You may also have noticed with some experimentation with globs that if the pattern does not match anything, it expands to itself, unchanged:
$ printf '%s\n' c* c*
Because none of our test files start with c, the glob is unexpanded and unchanged. This may seem strange; surely it would be better if the pattern expanded to nothing at all? It makes more sense when you consider the behavior of many classic Unix commands; if there are no arguments, they default to assuming input is coming from standard input. For example:
$ cat -- c* cat: 'c*': No such file or directory
Because the pattern here did not expand, cat saw the c* argument, found the file named c* did not exist, and reported that to us, with an error message that ...
