I don't understand why * returns itself when there's no match. This answer states that this is the case, but I don't understand the rationale for this behaviour. Why doesn't *, or any generic pattern, just return an empty string in case of no match?
$ls # Look, no files
$touch a # Add a file
$echo * # Works as expected
a
$rm a # Remove the file
$echo * # Will output a '*'. Why not ''?
*
$* # Ok, * will fail, but how come the previous output?
-bash: *: command not found
$
The * is actually being expanded by bash (whatever your shell is) and then it is passed on to the echo. The echo command does nothing but prints it to standard output. Read this document - File name expansion. It says-
Bash scans each word for the characters "*", "?", and "[". If one of these characters appears, then the word is regarded as a PATTERN, and replaced with an alphabetically sorted list of file names matching the pattern. If no matching file names are found, and the shell option nullglob is disabled, the word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed.
So actually when bash cannot find any matching it left '*' unchanged and echo prints that.
Reason The reason bash doesn't return an empty statement by default cause there can be cases where the user doesn't want to use the '*' as wildcard and so he doesn't need the expansion of '*'. And hence in this case expanding the '*' to empty string would have erroneous. However this default behaviour can be overridden by nullglob option.
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