I have a number of bash scripts which invoke R scripts for plotting things. Something like: 

```
#!/bin/bash
R --vanilla --slave <<RSCRIPT
cat("Plotting $1 to $2\n")
input <- read.table("$1")
png("$2")
plot(as.numeric(input[1,]))
dev.off()
RSCRIPT

```

The problem is that despite `--slave`, the call to `dev.off()` prints the message `null device 1`. Once there are a lot of plots being done, or for more complex scripts which plot to a number of files, this gets to be a real hassle.

Is there some way to suppress this message?