This task   (the reverse of   URL encoding   and distinct from   URL parser)   is to provide a function
or mechanism to convert an URL-encoded string into its original unencoded form.



Test cases

   The encoded string   "http%3A%2F%2Ffoo%20bar%2F"   should be reverted to the unencoded form   "http://foo bar/".
   The encoded string   "google.com/search?q=%60Abdu%27l-Bah%C3%A1"   should revert to the unencoded form   "google.com/search?q=`Abdu'l-Bahá".


proc urlDecode {str} {
    set specialMap {"[" "%5B" "]" "%5D"}
    set seqRE {%([0-9a-fA-F]{2})}
    set replacement {[format "%c" [scan "\1" "%2x"]]}
    set modStr [regsub -all $seqRE [string map $specialMap $str] $replacement]
    return [encoding convertfrom utf-8 [subst -nobackslash -novariable $modStr]]
}