refactor parallel code

openos/cat.lua

@@ -0,0 +1,30 @@
+local shell = require("openos.shell")
+local fs = require("openos.filesystem")
+
+local args = shell.parse(...)
+local ec = 0
+if #args == 0 then
+  args = {"-"}
+end
+
+for i = 1, #args do
+  local arg = shell.resolve(args[i])
+  if fs.isDirectory(arg) then
+    io.stderr:write(string.format('cat %s: Is a directory\n', arg))
+    ec = 1
+  else
+    local file, reason = fs.open(arg)
+    if not file then
+      io.stderr:write(string.format("cat: %s: %s\n", args[i], tostring(reason)))
+      ec = 1
+    else
+      local chunk = file.readAll()
+      file:close()
+      if chunk then
+        io.write(chunk)
+      end
+    end
+  end
+end
+
+return ec