Moving files and directories to a sub-folder in UNIX

When I type

mv ../* . 
mv: cannot move '../<dir name>' to a subdirectory of itself, './<dir name>'

How does the shell/mv command detect this behav开发者_开发问答iour?

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As far as I know, mv uses the rename() POSIX syscall, for which the specification says:

The rename() function shall fail if:

(...)

[EINVAL] [CX] The new directory pathname contains a path prefix that names the old directory.

... along with a myriad of other detailed failure modes.

The operating system presumably implements the detection at the general VFS layer by comparing the inode numbers of the intermediate directories along the hierarchy.

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The shell is responsible for expanding wildcards like * before passing the command line to mv and its does so directly, based solely on what files/directories exist, with no knowledge of what the program is or what it might want to do with those names. So in this case, ../* is expanded to every file/directory name in the parent directory, including the current directory <dir name>. Then mv goes through the list of arguments it receives, trying to move every one except for the last into the last, which causes the error you see.