usage error when moving files of one extension to a directory - bash

Question

I have files with extension .mp3 that are in different folders within a directory, and I need to move them all to one directory to work with. I have looked at multiple tutorials and questions on SO, and no matter what I try, I either get
usage: mv [-f | -i | -n] [-v] source target
mv [-f | -i | -n] [-v] source ... directory
or "No such file or directory".
There are way too many to into each individual folder, but for now I cd into one of the folders. With this:
mv *.mp3 /Users/myname/Volumes/LaCie/model/folder/media
I get the "usage" error above. I looked at Moving files to a directory and tried:
find . | grep ".mp3" | xargs mv /Users/myname/Volumes/LaCie/model/folder/media
and get same error.
What am I doing wrong? What is the correct syntax? Also, will I be able to extract the mp3 files and move them if I'm in a directory that contains the directory with the files, but not in that directory itself? I appreciate insights into this. Thanks.
EDIT: A major part of this issue was that the path when using /Volumes starts with /Volumes. I was doing /Users/myname/Volumes and that was one reason I had so much trouble.

Answer 1

The problem with the way you're using xargs is that by default, xargs will append the arguments to the end of the command string you've provided it. So you'll end up running a bunch of mv commands that look like this:
mv /Users/myname/Volumes/LaCie/model/folder/media foo.mp3
You can fix that by telling xargs where to place the arguments within the command:
<other commands> | xargs -I{} mv {} /Users/myname/Volumes/LaCie/model/folder/media
The -I option lets you provide any arbitrary string as a placeholder for where the args should go. I used {} just because that seems to be the conventional token that you see used in similar contexts (such as with the -exec option of find, as shown below).
But there's an easier way to do it, using the find command's -exec option:
find . -name '*.mp3' -exec mv {} /Users/myname/Volumes/LaCie/model/folder/media \;
Also note the -name '*.mp3' part, which lets you get rid of the | grep ".mp3" part.
Lastly, just to be safe, I'd personally put a / at the end of your destination path. If the media directory doesn't exist in /Users/myname/Volumes/LaCie/model/folder, or if a non-directory item (such as a regular file or a symlink) named media exists in that location, then the find command above will happily just move all your mp3 files, one at a time, to that folder, creating a file named media there each time. And you will have lost all of your mp3 files except for the last one, which will now be a file named media.
However, with a trailing /, if media is not a directory, the mv commands will fail with an error saying so. So the revised command would be:
find . -name '*.mp3' -exec mv {} /Users/myname/Volumes/LaCie/model/folder/media/ \;
Update: Per Gordon Davisson's comment below, you should also consider adding -i or -n to the mv command, to avoid accidentally overwriting files with duplicate names. For example, if you have a/foo.mp3 and b/foo.mp3, the above command will overwrite one with the other. The -i option will cause mv to prompt you to confirm each file move, whereas the -n option (a.k.a. --no-clobber) will prevent mv from overwriting a file if a file with the same name already exists.

Answer 2

There are different implementations and versions of mv. You can check the allowed syntax of your version using man mv.
If you have GNU mv you could use mv -t target/dir *.mp3.
Most implementations should support mv *.mp3 target/dir.
If your mv only supports the absolute minimum of mv source target with exactly one source and one target file you can use the following command which should always work if target/dir/ exists.
for i in *.mp3; do mv "$i" "target/dir/$i"; done