Bash Shell Script – Flattening Directory Hierarchy Preserving Directory Names

_{Warning: I typed most of these commands directly in my browser. Caveat lector.}

With zsh and zmv:

zmv -o -i -Qn '(**/)(*)(D)' '${1//\//-}$2'

Explanation: The pattern **/* matches all files in subdirectories of the current directory, recursively (it doesn't match files in the current directory, but these don't need to be renamed). The first two pairs of parentheses are groups that can be refered to as $1 and $2 in the replacement text. The final pair of parentheses adds the D glob qualifier so that dot files are not omitted. -o -i means to pass the -i option to mv so that you are prompted if an existing file would be overwritten.

With only POSIX tools:

find . -depth -exec sh -c '
    for source; do
      case $source in ./*/*)
        target="$(printf %sz "${source#./}" | tr / -)";
        mv -i -- "$source" "${target%z}";;
      esac
    done
' _ {} +

Explanation: the case statement omits the current directory and top-level subdirectories of the current directory. target contains the source file name ($0) with the leading ./ stripped and all slashes replaced by dashes, plus a final z. The final z is there in case the filename ends with a newline: otherwise the command substitution would strip it.

If your find doesn't support -exec … + (OpenBSD, I'm looking at you):

find . -depth -exec sh -c '
    case $0 in ./*/*)
      target="$(printf %sz "${0#./}" | tr / -)";
      mv -i -- "$0" "${target%z}";;
    esac
' {} \;

With bash (or ksh93), you don't need to call an external command to replace the slashes by dashes, you can use the ksh93 parameter expansion with string replacement construct ${VAR//STRING/REPLACEMENT}:

find . -depth -exec bash -c '
    for source; do
      case $source in ./*/*)
        source=${source#./}
        target="${source//\//-}";
        mv -i -- "$source" "$target";;
      esac
    done
' _ {} +

You can do this with GNU find and GNU mv:

find /dir1 -mindepth 2 -type f -exec mv -t /dir1 -i '{}' +

Basically, the way that works if that find goes through the entire directory tree and for each file (-type f) that is not in the top-level directory (-mindepth 2), it runs a mv to move it to the directory you want (-exec mv … +). The -t argument to mv lets you specify the destination directory first, which is needed because the + form of -exec puts all the source locations at the end of the command. The -i makes mv ask before overwriting any duplicates; you can substitute -f to overwrite them without asking (or -n to not ask or overwrite).

As Stephane Chazelas points out, the above only works with GNU tools (which are standard on Linux, but not most other systems). The following is somewhat slower (because it invokes mv multiple times) but much more universal:

find /dir1 -mindepth 2 -type f -exec mv -i '{}' /dir1 ';'