args<-commandArgs(TRUE)

vmcn<-as.integer(args[1])

library(ggplot2)
library(grid)

file<-read.table("my file.txt",header=F)

ggplot(file,aes(x=V1))+geom_histogram(binwidth=1,aes(y=..count../vmcn*100))+theme_bw()

ggsave(filename="myfile.pdf",width=4,height=4)

Rscript plot.r 5000

Error in eval(expr, envir, enclos) : object 'vmcn' not found
Calls: print ... <Anonymous> -> as.data.frame -> lapply -> FUN -> eval
Execution halted