Par[ameter $Package::|$Project::|$ServerOption::]parameter_name[(data_type)];literal_value Optional. Provides a literal value ...

Par[ameter] [$Package::|$Project::|$ServerOption::]parameter_name[(data_type)];literal_value

Optional. Provides a literal value for a parameter. Multiple /Parameter options
can be specified. The $Package::, $Project::, or $ServerOption:: name prefix 
can be specified to indicate the type of parameter.  The default parameter type
is package. For non-string parameter values the data type should be specified
in parenthesis following the parameter name.

The following is an example of executing a package that is provided a the value
myvalue to for the project parameter myparam and the integer value 12 for the
package parameter anotherparam.

dtexec /isserver "\SSISDB\MyFolder\MyProject\MyPackage.dtsx" /server "." /parameter $Project::myparam;myvalue /parameter anotherparam(int32);12