For those wondering how to generate random numbers, it's simple if you don't care about a little computational overhead: </dev/urandom tr -dc 0-9 | head -c 15 (substitute 0-9 for any character set like a-zA-Z or \ -~). I use this to generate random PIN numbers after it took too long to read the pwgen man page, and I might start to use it as replacement for pwgen altogether since it only uses very basic tools that are available everywhere, unlike pwgen.

To explain the command: we read urandom into tr's stdin; tr translates (like "echo haha | tr a u"); with -d, tr deletes instead of substituting; with -c, it takes the compliment set (so everything except what you specify). Basically we're filtering characters or of urandom's output. Finally, we limit the output to a certain number of characters.