Using shell escape to access system time

Question

In an earlier question, I asked for analogs of \pdfelapsedtime (which measures the time since the start of the current run) in XeTeX and LuaTeX. A LuaTeX solution was provided, and is now part of Heiko's pdftexcmds package. However, no XeTeX solution was provided. The only approach I can see to measuring time in XeTeX is to use shell-escape.

With pdfTeX on a Unix system I would build a wrapper around

\everyeof{\noexpand}
\catcode`\%=12
\message{\input|"date +%s.%N"}

(compile with pdftex --shell-escape).

1. Is there an analog of the \input|... construction for XeTeX? (When writing this question I thought that this construction would work.)

2. How can the system time be accessed in various os?

Answer 1

Pipe support

pdfTeX support pipes since version 1.40.0 (released 2007-01-01). From NEWS:

shell escape: if the first character of a filename for \openin, \openout \input is a pipe symbol (|), the filename is assumed to be a request for a pipe to a command line that is given in the rest of the filename

The feature is enabled in different ways depending on the TeX distribution:

• TeX Live: --shell-restricted (default) allows some few commands to be called (e.g. kpsewhich, makeindex. See variable shell_escape_commands in texmf.cnf. Otherwise full shell escape rights are needed. They can be set by option `--shell-escape'.
• MiKTeX: Pipe support is activated by `--enable-pipes'. Shell escape options do not affect pipes.

Package catchfile (for plain and LaTeX formats) will add \CatchPipeDef and \CatchPipeEdef in version 2012/07/30 v1.6 to support pdfTeX's pipe feature.

LuaTeX does not have the same pipe feature of pdfTeX, because it has the Lua function io.popen that can be used for that purpose. Pacakge pdftexcmds provides \pdf@pipe as wrapper for convenience.

XeTeX: I could not get pipes running and working neither in TL2011/Linux nor MiKTeX 2.9. In the latter case I could only catch an empty line instead of the intended program output.

OS independent command line

Nowadays TeX distributions often include LuaTeX with its program texlua. For example, the following Lua script prints the time in seconds since 1970-01-01:

if os.gettimeofday then
  print(os.gettimeofday())
else
  print(os.date("%s"))
end

Then the command call

texlua gettimeofday.lua

prints 1343650327.0485, for example.

However if gettimeofday.lua is not in the current directory, texlua will not find it, because its kpathsea module is not active. At least TL and MiKTeX provide kpsewhich for finding the file.

Example for pdfTeX and the new version (2012/07/30 v1.6) of package catchfile:

\CatchPipeEdef\ScriptGettimeofday{kpsewhich gettimeofday.lua}{\endlinechar=-1}
\CatchPipeEef\CurrentTime{texlua \ScriptGettimeofday}{\endlinechar=-1}

Macro \CurrentTime contains the result. Or with low level commands (with e-TeX), it is something like:

\begingroup
  \everyeof{\noexpand}%
  \endlinechar=-1 %
  \edef\file{\input |"kpsewhich gettimeofday.lua"}
  \xdef\CurrentTime{\input |"texlua \file"}
  % Use \@@input in LaTeX instead of the redefined \input
\endgroup

PS: The new version of package catchfile: catchfile-1.6.pdf
(The .dtx file is attached to the PDF. Run tex on catchfile.dtx to unpack the package.)

Answer to Bruno's comment:

If pipes are not available, then the ordinary write18 feature can be used. However there are many downsides:

• Slower (file writing, searching and reading)
• The wrong file might be found. That can be tested by writing some random bytes in a file with the write18 process and reading them back and checking, whether bytes are the same.
• The solution cannot be made expandable.
• More things that can break: File is not written (e.g. readonly directory), cannot be found, the wrong file is found, …
• Unique temporary file names needed to avoid conflicts in multi-user systems or multiple processes at the same time.
• Cleanup: Delete commands are again OS dependent (rm in Unix, del in Windows). or the temporary files remain.

Answer 2

One approach, based on Heiko Oberdiek's answer to this question, and egreg's answer to a similar question is the code below. It's made more complicated because I don't know how to pass parameters to a lua script interpreted using texlua, so I hard-code the parameter \blf@time@base in the lua file each time a function is called.

Since the absence of pipes in XeTeX forbids any expandable solution, the function \pdf@setelapsedtime should be called before each time \pdf@elapsedtime is used. This solution using \write18 has all the drawbacks noted in Heiko's answer. In particular, each \test takes 0.1 seconds on my system, which is rather slow.

\catcode`\@=11
\newwrite\blf@time@write
\newread \blf@time@read
\gdef\blf@time@base{0}%
\protected\gdef\blf@time@aux#1#2%
  {%
    \begingroup
      \escapechar=-1
      \immediate\openout\blf@time@write\jobname.lua%
      \immediate\write\blf@time@write
        {%
          os.remove("\jobname.timestamp")
          if os.gettimeofday then
            time = os.gettimeofday()
          else
            time = os.date("\string\%s")
          end
          val = .5 + 65536 * (time - \blf@time@base)
          if val > 2147483647 then
            val = 2147483647
          end
          io.output("\jobname.timestamp"):write(string.format("%
            \string\%f\string\\n\string\%d", time, val))
        }%
      \immediate\closeout\blf@time@write
      \immediate\write18{texlua \jobname.lua}%
      \endlinechar-1%
      \immediate\openin\blf@time@read\jobname.timestamp
      \readline\blf@time@read to \blf@time@tmp
      #1%
      \readline\blf@time@read to \blf@time@tmp
      #2%
      \immediate\closein\blf@time@read
    \endgroup
  }%
\protected\gdef\pdf@resettimer
  {\blf@time@aux{\xdef\blf@time@base{\blf@time@tmp}}{}}%
\protected\gdef\pdf@setelapsedtime
  {%
    \blf@time@aux{}%
      {\protected\xdef\pdf@elapsedtime{\numexpr\blf@time@tmp\relax}}%
  }%
\pdf@resettimer
\pdf@setelapsedtime


\def\test
  {%
    \pdf@setelapsedtime
    \message{\the\pdf@elapsedtime}%
  }
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\test\test\test\test\test\test\test\test\test\test
\bye

Compile with xetex --shell-escape <filename>.tex.