Render R markdown to PDF from command line

I have been using Makefiles where command line tools for building a project are not generally available. This includes LaTeX documents and recently R projects.

So here is an R script that can be used to render R markdown to PDF.

#!/usr/bin/env R

# Render R markdown to PDF.
# Invoke with:
# > R -q -f make.R --args my_report.Rmd

# load packages
require(rmarkdown)

# require a parameter naming file to render
if (length(args) == 0) {
    stop("Error: missing file operand", call. = TRUE)
} else {
    # read report to render from command line
    for (rmd in commandArgs(trailingOnly = TRUE)) {
        # render Rmd to PDF
        if ( grepl("\\.Rmd$", rmd) && file.exists(rmd)) {
            render(rmd, pdf_document())
        } else {
            print(paste("Ignoring: ", rmd))
        }
    }
}

It will process Rmd files listed after the --args parameter. This script can then be invoked from Makefile:

#!/usr/bin/env make

.PHONY: all clean
.SUFFIXES: .Rmd .pdf

DOCS = my-report
RMDS = $(patsubst %, %.Rmd, $(DOCS))
R = /usr/bin/R

Rmd: $(patsubst %.Rmd, %.pdf, $(RMDS))

.Rmd.pdf:
 @$(R) --quiet --file=make.R --args $<

all: clean Rmd

clean:
 @rm -f $(patsubst %.Rmd, %.pdf, $(RMDS))