create_pages.sh

#!/usr/local/bin/bash
#
# Create HTML pages for Categories and Tags in posts.
#
# Usage:
#     Call from the '_posts' sibling directory.
#
# v2.2
# https://github.com/cotes2020/jekyll-theme-chirpy
# © 2020 Cotes Chung
# Published under MIT License

set -eu

TYPE_CATEGORY=0
TYPE_TAG=1

category_count=0
tag_count=0


_read_yaml() {
  local _endline="$(grep -n "\-\-\-" "$1" | cut -d: -f 1 | sed -n '2p')"
  head -"$_endline" "$1"
}


read_categories() {
  local _yaml="$(_read_yaml "$1")"
  local _categories="$(echo "$_yaml" | grep "^categories:")"
  local _category="$(echo "$_yaml" | grep "^category:")"

  if [[ ! -z "$_categories" ]]; then
    echo "$_categories" | sed "s/categories: *//;s/\[//;s/\].*//;s/, */,/g;s/\"//g;s/'//g"
  elif [[ ! -z "_category" ]]; then
    echo "$_category" | sed "s/category: *//;s/\[//;s/\].*//;s/, */,/g;s/\"//g;s/'//g"
  fi
}


read_tags() {
  local _yaml="$(_read_yaml "$1")"
  echo "$_yaml" | grep "^tags:" | sed "s/tags: *//;s/\[//;s/\].*//;s/, */,/g;s/\"//g;s/'//g"
}


init() {

  if [[ -d categories ]]; then
    rm -rf categories
  fi

  if [[ -d tags ]]; then
    rm -rf tags
  fi

  if [[ ! -d _posts ]]; then
    exit 0
  fi

  mkdir categories tags
}


create_category() {
  if [[ ! -z $1 ]]; then
    local _name=$1
    local _filepath="categories/$(echo "$_name" | sed 's/ /-/g' | awk '{print tolower($0)}').html"

    if [[ ! -f "$_filepath" ]]; then
      echo "---" > "$_filepath"
      echo "layout: category" >> "$_filepath"
      echo "title: $_name" >> "$_filepath"
      echo "category: $_name" >> "$_filepath"
      echo "---" >> "$_filepath"

      ((category_count=category_count+1))
    fi
  fi
}


create_tag() {
  if [[ ! -z $1 ]]; then
    local _name=$1
    local _filepath="tags/$( echo "$_name" | sed "s/ /-/g;s/'//g" | awk '{print tolower($0)}' ).html"

    if [[ ! -f "$_filepath" ]]; then

      echo "---" > "$_filepath"
      echo "layout: tag" >> "$_filepath"
      echo "title: $_name" >> "$_filepath"
      echo "tag: $_name" >> "$_filepath"
      echo "---" >> "$_filepath"

      ((tag_count=tag_count+1))
    fi
  fi
}


#########################################
# Create HTML pages for Categories/Tags.
# Arguments:
#   $1 - an array string
#   $2 - type specified option
#########################################
create_pages() {
  if [[ ! -z $1 ]]; then
    # split string to array
    IFS_BAK=$IFS
    IFS=','
    local _string=$1

    case $2 in

      $TYPE_CATEGORY)
        for i in ${_string#,}; do
          create_category "$i"
        done
        ;;

      $TYPE_TAG)
        for i in ${_string#,}; do
          create_tag "$i"
        done
        ;;

      *)
        ;;

      esac

      IFS=$IFS_BAK
  fi

}


main() {

  init

  for _file in $(find "_posts" -type f \( -iname \*.md -o -iname \*.markdown \))
  do
    local _categories=$(read_categories "$_file")
    local _tags=$(read_tags "$_file")

    create_pages "$_categories" $TYPE_CATEGORY
    create_pages "$_tags" $TYPE_TAG
  done

  if [[ $category_count -gt 0 ]]; then
    echo "[INFO] Succeed! $category_count category-pages created."
  fi

  if [[ $tag_count -gt 0 ]]; then
    echo "[INFO] Succeed! $tag_count tag-pages created."
  fi
}

main