markdownToHTML.sh

#!/bin/bash
set -eEuo pipefail
IFS=$'\n\t'

# Fetch location of this script.
dir_name="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"


#
# Arguments
#

# First argument should be either the path to a markdown file
#   that will be used as input
#   or '--stdin', in which case the script will read from the standard input.
#
# Second argument should be either the path to a file
#   to which the HTML output will be written,
#   or '--stdout', in which case the script will write to the standard output.
#
# If no argument is provided, we use standard input/output.
#
# If just one argument is provided, we use this argument as input file and write to standard output.


using_stdin=false
using_stdout=false

case "$#" in

  0)
    using_stdin=true
    input_file=/dev/stdin
    using_stdout=true
    ;;

  1)
    using_stdout=true
    if [ "${1,,}" == "--stdin" ]; # convert to lowercase
    then
        using_stdin=true
        input_file=/dev/stdin
    else
        input_file=${1}
    fi
    ;;

  2)
    if [ "${1,,}" == "--stdin" ]; # convert to lowercase
    then
        using_stdin=true
        input_file=/dev/stdin
    else
        input_file=${1}
    fi
    if [ "${2,,}" == "--stdout" ];  # convert to lowercase
    then
        using_stdout=true
    fi
    ;;
  *)
    echo "Usage: markdownToHTML.sh INPUTFILE OUTPUTFILE"
    echo "    INPUTFILE may be --stdin to read from the standard input"
    echo "    OUTPUTFILE may be --stdout to write to the standard output"
    echo "    If no arguments are provided, assume --stdin and --stdout."
    echo "    If one argument is provided, this argument is INPUTFILE, assume --stdout."
    exit 1
    ;;
esac

#
# Processing environment variables
#

# This script uses the following environment variables.
#
# GITHUB_USERNAME &
# GITHUB_TOKEN:
#     If GITHUB_USERNAME is set, the request sent to the github API using curl
#     will use the provided username and token (/password).
#     This script will work even without authentification (default behavior),
#     but you will be limited to a certain number of requests per hour.
#     If you provide a username, this limit is much higher.
#     I recommend creating and using a "Fine-grained personal access tokens"
#     (GitHub > Account Settings > Developer settings > Personal Access Tokens > Fine-grained tokens)
#     that has no account permissions and no permissions for any of your repositories.
#
# SKIP_REPLACEMENT: Whether to replace 'user-content-' in the HTML file.
#     Not set or set to "false" (default behavior):
#       ...
#     Set to "true":
#         Don't execute replacement.
#         (Links to headings will not work without JS magic.-)
#
# TITLE: The contents of the title tag in the HTML file.
#     Will be typically shown as the title of the browser window.
#     If not set (default), we will use the filename (without path and extension) as title.
#
# LINK_CSS: Whether to link to the CSS files or whether to paste them.
#     Not set or set to "false" (default):
#         Script will paste the contents of the CSS files into the output file.
#         CSS files DO need to be present when running this script.
#     Set to "true":
#         Script will emit a <link> tag.
#         CSS files do not need to be present when running this script.
#
# CSS_FILES: a comma-separated list of paths to css files.
#   Default value: "css/github-markdown.css,css/normalize.css,css/style.css"
#   Note that if LINK_CSS is not set (default behavior), the contents of these files will be pasted into the output file.
#   This in particular means that the files need to be present when running this script.
#

# set default value for CSS_FILES
if [ -z "${CSS_FILES+x}" ]
then
    # Not using inline mode.
    # We simply use the relative path "css/"
    #   and hope that the user will put the CSS files there.
    CSS_FILES=css/github-markdown.css,css/normalize.css,css/style.css
fi


#
# Step 0: Acquire temporary file
#

temp_file=$(mktemp /tmp/styleincludes.template.html.XXXXXX)

# set up a trap that deltes the temp file when this script terminates
trap 'rm -f $temp_file' 0 2 3 15


#
# Step 1: Head template
#

cat "$dir_name/templates/head.html" >> "$temp_file"


#
# Step 2: Title
#

if [ -z "${TITLE+x}" ]
then
    # TITLE variable is not set.
    # If we are given a filename, we will use the filename as title.
    # If the input is given via STDIN, we omit the title.
    if [ "$using_stdin" != "true" ];
    then
        filename=$(basename -- "${1}") # get just the filename
        filename="${filename%.*}" # remove extension
        echo "<title>$filename</title>" >> "$temp_file"
    fi
else
    # TITLE is set, use it
    echo "<title>$TITLE</title>" >> "$temp_file"
fi


#
# Step 3: CSS files
#

# process CSS_FILES as a comma separated list
oldIFS=$IFS
IFS=","
for style_file in ${CSS_FILES}
do
    # echo $style_file

    if [ -z "${LINK_CSS+x}" ] || [ "$LINK_CSS" != "true" ];
    then
        # Using inline mode.
        # Actually paste the contents of the css files into the output.

        style_file_without_path=$(basename -- "$style_file")

        # Relative paths are always assumed to be relative
        # to the location of this script.
        if [[ ! "$style_file" = /* ]]; then
            style_file="$dir_name/$style_file"
        fi

        echo "<!-- contents of $style_file_without_path -->" >> "$temp_file"
        echo "<style>" >> "$temp_file"
        cat "$style_file" >> "$temp_file"
        echo "</style>"  >> "$temp_file"
    else
        # Not using inline mode.
        # Simply emit a link tag.
        echo "<link rel=\"stylesheet\" href=\"$style_file\">" >> "$temp_file"
    fi
done
IFS=$oldIFS


#
# Step 4: Center template
#

cat "$dir_name/templates/center.html" >> "$temp_file"


#
# Step 5: Markdown conversion using the GitHub API
#

authstring=""
if [ -n "${GITHUB_USERNAME+x}" ]
then
    authstring="-u $GITHUB_USERNAME:$GITHUB_TOKEN"
fi

jq --slurp --raw-input '{"text": "\(.)", "mode": "markdown"}' < "$input_file" |
    curl "$authstring" -s --data @- https://api.github.com/markdown >> "$temp_file"


#
# Step 6: Foot template
#

cat "$dir_name/templates/foot.html" >> "$temp_file"


#
# Step 7: Get rid of 'user-content-' (unless SKIP_REPLACEMENT has been specified)
#

if [ -z "${SKIP_REPLACEMENT+x}" ] || [ "$SKIP_REPLACEMENT" != "true" ];
then
    sed -i 's/<a id="user-content-/<a id="/g' "$temp_file"
fi


#
# Step 8: Output
#

if [ "$using_stdout" == "true" ];
then
    cat "$temp_file"
else
    cp "$temp_file" "${2}"
    echo "Succesfully written HTML to ${2}"
fi