Author: Irtza Sharif
Function: returns the value of an attribute in an xml file
if no infile is specified it will read from standard input and if no outfile is specified it will write to standard output.
infile is an XML file
outfile will be where the attribute value is dumped
xml_path is the path to the tag containing the attribute
attribute is the name of the attribute to retrieve the value of
value is the value to which u wish to set the attribute