R script - Write to file from within a laravel app fails

I have been encountering some problems when trying to get R to output content to a file from within my laravel app.

Scenario where output works

When i call my R script from the command line like so:

vagrant@homestead:~/path/to/my-laravel-project/storage/marker$ Rscript marker.R --assessment=123456 --host=127.0.0.1 --user=homestead --pass=secret --db=db_name

I can get output either to the command line or to a file using sink commands:

zz <- file("r_out.txt", open = "wt")
sink(zz)
sink(zz, type = "message")
sink(type = "message")
...
sink()

or even just

sink("r_out.txt", append=FALSE, split=TRUE)

Scenario where output is missing

However, when i call the R script from within my application using an api call like so:

http://ift.tt/2c00EYE

The R script runs but fails to write to the output file at all.

Additional Notes

• The output file is in the same directory as the R script
• The file permissions are 775 and the file is writeable
• Both the R script and the output file are within the laravel storage directory
• The R script does everything else (i.e. it marks my assessments) but it does not write to the file
• There are no errors being returned from the R script when it is run
• The environment this has been developed on is a laravel/homestead vagrant box with all of the standard R script packages for R and RMySQL installed manually

My question is this: Why would R sink() work on the command line but not when called from within my application?

Any help would be very much appreciated!

via Chebli Mohamed