download fifty years of National Health Interview Survey documentation PDFs

download all files from an FTP site.R

#install RCurl on your version of R if you don't already have it
#just run this once
#install.packages("RCurl")

#program start
#load the RCurl package
library(RCurl)

#set your output folder - this is where the pdfs will get saved
setwd("R:/National Health Interview Survey/documentation")

#main NHIS FTP directory with documentation
nhis_doc_ftp <- "ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_Documentation/NHIS/"

#loop through 1963 - 2010
for ( year in 1963:2010 ){

	#create the full string to the FTP folder of the current year
	year_ftp_dir <- paste( nhis_doc_ftp , year , "/" , sep="" )
	
	#figure out what all of the files within that folder are named
	filenames <- getURL( year_ftp_dir , dirlistonly=T )
	filenames <- tolower( strsplit(filenames, "\r*\n")[[1]] )
	
	#as written, the program downloads EVERY file in each year's directory
	#however, if you only want to download files with "person" or "core" in their filename
	#uncomment this line..
	#save only the files with the word "person" or "core" in them
	#filenames <- filenames[ grepl("person" , filenames) | grepl("core" , filenames) ]
	
	#loop through all of those files and save them to your working directory
	for ( i in filenames ){ 
	
		#determine the year directory
		pth <- paste( "./" , year , "/" , sep="" )
		#if the directory doesn't exist, make it!
		if (!file.exists(pth)){
			dir.create(pth)
		}

		download.file( paste( year_ftp_dir , i , sep="" ) , paste( "./" , year , "/" , i , sep = "" ) , mode="wb" )
	}	
}