A small script to convert my Gemtext journal into an atom feed

jnl2atm.sh

#!/usr/bin/env bash

BASE_DOMAIN="ruario.flounder.online"
MICROLOG_FILENAME="journal.gmi"
MICROLOG_URL="//$BASE_DOMAIN/$MICROLOG_FILENAME"
ATOM_FILENAME="${MICROLOG_FILENAME%.gmi}-atom.xml"
ATOM_URL="//$BASE_DOMAIN/$ATOM_FILENAME"
MICROLOG_TITLE="Ruari's Journal"
AUTHOR_NAME=ruario
MAX_FEEDS=20
LINE_LENGTH=55

date_convert () {
if [ `uname -s` = Linux ]; then
  date -ud "$1" +'%FT%H:%M:00Z'
else
  date -ujf '%F %H:%M %z' "$1" +'%FT%H:%M:00Z'
fi
}

safe_echo () {
  printf '%s\n' "$1" | sed 's/\&/\&#x26;/g;s/</\&#x3C;/g'
}

clip_line () {
  while IFS= read -r l;
  do
    if [ "$PREFORMAT" = ON ]; then
      printf '%s\n' "$l"
    else
      case "$l" in
        '* '*) # Lists
          printf '%s\n' "$l" | fmt -w "$(($LINE_LENGTH - 2))" | sed -E 's/^([^\*])/  \1/'
          ;;
        '=>'*) # Links
          printf '%s\n' "$l" | sed -E 's/^=>[[:blank:]]*([^[:blank:]]+)[[:blank:]]+(.*)/~ \2:\n\1\n/;s/^=>[[:blank:]]*([^[:blank:]]+)/~ :\n\1/' \
          | while IFS= read -r ll;
          do
            case "$ll" in
              ~*)
                printf '%s\n' "$ll" | fmt -w "$(($LINE_LENGTH - 2))" | sed -E 's/^([^\~])/  \1/'
                ;;
              *)
                printf '%s\n' "$ll"
                ;;
            esac
          done
          ;;
        '>'*) # Quote
          printf '%s\n' "$l" | sed -E 's/^>[[:blank:]]?//' | fmt -w "$(($LINE_LENGTH - 2))" | sed 's/^/> /'
          ;;
        *)
          printf '%s\n' "$l" | fmt -w "$LINE_LENGTH"
          ;;
      esac
    fi
  done
}

PREFORMAT=OFF
PRINT_HEADER=ON
FULL_DATE_AVAILABLE=NO
NEW_SECTION_START=NO
CLOSE_ENTRY=NO
FEED_COUNTER=0
{
while IFS= read -r LINE;
do
  if [ "$NEW_SECTION_START" = YES ]; then
    if [ "$PRINT_HEADER" = ON ]; then
      cat <<EOF
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <title>$MICROLOG_TITLE</title>
  <link rel="self" href="$ATOM_URL"/>
  <link href="$MICROLOG_URL"/>
  <updated>$(date_convert "$JRNLDAY $JRNLTIME")</updated>
  <author>
    <name>$AUTHOR_NAME</name>
    <uri>gemini://$BASE_DOMAIN/</uri>
  </author>
  <id>gemini:$MICROLOG_URL</id>
EOF
    PRINT_HEADER=OFF
    fi
    if [ "$SECTION_INTRO" = YES ]; then
      if [ "$CLOSE_ENTRY" = YES ]; then
        if [ "$FEED_COUNTER" -ge "$(( $MAX_FEEDS - 1 ))" ]; then
          break
        fi
        cat <<EOF
</pre></div></content>
  </entry>
EOF
        FEED_COUNTER="$(( $FEED_COUNTER + 1 ))"
      fi
      CLOSE_ENTRY=YES
      cat <<EOF
  <entry>
    <title>@${JRNLTIME}—$JRNLTITLE</title>
    <link rel="alternate" href="$MICROLOG_URL"/>
    <id>gemini:$MICROLOG_URL/$JRNLDAY-$(echo "$JRNLTIME" | cut -d' ' -f1 | tr -d ':')</id>
    <updated>$(date_convert "$JRNLDAY $JRNLTIME")</updated>
    <summary type="text">$JRNLSUMMARY</summary>
    <content type="xhtml"><div xmlns="http://www.w3.org/1999/xhtml"><pre>
EOF
      safe_echo "$FIRSTLINE" | clip_line
      SECTION_INTRO=NO
    fi
    case "$LINE" in
      '## '*)
        JRNLDAY=$(echo $LINE | cut -d' ' -f2-)
        ;;
      '### '*)
        JRNLTIME=$(echo $LINE | cut -d' ' -f2-)
        NEW_SECTION_START=NO
        SECTION_INTRO=YES
        ;;
      '```'*)
        if [ "$PREFORMAT" = OFF ]; then
          PREFORMAT=ON
        else
          PREFORMAT=OFF
        fi
        ;;
      '⁂')
        break
        ;;
      *)
        safe_echo "$LINE" | clip_line
        ;;
    esac
  elif [ "$FULL_DATE_AVAILABLE" = YES ]; then
    case "$LINE" in
      [[:alnum:]\>=@\'\"~]*)
        JRNLSUMMARY="$(printf '%s\n' "$LINE" | sed -E 's/^=>[[:blank:]]*[^[:blank:]]+[[:blank:]]+//;s/\&/\&#x26;/g;s/</\&#x3C;/g')"
        JRNLTITLE="$(printf '%s\n' "$JRNLSUMMARY" | cut -c 1-49 | sed "s/$/…/")"
        FIRSTLINE="$LINE"
        NEW_SECTION_START=YES
        ;;
      *)
        :
        ;;
    esac
  else
    case "$LINE" in
      '## '*)
        JRNLDAY=$(echo $LINE | cut -d' ' -f2-)
        ;;
      '### '*)
        FULL_DATE_AVAILABLE=YES
        JRNLTIME=$(echo $LINE | cut -d' ' -f2-)
        SECTION_INTRO=YES
        ;;
      *)
        :
        ;;
    esac
  fi
done < $MICROLOG_FILENAME

cat <<EOF
</pre></div></content>
  </entry>
</feed>
EOF
} | cat -s > $ATOM_FILENAME

echo "Created: $ATOM_FILENAME"