Generate me some appropriate license plates!
bash (95 chars)

Save the script as m in a folder in your PATH with execute bit set.

Run as bash m. The plates are stored in file p

l(){ tr -dc $1&lt;/dev/urandom|head -c3;};egrep -ve"ASS|666|69|KKK|SHT" -fp&gt;&gt;p&lt;&lt;&lt;`l 0-9`-`l A-Z`;m


This is equivalent to running the following:

# Print three random numbers and three random letters
echo $(tr -dc 0-9 &lt; /dev/urandom | head -c3)-$(tr -dc A-Z &lt; /dev/urandom | head -c3) |

# Print only plates not matching the blacklist or any line of p
# Append the plates ton p
egrep -v -e "ASS|666|69|KKK|SHT" -f p &gt;&gt; p

# Execute itself again
m 


Caveat: The final m should actually be exec m (+5 chars) in order to avoid leaving processes waiting for completion (but you can have thousands without much problem)

Credit goes to  http://www.cyberciti.biz/faq/linux-random-password-generator/ for the idea of using tr -dc