Css Shell Command

[Ken Kwok <kenkwok@cmu.edu>]

I'm writing a css script to automate training. One of the things I'd
like
to do is to create a new directory to store trained network weights for
each
training run. 

Here's a css snippet which I thought would do this:
int i; // training counter
for(i=0; i<10; i++) {
String ProjDir = "test"+i;
shell ("mkdir " + ProjDir);
.....etc
}

However, when I tried loading it, the css compiler complained:
commands are only available from the shell line 9: shell ("mkdir " +
ProjDir);

Anyone know what the correct syntax is for doing this?