Bash script which watch Postfix virtual user mailbox folder

watch.sh

#!/bin/bash

#
# Watch Postfix virtual user mailbox folder.
#
# inotify-tools APT package is required
#

DEFAULT_USER="test"
DEFAULT_DOMAIN="yahoo.dev"
DEFAULT_MAILBOXES_DIR="/var/mail/virtual"
DEFAULT_DIR="new"

usage()
{
  printf "Usage: ./watch.sh [USER] [DOMAIN] [cur|new|tmp] [MAILBOXES_FOLDER]\n\n"
  exit 3
}

error()
{
  echo "Error: $*"
  exit 1
}

check_requirements()
{
  reqcmd="awk date grep inotifywait sed"
  for cmd in $reqcmd
  do
    if ! which $cmd &>/dev/null; then
      error "$cmd command is required by this script"
    fi
  done
}

watch_mailbox()
{
  user=$1
  domain=$2
  dir=$3
  mboxesdir=$4
  if [ -z "$user" ]; then
    user=$DEFAULT_USER
  fi
  if [ -z "$domain" ]; then
    domain=$DEFAULT_DOMAIN
  fi
  if [ -z "$dir" ]; then
    dir=$DEFAULT_DIR
  fi
  if [ -z "$mboxesdir" ]; then
    mboxesdir=$DEFAULT_MAILBOXES_DIR
  fi
  mbox_dir=$mboxesdir/$domain/$user/$dir
  clear && show_messages $mbox_dir
  inotifywait -q -m $mbox_dir -e create -e move -e delete |
    while read path action file; do
      # echo "The file '$file' appeared in directory '$path' via '$action'"
      clear && show_messages $mbox_dir
    done
}

show_messages()
{
  msgs_dir=$1
  if [ ! -d "$msgs_dir" ]; then
    error "$msgs_dir folder not found"
  fi
  msgc=0
  msgs=$(ls $msgs_dir)
  for msg in $msgs
  do
    if show_message $msgs_dir/$msg; then
      ((msgc++))
    fi
  done
  printf "\nFound $msgc message(s) in mailbox. Press CTRL+C to abort..."
}

show_message()
{
  msg=$1
  if [ -z "$1" ]; then
    error "Message filename is missing"
  fi
  if [ ! -f "$1" ]; then
    error "Message file not found"
  fi

  ## Date: Fri, 15 May 2015 11:39:06 +0200
  ## From: postmaster@localhost
  ## To: test@yahoo.dev
  ## Subject: Welcome
  msgdate=$(grep -m 1 '^Date: ' $msg|awk '{$1=""; print $0}'|sed 's/^ *//g')
  msgfrom=$(grep -m 1 '^From: ' $msg|awk '{print $2}')
  msgto=$(grep -m 1 '^To: ' $msg|awk '{print $2}')
  msgsubject=$(grep -m 1 '^Subject: ' $msg|awk '{$1=""; print $0}'|sed 's/^ *//g')
  shortdate=$(date -d "$msgdate" +%Y-%m-%d" "%H:%M:%S)

  #echo "msgdate: $msgdate"
  #echo "msgfrom: $msgfrom"
  #echo "msgto: $msgto"
  #echo "msgsubject: $msgsubject"
  #echo "shortdate: $shortdate"

  if [ -z "$msgdate" ]; then
    ## Parsing failed, maybe file is not a message ?
    return 1
  fi

  echo "$shortdate $msgfrom $msgto $msgsubject" && return 0
}

## MAIN SCRIPT
if [ "$1" == "-h" ]; then
  usage
fi
check_requirements
watch_mailbox $1 $2 $3 $4