#!/bin/bash
#  Script by Francisco Lobo,
#+ and slightly modified and commented by ABS Guide author.
#  Used in ABS Guide with permission. (Thank you!)

# This script will not run under Bash versions -lt 3.0.


E_MISSING_ARG=87
if [ -z "$1" ]
then
  echo "Usage: $0 mailbox-file"
  exit $E_MISSING_ARG
fi

mbox_grep()  # Parse mailbox file.
{
    declare -i body=0 match=0
    declare -a date sender
    declare mail header value


    while IFS= read -r mail
#         ^^^^                 Reset $IFS.
#  Otherwise "read" will strip leading & trailing space from its input.

   do
       if [[ $mail =~ ^From  ]]   # Match "From" field in message.
       then
          (( body  = 0 ))           # "Zero out" variables.
          (( match = 0 ))
          unset date

       elif (( body ))
       then
            (( match ))
            #  echo "$mail"
            #  Uncomment above line if you want entire body
            #+ of message to display.

   elif [[ $mail ]]; then
      IFS=: read -r header value <<< "$mail"
      #                          ^^^  "here string"

      case "$header" in
      [Ff][Rr][Oo][Mm] ) [[ $value =~ "$2" ]] && (( match++ )) ;;
      # Match "From" line.
      [Dd][Aa][Tt][Ee] ) read -r -a date <<< "$value" ;;
      #                                  ^^^
      # Match "Date" line.
      [Rr][Ee][Cc][Ee][Ii][Vv][Ee][Dd] ) read -r -a sender <<< "$value" ;;
      #                                                    ^^^
      # Match IP Address (may be spoofed).
      esac

       else
          (( body++ ))
          (( match  )) &&
          echo "MESSAGE ${date:+of: ${date[*]} }"
       #    Entire $date array             ^
          echo "IP address of sender: ${sender[1]}"
       #    Second field of "Received" line    ^

       fi


    done < "$1" # Redirect stdout of file into loop.
}


mbox_grep "$1"  # Send mailbox file to function.

exit $?

# Exercises:
# ---------
# 1) Break the single function, above, into multiple functions,
#+   for the sake of readability.
# 2) Add additional parsing to the script, checking for various keywords.



$ mailbox_grep.sh scam_mail
  MESSAGE of Thu, 5 Jan 2006 08:00:56 -0500 (EST) 
  IP address of sender: 196.3.62.4