By some case, we have to execute system command and redirect input/output to 
pecified files, such as initialize mysql database: 
  mysql < init_db.sql >log.txt
  
  To run this kind of command by Ant is not very convenient, Because Ant only 
support output redirect and doesn't support input redirect. we have to specify 
os and do as: 

  <exec executable="cmd" os="Windows 2000" output="log.txt">
    <arg line="/c mysql &lt; init_db.sql>
  </exec>
  <exec executable="/bin/sh" os="Linux" output="log.txt">
    <arg line="-c mysql &lt; init_db.sql>
  </exec>

  It's not convenient. my suggestion is to add "input" attribute for task exec. 
So that we can just write one line as:
  <exec executable="mysql" input="init_db.sql" output="log.txt" />
and run it any where.

  BTW, I met the problem for initialize mysql database in my project. If you 
have good suggestion. Please let me know.

Thanks & Best regards,
David