuven M. Lerner's At the Forge: Automate Sysadmin Tasks with Python's os.walk Function
Dave Taylor's Work the Shell: Normalizing Filenames and Data with Bash
Zack Brown's diff -u: What's New in Kernel Development
Glyn Moody's Open Sauce: Now Is the Time to Start Planning for the Post-Android World

Subscribers, you can download your October issue now.

Not a subscriber? It’s not too late. Subscribe today and receive instant access to this and ALL back issues since 1994!

Want to buy a single issue? Buy the August magazine or other single back issues in the LJ store.

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Compojure

Reuven Lerner — Thu, 26 Dec 2013 21:02:14 +0000

by Reuven Lerner

In my last article, I started discussing Compojure, a Web framework written in the Clojure language. Clojure already has generated a great deal of excitement among software developers, in that it combines the beauty and expressive elegance of Lisp with the efficiency and ubiquity of the Java Virtual Machine (JVM). Clojure has other traits as well, including its famous use of software transactional memory (STM) to avoid problems in multithreaded environments.

As a Web developer and a longtime Lisp aficionado, I've been intrigued by the possibility of writing and deploying Web applications written in Clojure. Compojure would appear to be a simple framework for creating Web applications, built on lower-level systems, such as "ring", which handles HTTP requests.

In my last article, I explained how to create a simple Web application using the "lein" system, modify the project.clj configuration file and determine the HTML returned in response to a particular URL pattern ("route"). Here, I try to advance the application somewhat, looking at the things that are typically of interest to Web developers. Even if you don't end up using Clojure or Compojure, I still think you'll learn something from understanding how these systems approach the problem.

Databases and Clojure

Because Clojure is built on the JVM, you can use the same objects in your Clojure program as you would in a Java program. In other words, if you want to connect to a PostgreSQL database, you do so with the same JDBC driver that Java applications do.

Installing the PostgreSQL JDBC driver requires two steps. First, you must download the driver, which is available at https://jdbc.postgresql.org. Second, you then must tell the JVM where it can find the classes that are defined by the driver. This is done by setting (or adding to) the CLASSPATH environment variable—that is, put the driver in:


export CLASSPATH=/home/reuven/Downloads:$CLASSPATH

Once you have done that, you can tell your Clojure project that you want to include the PostgreSQL JDBC driver by adding two elements to the :dependencies vector within the defproject macro:

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