On Wed, 25 Feb 2015, Pablo Rodriguez wrote:

> Dear list,
>
> I need to get the number of pages from an external PDF file that I also
> define with an \env.
>
> I think I could get something like this.:
>
>    \def\Myfilename{\env{filename}}
>    doc = epdf.open(arg[\MyFilename])
>    total_pages_ =  doc:getNumPages()
>    \def\Mypages{total_pages}
>
> But mixing both lua and ConTeXt commands the wrong way won’t work.
>
> Sorry, but this is all Greek to me. Although I see how it could be done,
> I cannot write the code for this.
>
> Which is the right way to get the code above working?

From my old cut-n-paste module (to format two column pdfs into one column 
so that they are easier to read on an eink reader)

\useexternalfigure[cnp:name][\cut!n!paste!parameter\c!name]% Is this really needed?
\getfiguredimensions[cnp:name]%
\edef\cut!n!paste!NOfpages {\noffigurepages}%

Aditya

[1]: 
https://github.com/adityam/cut-n-paste/blob/master/tex/context/third/cut-n-paste/t-cut-n-paste.tex