If you want the output to print to the terminal it is best to use Rscript
Rscript a.R
Note that when using R CMD BATCH a.R that instead of redirecting output to standard out and displaying on the terminal a new file called a.Rout will be created.
R CMD BATCH a.R # Check the output cat a.Rout
One other thing to note about using Rscript is that it doesn’t load the methods package by default which can cause confusion. So if you’re relying on anything that methods provides you’ll want to load it explicitly in your script.
If you really want to use the ./a.R way of calling the script you could add an appropriate #! to the top of the script
#!/usr/bin/env Rscript
sayHello <- function(){
print('hello')
}
sayHello()
I will also note that if you’re running on a *unix system there is the useful littler package which provides easy command line piping to R. It may be necessary to use littler to run shiny apps via a script? Further details can be found in this question.