On join

The on JOIN event trigger when a user joins a channel.

on <level>:JOIN:<#[,#]>:<commands>

Note that this event also triggers when you join a channel yourself.

Examples

on *:JOIN:#: { 
 echo -t $chan < $+ $nick $+ > has just joined $chan $+ .
}

This will echo whenever someone has joined a channel and echo it to this channel. You can use this to modify mIRC's layout.

on *:JOIN:#yourchan: {
 notice $nick Hello $nick $+ ! Enjoy your stay here in $chan $+ .
}

This will notice everyone joining #yourchan (you have to replace it with your chan of course). You can use it to have your own welcome-message.

on me:*:JOIN:#: {
 echo -s I have just joined $chan
}

The example reacts on you joining a channel. Note that it is no mistake, the prefix is "me:".

See Also

To react on parts, take a look at the On part event.