Update phpBB 3 forum post, replacing it's content with specified file

update_post.sh

#!/bin/bash
# Script Name: update_post.sh
# Author: John Doe
# Date: 2025-02-04
# Description: Update phpBB 3 forum post, replacing it's content with specified file

set -o errexit
set -o nounset
set -o pipefail

USERNAME="John Doe"
PASSWORD="123456"
POST_ID=178068
FILE="new_content.md"

HOST="https://forum.farmanager.com"
LOGIN_URL="$HOST/ucp.php?mode=login"
POST_URL="$HOST/posting.php?mode=edit&p=$POST_ID"

extract_value() {
  echo $OUTPUT | sed -nE "s/.*name=\"$1\"[^>]* value=\"([^\"]*)\".*/\1/p"
}

#retrieve cookies
OUTPUT=$(curl -s "$LOGIN_URL")
curl -s $LOGIN_URL -c cookies.txt \
  -d "username=$USERNAME" \
  -d "password=$PASSWORD" \
  -d "autologin=on" \
  -d "creation_time=$(extract_value creation_time)" \
  -d "form_token=$(extract_value form_token)" \
  -d "sid=$(extract_value sid)" \
  -d "login=Login" \
  | grep 'class="error"' || true

case "$(sed -n 's/.*phpbb3_sxb2q_u\t\([^\t]*\).*/\1/p' cookies.txt)" in
  1)
    exit 1;;
  "")
    exit 1;;
esac

#get necessary posting information
OUTPUT=$(curl -s $POST_URL -b cookies.txt)

#post the message
echo Posting...
sleep 1 #otherwise fails
STATUS_LINE=$(
curl $POST_URL -sib cookies.txt \
  -d "subject=$(extract_value subject)" \
  --data-urlencode "message@$FILE" \
  -d "edit_post_message_checksum=$(extract_value edit_post_message_checksum)" \
  -d "edit_post_subject_checksum=$(extract_value edit_post_subject_checksum)" \
  -d "post=Submit" \
  -d "no_edit_log=on" \
  -d "creation_time=$(extract_value creation_time)" \
  -d "form_token=$(extract_value form_token)" \
  | head -n 1)

if [[ "$STATUS_LINE" == *302* ]]; then
  echo Done.
else
  echo Oops!
fi

#cleanup
rm cookies.txt