Write a script that accepts a compressed file name as argument (which could be .gz, .bz2 or .zip). It looks at the extension and decompresses the file using the correct decompression program, but only...

Write a script that accepts a compressed file name as argument (which could be .gz, .bz2 or .zip). It looks at the extension and decompresses the file using the correct decompression program, but only if decompressed file (or one with the same name) doesn't exist.