Exec Command is not working in sql server - php

Question

I am working on database migration. I have written a code for executing the command that retrieves the data from database and pushes into a csv file. This Works fine in MySQL but when I try to do the same in SQL Server it does not work. Infact when I copy paste the same command into command prompt it works fine. I double checked everything. I do not understand why its not working. It returns blank output. I have already tried many of the solutions provided before. None works. Any help on this is most appreciated.
Here is the code I am using:
//$sqlsrv is used to determine the database server type
$str_query = voc_get_query_string($query);
$output_uri = 'temporary://' . user_password();
$file_path = drupal_realpath($output_uri . '.csv');
if($sqlsrv){
$exec_path = drupal_realpath('private://Binn\sqlcmd');
}else{
$exec_path = drupal_realpath('private://mysql');
}
$sql_uri = 'temporary://' . user_password();
$sql_path = drupal_realpath($sql_uri);
$fp = fopen($sql_path, 'w');
fputs($fp, $str_query);
fclose($fp);
global $databases;
if ($sqlsrv) {
$cmd = ($exec_path .
' -S ' . $databases['default']['default']['host'] .
' -d ' . $databases['default']['default']['database'] .
' -U ' . $databases['default']['default']['username'] .
' -P ' . $databases['default']['default']['password'] .
' -i ' . $sql_path . '>>'. $file_path .
' -s '. '"," -W -m10 -r1');
}
else {
$cmd = ($exec_path . ' ' . $databases['default']['default']
['database'] .
' -h ' . $databases['default']['default']['host'] .
' -u ' . $databases['default']['default']['username'] .
' -p ' . $databases['default']['default']['password'] . ' < '
. $sql_path .
' > ' . $file_path);
}
exec($cmd);
watchdog('cmd', var_export($cmd, TRUE));