[examples/truncate] Add example for osx.chsize().

examples/truncate.lua

@@ -0,0 +1,42 @@
+#!/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))