Help with script that reads and writes java console Minecraft

Hi

I am looking for an easy way to lock game mode (0) for everyone included op on a Minecraft server. It can be a script that every time a player changes game to 1 the script changes back to 0. What the player writes is visible in the java console. I am not good at script programming and my guess is that this is easy for someone who is good script programming. The OS is OSX. I appreciate all help on this.

gamemode <playername> <0|1> Changes the game mode for playername to Survival (0) mode or Creative (1) mode.

Example player player1 writes to set gamemode 1:
gamemode player1 1
Example player player1 writes to set gamemode 0:
gamemode player1 0

I want gamemode to be set to 0 always so I am looking for something like:

Example player player1 writes to set gamemode 1:
gamemode player1 1
On the CONSOLE
2012-02-20 19:59:26 [INFO] player1 issued server command: gamemode player1 1
The script writes:
gamemode player1 0
On the CONSOLE

The script code for the test is something like this
if echo $line | grep -q 'gamemode'
if echo $line | grep -q ' 1'; then
echo $line | sed s/' 0'/' 1'/ >> stdin.commandlist
fi
fi

Minecraft Server is a java program which starts like this:
Java -Xmx2024M -Xms2024M -jar minecraft_server.jar nogui
174 recipes
27 achievements
2012-02-20 09:22:26 [INFO] Starting minecraft server version 1.1
2012-02-20 09:22:26 [INFO] Loading properties
2012-02-20 09:22:26 [INFO] Starting Minecraft server on 5.66.29.122:25565
2012-02-20 09:22:26 [INFO] Preparing level "world"
2012-02-20 09:22:26 [INFO] Default game type: 0
2012-02-20 09:22:27 [INFO] Preparing start region for level 0

Thanks