I am pretty sure chromatic is correct with the concantenation thing. That and random was not defined for me.

#!/usr/bin/perl -w
use strict;
my $tempDir = '/home/pencilneckgeek/tmp/' + rand(10000);
print $tempDir, "\n";
[download]

Results:
Argument "/home/pencilneckgeek/tmp/" isn't numeric in add at - line 2.
2723.31736981869
Where the big number is supposed to be $tempDir, which is obviously not what you wanted.