Linux recursive copy files to its parent folder

I suspect that while you say copy, you actually mean to move the files up to their respective parent directories. It can be done easily using find:

$ find . -name '*.txt' -type f -execdir mv -n '{}' ../ \;

The above command recurses into the current directory . and then applies the following cascade of conditionals to each item found:

1. -name '*.txt' will filter out only files that have the .txt extension
2. -type f will filter out only regular files (eg, not directories that – for whatever reason – happen to have a name ending in .txt)
3. -execdir mv -n '{}' ../ \; executes the command mv -n '{}' ../ in the containing directory where the {} is a placeholder for the matched file's name and the single quotes are needed to stop the shell from interpreting the curly braces. The ; terminates the command and again has to be escaped from the shell interpreting it.

I have passed the -n flag to the mv program to avoid accidentally overwriting an existing file.

The above command will transform the following file system tree

dir1/
    dir11/
        file3.txt
        file4.txt
    dir12/
    file2.txt
dir2/
    dir21/
        file6.dat
    dir22/
        dir221/
        dir221/file8.txt
        file7.txt
    file5.txt
dir3/
    file9.dat
file1.txt

into this one:

dir1/
    dir11/
    dir12/
    file3.txt
    file4.txt
dir2/
    dir21/
        file6.dat
    dir22/
        dir221/
        file8.txt
    file7.txt
dir3/
    file9.dat
file2.txt
file5.txt

To get rid of the empty directories, run

$ find . -type d -empty -delete

Again, this command will traverse the current directory . and then apply the following:

1. -type d this time filters out only directories
2. -empty filters out only those that are empty
3. -delete deletes them.

Fine print: -execdir is not specified by POSIX, though major implementations (at least the GNU and BSD one) support it. If you need strict POSIX compliance, you'll have to make do with the less safe -exec which would need additional thought to be applied correctly in this case.

Finally, please try your commands in a test directory with dummy files, not your actual data. Especially with the -delete option of find, you can loose all your data quicker than you might imaging. Read the man page and, if that is not enough, the reference manual of find. Never blindly copy shell commands from random strangers posted on the internet if you don't understand them.