从命令行运行 r 脚本

I have a file, called a.r, it has a chmod of 755,

sayHello <- function(){
   print('hello')
}

sayHello()

How can I run this via command-line?

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

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.

You need the ?Rscript command to run an R script from the terminal.

Check out http://stat.ethz.ch/R-manual/R-devel/library/utils/html/Rscript.html

Example

## example #! script for a Unix-alike

#! /path/to/Rscript --vanilla --default-packages=utils
args <- commandArgs(TRUE)
res <- try(install.packages(args))
if(inherits(res, "try-error")) q(status=1) else q()

One more way of running an R script from the command line would be:

R < scriptName.R --no-save  

or with --save.

See also What's the best way to use R scripts on the command line (terminal)?.

This does not answer the question directly. But someone may end up here because they want to run a oneliner of R from the terminal. For example, if you just want to install some missing packages and quit, this oneliner can be very convenient. I use it a lot when I suddenly find out that I miss some packages, and I want to install them to where I want.

R -e 'install.packages(c("package1", "package2"))' # install to default location. 
sudo R -e 'install.packages(c("package1", "package2"), lib="/usr/local/lib/R/site-library")' # install to location that requires root. 

How to run Rmd in command with knitr and rmarkdown by multiple commands and then Upload an HTML file to RPubs

Here is a example: load two libraries and run a R command

R -e 'library("rmarkdown");library("knitr");rmarkdown::render("NormalDevconJuly.Rmd")'

R -e 'library("markdown");rpubsUpload("normalDev","NormalDevconJuly.html")'

Yet another way to use Rscript for *Unix systems is Process Substitution.

Rscript <(zcat a.r)
# [1] "hello"

Which obviously does the same as the accepted answer, but this allows you to manipulate and run your file without saving it the power of the command line, e.g.:

Rscript <(sed s/hello/bye/ a.r)
# [1] "bye"

Similar to Rscript -e "Rcode" it also allows to run without saving into a file. So it could be used in conjunction with scripts that generate R-code, e.g.:

Rscript <(echo "head(iris,2)")
# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa

Just for documentation. Sometines you need to run the scrip as sudo:

sudo Rscript path/to/your/file.R