About a month ago I've written a simple domain checker, which is using whois.net to get the domains availiable. The main goal was to find free 3-symbols domains.
BASH:
#!/bin/sh
if [ $# -lt 1 ]
then
echo "usage: `basename $0` extension
Check domains avaliability
examples:
`basename $0` com
";
exit 2;
fi
EXT=$1;
LAST_FILENAME=/tmp/dc_$USER$EXT.last
if [ -f "$LAST_FILENAME" ]; then LAST_DOMAIN=`cat $LAST_FILENAME`; fi
for DOMAIN in {{0..9},{a..z},-}{{0..9},{a..z},-}{{0..9},{a..z},-}
do
if [ "$DOMAIN" \< "$LAST_DOMAIN" ]; then continue; fi
trap "echo $DOMAIN > $LAST_FILENAME;exit;" SIGHUP SIGINT SIGTERM
STATUS_STRING=`wget -qO - http://www.whois.net/whois_new.cgi\?d\=$DOMAIN\&tld\=$EXT | grep 'Status'`
echo "$STATUS_STRING" | grep 'free' &&
echo "$DOMAIN.$EXT" >> ~/domains_found_$EXT.txt &&
echo "the domain is free: $DOMAIN.$EXT" | mail -c my@mail.com -s "free domain" other@mail.com
sleep 7
done
The thing is very simple and the results can be kept on. Additionally it sends mail messages about each found domain. Lets see, what it brought for the .de domains ( about 9000 free domains was found

)