#!/bin/env lua
-- Stripped down version of util-linux coreutils(1).
--
-- SYNOPSIS:
-- truncate.lua <size> <file>
--
-- Size may have a suffix: K (kilobytes), M (megabytes), G (gigabytes) with K = 1024
--
-- Example use:
-- lua truncate.lua 10K myfile
--
-- Author: Lorenzo Cogotti, The DoubleFourteen Code Forge

local osx = require 'osx'

local size = assert(select(1, ...), "Missing size argument")
local path = assert(select(2, ...), "Missing file path")

local function parsesize(s)
    local u = s:sub(-1)
    local scale = 1

    if u == 'K' then
        scale = 1024
        s = s:sub(1, -2)
    elseif u == 'M' then
        scale = 1024*1024
        s = s:sub(1, -2)
    elseif u == 'G' then
        scale = 1024*1024*1024
        s = s:sub(1, -2)
    end

    local v = tonumber(s)
    if not v or v < 0 then
        error("'"..s.."' is not a valid file size")
    end
    return v * scale
end

size = parsesize(size)
assert(osx.chsize(path, size))