lua-string match the magic characters

to escapse the magic character , we have to use ‘%’ to turn off pattern match when call string.find or gsub functions

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function test_string()
    local name = "res${CALLERID(name)}"
    local s1,s2 = string.gsub(name,"$%{CALLERID%(name%)%}", "lilizhou")
    print(s1)
    print(s2)
end

in the exampe, we try to replace the whole string ‘${CALLERID(name)}’ with a new string.