Please disregard. I figured it out. For anyone having a same issue the solution is below:
For example I am invoking sqcmd as below
sqlcmd -S myServer\instanceName -i "\\myserver\my path\myScript.sql"
In the execute process atsk general tab , set Executable property to : C:\Program Files\Microsoft SQL Server\100\Tools\Binn\sqlcomd.exe
in Expressions tab, select Arguments and type in below expression
"-S " + @[User::InstanceName] + " -i " + " \"" + @[User::FilePath] + "\""
where InstanceName and FilePath are my package variables set to the sql instance and teh path to the sql script.
Since my script path has spaces I put the " around the file name. The escape charcter for SSIS expressions is \" for quote.