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Capistrano: How to find out which version of your application is currently live

When deploying, Capistrano puts a REVISION file into your application's release directory. It contains the hash of the commit which was deployed.

If you want to know the currently deployed release, simply SSH to a server and view that file.

$ cat /var/www/my-project/current/REVISION
cf8734ece3938fc67262ad5e0d4336f820689307

Capistrano task

When your application is deployed to multiple servers, you probably want to see a result for all of them.
Here is a Capistrano task that checks all servers with the :app role.

```rub…

Repeats

Linux: Shell script to easily update chromedriver

Updating Chromedriver is often a hassle: If you use chromium-chromedriver from the Ubuntu sources, it usually won't be updated when a new Chrome version is released. Manually downloading it from the official page is a very manual process. And I don't really want to use remote code like the "webdrives" gem because of paranoia.

Cry no more, for here is a tiny bash script that will download the latest chromedriver version and place it inside ~/bin. (If you use a different location, adjust accordingly).

```
#!/bin/bash

VERSION_URL="https:…

Bash script to list commits by Pivotal Tracker ID

The main benefit of our convention to prefix commits by their corresponding Pivotal Tracker ID is that we can easily detect commits that belong to the same story. You can either do that manually or use the bash script below by copying it somewhere to your .bashrc.

```bash
# Usage: ptcommits '#123456'
function ptcommits {
if test "$1"
then
git log –oneline | grep "$1" | grep "^[a-z0-9]*" -o | xargs –no-run-i…

Joining PDFs with Linux command line

There are several ways to merge two (or more) PDF files to a single file using the Linux command line.

If you're looking for graphical tools to edit or annotate a PDF, we have a separate card for that.

pdfjam

The pdfjoin binary from pdfjam is probably already installed on your system. Usage:

pdfjoin one.pdf two.pdf --outfile out.pdf

Pages from joined documents might be rotated. To avoid this, call it like this:

pdfjoin one.pdf two.pdf --outfile out.pdf --paper a4paper --rotateoversize false

Fo…

Fix for "Rails assets manifest file not found" in Capistrano deploy

If you use webpacker in your Rails application, and you have completely disabled Sprockets, you might get the following error when trying to deploy: Rails assets manifest file not found. This happens inside the deploy:assets:backup_manifest task.

This task is build for Sprockets and does not work with webpacker. Simply skip it, by adding the following line to your config/deploy.rb:

Rake::Task["deploy:assets:backup_manifest"].clear_actions
Linked contentRepeats

Linux: Running a single unique instance of command + arguments

run-one is a wrapper script that won't run the given command while another instance of it is running. Is brings several utility commands that offer similar behavior.

```
NAME
run-one - run just one instance at a time of some command and unique set of arguments (useful for cronjobs, eg)

SYNOPSIS
run-one COMMAND [ARGS]

   run-this-one COMMAND [ARGS]

   run-one-constantly COMMAND [ARGS]

   keep-one-running COMMAND [ARGS]

   run-one-until-success COMMAND [ARGS]

   run-one-until-failure COMMAND [ARGS]

Linked content

Installing Ruby 2.3 or below on Ubuntu 17 and above

From Ubuntu 17, rbenv fails to install Ruby below 2.4 because of a mismatching OpenSSL dependency: it needs libssl1.0-dev for the installation process, but recent Ubuntus come with libssl-dev.

From the linked StackOverflow comment:

As far as I know (and tested), Ruby versions < 2.4 requires libssl1.0, while >2.4 libssl1.1+. The two libssl packages conflict with each other, so you can't have both of them, so I had to juggle the libs in order to install the required ruby version. To make things even funnier (or more complicated),…

Linked content

How to inspect the HTML of an email in Thunderbird

Inspecting the source of an email does not always reveal the plain HTML source, but some encoded byte mess. In order to inspect the HTML anyways, you can use a little trick:

While composing a message, select all (Ctrl + A), then navigate to Insert > HTML on the message window.

If you need to inspect a received message, hit "Reply" to turn it into composition mode.

Linked contentRepeats

How to send HTTP requests using cURL

  • Reading a URL via GET:

    curl http://example.com/
    
  • Defining any HTTP method (like POST or PUT):

    curl http://example.com/users/1 -XPUT
    
  • Sending data with a request:

    curl http://example.com/users -d"first_name=Bruce&last_name=Wayne"
    

    If you use -d and do not set an HTTP request method it automatically defaults to POST.

  • Performing basic authentication:

    curl http://user:password@example.com/users/1
    
  • All together now:

    curl http://user:password@example.com/users/1 -XPUT -d"screen_name=batman"
    

Deal with certain travis CI failures

Travis changed their default distribution from Ubuntu 14.04 (trusty) to 16.04 (precise). This might break your test setup for new builds.

You can solve this issue by freezing your test distribution in the .travis.yml to Ubuntu 14.04 until you have the time to solve all the issues you will have in 16.04:


dist: trusty

Error details

Here are few indicators that you ran into this issue:

Connection to the PostgreSQL database does not work anymore

Your travis-ci builds might have started failing on the usual

```
psql -c…

Repeats

Documenting your Rails project's Node.js version in .nvmrc

Not all versions of Node.js are compatible with each other. Also npm packages may require a minimum or maximum version of Node.js. We use nvm on our development PCs so we can operate multiple versions of Node.js in parallel.

To make sure that all developers use a compatible version of Node.js, your Rails project should declare the required Node.js in a file called .nvmrc.

When a .nvmrc exists, developers can cd in your project directory and activate…

Yarn: How to recognize that you are using a different node version than your colleagues

The issue in this card can occur if the node_modules directory is checked into your Git repository. We usually recommend to exclude node_modules from version control.

In any case you should document which version of node to use in your project in a .nvmrc file.


I saw a strange behaviour after we introduced webpack in one of our projects and finally found out the reason: The person who committed the files used a node version that is older than mine.

Every time I wanted to run my rai…

Linked contentDeprecated

Execution of shell code in Ruby scripts

Deprecated ways to execute shell code in Ruby

This is just a reference for legacy code. For new code, always use capture3.

%x{ } or backticks – quick and easy

Returns the standard output of running the given command in a subshell. This is an alias for `…`, and you can use string interpolation.

Example:

name = 'ls'
result = `which #{name}`

It does not escape anything you inject in the string.

If you want to find out if the call was …

Linked contentDeprecated

How to install npm packages globally without sudo on Linux

All quoted.

  1. Set up a package root in your homedir to hold the Node "global" packages:

    $ NPM_PACKAGES="$HOME/.npm-packages"
    $ mkdir -p "$NPM_PACKAGES"
    
  2. Set NPM to use this directory for its global package installs:

    $ echo "prefix = $NPM_PACKAGES" >> ~/.npmrc
    
  3. Configure your PATH and MANPATH to see commands in your $NPM_PACKAGES prefix by adding the following to your .bashrc:

    ```
    # NPM packages in homedir
    NPM_PACKAGES="$HOME/.npm-packages"

    Tell our environment about user-ins…

How to: Migrate from CoffeeScript to ES6

It is quite easy to migrate from CoffeeScript to ES6. You can use decaffeinate to convert your CoffeeScript source to modern JavaScript.

Installation

  • Install the NPM module globally yarn global add decaffeinate
  • Add the following line to your ~/.bashrc to export the Yarn binaries in your Bash
export PATH="$PATH:$(yarn global bin)"
  • Run decaffeinate some.coffee to get the converted modern JavaScript file.

Notes

  • decaffeinate will add some [suggestions](https://gith…

How to test Autoprefixer and CSSnext in PostCSS

PostCSS is a tool for transforming styles with JS plugins. In Webpacker you can configure the plugins and their settings via the postcss.config.js file.

module.exports = {
  plugins: [
    require('postcss-import'),
    require('postcss-flexbugs-fixes'),
    require('postcss-preset-env')({
      autoprefixer: {
        flexbox: 'no-2009'
      },
      stage: 3
    })
  ]
}

Note: Stage 3 means you can use all CSS features that are listed as "This idea is becoming part of the web". Do not use …

Repeats

When reading model columns during class definition, you must handle a missing/empty database

When doing some meta-programming magic and you want to do something for all attributes of a class, you may need to access connection or some of its methods (e.g. columns) during class definition.

While everything will be fine while you are working on a project that is in active development, the application will fail to boot when the database is missing or has no tables. This means that Raketasks like db:create or db:migrate fail on a freshly cloned project.

The reason is your environment.rb which is loaded for Raketasks and calls…

Migration from the Asset Pipeline to Webpacker

This is a short overview of things that are required to upgrade a project from the Asset Pipeline to Webpacker. Expect this upgrade to take a few days even the diff is quite small afterwards.

Preparations

1. Find all libraries that are bundled with the asset pipeline. You can check the application.js and the application.css for require and import statements. The source of a library is most often a gem or a vendor directory.
2. Find an working example for each library in the application and write it down.
3. Find out the ver…

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