The following is probably specific to Linux systems. I recently installed FICO Xpress optimizer, which comes with an R library to provide an API for R code. FICO requires a license file (or a license server -- I went with a static file since I'm a single user) and adds an assortment of environment variable to the bash shell, including one pointing to the license file. So far, so good.
Xpress comes with example files, including example R scripts. So I cranked up RStudio, opened the simplest example ("first_lp_problem.R", which is just what it sounds like) and executed it line by line. The problem setup lines worked fine, but the first Xpress API call died with an error message saying it couldn't find the license file in directory "." (i.e., the current working directory). The same thing happened when I tried to source the file in the RStudio console.
To make a long story somewhat shorter, after assorted failed attempts to sort things out it occurred to me to run R in a terminal and source the example file there. That ran smoothly. So the problem was with RStudio, not with R. Specifically, it turns out that RStudio runs without loading any bash environment variables.
After assorted failed attempts at a fix (and pretty much wearing out Google), I found the following solution. In my home directory ("/home/paul", a.k.a. "~") I created a text file named ".Renviron". In it, I put the line "XPAUTH_PATH=/home/paul/.../xpauth.xpr", where "..." is a bunch of path info you don't need to know and "xpauth.xpr" is the name of the license file. If you already have a ".Renviron" file, you can just add this line to it. The example script now runs fine in RStudio. Note that there are a gaggle of other bash environment variables created by Xpress, none of which presumably are known to RStudio, but apparently the license file path is the only needed by the API (at least so far). If I trip over any other omissions later on, presumably I can add them to ".Renviron".
