Generate Dates for Markdown Files

#!/bin/bash
# Contents of .git/hooks/pre-commit
# Replace `last_modified_at` timestamp with current time


for b in $(find ./ -name '*.md'); do
  if [ $(cat $b | head -n 1 | grep '\-\-\-') ]; then
      echo "already have meta"
  else
    cat $b | sed '1s/^/---\n---\n/' > tmp
    mv tmp $b
  fi

  if grep -q last_modified_at $b; then
      echo "no change"
  else
    cat $b | sed '1 {/---.*/,/---.*/{0,/---/{s/---/---\nlast_modified_at:/}}}' > tmp
    mv tmp $b
  fi

  cat $b | sed "/---.*/,/---.*/s/^last_modified_at:.*$/last_modified_at: $(date -r $b "+%Y-%m-%dT%H:%M:%S")/" > tmp
  mv tmp $b
done