diff --git a/l3build-check.lua b/l3build-check.lua
index fb624e7e..f7782af6 100644
--- a/l3build-check.lua
+++ b/l3build-check.lua
@@ -134,7 +134,7 @@ local function normalize_log(content,engine,errlevels)
        not match(line, "%.%.%.$") then
       return "", (lastline or "") .. line
     end
-    local line = (lastline or "") .. line
+    line = (lastline or "") .. line
     lastline = ""
     -- Zap ./ at begin of filename
     line = gsub(line, "%(%.%/", "(")
@@ -696,17 +696,17 @@ function runtest(name, engine, hide, ext, pdfmode, breakout)
   cp(lvtfile, fileexists(testfiledir .. "/" .. lvtfile)
     and testfiledir or unpackdir, testdir)
   local checkopts = checkopts
-  local engine = engine or stdengine
+  engine = engine or stdengine
   local binary = engine
-  local format = gsub(engine,"tex$",checkformat)
+  format = gsub(engine,"tex$",checkformat)
   -- Special binary/format combos
   if specialformats[checkformat] and next(specialformats[checkformat]) then
     local t = specialformats[checkformat]
-    if t[engine] and next(t[engine]) then
-      local t = t[engine]
-      binary    = t.binary  or binary
-      checkopts = t.options or checkopts
-      format    = t.format  or format
+    local t_ngn = t[engine]
+    if t_ngn and next(t_ngn) then
+      binary    = t_ngn.binary  or binary
+      checkopts = t_ngn.options or checkopts
+      format    = t_ngn.format  or format
     end
   end
   -- Finalise format string
@@ -807,11 +807,11 @@ function runtest(name, engine, hide, ext, pdfmode, breakout)
   for _,filetype in pairs(auxfiles) do
     for _,file in pairs(filelist(testdir, filetype)) do
       if match(file,"^" .. name .. ".[^.]+$") then
-        local ext = match(file, "%.[^.]+$")
-        if ext ~= lvtext and
-           ext ~= tlgext and
-           ext ~= lveext and
-           ext ~= logext then
+        local e7n = match(file, "%.[^.]+$")
+        if e7n ~= lvtext and
+           e7n ~= tlgext and
+           e7n ~= lveext and
+           e7n ~= logext then
            local newname = gsub(file,"(%.[^.]+)$","." .. engine .. "%1")
            if fileexists(testdir,newname) then
              rm(testdir,newname)
@@ -908,17 +908,12 @@ function check(names)
         end
       end
     end
-    -- https://stackoverflow.com/a/32167188
-    local function shuffle(tbl)
-      local len, random = #tbl, rnd
-      for i = len, 2, -1 do
-          local j = random(1, i)
-          tbl[i], tbl[j] = tbl[j], tbl[i]
-      end
-      return tbl
-    end
     if options["shuffle"] then
-      names = shuffle(names)
+      -- https://stackoverflow.com/a/32167188
+      for i = #names, 2, -1 do
+        local j = rnd(1, i)
+        names[i], names[j] = names[j], names[i]
+      end
     end
     -- Actually run the tests
     print("Running checks on")
diff --git a/l3build-file-functions.lua b/l3build-file-functions.lua
index c80a761b..2dfaa791 100644
--- a/l3build-file-functions.lua
+++ b/l3build-file-functions.lua
@@ -36,7 +36,6 @@ local execute          = os.execute
 local exit             = os.exit
 local getenv           = os.getenv
 local remove           = os.remove
-local os_time          = os.time
 local os_type          = os.type
 
 local luatex_revision  = status.luatex_revision
@@ -183,6 +182,7 @@ function abspath(path)
   error(msg)
 end
 
+-- TODO: Fix the cross platform problem
 function escapepath(path)
   if os_type == "windows" then
     local path,count = gsub(path,'"','')
@@ -214,22 +214,21 @@ end
 -- Copy files 'quietly'
 function cp(glob, source, dest)
   local errorlevel
-  for i,_ in pairs(tree(source, glob)) do
-    local source = source .. "/" .. i
+  for p_rel,p_cwd in pairs(tree(source, glob)) do
     if os_type == "windows" then
-      if attributes(source)["mode"] == "directory" then
+      if attributes(p_cwd)["mode"] == "directory" then
         errorlevel = execute(
-          'xcopy /y /e /i "' .. unix_to_win(source) .. '" "'
-             .. unix_to_win(dest .. '/' .. i) .. '" > nul'
+          'xcopy /y /e /i "' .. unix_to_win(p_cwd) .. '" "'
+             .. unix_to_win(dest .. '/' .. p_rel) .. '" > nul'
         )
       else
         errorlevel = execute(
-          'xcopy /y "' .. unix_to_win(source) .. '" "'
+          'xcopy /y "' .. unix_to_win(p_cwd) .. '" "'
              .. unix_to_win(dest .. '/') .. '" > nul'
         )
       end
     else
-      errorlevel = execute("cp -RLf '" .. source .. "' '" .. dest .. "'")
+      errorlevel = execute("cp -RLf '" .. p_cwd .. "' '" .. dest .. "'")
     end
     if errorlevel ~=0 then
       return errorlevel
@@ -302,10 +301,10 @@ function tree(path, glob)
   end
   local dirs = {["."] = cropdots(path)}
   for pattern, criterion in gmatch(cropdots(glob), "([^/]+)(/?)") do
-    local criterion = criterion == "/" and is_dir or always_true
-    local function fill(path, dir, table)
+    criterion = criterion == "/" and is_dir or always_true
+    local function fill(path_a, dir, table)
       for _, file in ipairs(filelist(dir, pattern)) do
-        local fullpath = path .. "/" .. file
+        local fullpath = path_a .. "/" .. file
         if file ~= "." and file ~= ".." and
           fullpath ~= builddir
         then
@@ -319,13 +318,13 @@ function tree(path, glob)
     local newdirs = {}
     if pattern == "**" then
       while true do
-        local path, dir = next(dirs)
-        if not path then
+        local path_a, dir = next(dirs)
+        if not path_a then
           break
         end
-        dirs[path] = nil
-        newdirs[path] = dir
-        fill(path, dir, dirs)
+        dirs[path_a] = nil
+        newdirs[path_a] = dir
+        fill(path_a, dir, dirs)
       end
     else
       for path, dir in pairs(dirs) do
@@ -357,7 +356,7 @@ function mkdir(dir)
   if os_type == "windows" then
     -- Windows (with the extensions) will automatically make directory trees
     -- but issues a warning if the dir already exists: avoid by including a test
-    local dir = unix_to_win(dir)
+    dir = unix_to_win(dir)
     return execute(
       "if not exist "  .. dir .. "\\nul " .. "mkdir " .. dir
     )
@@ -368,10 +367,10 @@ end
 
 -- Rename
 function ren(dir, source, dest)
-  local dir = dir .. "/"
+  dir = dir .. "/"
   if os_type == "windows" then
-    local source = gsub(source, "^%.+/", "")
-    local dest = gsub(dest, "^%.+/", "")
+    source = gsub(source, "^%.+/", "")
+    dest = gsub(dest, "^%.+/", "")
     return execute("ren " .. unix_to_win(dir) .. source .. " " .. dest)
   else
     return execute("mv " .. dir .. source .. " " .. dir .. dest)
diff --git a/l3build-help.lua b/l3build-help.lua
index 8627e14f..6431ac54 100644
--- a/l3build-help.lua
+++ b/l3build-help.lua
@@ -39,7 +39,7 @@ end
 function help()
   local function setup_list(list)
     local longest = 0
-    for k,v in pairs(list) do
+    for k,_ in pairs(list) do
       if k:len() > longest then
         longest = k:len()
       end
@@ -70,7 +70,7 @@ function help()
   end
   print("")
   print("Valid options are:")
-  local longest,t = setup_list(option_list)
+  longest,t = setup_list(option_list)
   for _,k in ipairs(t) do
     local opt = option_list[k]
     local filler = rep(" ", longest - k:len() + 1)
diff --git a/l3build-install.lua b/l3build-install.lua
index 92bfa126..cea9aa19 100644
--- a/l3build-install.lua
+++ b/l3build-install.lua
@@ -97,7 +97,7 @@ function uninstall()
   if errorlevel ~= 0 then return errorlevel end
   -- Finally, clean up special locations
   for _,location in ipairs(tdslocations) do
-    local path,glob = splitpath(location)
+    local path = splitpath(location)
     errorlevel = zapdir(path)
     if errorlevel ~= 0 then return errorlevel end
   end
@@ -140,11 +140,11 @@ function install_files(target,full,dry_run)
           end
           local matched = false
           for _,location in ipairs(tdslocations) do
-            local path,glob = splitpath(location)
-            local pattern = glob_to_pattern(glob)
+            local l_dir,l_glob = splitpath(location)
+            local pattern = glob_to_pattern(l_glob)
             if match(filename,pattern) then
-              insert(paths,path)
-              insert(filenames,path .. sourcepath .. filename)
+              insert(paths,l_dir)
+              insert(filenames,l_dir .. sourcepath .. filename)
               matched = true
               break
             end
@@ -162,12 +162,12 @@ function install_files(target,full,dry_run)
     if next(filenames) then
       if not dry_run then
         for _,path in pairs(paths) do
-          local dir = target .. "/" .. path
-          if not cleanpaths[dir] then
-            errorlevel = cleandir(dir)
+          local dir_a = target .. "/" .. path
+          if not cleanpaths[dir_a] then
+            errorlevel = cleandir(dir_a)
             if errorlevel ~= 0 then return errorlevel end
           end
-          cleanpaths[dir] = true
+          cleanpaths[dir_a] = true
         end
       end
       for _,file in ipairs(filenames) do
@@ -192,17 +192,17 @@ function install_files(target,full,dry_run)
       exclude = exclude or { }
       dir = dir or currentdir
       local includelist = { }
-      local excludelist = { }
+      local excludelist_a = { }
       for _,glob_table in pairs(exclude) do
         for _,glob in pairs(glob_table) do
           for file,_ in pairs(tree(dir,glob)) do
-            excludelist[file] = true
+            excludelist_a[file] = true
           end
         end
       end
       for _,glob in pairs(include) do
         for file,_ in pairs(tree(dir,glob)) do
-          if not excludelist[file] then
+          if not excludelist_a[file] then
             insert(includelist, file)
           end
         end
diff --git a/l3build-manifest-setup.lua b/l3build-manifest-setup.lua
index e00f48ff..e0da78e5 100644
--- a/l3build-manifest-setup.lua
+++ b/l3build-manifest-setup.lua
@@ -221,18 +221,16 @@ end
 --]]
 
 manifest_sort_within_match = manifest_sort_within_match or function(files)
-  local f = files
-  table.sort(f)
-  return f
+  table.sort(files)
+  return files
 end
 
 manifest_sort_within_group = manifest_sort_within_group or function(files)
-  local f = files
   --[[
       -- no-op by default; make your own definition to customise. E.g.:
-      table.sort(f)
+      table.sort(files)
   --]]
-  return f
+  return files
 end
 
 --[[
diff --git a/l3build-stdmain.lua b/l3build-stdmain.lua
index b086eb07..48d596f0 100644
--- a/l3build-stdmain.lua
+++ b/l3build-stdmain.lua
@@ -22,6 +22,8 @@ for those people who are interested.
 
 --]]
 
+local lfs = require("lfs")
+
 local exit   = os.exit
 local insert = table.insert
 
diff --git a/l3build-tagging.lua b/l3build-tagging.lua
index aa84b0d5..3dbe4b17 100644
--- a/l3build-tagging.lua
+++ b/l3build-tagging.lua
@@ -51,7 +51,7 @@ local function update_file_tag(file,tagname,tagdate)
   else
     local path = dirname(file)
     ren(path,filename,filename .. ".bak")
-    local f = assert(open(file,"w"))
+    f = assert(open(file,"w"))
     -- Convert line ends back if required during write
     -- Watch for the second return value!
     f:write((gsub(updated_content,"\n",os_newline)))
diff --git a/l3build-typesetting.lua b/l3build-typesetting.lua
index 0ae25a90..da57cb84 100644
--- a/l3build-typesetting.lua
+++ b/l3build-typesetting.lua
@@ -49,9 +49,9 @@ end
 
 -- An auxiliary used to set up the environmental variables
 function runcmd(cmd,dir,vars)
-  local dir = dir or "."
-  local dir = abspath(dir)
-  local vars = vars or {}
+  dir = dir or "."
+  dir = abspath(dir)
+  vars = vars or {}
   -- Allow for local texmf files
   local env = os_setenv .. " TEXMFCNF=." .. os_pathsep
   local localtexmf = ""
@@ -80,7 +80,7 @@ function biber(name,dir)
 end
 
 function bibtex(name,dir)
-  local dir = dir or "."
+  dir = dir or "."
   if fileexists(dir .. "/" .. name .. ".aux") then
     -- LaTeX always generates an .aux file, so there is a need to
     -- look inside it for a \citation line
@@ -105,7 +105,7 @@ function bibtex(name,dir)
 end
 
 function makeindex(name,dir,inext,outext,logext,style)
-  local dir = dir or "."
+  dir = dir or "."
   if fileexists(dir .. "/" .. name .. inext) then
     if style == "" then style = nil end
     return runcmd(makeindexexe .. " " .. makeindexopts
@@ -119,15 +119,15 @@ function makeindex(name,dir,inext,outext,logext,style)
 end
 
 function tex(file,dir,cmd)
-  local dir = dir or "."
-  local cmd = cmd or typesetexe .. typesetopts
+  dir = dir or "."
+  cmd = cmd or typesetexe .. typesetopts
   return runcmd(cmd .. " \"" .. typesetcmds
     .. "\\input " .. file .. "\"",
     dir,{"TEXINPUTS","LUAINPUTS"})
 end
 
 local function typesetpdf(file,dir)
-  local dir = dir or "."
+  dir = dir or "."
   local name = jobname(file)
   print("Typesetting " .. name)
   local fn = typeset
@@ -141,7 +141,7 @@ local function typesetpdf(file,dir)
     print(" ! Compilation failed")
     return errorlevel
   end
-  pdfname = name .. pdfext
+  local pdfname = name .. pdfext
   rm(docfiledir,pdfname)
   return cp(pdfname,dir,docfiledir)
 end
@@ -226,7 +226,7 @@ function doc(files)
             end
             -- Now know if we should typeset this source
             if typeset then
-              local errorlevel = typesetpdf(srcname,path)
+              errorlevel = typesetpdf(srcname,path)
               if errorlevel ~= 0 then
                 return errorlevel
               else
diff --git a/l3build-unpack.lua b/l3build-unpack.lua
index d5c8e301..83466c07 100644
--- a/l3build-unpack.lua
+++ b/l3build-unpack.lua
@@ -22,8 +22,6 @@ for those people who are interested.
 
 --]]
 
-local execute          = os.execute
-
 -- Unpack the package files using an 'isolated' system: this requires
 -- a copy of the 'basic' DocStrip program, which is used then removed
 function unpack(sources, sourcedirs)
diff --git a/l3build-upload.lua b/l3build-upload.lua
index 7270ebfc..a4dcf108 100644
--- a/l3build-upload.lua
+++ b/l3build-upload.lua
@@ -78,6 +78,12 @@ end
 -- if upload is anything else, the user will be prompted whether to upload.
 -- For now, this is undocumented. I think I would prefer to keep it always set to ask for the time being.
 
+local ctan_post -- this is private to the module
+
+-- TODO: next is a public global method,
+-- but following functions are semantically local
+-- despite they are declared globally.
+
 function upload(tagnames)
 
   local uploadfile = ctanzip..".zip"
@@ -100,7 +106,7 @@ function upload(tagnames)
 
   uploadconfig.note =   uploadconfig.note  or file_contents(uploadconfig.note_file)
 
-  local tagnames = tagnames or { }
+  tagnames = tagnames or { }
   uploadconfig.version = tagnames[1] or uploadconfig.version
 
   local override_update_check = false
@@ -214,7 +220,7 @@ end
 
 function shell(s)
   local h = assert(popen(s, 'r'))
-  t = assert(h:read('*a'))
+  local t = assert(h:read('*a'))
   h:close()
   return t
 end
@@ -248,11 +254,13 @@ function construct_ctan_post(uploadfile,debug)
   ctan_field("uploader",     uploadconfig.uploader,      255, "Name of uploader",                    true,  false )
   ctan_field("version",      uploadconfig.version,        32, "Package version",                     true,  false )
 
+  --[=[ `qq` is unused because line 258 is commented
   -- finish constructing the curl command:
   local qq = '"'
   if os_type == "windows" then
     qq = '\"'
   end
+  --]=]
 -- commandline   ctan_post = ctan_post .. ' --form ' .. qq .. 'file=@' .. tostring(uploadfile) .. ';filename=' .. tostring(uploadfile) .. qq
   ctan_post = ctan_post .. '\nform="file=@' .. tostring(uploadfile) .. ';filename=' .. tostring(uploadfile) .. '"'
 
@@ -352,7 +360,7 @@ function file_contents (filename)
     local f= open(filename,"r")
     if f==nil then
       return nil
-    else 
+    else
       local s = f:read("*all")
       close(f)
       return s