Jekyll_pre

This Jekyll plugin provides 3 new Liquid tags that work together:

• A pre block tag that can be displayed various ways.

  {% pre [Options] [free text label] %}
  Contents of pre tag
  {% endpre %}

  Options are:

  • class="class1 class2" – Apply CSS classes

  • clear – Line break after floating HTML elements

  • copyButton – Generate a copy button

  • dark – Dark mode

  • dedent – Remove leading spaces common to all lines, like Ruby's <<~ squiggly heredoc (default is false)

  • label='This is a label' – Apply text above pre tag. The label parameter value can also be specified in free text. For example, the following produce the same results:

    • {% pre label="This is a label" %}
      Contents of pre tag
      {% endpre %}

    • {% pre This is a label %}
      Contents of pre tag
      {% endpre %}

  • number – Number the lines

  • shell – Equivalent to label='Shell'

  • style – Apply inline CSS styles

  The generated <pre></pre> tag has an data-lt-active="false" attribute, so LanguageTool does not check the spelling or grammar of the contents.

• A noselect tag that can renders HTML content passed to it unselectable, and generates a $ prompt if no content is provided.

  {% pre %}
  {% noselect [optional text string, defaults to $]%}Command
  {% noselect unselectable output goes here %}
  {% endpre %}

• An exec tag that executes shell commands and incorporates the command and its output into the content of the pre tag. Environment variables are evaluated, output data is escaped, whitespace is condensed, and wrapped in the same unselectable class as does unselectable.

  {% exec [Options] [shell command] %}

  Options are:

  • cd="relative/or/absolute/directory" - Change to specified directory before executing shell command. Environment variables in the directory path will be expanded.

  • die_if_nonzero – Set false to treat non-zero return codes as non-fatal. Instead of terminating Jekyll with an error message, the message will be displayed as an error by the Jekyll logger, and a red message will appear in place of the result on the web page.

  • die_if_error – Set false to treat exceptions generated by this plugin as non-fatal. Instead of terminating Jekyll with an error message, the message will be displayed as an error by the Jekyll logger.

  • no_escape – Do not HTML escape the result of running the shell command.

  • no_stderr - Discard STDERR output. This is helpful for suppressing annoying groff error messages that are emitted when the exec subcommand runs man. Use it like this:

    {% pre copyButton dedent shell %}
    {% noselect %}{% exec no_stderr man netplan %}
    {% endpre %}

  • no_strip – Do not remove leading and trailing whitespace from the result.

  • wrapper_class class applied to outer div.

  • wrapper_style style applied to outer div.

For all keyword options, including keyword options for the pre and exec tags:

• Option values specified in the document may be provided. If a value is not provided, the value true is assumed. Otherwise, if a value is provided, it must be wrapped in single or double quotes.

• Option values specified in _config.yml must be provided, and the value true cannot be implied. Values that do not contain special characters may be wrapped in single or double quotes.

The following sets die_if_error true:

{% pre die_if_error %} ... {% endpre %}

The above is the same as writing:

{% pre die_if_error='true' %} ... {% endpre %}

Or writing:

{% pre die_if_error="true" %} ... {% endpre %}

Neglecting to provide surrounding quotes around the provided value causes the parser to not recognize the option. Instead, what you had intended to be the keyword/value pair will be parsed as part of the command. For the pre tag, this means the erroneous string becomes part of the label value, unless label is explicitly specified. For the exec tag, this means the erroneous string becomes part of the command to execute. The following demonstrates the error.

{% pre die_if_error=false %} ... {% endpre %}

The above causes the label to be die_if_error=false.

{% exec die_if_error=false ls %} ... {% endpre %}

The above causes the command to be executed to be die_if_error=false ls instead of ls.

See demo/assets/css/style.css for the CSS declarations, between /* Start of pre tag css */ and /* End of pre tag css */.

Default options can be set for the pre tag by entries in _config.yml. The following demonstrates setting a default value for every possible option:

pre:
  class: bg_yellow
  clear: true
  dark: true
  dedent: true
  highlight: 'Error:.*'
  label: Shell
  copyButton: true
  number: true
  style: 'font-face: courier'
  wrapper_class: rounded shadow
  wrapper_style: 'padding: 2em; border: thin green dashed;'

The default values used on mslinn.com are:

pre:
  dedent: true
  label: Shell
  copyButton: true

Specifying a default value for die_if_error in _config.yml could be done as follows:

pre:
  die_if_error: true

pre:
  die_if_error: "true"

pre:
  die_if_error: 'true'

More information is available on Mike Slinn’s website.

Add this line to your application's Gemfile, within the jekyll_plugins group:

group :jekyll_plugins do
  gem 'jekyll_pre'
end

And then execute:

$ bundle

The following examples are rendered on Mike Slinn’s website.

{% pre dedent %}
    This line was indented 4 spaces
      This line was indented 6 spaces
    This line was indented 4 spaces
{% endpre %}

Which renders as:

This line was indented 4 spaces
  This line was indented 6 spaces
This line was indented 4 spaces

This example does not generate a copy button and does not demonstrate noselect.

{% pre %}
Contents of pre tag
{% endpre %}

Generates:

<pre data-lt-active='false' class='maxOneScreenHigh copyContainer' id='id377433c30186'>Contents of pre tag</pre>

Which renders as:

Contents of pre tag

This example generates a copy button and does not demonstrate noselect.

{% pre copyButton %} Contents of pre tag {% endpre %}

Generates:

<pre data-lt-active='false' class='maxOneScreenHigh copyContainer' id='id6a831a3e8992'><button class='copyBtn' data-clipboard-target='#id6a831a3e8992' title='Copy to clipboard'><img src='images/clippy.svg' alt='Copy to clipboard' style='width: 13px'></button>Contents of pre tag</pre>

Which renders as (note the clipboard icon at the far right):

This example generates a copy button and does demonstrates the default usage of noselect, which renders an unselectable dollar sign followed by a space.

{% pre copyButton %}
{% noselect %}Contents of pre tag
{% endpre %}

Generates:

<pre data-lt-active='false' class='maxOneScreenHigh copyContainer' id='id1e4a8fe53480'><button class='copyBtn' data-clipboard-target='#id1e4a8fe53480' title='Copy to clipboard'><img src='/assets/images/clippy.svg' alt='Copy to clipboard' style='width: 13px'></button><span class='unselectable'>$ </span>Contents of pre tag</pre>

Which renders as:

This example generates a copy button and does demonstrates the noselect being used twice: the first time to render an unselectable custom prompt, and the second time to render unselectable output.

{% pre copyButton %}
{% noselect >>> %}Contents of pre tag
{% noselect How now brown cow%}
{% endpre %}

Generates:

<pre data-lt-active='false' class='maxOneScreenHigh copyContainer' id='idb58a6cf1761c'><button class='copyBtn' data-clipboard-target='#idb58a6cf1761c' title='Copy to clipboard'><img src='/assets/images/clippy.svg' alt='Copy to clipboard' style='width: 13px'></button><span class='unselectable'>>>> </span>contents of pre tag
<span class='unselectable'>How now brown cow</span></pre>

Which renders as:

A regular expression can be passed to the highlight option. This causes text that matches the regex pattern to be wrapped within a <span class="bg_yellow"></span> tag.

The CSS stylesheet used for this page contains the following:

.bg_yellow {
  background-color: yellow;
  padding: 2px;
}

This example demonstrates highlighting text that matches a regular expression. Regular expressions match against lines, which are delimited via newlines (\n).

{% pre copyButton highlight="Line 2" %}
Line 1
  Line 2
    Line 3
      Line 4
    Line 5
  Line 6
Line 7
{% endpre %}

Regular expressions match against lines, which are delimited via newlines (\n). Thus to match an entire line that contains a phrase, specify the regex as .*phrase.*. The following matches 3 possible phrases (2, 4 or 6), then selects the entire line if matched.

{% pre copyButton highlight=".*(2|4|6).*" %}
Line 1
  Line 2
    Line 3
      Line 4
    Line 5
  Line 6
Line 7
{% endpre %}

This example floats an image to the right. The jekyll_pre plugin’s clear option moves the generated HTML below the image.

<img src="jekyll.webp" style="float: right; width: 100px; height: auto;">
{% pre clear copyButton label='Clear example' %}
Using clear, copyButton and label parameters
{% endpre %}

The following executes ls -alF / and displays the output.

{% pre clear copyButton label='Exec without error' %}
{% noselect %}{% exec die_if_nonzero='false' ls -alF / %}
{% endpre %}

The following changes to the home directory ($HOME), then executes pwd and displays the output.

{% pre clear copyButton label='Exec without error' %}
{% noselect %}{% exec cd="$HOME" die_if_nonzero='false' pwd %}
{% endpre %}

The following executes echo $USER and displays the output.

{% pre clear copyButton label='Exec display $USER' %}
{% noselect %}{% exec die_if_nonzero='false' echo $USER %}
{% endpre %}

The code I wrote to generate the above CSS was a good example of how the plugins work together with the from and to tags from my from_to_until plugin:

{% capture css %}{% flexible_include '_sass/mystyle.scss' %}{% endcapture %}
{% pre copyButton %}{{ css | from: '.copyBtn' | to: '^$' | strip }}

{{ css | from: '.copyContainer' | to: '^$' | strip }}

{{ css | from: '.maxOneScreenHigh' | to: '^$' | strip }}

{{ css | from: '.unselectable' | to: '^$' | strip }}
{% endpre %}

After checking out the repo, run bin/setup to install dependencies.

You can also run bin/console for an interactive prompt that will allow you to experiment.

A test website is provided in the demo directory.

1. Set breakpoints.

2. Initiate a debug session from the command line:

   $ bin/attach demo

3. Once the Fast Debugger signon appears, launch the Visual Studio Code launch configuration called Attach rdebug-ide.

4. View the generated website at http://localhost:4444

To build and install this gem onto your local machine, run:

$ bundle exec rake install

Examine the newly built gem:

$ gem info jekyll_pre

*** LOCAL GEMS ***

jekyll_pre (1.0.0)
    Author: Mike Slinn
    Homepage:
    https://github.com/mslinn/jekyll_pre
    License: MIT
    Installed at: /home/mslinn/.gems

    Generates Jekyll logger with colored output.

To release a new version,

1. Update the version number in version.rb.

2. Commit all changes to git; if you don't the next step might fail with an unexplainable error message.

3. Run the following:

   $ bundle exec rake release

   The above creates a git tag for the version, commits the created tag, and pushes the new .gem file to RubyGems.org.

1. Fork the project
2. Create a descriptively named feature branch
3. Add your feature
4. Submit a pull request

The gem is available as open source under the terms of the MIT License.