filesystems - Best practice for cross-platform file system manipulations in GAMS

Question

I would like to manipulate the file system from some GAMS code. I am coming to this project mid-stream, and as a GAMS newbie, but am used to writing cross-platform file manipulations in other languages. It would be good for this code to be cross-platform Linux and Windows. Right now there is a commented-out line

*$call 'mkdir "%runfolder%"'

that I would like to un-comment (enable), however, I am having a hard time finding documentation on whether this would work cross-platform (I suspect not), and if not, how I could do this in a cross-platform way.

How can I manipulate the file system in a way that is guaranteed to work cross-platform?

Answer 1

Try using a global variable that defines the file separator. You can do this by querying the system.filesys system variable and setting the value accordingly. Such as:

* ----- Platform Specific Adjustments
* Setup the file separator to use for relative pathnames 
$iftheni %system.filesys% == DOS $setglobal filesep ""
$elseifi %system.filesys% == MS95 $setglobal filesep ""
$elseifi %system.filesys% == MSNT $setglobal filesep ""
$else $setglobal filesep "/"
$endif

Then you can use this when you need to specify paths, as in:

* ----- Set data and output directories
* By default look for data in the sibling directory "data"
$if NOT set data_dir    $setglobal data_dir ..%filesep%data%filesep%   

Note that GAMS doesn't let you indent $if and related directives.