[R] R looks for a folder not specified

Dear R community, I have been getting this warning message after running a function sourced from an R script, and can't seem to work out why R is looking for a folder that wasn't even specified (it attaches a \NA to the specified directory, where assess_rev has not asked to do so at all. R code h

[R] What does the shell() command do?

Dear R community, I am trying to understand what the shell() function does. An example is: xfile <- shell(paste("dir/b ", paste(directory.folder,"file.name",sep="")),intern=T) I'm afraid I wasn't able to completely understand the explanation under the Help files. Thanks for your help! Leanne