Shell Programming and Scripting

When I go

Code:

$ echo *

I get a directory listing.

When I go

Code:

$ echo * *

I get a directory listing, followed by a second identical directory listing.

When I go

Code:

$ echo **

I only get one directory listing. What happens to the second asterisk in this case? Why doesn't it expand? I haven't been able to sleep because of this question. Can anyone help?

In the first case your have two arguments and in the second case you have one argument. If an argument contains an asterisk, the argument is expanded into a list of filenames that match it. Suppose you have a directory with a single file names "b". This command:
echo b*
will still echo "b". The asterisk stands for "zero or more characters". The "b*" pattern would also match files like b1 b2 bbbbb and so on. Now consider:
echo b**
Remember that b* matched a simple b. There is no need for extra characters to satisfy the asterisk. So b* b** b*** b***** and so on all will match a file named just "b". In the same way, * matches all filenames (except those that start with a dot). And ** *** **** and so on just match the same list as a simple *. However, time is spent processing those superfluous asterisks, so it is a waste or resources.

Thanks for the great explanation, Perderabo. It makes sense to me now.

PS- thanks for the quick reply. I just discovered this forum and it rocks!