Open an XML file, want to put all files identified as $path $string substitution for a string variable path, the path variable is the string before the replacement, should how to replace, I ask you, thank you,

 
Path=myreg. GetValue (" SetupPath "). The ToString (); 
XmlDocument doc=new XmlDocument (); 
If (the File. The Exists (" a.x ml "))//
{
Doc. The Load (" a.x ml "); 
Doc. Replace (" $$" path, the path). 
Console. WriteLine (" the file has been modified!" ); 
} 
The else 
{
Console. WriteLine (" the file does not exist!" ); 
} 
Doc. Save (" a.x ml "); 
Console. WriteLine (" a.x ml successfully saved ");