Postgres WAL Archive Script (archive_command) checking File Integrity based upon the checksum of source and target

wal_archive.sh

#!/bin/bash

# -----------------
# DISCLAIMER !!!
# To be used as is.

# --------------------
# Syntax = wal_archive.sh wall_source_fullpath wall_name
# archive_command='wal_archive.sh "%p" "%f"'
# PS: The order is %p followed by %f

wal_archives_dir='/var/lib/postgresql/wal.archives/main_9.5'
# wal_archives_dir='/mnt/wal.archives'

wal_source="${1}" # %p is the full path
wal_filename="${2}" # %f is the filename

echo "Params !!"
echo "  -- Source WAL ${wal_source}"
echo "  -- WAL Filename ${wal_filename}"

target_file="${wal_archives_dir}/${wal_filename}"

echo "Archives !!"
echo "  -- Archive Location ${wal_archives_dir}"
echo "  -- Archive Fullpath ${target_file}"

# Customize the checksum file as per the OS
function checksum()
{
   chk_file="${1}"
   # mac 
   md5 "${chk_file}" | awk '{print $4}'
   # ubuntu
   # md5sum "${chk_file}" | awk '{print $1}'
}

echo "Checksum !!"
wal_checksum=$(checksum "${wal_source}")
echo "  -- WAL Hash ${wal_checksum}"

if [ -f "${target_file}" ];
then
  # Checksum
  target_checksum=$(checksum "${target_file}")
  if [[ $target_checksum == $wal_checksum ]];
  then
    echo "  -- File was already copied correctly !! Ignored"
    exit 0
  fi
fi

echo "  -- Beginning to copy file ... "
cp "${wal_source}" "${target_file}"
target_checksum=$(checksum "${target_file}")
if [[ $target_checksum == $wal_checksum ]];
then
  echo "  -- File is copied correctly"
  exit 0
fi

exit 1