Avoid inputting a file multiple times

Question

I have a revision string automatically saved to a file VERSION (it is the output of git describe and usually looks like v2.2-19-g0a51c27), and define a command

\newcommand*\fileversion{\input{VERSION}}

However, each time the command is used, the file is read once. So if I put the command on every page, VERSION will be read many times (= number of pages).

Currently I use savebox to avoid this problem but unfortunately this can not pick up the surrounding formatting style, for example, if surrounding text is in footnotesize, the savebox still uses normal size.

I also tried \edef\fileversion{\input{VERSION}} but somehow TeX gave me 'stack limit' error.

So my question is how to define a command that expands to the contents of VERSION and not \input{VERSION}.

Answer 1

A solution in plain tex could be like this (assuming a one-line file)

\newread\versionread
\immediate\openin\versionread = VERSION
\immediate\read\versionread to \fileversion
\immediate\closein\versionread

A (much) sneakier definition of \fileversion is also possible if you are using the etex extensions (which is probably true these days):

\makeatletter
{\everyeof{\noexpand}\xdef\fileversion{\@@input VERSION }}
\makeatother

Answer 2

Expanding on what Taco has just posted, I'd go for

\newcommand*\fileversion{%
  \newread\myread
  \openin\myread=VERSION 
  \read\myread to \fileversion
  \closein\myread
  \fileversion
}

as this will automatically redefine itself and print the version on first use.

Answer 3

I am pretty sure you're using LuaTeX :)

\edef\fileversion{%
  \directlua{
    local f = io.open('VERSION')
    tex.print(f:read())
    f:close()
}}