Minecraft world switcher in Bash

#! /bin/bash

# Take your world directory name as an argument
world=$1

# Set homedir (in case you run your server from somewhere else)
homedir="/home/minecraft"

# If no world name passed, then set to default "world"
if [ -z "$world" ];then
  world="world"
fi

# Does the world directory even exist?
if [ -e "$homedir/$world" ]
  then
# Swap the "level-name=" value with the pased name
    cat "$homedir"/server.properties | sed 's\level-name=.*$\level-name='$world'\g'> /tmp/serverprops.temp

# Write to a temp file, then swap it to the main file (to avoid read/write clashes; I read that somewhere...
    mv /tmp/serverprops.temp "$homedir"/server.properties

# Start the server so we don't have to type in the cryptic command line every.damn.time
    java -jar -Xms1024M -Xmx1024M /usr/lib/minecraft/minecraft_server.1.8.1-pre5.jar nogui
# ..and if the world DOESN'T exist... complain
  else
    printf "Error - world \"$world\" not found\n"
    exit 1
fi

# All done
exit 0