Bash Script for generating Jekyll Markdown posts

• Did I really get bored again?
• Let’s automate creating a new post
  • Parsing arguments in Bash script
  • Parsing non-option arguments
  • Playing with Variables & Parsing
    • Parse title
    • Parse date, time, timezone
    • Create filename variable
  • Create a New Post
    • Create file in _posts/
  • Inject Front Matter
  • Generate Table of Contents

Did I really get bored again?

It seems like my default pattern of being bored on Sundays was broken. This time I was bored on a Saturday. With nothing much to do, and laziness drowning my desire for physical activity, I started browsing through my ever-increasing list of side projects. However, working on a side project felt like a major chore at that moment, so I thought about writing a couple of blog posts, detailing some of my recent activities.

Energized by the idea, I opened up my local Jekyll environment, and was about to create a new post, when I was struck with the frustration of creating a new file yyyy-mm-dd-title-of-the-post.md inside the _posts directory.

Not only that, I also had to add front matter to each of the posts, which was different for each post.

---
layout: <layout>
title:  "The Title of the post"
date: yyyy-mm-dd hh:mm:ss +TIMEZONE
categories: <category>
---

To do this for each and every post is a frustration that cannot be borne. So, in the spirit of a regular developer, let’s automate this mundane task.

---

Let’s automate creating a new post

There are many things to automate here, but for simplicity sake, let’s automate the following:

• generation of the post inside _posts with the proper filename
• injecting front matter with dynamic content

To achieve the above, we must get the dynamic content somehow.

This automation is to be done using a bash script. Since my development environment is Linux (Ubuntu) this will be a good enough method.

The bash script will take in arguments when the script is called form the terminal.

Parsing arguments in Bash script

For the aforementioned requirements, we need category, title, layout as option-arguments. Since this is a bash script, let’s also add help as another category.

Let’s define each of those categories a little.

• title
  • to be used in front matter, and also used to generate filename
  • takes a string as input eg: "this is a title"
• category
  • to be used in front matter
  • can have values {miscellaneous, programming, poems, songs, stories}
  • has a default value as miscellaneous
  • takes a string as input eg: "programming"
• layout - to be used in front matter
  • to be used in front matter
  • has a default value as post
  • takes string as input eg: "page"
• help
  • has no non-option argument

To achieve the above, we shall use [GNU getopts] library, which is installed by default in Linux.

We shall parse both long-option and short-option arguments.

SHORT=c:l:t:h
LONG=category:,layout:,title:,help
OPTS=$(getopt --name create_post -o $SHORT --long $LONG -- "$@")
eval set -- "$OPTS"

while :
do
  case "$1" in
    -c | --category )
      category="$2"
      shift 2
      ;;
    -l | --layout )
      layout="$2"
      shift 2
      ;;
    -t | --title )
      title="$2"
      shift 2
      ;;
    -h | --help)
      help
      exit 2
      ;;
    --)
      shift;
      break
      ;;
  esac
done

Using the --help or -h option will run the function help which in turn calls other functions.

1. description - short description of what this bash script does
2. usage - syntax for usage
3. example_usage - examples of using the script
4. options - the different options allowed in the script

Once the arguments are parsed, we also need to check variables & set defaults.

Parsing non-option arguments

# check title cannot be empty
if [[ -z "$title" ]]; then
    echo "--title is non-optional argument"
    echo "Check out some example usages."
    echo
    example_usage
    echo
    ask_help
    echo
    exit 1 # exit with error
fi

# check layout & title
# if empty, populate with default value
[ -z "$category" ] && category=$DEFAULT_CATEGORY
[ -z "$layout" ] && layout=$DEFAULT_LAYOUT

Title is a non-optional argument, and if it’s not provided, show some examples, show instruction to ask help, and exit script.

Category, and Layout are set to default values if they are not provided.

Playing with Variables & Parsing

Using the values of the options which are set to corresponding variables, let’s create more variables which will later be used to generate file, as well as to inject dynamic front matter.

Parse title

Title is provided as a string eg: "this is a title"

This can directly be injected into front matter, but for generating the filename we need to parse it further.

echo $title | tr -c '[:alnum:]\~n\r' ' ' | awk '{$1=$1};1' | tr -c '[:alnum:]\n\r' '-' | tr 'A-Z' 'a-z')

The parsing is done in 4 steps:

1. substitute all special chars (non-alphanum) with space
2. remove start, trailing space + remove multiple-spaces, tabs & replace with single space
3. substitute space with - (hyphen)
4. convert entire string to lowercase

There’s an interesting bug that was found here.

Since the non-optional arguments, especially title can be any string, if the string contains !x where x can be certain special characters, strings, or a combination of both, this triggers Bash History Expansion, which is an unwanted behaviour here. History expansion will modify the input depending on what value x has.

This Bash History Expansion cannot be avoided in the script, since the expansion is done in the interactive shell where this script is called from.

To avoid the aforementioned behaviour, there are 2 steps we can take:

• Set the Bash History Expansion to off.

I’ve permanently set it off by adding set +H to my .bashrc since I can’t imagine any situation where this Bash History Expansion to be useful.

• Use ‘ (single-quote) instead of “ (double-quote) while entering strings.

This is a lazy alternative, but should be used to avoid errors.

In my case, I couldn’t be bothered to remember to use ‘ (single-quote) every time, so setting off Bash Expansion was the way to go.

Parse date, time, timezone

Date, time, and timezone will be used in filename & front matter.

parsed_date=$(date +"%Y-%m-%d")
parsed_time=$(date +"%T")
timezone=$(date +"%z")

Create filename variable

The filename variable will be used to create the file inside _posts/ directory.

filename="$parsed_date-$parsed_lowercase_title.md"

Create a New Post

Let’s create the file in posts/ directory and inject it with front matter.

Create file in _posts/

First, let’s check if a file with the same filename exists. If it does, exist, else, let’s create the file.

if [[ -f ./_posts/$filename ]]; then
    echo "Error creating file with title='$title'"
    echo "File: $filename already exists inside _posts/"
    echo "Use a different 'title' to create another file."
    echo
    exit 1 #exit with error
else
    # create the file inside _posts
    touch ./_posts/$filename
    echo "created $filename inside _posts/"
    echo
fi

Inject Front Matter

Each file in _posts expects a front matter:

---
layout: page
title: <category>
permalink: /<category>/
---

Let’s inject the dynamic front-matter from the bash script into the file created above.

# inject front matter into the file
echo "---" >> ./_posts/$filename
echo "layout: $layout" >> ./_posts/$filename
echo "title:  \"$title\"" >> ./_posts/$filename
echo "date: $parsed_date $parsed_time $timezone" >> ./_posts/$filename
echo "categories: $category" >> ./_posts/$filename
echo "---" >> ./_posts/$filename

Generate Table of Contents

I also want to add a table of contents for each post, which is autogenerated using the headers (h2, h3, h4)

To do this, multiple options are available, and I chose the default approach in Jekyll provided by Kramdown.

I also want to style the TOC to be a little more appealing, and to achieve that, let’s inject some inline CSS as well.

printf "\n<style type='text/css'>#markdown-toc::before" >> ./_posts/$filename
printf "{content:'Table of Contents';font-weight:700}" >> ./_posts/$filename
printf "#markdown-toc{border:3px solid #aaa;padding:1.5em;" >> ./_posts/$filename
printf "margin-left:0;display:inline-block}</style>\n" >> ./_posts/$filename
printf "\n* TOC\n" >> ./_posts/$filename
printf "{:toc}\n" >> ./_posts/$filename

After, everything above has executed perfectly, it will look like:

View the entire script.

---

Check out the entire series of posts related to Blog Setup

• How did my GitHub Blog begin?
• Bash Script for generating Jekyll Markdown posts
• Update Bash Script to inject links for each Jekyll post created
• Add metadata to my Jekyll Blog
• Theming my Jekyll Github Blog