Since I have no experience with R, I can not answer your question directly.

However, have you considered using Perl to generate your R command input file with whatever parameters you need, then load that new command file into R?

> cat 644967.pl
#!/usr/bin/env perl
 
use warnings;
use strict;
 
my $x = shift;
my $cmd_file = 'cmd.txt';
open my $OUT_FH, '>', $cmd_file or die "Can not open $cmd_file $!\n";
print $OUT_FH <<"EOF";
x <- c(1:$x)
y <- c(x^2)
png(filename="plot.png", bg="transparent")
plot(x, y)
dev.off()
EOF
close $OUT_FH or die "Can not close $cmd_file $!\n";
 
>
> ./644967.pl 13
>
> cat cmd.txt
x <- c(1:13)
y <- c(x^2)
png(filename="plot.png", bg="transparent")
plot(x, y)
dev.off()
>
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