2 files changed, 15 insertions, 12 deletions
diff --git a/core/.os.luadoc b/core/.os.luadoc
index 4dd473fa..5891060b 100644
--- a/core/.os.luadoc
+++ b/core/.os.luadoc
@@ -14,11 +14,10 @@ module('os')
 -- @param argv A command line string that contains the program's name followed
 --   by arguments to pass to it. `PATH` is searched for program names.
 -- @param cwd Optional current working directory (cwd) for the child
---   process. The default value is `nil`, which inherits the parent's cwd.
+--   process. When omitted, the parent's cwd is used.
 -- @param env Optional list of environment variables for the child process.
---   Each element in the list is a 'KEY=VALUE' string. The default value is
---   `nil`, which inherits the parent's environment.
---   This parameter should be omitted completely instead of specifying `nil`.
+--   Each element in the list is a 'KEY=VALUE' string. When omitted, the
+--   parent's environment is used.
 -- @param stdout_cb Optional Lua function that accepts a string parameter for a
 --   block of standard output read from the child. Stdout is read asynchronously
 --   in 1KB or 0.5KB blocks (depending on the platform), or however much data is
@@ -32,8 +31,8 @@ module('os')
 -- @param exit_cb Optional Lua function that is called when the child process
 --   finishes. The child's exit status is passed.
 -- @return proc or nil plus an error message on failure
--- @usage os.spawn('lua buffer.filename', nil, print)
--- @usage proc = os.spawn('lua -e "print(io.read())"', nil, print)
+-- @usage os.spawn('lua buffer.filename', print)
+-- @usage proc = os.spawn('lua -e "print(io.read())"', print)
 --        proc:write('foo\n')
 -- @class function
 -- @name os.spawn
diff --git a/core/init.lua b/core/init.lua
index 25c28043..71e65c4f 100644
--- a/core/init.lua
+++ b/core/init.lua
@@ -18,14 +18,18 @@ keys = require('keys')
 _M = {} -- language modules table
 -- pdcurses compatibility.
 if CURSES and WIN32 then
-  function os.spawn(argv, cwd, ...)
+  function os.spawn(argv, ...)
     local current_dir = lfs.currentdir()
-    if cwd then lfs.chdir(cwd) end
+    local i = 1
+    if type(select(i, ...)) == 'string' then
+      lfs.chdir(select(i, ...)) -- cwd
+      i = i + 1
+    end
+    if type(select(i, ...)) == 'table' then i = i + 1 end -- env (ignore)
     local p = io.popen(argv..' 2>&1')
-    local cb_index = type(select(1, ...)) ~= 'table' and 1 or 2 -- ignore env
-    local stdout_cb, exit_cb = select(cb_index, ...), select(cb_index + 2, ...)
-    if stdout_cb then stdout_cb(p:read('a')) end
-    if exit_cb then exit_cb(select(3, p:close())) else p:close() end
+    if select(i, ...) then select(i, ...)(p:read('a')) end -- stdout_cb
+    local status = select(3, p:close())
+    if select(i + 2, ...) then select(i + 2, ...)(status) end -- exit_cb
     lfs.chdir(current_dir)
     return p
   end