# Simply opens the file in the first argument and draws a histogram as png
# as the file.png or the second argument if provided

##  Capture command line arguments
args <- (commandArgs(TRUE))

##  Read in tab-delimited file as a table
##  Use the first line as column headers
data <- read.table(args[1], head=FALSE, as.is=TRUE)

##  Apply user-defined output filename, if it was specified
if (length(args) > 1){
  outfile <- args[2]
} else {
  outfile <- paste(args[1], ".png", sep="")
}

##  Initialize PNG output file and specify dimensions
png(file=outfile, w=600, h=500)

##  Print a histogram to the PNG file with custom labels
hist(data$V2, nclass=50, xlab="Read length", main="Distribution of lengths")

##  Close output file
dev.off()