从bash脚本调用时，为什么此R脚本不起作用？

我有以下R脚本，并在其中添加了注释，以使汽车成为我要达到的目标的简单示例：

#!/usr/bin/env Rscript

# the arguments come in this way: 
# args[1] is a file containing the maximum speeds of different cars (one per line) 
# args[2] is the title that the plot will have
# args[3] contains the horsepower of the engine of the first car in args[1] (the lowest)
# args[4] contains the horsepower of the engine of the last car in args[1] (the highest)
# NOTE1: the speeds in args[1] must be listed starting from the car 
# with the lowest horsepower to the car with the highest horsepower 
# NOTE2: in args[1], a car must differ from the next one by 1 horsepower, i.e., if
# there are 5 speeds, and the horsepower of the first car in the file is 30, then the 
# the horsepower of the second one must be 31, the third one 32, .... the fifth one must
# be 34.


args<-commandArgs(TRUE)

# creating the vector with the horsepower of each car

horsepowers = numeric()

for (i in args[3]:args[4]) {

        horsepowers = c(horsepowers,i)

}

# reading file with speeds and getting vector with speeds

speeds <- read.csv(file=args[1],head=FALSE,sep="\n")$V1

# creating plot with speeds in previous vector

outputTitle = gsub(" ","", args[2] , fixed=TRUE)

pdf(paste(outputTitle, ".pdf", sep = ""))

plot(horsepowers, speeds, type="o", col="red", xlab="horsepowers", ylab="speeds")

# giving a title to the plot

title(main=args[2], col.main="Black")

我有一个样本文件myFile，它的速度为5辆车，看起来像这样

150
156
157
161
164

并假设第一辆车的马力为30，因此将使最后一辆车的马力为34（请记住，第一速度对应于马力最低的汽车，第二速度对应于马力最低的汽车，依此类推；汽车必须相差1马力，否则脚本中的for循环就没有意义了）。因此，如果我在命令行中像这样运行脚本：

./myPlotter.R myFile "My Title" 30 34

它可以正常工作并绘制图（我裁切了y标签，x标签和标题，只是因为它们与上面的汽车示例不匹配，但是使用的脚本是相同的，我只是更改了汽车示例的变量名） ：

但是，从以下bash脚本调用时：

#!/bin/bash

while getopts ":a:1:2:3:4" arg; do

case "$arg" in

a)
    option=$OPTARG
    ;;
1)
    fileWithSpeeds=$OPTARG
    ;;
2)
    titleOfGraph=$OPTARG
    ;;
3)
    lowestHP=$OPTARG
    ;;
4)
    highestHP=$OPTARG
    ;;

esac

done

# I do not think that this if statement makes any difference for this example
# but I left it there just in case

if [ $option == "option1" ]; then

        ./myPlotter.R $fileWithSpeeds $titleOfGraph $lowestHP $highestHP

fi

如此：

./bashPlot.sh -a option1 -1 myFile -2 "My Title" -3 30 -4 34

我收到以下错误：

Error in args[3]:args[4] : NA/NaN argument
Execution halted

是什么原因造成的？

摘要：我有一个R脚本，当从命令行调用时，它可以正常工作，但是从带有从getopts中获取的参数的bash脚本中调用时，则给出错误。