Web Service Request with Curl

I have requirement where i need to use a curl command to invoke a Webservice and then get a response out of it. I know there are many post with using curl but m question is how can i use curl command to pass the parameters which may be in the request.xml. I cant use the file as a input. Below is the sample file I want a curl command which will run the request and get me a response without an input file.

<soapenv:Header/>
<soapenv:Body>
<web:LogOnUser>
<web:username> </web:username>
<web:password> </web:password>
</web:LogOnUser>
</soapenv:Body>
</soapenv:Header>