I just noticed a Superuser question with ~80000 views where people were still generally-clueless about a commandline trick with file-copying. As there was only a slight variation of this mentioned, I’m going to share it here.

So, the following command can be interpreted two different ways:

$ cp -r dir1 dir2

• If dir2 exists, copy dir1 into dir2 as basename(dir1).
• If dir2 doesn’t exist, copy dir1 into dirname(dir2) and name it basename(dir1).

What if you want to always copy the contents of dir1 into dir2? Well, you’d do this:

$ cp -r dir1/* dir2

However, this will ignore any hidden files in dir1. Instead, you can add a trailing slash to dir1:

$ cp -r dir1/ dir2

This will deterministically pour the contents of dir1 into dir2.

Example:

/tmp$ mkdir test_dir1
/tmp$ cd test_dir1/
/tmp/test_dir1$ touch aa
/tmp/test_dir1$ touch .bb
/tmp/test_dir1$ cd ..
/tmp$ mkdir test_dir2

/tmp$ cp -r test_dir1/* test_dir2
/tmp$ ls -1a test_dir2
.
..
aa

/tmp$ cp -r test_dir1/ test_dir2
/tmp$ ls -1a test_dir2
.
..
.bb
aa

The Superuser question insisted that you needed a period at the end of the from argument which isn’t accurate (but will still work).