Parse and extract data from Gmail to Google Sheet. Read full article here: http://blog.gsmart.in/parse-and-extract-data-from-gmail-to-google-sheets/

## messages.html
<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
    <title>Message Display Test</title>
    <link rel="stylesheet" href="https://ssl.gstatic.com/docs/script/css/add-ons1.css">
  </head>
  <body style="padding:3em;">
  <h1>Messages</h1>
    <ul>
    <? for(var m=0;m<messages.length;m++){ ?>
    <li><?= messages[m].getSubject() ?></li>
    <p><?= messages[m].getPlainBody() ?></p>
    <? } ?>
    </ul>
  </body>
</html>

## parse-extract-from-gmail.js


function getRelevantMessages()
{
  var threads = GmailApp.search("newer_than:1d AND from:citicorp.com AND subject:Transaction confirmation AND -label:payment_processing_done",0,100);
  var messages=[];
  threads.forEach(function(thread)
                  {
                    messages.push(thread.getMessages()[0]);
                  });
  return messages;
}

function parseMessageData(messages)
{
  var records=[];
  for(var m=0;m<messages.length;m++)
  {
    var text = messages[m].getPlainBody();

    var matches = text.match(/Rs\.\s+([\d\,\.]+)\s+(?:spent on card)\s+(\d+)\s+(?:on)\s+([\d\-A-Z]+)\s+(?:at)\s+([\w\s]+)\./);

    if(!matches || matches.length < 5)
    {
      //No matches; couldn't parse continue with the next message
      continue;
    }
    var rec = {};
    rec.amount = matches[1];
    rec.card = matches[2];
    rec.date= matches[3];
    rec.merchant = matches[4];

    //cleanup data
    rec.amount = parseFloat(rec.amount.replace(/,/g, ''));

    records.push(rec);
  }
  return records;
}

function getMessagesDisplay()
{
  var templ = HtmlService.createTemplateFromFile('messages');
  templ.messages = getRelevantMessages();
  return templ.evaluate();
}

function getParsedDataDisplay()
{
  var templ = HtmlService.createTemplateFromFile('parsed');
  templ.records = parseMessageData(getRelevantMessages());
  return templ.evaluate();
}

function saveDataToSheet(records)
{
  var spreadsheet = SpreadsheetApp.openByUrl("https://docs.google.com/spreadsheets/d/1ql-S5TjH5KoekRvRqiwuyequyxhgas/edit#gid=0");
  var sheet = spreadsheet.getSheetByName("Sheet1");
  for(var r=0;r<records.length;r++)
  {
    sheet.appendRow([records[r].date,records[r].card, records[r].merchant, records[r].amount ] );
  }

}

function processTransactionEmails()
{
  var messages = getRelevantMessages();
  var records = parseMessageData(messages);
  saveDataToSheet(records);
  labelMessagesAsDone(messages);
  return true;
}

function labelMessagesAsDone(messages)
{
  var label = 'payment_processing_done';
  var label_obj = GmailApp.getUserLabelByName(label);
  if(!label_obj)
  {
    label_obj = GmailApp.createLabel(label);
  }

  for(var m =0; m < messages.length; m++ )
  {
     label_obj.addToThread(messages[m].getThread() );
  }

}

function doGet()
{
  return getParsedDataDisplay();

  //return getMessagesDisplay();
}

## parsed.html
<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
    <title>Data parsed from emails</title>
    <link rel="stylesheet" href="https://ssl.gstatic.com/docs/script/css/add-ons1.css">
  </head>
  <body style="padding:3em;">
    <h2>Parsed data from Messages</h2>
    <table style="width:420px">
    <thead>
    <tr>
    <th>Date</th><th>Merchant</th><th>Card</th><th>Amount</th>
    </tr>
    </thead>
    <tbody>
    <? for(var m=0;m<records.length;m++){ ?>
    <tr>
    <td><?= records[m].date ?></td>
    <td><?= records[m].merchant ?></td>
    <td><?= records[m].card ?></td>
    <td><?= records[m].amount ?></td>
    </tr>
    <? }?>
    </tbody>
    </table>
    <div class="block">
    <button id="save_to_sheet" class="blue">Save Data to Sheet</button>
    <span id="saving_label" style="visibility:hidden">Saving ...</span>
    </div>
    <script>
    document.querySelector("#save_to_sheet").addEventListener("click",
    function(e)
    {
       var self=this;
       self.style.visibility = 'hidden';
       var saving_label = document.querySelector("#saving_label");
       saving_label.style.visibility = 'visible';
       google.script.run.withSuccessHandler(function()
       {
         alert("Saved expense data");
         self.style.visibility = 'visible';
         saving_label.style.visibility = 'hidden';

       }).withFailureHandler(function()
       {
         alert("an error occured while saving");
         self.style.visibility = 'visible';
         saving_label.style.visibility = 'hidden';
       }).processTransactionEmails();

    });
    </script>
  </body>
</html>