web/_scripts/sh/dump_lastmod.sh

#!/bin/bash
#
# Find out the posts that have been modified and record
# its lastmod information to file '_data/updates.yml'
#
# 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

POST_DIR=_posts
OUTPUT_DIR=_data
OUTPUT_FILE=updates.yml


_init() {

  if [[ ! -d "$OUTPUT_DIR" ]]; then
    mkdir "$OUTPUT_DIR"
  fi

  if [[ -f "$OUTPUT_DIR/$OUTPUT_FILE" ]]; then
    rm -f "$OUTPUT_DIR/$OUTPUT_FILE"
  fi

  if [[ ! -d $POST_DIR ]]; then
    exit 0
  fi
}


_has_changed() {
  local _log_count=`git log --pretty=%ad $1 | wc -l | sed 's/ *//'`
  _log_count=$(($_log_count + 0))

  if [[ $_log_count > 1 ]]; then
    return 0 # true
  fi

  return 1 # false
}


###################################
# Storage the posts' lastmod.
#
# Args:
#     - $1 the post's filename
#     - $2 the post's filepath
# Output:
#     the file '_data/updates.yml'
###################################
_dump() {
  local _lasmod="`git log -1 --pretty=%ad --date=iso $2`"

  if [[ ! -f "$OUTPUT_DIR/$OUTPUT_FILE" ]]; then
    touch "$OUTPUT_DIR/$OUTPUT_FILE"
  fi

  echo "-" >> "$OUTPUT_DIR/$OUTPUT_FILE"
  echo "  filename: '$1'" >> "$OUTPUT_DIR/$OUTPUT_FILE"
  echo "  lastmod: '$_lasmod'" >> "$OUTPUT_DIR/$OUTPUT_FILE"
}


main() {

  _init

  local _count=0

  for _file in $(find ${POST_DIR} -type f \( -iname \*.md -o -iname \*.markdown \))
  do
    _filename=$(basename $_file | sed 's/[0-9]\([0-9]*-\)//g;s/\..*//' ) # remove date and extension

    if _has_changed "$_file"; then
      _dump "$_filename" "$_file"
      ((_count=_count+1))
    fi

  done

  if [[ $_count > 0 ]]; then
    echo "[INFO] Success to update lastmod for $_count post(s)."
  fi
}


main