Function for parsing a string

I have a string of the below format

name1=value1; name2=value2;name 3=value3 ;name4 = value4

Can some one please get me ready with a function which gets the above string and name part as input which flushes out the value part as output. For example, if I pass the above string and "name 3" as input to the function, the function should return me the string "value3"

Xavier Ruben Fernando B