53

For instance, I want to include a figure: ~/figures/figure.pdf. On my Linux box, this is /home/me/figures/figure.pdf, but on OS X it is /Users/me/figures/figure.pdf. I'd like it if there is an environment variable like $HOME so that the latex file can compile on both machines \includegraphics{$HOME/figures/figure.pdf}. (Of course it wouldn't use the $ sign).

I just found this post, but Is write18 the most native way? And, in the given example, the assignment wouldn't actually define the variable in LaTex. I tried

\immediate\write18{echo "\newcommand{\HOME}{$HOME}" > var.tex}

But gives me this error:

! Argument of \@gobble has an extra }.

So now I am at a loss.

1

3 Answers 3

44

If you have a recent TeX Live (2010 or later) or MiKTeX (v. 2.9), then the following works (and does not need the -shell-escape command line option):

\usepackage{catchfile}
\newcommand{\getenv}[2][]{%
  \CatchFileEdef{\temp}{"|kpsewhich --var-value #2"}{\endlinechar=-1}%
  \if\relax\detokenize{#1}\relax\temp\else\let#1\temp\fi}

\getenv[\HOME]{HOME}

If you only say \getenv{VAR} then the value of the variable is printed instead of being stored in a control sequence.

Not only HOME can be used, but any environment variable and also the "pseudovariables" defined in the TeX kpathsea system such as TEXMF or TEXINPUTS.

Note that this works only with pdflatex. With other engines or older distributions, shell escape is needed. Of course LuaTeX has its methods for interacting with the system.


A version that works with all recent engines is

\documentclass{article}

\usepackage{ifxetex,ifluatex}

\ifxetex
  \usepackage{catchfile}
  \newcommand\getenv[2][]{%
    \immediate\write18{kpsewhich --var-value #2 > \jobname.tmp}%
    \CatchFileDef{\temp}{\jobname.tmp}{\endlinechar=-1}%
    \if\relax\detokenize{#1}\relax\temp\else\let#1\temp\fi}
\else
  \ifluatex
    \newcommand\getenv[2][]{%
      \edef\temp{\directlua{tex.sprint(
        kpse.var_value("\luatexluaescapestring{#2}") or "" ) }}%
      \if\relax\detokenize{#1}\relax\temp\else\let#1\temp\fi}
  \else
    \usepackage{catchfile}
    \newcommand{\getenv}[2][]{%
      \CatchFileEdef{\temp}{"|kpsewhich --var-value #2"}{\endlinechar=-1}%
      \if\relax\detokenize{#1}\relax\temp\else\let#1\temp\fi}
  \fi
\fi

\begin{document}
\getenv[\HOME]{HOME}\show\HOME
\end{document}

In the case of xetex an auxiliary file \jobname.tmp is written and -shell-escape is necessary.

Note: the LuaTeX method has been suggested by Patrick Gundlach. If the variable is unset or not known to kpathsea, the empty string will result.


UPDATE 2019

With recent and up-to-date TeX distributions, the following works with every engine (except, of course, Knuth TeX): pdflatex, xelatex, lualatex, platex and uplatex. Unrestricted shell escape is not necessary.

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\getenv}{om}
 {
  \sys_get_shell:nnN { kpsewhich ~ --var-value ~ #2 } { } \l_tmpa_tl
  \tl_trim_spaces:N \l_tmpa_tl
  \IfNoValueTF { #1 }
   {
    \tl_use:N \l_tmpa_tl
   }
   {
    \tl_set_eq:NN #1 \l_tmpa_tl
   }
 }

\ExplSyntaxOff

\begin{document}

\getenv[\HOME]{HOME}\show\HOME

\end{document}
16
  • 2
    I'd like to use \getenv[VAR]{envvar} in a situation where envvar may not have been defined. I've been trying unsuccessfully to condition on the output of \getenv in this case. Is it possible to modify the command so that it returns something like UNDEFINED if there environment variable hasn't been defined?
    – Leo Simon
    Commented Oct 24, 2016 at 17:25
  • @LeoSimon Add before the \if\relax lines, the line \ifx\temp\empty\def\temp{UNDEFINED}\fi Or do a test for emptyness when the macro is used.
    – egreg
    Commented Oct 24, 2016 at 17:51
  • Thanks for the suggestion, but I can't get it to work. Here's an MWE, although I don't know how to put code into a comment \documentclass{article} \usepackage{catchfile} \newcommand{\getenv}[2][]{% \CatchFileEdef{\temp}{"|kpsewhich --var-value #2"}{}% \ifx\temp\empty\def\temp{UNDEFINED}\fi \if\relax\detokenize{#1}\relax\temp\else\let#1\temp\fi} \begin{document} The getenv command should return UNDEFINED but returns \getenv{NOT_DEFINED} \end{document} In this example \getenv{NOT_DEFINED} returns empty
    – Leo Simon
    Commented Dec 4, 2016 at 21:07
  • @LeoSimon If you have a followup question, please ask one
    – egreg
    Commented Dec 5, 2016 at 0:04
  • 1
    @GilbertoT. \endlinechar=-1 was missing.
    – egreg
    Commented Dec 30, 2019 at 22:12
15

@egreg has already answered your question so I thought I'd not answer it. That is suggest not relying on environment variables for this. If the latex file just goes \includegraphics{figures/figure.pdf}

then if $HOME/figures// is in TEXINPUTS environment variable or texmf.cnf configuration setting then the file will be found without LaTeX explicitly needing to access the machine-specific information. This keeps machine specific information and directory structure in the kpathsearch system which is optimised to deal with that rather than the macro layer which tries as far as possible to avoid such issues.

Also for the specific case of home directory you can (on web2c systems on at least linux and windows/cygwin, but I assume the others too) use \string~/figures/figure.pdf as kpathsea understands ~ as the home directory (but you have to pass it a literal ~ not the normal active definition for a non-breakable space, hence the \string.

3

The updated answer from @egreg for new versions did not work for me however this did:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\getenv}{om}
{
  \sys_get_shell:nnN{ kpsewhich ~ --var-value ~ #2 }{}#1
}

\ExplSyntaxOff

\begin{document}

\getenv[\HOME]{HOME}
\HOME

\end{document}

I do not know if this is the expected behaviour but it works for me and based on the documentation for \sys_get_shell:nnN it seems to be the intended behaviour.

4
  • Not sure why you say “it doesn't work”, because your macro just does the same as mine, with the difference that you can't just say \getenv{FOO} to simply print the value. Oh, and you'll get some weird error if you don't specify the optional argument.
    – egreg
    Commented Jun 3, 2020 at 21:12
  • Oh I didn't even notice you specified the second parameter as optional. Your version leads to an error during compilation. Upon further inspection I got your version working by removing the \show
    – Septatrix
    Commented Jun 3, 2020 at 21:21
  • \show uses the error message mechanism. I used it just to print on the terminal the value assigned to \HOME.
    – egreg
    Commented Jun 3, 2020 at 21:26
  • Note that \usepackage{xstring} can be used to strip the extra space in the \HOME token with \StrGobbleRight{\HOME}{1}[\strippedHOME]
    – jlettvin
    Commented Nov 9, 2023 at 18:37

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