Glob that doesn't match anything expands to itself, rather than to nothing

问题

I want to iterate over the files in a folder of a special type (like .test):

So I wrote a little script names for_loop:

for f in *.test
do
 echo 'This is f: '${f}
done

After (chmod +x for_loop) I can start it with ./for_loop.

If there are .test-files, everthing is fine, BUT if there is no file in the folder that matches *.test, the for-loop is still executed once. In this case the output looks like:

This is f: *.test

But I thought that if there were no files in the folder that match the glob pattern, there would be no output. Why is this not the case?

回答1:

This is the default behaviour.

to get rid of it, enable nullglob:

shopt -s nullglob

From Greg's Wiki - nullglob:

nullglob expands non-matching globs to zero arguments, rather than to themselves.

...

Without nullglob, the glob would expand to a literal * in an empty directory, resulting in an erroneous count of 1.

Or use zsh, which has this glob enabled by default!

$ for f in *.test; do echo "$f"; done
zsh: no matches found: *.test

来源：https://stackoverflow.com/questions/33898250/glob-that-doesnt-match-anything-expands-to-itself-rather-than-to-nothing