Execute System Command In LuaTeX

Question

(Edit: How to do file system operations and binary execution with LuaTeX in an OS-independent manner? I had written a set of macros for pdfTeX to do this using the \write18 command. These macros were meant to be usable under both Windows and Linux, giving some "higher level" control. Now I wanted the macros to also support LuaTeX. My first experiments were unsuccessful, however. Trying to reduce the problem by omitting all macros and executing LuaTeX on the command line mislead the focus to an unimportant problem before I found a solution some days later.)

In a minimal testing environment (see Minimal Testing Environment For LuaMetaTeX) I can do the initial memory dump

    luatex --ini ./plain.tex \dump

and then I would expect the following command to list the directory:

    luatex --fmt=./plain.fmt --shell-escape \directlua {os.execute ("dir")}\end

but it just tells me:

    This is LuaTeX, Version 1.13.2 (TeX Live 2021/W32TeX)
     system commands enabled.
    No pages of output.
    Transcript written on texput.log.

So how do I execute system commands under LuaTeX as it is possible under pdfTeX with \write18?

Answer 1

I over-minimized this test by entering a LuaTeX command at the shell prompt without the necessary quoting, as @David explained, so I did not get the expected output. Within a document, the same command must not be quoted, and the problem shifts to getting the output from the system into a command sequence. The idea is being able to run under both unix and windows while failing gracefully under pdfTeX or if --shell-escape is not set.

    \def \system #1#2#3{{%
      % #1: unix command, #2: windows command, #3: control sequence (return value) 
      \xdef #3{}%
      \ifx \directlua \undefined
        \message {! No \string\directlua\space support (LuaTeX required).}%
      \else
        \edef \escapestate {\directlua {tex.write (status.shell_escape)}}%
        \def \one {1}%
        \ifx \escapestate \one
          \edef \ostype {\directlua {tex.print (os.type)}}%
          \def \unix {unix}% os.type can be "unix", "windows", or "msdos"
          \directlua {% 
            \ifx \ostype \unix
              local file = io.popen ([[#1]]);
              os.execute ([[#1]]);
            \else
              local file = io.popen ([[#2]]);
              os.execute ([[#2]]);
            \fi 
            local content = file:read "*a";
            file:close ();        
            tex.toks [5] = content; }%
          \xdef #3{\the \toks 5}%
        \else \message {! No --shell-escape switch set for system command.}\fi
      \fi }}  

    \bgroup \newlinechar = 10     
      \system {setterm --clear}{cls}\myresult  
      \system {time}{time /t}\myresult
        \message {^^JSystem time:^^J\myresult}   
      \system {cd}{cd}\myresult
        \message {^^JCurrent folder:^^J\myresult}  
      \system {ls -l}{dir /b}\myresult
        \message {^^JFiles in current folder:^^J\myresult}  
      \system {set}{set}\myresult
        \message {^^JEnvironment variables:^^J\myresult}  
    \egroup \end

Save above file as curdir.tex and run:

    luatex --fmt=plain --output-format=pdf --shell-escape ./curdir.tex \end