mysqldump not producing any output

Question

I need to dump the entire database to a text file, but mysqldump is not outputting anything. Here is the command i'm executing via php script:

<?php
  $_user="root";
  $_pass="";
  $_db="somedb";
  $_host = "localhost";

  $filename = "somedb.zip";
  $target_fn = "test.txt";

  $command = 'c:\xampp\mysql\bin\mysqldump -u'.$_user.' -p'.$_pass.' -  
              h'.$_host." ".$_db.' > test.txt';
   try{
     exec( $command );
   } 
   catch(Exception $e){
     echo $e;
   }
?>

EDIT

I"m on a XAMPP stack.

EDIT After running the above command on a cmd, i realized it still prompts for a password. Perhaps an empty password is what the command is misinterpreting wrongly.

Answer 1

So the problem was the command syntax/structure for a blank password. Here is the correct command for a blank pass:

$command = 'C:\xampp\mysql\bin\mysqldump -u'.$_user.' -h'.$_host." ".$_db.' > test.txt';

Answer 2

$return_var = NULL;
$output = NULL;
$command = "/usr/bin/mysqldump -u mysql-user -h 123.145.167.189 -pmysql-pass database_name > /path-to-export/file.sql";
exec($command, $output, $return_var);

Try giving 2 more parameters to the exec

Reference