Convert Excel Files to CSV in Google Drive with Apps Script

The Google Apps Script uses the Advanced Drive API to covert Microsoft Excel files (XLS, XLSX) into CSV files and saves them into a specific Google Drive folder. The Excel sheets are deleted after the CSV files are saved in Drive.

Also see: Convert Google Sheets to PDF Files

The conversion engine may timeout if you have too many XLS/XLSX files in a Google Drive and in that case, you’d need to include the time check to ensure that the script doesn’t exceed the execution time limit.

function convertXLSFilesToCSV() {

    var oauthToken = ScriptApp.getOAuthToken(),
        sourceFolder = DriveApp.getFolderById(SOURCE_XLS_FOLDER),
        targetFolder = DriveApp.getFolderById(TARGET_CSV_FOLDER),
        mimes = [MimeType.MICROSOFT_EXCEL, MimeType.MICROSOFT_EXCEL_LEGACY];

    /* Written by Amit Agarwal */
    /* email: amit@labnol.org  */
    /* website: www.ctrlq.org */

    for (var m = 0; m < mimes.length; m++) {

        files = sourceFolder.getFilesByType(mimes[m]);

        while (files.hasNext()) {

            var sourceFile = files.next();

            // Re-upload the XLS file after convert in Google Sheet format
            var googleSheet = JSON.parse(UrlFetchApp.fetch(
                "https://www.googleapis.com/upload/drive/v2/files?uploadType=media&convert=true", {
                    method: "POST",
                    contentType: "application/vnd.ms-excel",
                    payload: sourceFile.getBlob().getBytes(),
                    headers: {
                        "Authorization": "Bearer " + oauthToken
                    }
                }
            ).getContentText());

            // The exportLinks object has a link to the converted CSV file
            var targetFile = UrlFetchApp.fetch(
                googleSheet.exportLinks["text/csv"], {
                    method: "GET",
                    headers: {
                        "Authorization": "Bearer " + oauthToken
                    }
                });

            // Save the CSV file in the destination folder
            targetFolder.createFile(targetFile.getBlob()).setName(sourceFile.getName() + ".csv");

            // Delete the processed file
            sourceFile.setTrashed(true);

        }
    }

}