about regex

string str = "(g: abc)"
how can get the string "abc"  from str?
i want to get the inside string if there is  "(g: *)" , and then when i get the string i want replace it with a link.
for example if string is like "(g: example)" 
i want to change it like this,  "<a href= 'search.aspx?f=example'> example </a>"
i hope you understand what i mean? so how can i do that?
thanks for answers
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