Detecting which directory is changing...

Suppose that you have some directory with a lot of subdirectories. Of all those subdirectories, one of them is changing in size, while all the others are of a constant size. The question is, how to detect which subdirectory is that?

This happened to me while I was downloading mail archives from IETF. lftp client, that I'm using, shows only a file that it is currently downloading, not a directory in which it is, i.e. the output looks something like this:

lftp ftp.ietf.org:/> mirror ietf-mail-archive
`2010-04.mail' at 518040 (50%) 120.1K/s eta:4s [Receiving data]                              

A solution to search for a given file won't work because this particular filename is in almost every directory.

The solution I used, was the following shell command:

$ ( du -sk *; sleep 5; du -sk * ) | sort | uniq -u
36204 mmusic
36848 mmusic

This command has to be executed inside ietf-mail-archive directory. It works as follows:

1. First 'du -sk *' command lists all directory sizes.
2. Then it sleeps for a five seconds (sleep 5) waiting for a directory that is currently changing, to change its size.
3. Again we get all the directory sizes using the second du -sk command.
4. Parentheses around all three are used so all of those commands execute within a subshell and that we receive output of both du commands.
5. Then, we sort output. Note that the directories that don't change will be one after the another, while the one that changes won't be. 
6. Finally, we use uniq command to filter out all the duplicate lines, meaning, only the directory that changed will be passed to the output.