Hi, I think there is a bug in `io.open` in --safer mode: \directlua{ io.open(tex.jobname .. '.tex'):close() } \bye If this document is run with `luatex --safer` it leads to `bad argument #1 to 'gsub' (string expected, got nil)`. The problem is a missing `not` in luatex-core.lua, function luatex_io_open_readonly: The default argument 'r' is used if an explicit argument is given and when no "how" argument is given it tries to interpret the non existing argument. This can be fixed by (I omit the changes to `luatex-core.c` in the diff, they are auto-generated anyway): diff --git a/source/texk/web2c/luatexdir/lua/luatex-core.lua b/source/texk/web2c/luatexdir/lua/luatex-core.lua index f2d55fd99..de7f12006 100644 --- a/source/texk/web2c/luatexdir/lua/luatex-core.lua +++ b/source/texk/web2c/luatexdir/lua/luatex-core.lua @@ -54,7 +54,7 @@ local function luatex_io_open(name,how) end local function luatex_io_open_readonly(name,how) - if how then + if not how then how = 'r' else how = gsub(how,'[^rb]','') Best regards, Marcel Krüger