Masking Telephone Digits

This complex function will mask either the last 4 numbers, or keep the first 8 only – depending on the length of the number.

function MaskDigits(s,c,t)
 s = string.gsub(s, "%d%d%d%d%d%d%d[%d%*#]*",
   function(n)
     local len=string.len(n)
     if (len>8)
     then return string.sub(n,1,8)..string.rep("X",len-8)
     else return string.sub(n, 1, -5)..string.rep("X", 4)
     end
   end)
 mem.write(c,s)
end

The gsub parameter “%d%d%d%d%d%d%d[%d%*#]*” will look for all strings that include 7 digits, followed by any number of digits, *, or # characters.

The anonymous function provided as a replacement for the string will:

  • Work out the length – stored in “len”
  • If the length is longer than 8 characters, it will keep the first 8 characters, and substitute the remaining characters with “X”.
  • If the length is less than, or equal to, 8 characters then it will effectively replace the last 4 characters with an “X”.

Obviously, any other combination is possible.

Links for string.gsub: