Var Expand

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-- version: 0.0.1

-- code: Ketmar // Avalon Group

-- public domain



-- expand $var and ${var} in string

-- ${var} can call Lua functions: ${string.rep(' ', 10)}

-- `$' can be screened with `\'

-- `...': args for $<number>

-- if `...' is just a one table -- take it as args

function ExpandVars (s, ...)

  local args = {...};

  args = #args == 1 and type(args[1]) == "table" and args[1] or args;

  -- return true if there was an expansion

  local function DoExpand (iscode)

    local was = false;

    local mask = iscode and "()%$(%b{})" or "()%$([%a%d_]*)";

    local drepl = iscode and "\\$" or "\\\\$";

    s = s:gsub(mask, function (pos, code)

      if s:sub(pos-1, pos-1) == "\\" then return "$"..code;

      else was = true; local v, err;

        if iscode then code = code:sub(2, -2);

        else local n = tonumber(code);

          if n then v = args[n]; end;

        end;

        if not v then

          v, err = loadstring("return "..code); if not v then error(err); end;

          v = v();

        end;

        if v == nil then v = ""; end;

        v = tostring(v):gsub("%$", drepl);

        return v;

      end;

    end);

    if not (iscode or was) then s = s:gsub("\\%$", "$"); end;

    return was;

  end;



  repeat DoExpand(true); until not DoExpand(false);

  return s;

end;





list = { "one", field = "hi!" };

name = "Lua"; status = "great"

print(

  ExpandVars(

    "${name} is $status. ${string.rep('#', 3)} \\${!} \\$isn't it? "..

      "${list.field}, ${list [1]}, $_VERSION, ${10/2}, ${'$'}, $1",

    {"arg"}));

  --> Lua is great. ### ${!} $isn't it? hi!, one, Lua 5.1, 5, $, arg

See Also

• StringInterpolation - other interpolation solutions
• TextTemplate